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1. dacs Target scintillator Ao 34 211 drive 86 9 5 279 13 41 E y ll ON i nO N YN al doi IA i TNA fi VA 1 Of AA t O i Nd 4 IN 1 t X AN oN yV N S A 71 750 a 43 182 25 i A Focusing quadrupole o gt 4 triplet y e A N On 4 39 306 NM 6 a 3 99 84 CRDC1 A O N S S IC Vacuum dE i um ao TKE inches pump ca centimeters N CRDC2 Figure 3 3 Top view of the Sweeper detector box The Sweeper s deflection angle of 43 and the target chamber with its two drives in front of the magnet are shown The CRDCs slide on rails and can be a maximum of 182 cm apart Image from Reference 44 magnet The angle and position of each particle is used to reconstruct the energy and angle of the nucleus at the reaction target Each detector is mounted on a rail parallel to the Sweeper magnet exit axis 43 from the beam line so they also can be positioned at distances that balance acceptance with velocity resolution for the specific experiment 3 3 1 Target Chamber As shown in Figure 3 2 the target position for the standard MoNA Sweeper config uration is downstream of the final focusing quadrupole triplet magnet Installed into the beam line here is a large bore six sided connection cross There are two remotely operated drive mechanisms attached to the cross each with multiple positions The first drive assembly has two positions to put a thin timing scintillator in or out 4
2. 1 5 1 One Neutron Knockout of Be 1 5 2 Ground State Wave Function of Be 2 Modular Neutron Array MoNA 2 DES e ARA OE eh ts OS ook eek 2 1 1 Detection Method taa Sa whe ook rd Widnes Ae Goa leh 2 1 2 Light Propagation tos 8 5 202 6 Bie eee A da 2 2 a A e Sa hs Be pee endo A Se Bs GE tee hak 2 2 1 Light To Signal Processing 262 Sar lt 2 db de 2 2 2 Digital Signal Conversion 2 teo Ed e ds ir eS 2 2 3 Timing Signal Processing 2 2 4 Light Amplitude Processing i a4 6 4 4 4 a 2 2 5 Level 1 Logic Modules sata tae pa pa ie P ee ek 2 2 6 Level 2 Logic Module 03 dad le Te lp te Te len UR een Dow Calibration ss ara E a RA A AR eee 2 3 1 Gain Matching the PMTs esas eri ze pes vl sel e e Pad 28 2 BIE nato AAA A Scag ane aa es 20 0 QDC Thresholds aa oe ah a a A ee RS 234 IDE Cabrio i a gt ude te ise A oh kes Geek ke BW ae 2 3 5 Position Calibration tv de 28 0 Time Offsets AAA A Pace T ag 3 MoNA Sweeper Experimental Setup DE ANO siie eiaa Sante Se EA AAA 3 2 MSU FSU Sweeper Magnet o o e 3 3 Charged Particle Detectors sto ala Oe Be oe Pd eS 3 3 1 Target Chamber O ae Se aoc eee ack Se Sas 332 SCRODS e seed eo Ec wy ee rss Webel hoes Ga vi xi xiv OU O0OO0 000000 NN e E 3 3 3 Ion Chamber 42 3 3 4 Thin Thick Plastic Scintillators a as 43 3 4 Reaction Residue Identification 0 a 43 3 4 1
3. O Ny D Cc pam 0 O O o 10 O x16 x16 x16 Level 1 Logic Diagram Counter Legend connector negated signal input gt output module 2 D 2 w Cc oO 3 Figure 3 7 The Level 1 logic code is programmed into nine XLM72 modules one for each layer The QDC gate outputs are used directly by the QDC modules for that layer as the integration window while the other output signals are used by the Level 2 logic gt left PMTs 51 q EA JA AO 15 14 13 12 11 10 Figure 3 8 Each cell is the average rate per second of raw CFD triggers for that MoNA module PMT counted by the Level 1 logic module The lighter color indicates a higher count rate D 2 a S UY PH 0 of hits every two seconds for each PMT and hold this value in a readable VME bus labeled Counter in Figure 3 7 A separate Tcl Tk program interfaces with the VME buffer and reads these channels and displays a diagnostic array of all the PMT rates for viewing during the run to ensure the voltages are still set properly and the PMTs are functioning normally This diagnostic display is shown in Figure 3 8 3 5 4 Level 2 Logic The Level 2 logic unit consists of a JTEC Virtex XLM logic module containing a larger Virtex FPGA This unit processes the majority bits and the mona start for all nine Level 1 logic modules along with th
4. Figure D 2 Tandem SpecTcl control window Customized Buttons The tandem spectcl tcl directory contains a few files that are sourced by the gray buttons with the blue lettering The 1D Raw button sources the tcl SpecGen tcl file The 1D Cal button sources the tcl CalcParameter1DSpectra tcl file The 2D Spectra button sources the tcl CalcParameter2DSpectra tcl file These three files can be edited to include any custom commands or spectra you choose D 4 2 Beamline Forward Tracking Forward tracking can only be completed after the beam line tracking detectors have been calibrated for from mask runs and the sweeper im gap variable is set to the 204 distance between them The Ppacs map button is used in conjunction with the Order Mass Charge Brho input frames to forward track the position and angle of the fragment at target from the information from the beam line tracking detectors These inputs should correspond to the mass and charge of the fragment you wish to track through the triplet magnet The Order should be set to 3 or higher if the forward map was made to a higher order The Brho input should correspond to the Brho value setting of the triplet Check the experiment s logbook for this number When a forward map file is made this Brho value is needed Once the input frames are filled with the appropriate values make sure the sweeper im track map maxparameters variable is set to 5 Now an appropriate for ward map must be
5. 0 05 1 15 2 25 3 35 4 Decay energy MeV Figure 4 28 The acceptance of MoNA for the El excitation of MBe to Be n as a function of decay energy system efficiency is 29 When acceptance cuts are taken into account the intrinsic efficiency of all the detectors eMoNA fp is calculated to be 68 This includes the target and thin scintillators focal plane CRDC1 and MoNA Table 4 3 lists the intrinsic efficiencies and geometric acceptances for the focal plane detectors as a whole and MoNA The uncertainties quoted for the are based on the simulation fit uncertainties and the range of fits that still match the data from Figure 4 25 This calculated intrinsic neutron efficiency of MoNA is 73 6 is determined by measuring or simulating all other variables from Equation 4 11 The result is in range of the design goal of 70 and consistent with the Geant simulations in Figure 4 7 Table 4 3 Detection intrinsic efficiencies and geometric acceptances for the Sweeper focal plane detectors and MoNA for 07503 Tlive MoNA fp MONA Mp 47 45 73 0 6 79 9 1 62 8 3 67 3 5 93 1200 Pes se DOG 1000 ST mona 800 Q Q o arbitrary units S S N Q O ay a iie LE ATT 0 0 05 1 15 2 25 3 35 4 45 5 Fragment theta degrees Figure 4 29 The fragment angle calculated through the CDCC method is compared to the angle simulated by ST mona to match the focal pla
6. 60 2599 1988 B A Brown 2007 Private communication P G Hansen and J A Tostevin Annu Rev Nucl Part Sci 53 219 2003 210 29 30 31 32 33 34 39 36 37 38 39 40 41 42 43 44 45 A Navin D W Anthony T Aumann T Baumann D Bazin Y Blumenfeld B A Brown T Glasmacher P G Hansen R W Ibbotson P A Lofy V Mad dalena K Miller T Nakamura B V Pritychenko B M Sherrill E Spears M Steiner J A Tostevin J Yurkon and A Wagner Phys Rev Lett 85 2 266 2000 S D Pain W N Catford N A Orr J C Angelique N I Ashwood V Bouchat N M Clarke N Curtis M Freer B R Fulton F Hanappe M Labiche J L Lecouey R C Lemmon D Mahboub A Ninane G Normand N Soic L Stuttge C N Timis J A Tostevin J S Winfield and V Ziman Phys Rev Lett 96 3 032502 2006 R C York et al Proposed Upgrade of the NSCL IEEE Part Accel Conf page 345 1998 A Del Guerra Nucl Instr and Meth 135 337 1976 D A Kellogg Phys Rev 90 2 224 1953 L Celano G Tagliente G D Erasmo A Pantaleo and N Colonna Nucl Instr and Meth A 392 304 1997 CAEN S p A Via Vetraia 11 55049 Viareggio LU Italy http www caen it nuclear Photonis dept Burle Industries Inc P O Box 60 9300 AB Roden Netherlands http www photonis com products photomultiplier tubes Magnetic Shield Corporat
7. Calibrate Xpos button The TkCon window will scroll through a list of the values fitted for each bar Scan the output and check that all the parameters have a reasonable slope value near 8 0 Reopen MoNA_setup_run tcl and change the Xposfitted flag to true and Save Close SpecTcl and reopen it The proper calibration will now be sourced to the program If done properly the width of an Xpos spectra of cosmic ray data from step 1 should be 200 cm and it should be centered about zero 182 C 6 Independent Tmean Offsets Setting the independent Tmean offsets may be done after an experiment is finished as long as a sufficiently long recorded run is taken at the end of the experiment but some timing and energy spectra during the experiment may look strange if this is not done before hand MoNA must be gain matched and the QDC TDC and Xpos slope offset values must be fitted Since the various triggering signals to the TDC s are not individually wired but instead chained the time for each TDC is slightly different Even though all the PMT s have been gain matched they still experience slightly different amplifying times These inconsistences lead to small but significant shifts in the average time calculated from the two TDC parameters Tmean In this process we will record cosmic rays passing through MoNA and gate on events that pass nearly straight down The speed of cosmic ray muons are very nearly 29 98 cm ns speed of lig
8. Yet another decay mode is through diffractive breakup of the 12Be nucleus 28 56 as it passes through the wave function of the Be target leading to 9Be and two neutrons in the decay channel since Be is only bound by 0 5 MeV and the energy imparted to the nucleus can be well above that This mode of decay has a non resonant structure and forms a broad background below the resonant peaks in the Be n decay energy spectrum Table 6 1 displays the single particle spectroscopic factors from the previous two experiments References 29 and 30 studying the admixture of three paired neutron shell levels in 2Be by neutron knockout to Be The values for Sexp quoted in the table are the spectroscopic factors from 2Be 1n knockout to the corresponding Be states third column and not necessarily only from the paired neutron states in the 12B wave function These Be states can be populated by 1n knockout reactions that may include configurations that are not simply paired neutrons above an inert l10Be core but can to contribute to the cross section to these states 78 While the first experiment 29 could only measure cross sections to the two bound states both experiments agree that roughly 50 of the total occupancy of the assumed two valence neutrons above a Be core are in configurations other than the 1s 12 or Op 12 for the ground state 12Be The second experiment 30 did not find all of 110 the remaining missing single p
9. and the energy by which the system is unbound Edecay The opening angle between the fragment and neutron in the lab 0 is calculated from the x y z coordinates of neutron and the reconstructed angle of the fragment The decay energy is then solved for as Edecay yin Em 2 Ee En pepn cos 0 mp Mn 3 7 The final decay energy depends more strongly on the neutron parameters than those of fragment due to its lighter mass Indeed using the neutron angle instead of the opening angle will not change the peak energy by more than 20 3 6 2 Charged Particle Reconstruction Since the invariant mass equation requires the momentum vector of the fragment where the decay reaction occurs at the reaction target the angles and positions recorded by the CRDCs after the Sweeper magnet must be transformed back to the target position using a measured magnet field map of the Sweeper magnet An inverse matrix is calculated that is specific for the magnet setting and the charged reaction residue 60 Table 3 3 The positions and angles at CRDC 1 are transformed to the y non dispersive position both angles and the relative energy at the reaction target Input Parameters at CRDC 1 Output Parameters at Target T Ox Ox Oy y y by de Inverse matrix A series of measurements were made for eight different Sweeper magnet currents using an array of seven Hall probes at over forty positions along 35 arcs wit
10. pseudo name parameterl parameter2 if parameterlisValid amp amp parameter2isValid return expr parameter1 parameter2 parameter2 else return 1 Note that the name of the pseudo should match the name of the parameter asso ciated with it that you just made The syntax here is not intuitive if you re not experienced in TclTk so let s take a minute to discuss it First note the parameterl parameter2 part of the com mand Remember when we made copies of existing spectra section 3 6 we had to tell SpecTcl what we were copying As you might suspect this is the same idea Be warned though any parameter you want to use in the pseudo calculation must be declared here The next part of the pseudo command is an if statement followed by the expres sion to return if true and the expression to return if false The if parameterlisValid amp amp parameter2isValid is a logical and all parts must be true in order for the conditional to be true This particular statement wants valid parameters the sign indicates that we re looking at the value of the parameter and isValid demands that there be something assigned to it note that this is case sensitive so pay close attention to your declarations If the terms of the conditional are met then the return expr parameter1 parameter2 parameter2 161 expression will be evaluated Note that we re telling SpecTcl to return the value of
11. 150 100 50 0 50 100 150 CRDC2 x position mm Figure 5 3 Sweeper focal plane acceptance of the 9Be residue from the 1n knockout of Be for run 2114 Transmission for this run is nearly 100 but the total count is much less than in run 2121 not be run with more than 10 particles per second The second setting at 2 9 Tm included less 9Be as shown in Figure 5 4 but cut 19 of the Be reactions The cross section measurement depends on determining the efficiency and geo metric acceptance of the residue to properly scale the recorded counts A tight beam focus in the dispersive direction x caused a large spread in the y direction extend ing beyond the acceptance of CRDC2 A timing limit on the drift time for CRDC2 caused a cut at about 100 mm as shown if Figure 5 5 The total CRDC acceptance was 67 6 of the reacted Be and was taken into account when calculating the cross section The efficiency of all the focal plane detectors were measured by a calibration run of the unreacted Be deflected into the focal plane through both CRDCs The measured charged particle efficiency of 361 was also factored into the cross section determination Because Be has no bound excited states the inclusive cross section directly mea sured the total knockout cross section to the ground state including stripping and diffraction and a negligible Coulomb component The cross sections for the single 100 450 100 50 0 50 100 150 CRDC2 x position
12. 4 4 1 Experimental Setup eo pace ow alates Be ala ae e 82 4 4 2 Virtual Photon Calculations idear diaria Peas 82 4 4 3 Experimental Comparison hiso e a e 84 4 4 4 Second Be Experiment for Efficiency Measurement 85 4 45 Measured Incoming Rate 87 4 4 6 Detector Acceptances iba a O RS ESS 89 4 4 7 Simulation Input Parameters o 91 4 4 8 System Efficiency A A doe ak a ewe Od ved 92 4 4 9 CDCC Cross Section Calculations 94 vil One Neutron Knockout of Be 96 Sly Introduction e dr ee aie te e E e e D a 96 5 2 Experimental Details oo db a a 97 53 Analysis A A AA a we A 98 5 3 1 Cross Section Calculations 0 a lee RS 98 5 3 2 Parallel Momentum Comparisons 104 Bel CONCIUSIOBS Sad Gels ee ee A in ee hw 107 Ground State of 12Be 108 Oot Introduction Eat aie BSA a te eS ee eS a 2g a 108 6 2 Experimental Details Eta Bac A ee Bee eS 111 E hg acts Bade ge oh he Bet ae ae Me RE te 112 6 3 1 Comparisons to Previous Results 114 6 3 2 Diffractive Breakup and Two Neutron Decay 119 ido Conclusions late ys Bk ee hb hh dhs is BR afew tn Bene 120 Outlook 122 7 1 Evaluation of Design 2 22 44 ge eee hd Bate Dk bale PE oS 122 7 2 Multiple Neutron Capabilities it a a a 122 7 3 Other Completed Experiments 126 Col Oxygen Isotopes eran eke Ae eee ee se 126 7 3 2 SL Coulomb Breakup coke 6 aa was 126 7 3 3
13. A 4 4 Desktop The Desktop directory is used by the Data U machines to create the desktop en vironment and the function call buttons There is a standard set of buttons in the user mona shared exp_desk directory gt cd 7 gt rm rf Desktop gt mkdir Desktop gt cd Desktop gt cp p user mona shared exp_desk Login to a Data U machine with the experimental account and from the KDE environment right click on a command button and check that the command path points to your current account or through an environment variable or to the correct user mona destination 137 A 5 Running Experiment While running the experiment be sure to always save the settings like xlm_values and cfd control files so they are up to date when copied by Readout from the links in the experiment current mona settings folder A 5 1 Edit Settings Files Please read the MoNA report on MoNA calibration 88 to understand which files do what within the Readout and SpecTcl programs Of particular importance are the dif ferent data packets created in the mona config MoNA hardware _run tcl file Some of the commonly used packets are mona bitpattern and ncans These are then added to the DAQ by the MoNA_readout_run tcl file and added to the SpecTcl unpacker by the MoNA_spectcl_run tcl file Edit these as needed within the mona config directory to add or subtract packets from the DAQ A 5 2 Orphaned Runs If Readout or the spdaq16 machin
14. Be experiments but have been used in other MoNA Sweeper experiments to assist in the reaction residue reconstruction A separate COSY INFINITY transformation matrix can be used to calculate the positions and angles of the incoming beam though the focusing quadrupole triplet in front of the target using the measured positions and angles of the beam line tracking detectors The dispersive position at the target can be used as an addition input to better reconstruct the energy of the charged particle 50 3 6 3 Energy and Angle of Neutrons After MoNA has been calibrated for time light response QDCs and position see Section 2 3 the momentum vector used to reconstruct the decay energy can be determined from the TDC related parameters The horizontal distance along any bar x axis is given by the calibrated time difference between the left and right time signals The distance from the target along the beam axis z axis and the vertical position y axis is determined by the layer and row These three dimensions are used to calculate the 3d position and angle relative to the target for the reacted neutron The neutron s velocity and consequently its energy is calculated from the position and the mean time ToFy Equation 2 4 62 Chapter 4 Performance MoNA s performance in terms of efficiency acceptance and resolution was tested with cosmic ray data and in beam neutron experiments and the results were compared to simulations
15. Meth A 401 329 1997 Saint Gobain Crystals amp Detectors Scintillation Products 12345 Kinsman Rd Newbury OH 44065 USA http www detectors saint gobain com home asp Th Blaich Th W Elze H Emling H Freiesleben K Grimm W Henning R Holzmann G Ickert J G Keller H Klingler W Kneissl R Konig R Ku lessa J V Kratz D Lambrecht J S Lange Y Leifels E Lubkiewicz M Proft W Prokopowicz C Schutter R Schmidt H Spies K Stelzer J Stroth W Walus E Wajda H J Wollersheim M Zinser and E Zude Nucl In str and Meth A 314 136 1992 N Fukuda T Nakamura N Aoi N Imai M Ishihara T Kobayashi H Iwasaki T Kubo A Mengoni M Notani H Otsu H Sakurai S Shimoura T Teranishi Y X Watanabe and K Yoneda Phys Rev C 70 5 054606 2004 209 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 B Luther T Baumann M Thoennessen J Brown P DeYoung J Finck J Hinnefeld R Howes K Kemper P Pancella G Peaslee W Rogers and S Tabor Nucl Instr and Meth A 505 33 2003 T Baumann J Boike J Brown M Bullinger J P Bychoswki S Clark K Daum P A DeYoung J V Evans J Finck N Frank A Grant J Hin nefeld G W Hitt R H Howes B Isselhardt K W Kemper J Longacre Y Lu B Luther S T Marley D McCollum E McDonald U Onwuemene P V Pancella G F Peaslee W A Peters M R
16. My appreciation also goes out to my friends Pete Anca Ali Mark Josh my brother Rob and those of you who know who you are I feel blest to have made it this far considering many of my friends that are better than I in many ways could not My grandparents have done a great job of building strong stable families for my parents and in turn for me I draw a lot of strength and courage from this base and feel supported constantly by its foundations My parents have always supported me even when maybe I should have been set straight Mom and dad you make me strive to live up to your investment in me I try forever to make you as proud as you have made me loved My wife Nicole who is currently working on our own real baby has brought joy into my life that I did not think was possible for me Honey I cherish every day you love me and pray I can keep you happy and safe forever You love me in ways that transcend my ability to describe Thank you Thank you all TABLE OF CONTENTS List of Figures List of Tables 1 Introduction 1 1 Magic Numbers and the Shell Model 1 2 Neutron Rich Nuclei e o 1 2 1 Neutron Unbound States 3 doo ra e a ay ene 8 1 3 Neutron Detection Tools ay ra aie EARL EA E 1 4 Commissioning Experiments od cg a Ga A AAA 1 4 1 Unbound He Ground State o o 1 4 2 Be Coulomb Breakup o 1 5 First Physics Results from MoNA Sweeper
17. an expression expr Again we insert a in front of the parameter name to use it s value Notice that if the conditions of the if statement are not satisified some other number is returned You should make this value marginally outside the spectrum you re defining so you don t see bad data in your spectrum Spectrum Finally you need to make a new spectrum to display the pseudo parameter you ve just defined The syntax is identical to creating a spectrum for a gated spectrum as above just use the pseudo parameter s name The command is Some very useful pseudo scripts have been written by A Ratkiewicz 91 One sorts all the MoNA hits by time within a set neutron time gate Another calculates the angles and velocities between internal MoNA hits like between the first and second hit to help with multiple neutron analysis These tcl scripts are located in the user mona tools directory B 5 3 Filtered Data SpecTcl allows one to filter out only selected parameters that can then be read in to a different SpecTcl quicker than re reading all the raw parameters and processing them This is useful if you have a large set of data runs that take a long time to read and if you ve calibrated all your parameters and are only concerned with a small subset of the total parameters made Since MoNA has over 1500 standard parameters not including the hit parameters it may be wise to crate a filtered file for the data This process req
18. mm Figure 5 4 Sweeper focal plane acceptance of the Be residue from the 1n knockout of 10Be for the production run 2121 is cut by the horizontal edge of CRDC2 at 150 mm Transmission is determined by integrating the Gaussian fit and is 81 4 particle stripping and diffraction channels were calculated using the eikonal ap proach 73 With the spectroscopic factor 025 calculated using the WBP interaction in the p shell 6 the total cross section can be determined by oi A A 1 C S Ostr 095 00 5 2 where A is the nuclear mass of Be Contributions from the wave function overlap or mismatch factor and the Coulomb cross section q were determined to be less than 1 and ignored in the present calculation 74 The WBP shell model interaction is specifically constructed for the 0p1s0d shell including perturbative effects from the neighboring 0s and Of 1p shells The experimental cross section was calculated with the theoretical cross sections listed in Table 5 1 along with the calibrated BaF yield of incoming 9Be of 5 5x 10 and 569 recorded 9Be residues Dividing out the charged particle detectors efficiencies 3641 and geometric acceptances 6746 and dividing by the 102 mg cm Be 101 60 40 2 5 mm 30 Counts per 1 3 o 0 150 100 50 0 50 100 CRDC2 y position mm Figure 5 5 Sweeper focal plane acceptance of the Be residue from the 1n knockout of 9Be for the production runs is
19. since the QDC integration window is shorter than the TDC range and readout first The rest of the MoNA Sweeper DAQ modules have time to digitize and await their turn at being read out by the data acquisition DAQ system When the DAQ computer is done reading the event an end of event signal is issued that enables the clear signal and closes the veto to ready all the electronics for the 56 next event 3 5 6 Auxiliary Inputs Additional detectors can be incorporated into the logic system through the auxiliary inputs The auxiliary A and B inputs can be substituted for the Sweeper focal plane s thin upper left PMT channel and used to enable the primary trigger Both A and B inputs have a down scaled option that allows one to automatically switch to these alternate triggers The down scaled factors are set through the user interface in powers of two The auxiliary C and D inputs can be substituted for the mona start from Level 1 as an alternate way of enabling the secondary trigger These auxiliary inputs have been tested and used successfully The target timing scintillator has been routed to the Aux A input and down scaled to record events where no particle travels to the thin scintillator in the back of the detector box Together with a beam line timing detector further upstream these events are used to determine the beam purity This is possible because nuclei with different mass to charge ratio will have
20. while the order for filling shell levels for stable nuclei would place the seventh neutron in the Op 2 shell level For Be this 1 27 state is at an excitation energy of 320 keV The ground state of 12B6 is mostly comprised of an admixture of different two neutron wave functions above a Be core Previous experiments have quantified the wave function as containing about 25 151 2 and about 25 0p1 2 paired neutron configurations 29 30 while the remaining 50 is thought to be mostly in the 0d 12 configuration 77 78 The strong component of the Od 12 wave function is thought to indicate correlations 108 JT 3 2 v d an 1 2 3 2 5 2 v0pi2 n 5 2 vs n v 0 0 0 0 1 2 P3 2 n 4 0 11 Be neutrons Figure 6 1 The diagram shows the simple shell level layout for 11Be after stripping of one valence neutron open circles from Be The first three levels in Be correspond to these single particle states 19 80 The resonant neutron decay channels to Be seen in the current study are highlighted from nucleon pairing as discussed in 79 and coupling to vibrational modes 77 The study is further complicated by the nature of the possible Be states after the 1n knockout of Be Ifa 1s 2 neutron is stripped from the 151 2 configuration the residue is in the ground state of Be Stripping from the Op 12 configuration leads to a decay via y ray emission of 320 ke
21. 300 250 e One MoNA bar Geant Madey arbitrary units S a 3 o o o al o 0 5 10 15 20 25 30 35 Deposited light MeVee Figure 4 4 Measured light response curve for 35 40 MeV neutrons compared to GEANT simulation using the Madey light response equation 4 1 by the FLUKA package of cross sections down to 20 MeV 53 54 below which neutron cross section tables from the evaluated nuclear data files ENDF 52 are used that incorporate various resonant reactions with carbon The inelastic and elastic neutron cross sections for carbon and hydrogen used by the FLUKA package are displayed in Figure 4 2 These are combined in appropriate proportions for BC408 plastic in Figure 4 3 4 1 2 Light Response The light produced by a charged particle passing through BC408 plastic 11 is differ ent for different charged particles This light response must be accurately simulated in order to determine the number of reactions that deposit enough energy to meet the threshold requirements of the detector Protons and alpha particles from the interac tion of the neutron in the plastic yield less light than an electron of equivalent kinetic energy due to their increased mass The GEANT simulation determines the number and energies of protons alpha particles and electrons produced by the interactions 66 2500 2000 1500 Counts 1000 500 60 60 70 80 90 100 110 120 130 140 Neutron kinetic energy MeV Figure 4 5 The Ga
22. 4 12 Plot of x versus yin MoNA for sample data 76 4 13 Sample plot of neutron angle relative to the beam axis 76 4 14 Plot of z position is MONA by layer 77 4 15 Sample decay energy spectra from ST mona simulation 79 4 16 Decay energy resolution from ST mona simulation 80 4 17 Decay energy of He fit with experimental resolutions 81 4 18 MBe calculated El cross section 0 0004 84 4 19 Isotope identification for 11Be Coulomb breakup 85 4 20 Focal plane data compared with ST mona simulation for 03048 86 4 21 Coulomb breakup decay energy compared to ST mona simulation 87 4 22 Isotope separation for Be Coulomb breakup acc hi po Rae oi bay 88 xii 4 23 Second isotope gate on ToF for 07508 4 24 Reaction residue gated and ungated neutron ToF 4 25 Focal plane data compared with ST mona simulation for 07503 4 26 Simulated y position at the thin focal plane scintillator 4 27 MoNA position data compared with simulation for 07503 4 28 Acceptance of MoNA as a function of Be decay energy 4 29 Fragment angle comparison for CDCC calculation 4 30 Cross section for CDCC and virtual photon methods 5 1 Reduction factor versus nucleon separation energies 5 2 Isotope identification plot for one neutron knockout of Be 5 3 Sweeper focal plane
23. 4 44 e 2 6 203 D 4 2 Beamline Forward Tracking sis das dd ie 204 D 4 3 Sweeper Inverse Tracking o 205 D 4 4 MoNA Timing ar aos a aa 206 D 4 5 Isotopic Separation bad a AE e 206 D 4 6 Decay Energy gow a da oe an de ie es 207 Diz Multiple Neutrons 4 408 a A Blas 207 PALS Dimitations epa eee a a cher laa her dd 208 II A A A A A ee 209 LIST OF FIGURES 1 1 Magic numbers from W S potential and spin orbit coupling 1 2 Clarion thenuclidesii lanas o A A A A a 1 3 Methods of studying nuclei near the neutron drip line 1 4 Computer image of original MONA design 2 1 Diagram of one MONA module 004 2 2 Diagram of MONA DAQ systeM e o 2 3 Left and right QDC response for cosmic ray muons 2 4 Sample routing map of Virtex FPGA 2 5 Cosmic ray muons flux through MoNA 2 6 Side view of MoNA array with cosmic ray muon tracks 2 7 Raw QDC spectrum for background run used for calibration 2 8 2 9 2 10 2 11 2 12 2 13 2 14 2 15 3 1 3 2 3 3 3 4 3 5 cosmic ray muon peak fit for raw QDC spectrum Raw QDC pedestal peak for PMT B 00 L Raw QDC pedestal peak for PMT B 02 L CFD threshold calibration West er tas Raw TDC spectrum with peaks from time calibrator Calibrated time difference spectrum for x position calibration Straight dow
24. A Ratkiewicz and W A Peters Time Sorting Pseudo Codes Technical report MSU NSCL 2005 http www cord edu dept physics mona analysis html A Ratkiewicz and W A Peters MoNA SpecTcl Guide Technical report MSU NSCL 2006 http www cord edu dept physics mona analysis html 214 93 K Yoneda and W A Peters MoNA Fitting Codes Technical report MSU NSCL 2004 http www cord edu dept physics mona analysis html 94 G A Christian and W A Peters MoNA Position Calibration Technical report MSU NSCL 2005 http www cord edu dept physics mona analysis html 95 D Bazin Tree Parameters Technical report MSU NSCL 2005 http docs nscl msu edu daq appnotes TreeParameter html 96 N Frank Sweeper Isotope Separation Technical report MSU NSCL 2005 http www cord edu dept physics mona analysis html 215
25. As mentioned above many standard programs used in the DAQ system rely on strict directory structures and files 134 A 4 1 Mona Copy the user mona mona directory structure to the experimental account gt cd gt cp rp user mona mona Xamine Files There are two Xamine files that get used to control the color and layout of Xamine To use the standard files simply copy them from the user mona directory gt cd gt cp p user mona Xamine A 4 2 Tandem Copy the user mona shared exp_tandem directory structure to a local tandem di rectory gt cd gt cp rp user mona shared exp_tandem tandem A 4 3 Experiment Readout needs an experiment account to run properly Create this by gt cd gt mkdir experiment When Readout is first tested it will automatically make the subdirectories current orphans and staged Also a folder is made after each run is completed called run H 135 Current The contents of the experiment current directory is copied into each run folder It can be made by hand before starting Readout All important setting files for the experiment should be linked to from the experiment current directory Since there are also sweeper settings files to be linked I make two folders gt cd experiment gt mkdir current gt cd current gt mkdir mona_settings gt mkdir sweeper_settings Then I fill the mona_settings folder with important MoNA file
26. E A J E 2500 E 7 S we 5 gt P gt gt 5 2000 1 58 300 z 1500 F 4 4 200 1000 F J 4 500 E J og o L J 0 150 100 50 0 50 100 150 20 0 20 40 60 80 100 120 140 CRDC2 x position mm CRDC2 y position mm Figure 4 25 The important focal plane parameters are compared to ST mona simu lated events for experiment 07503 Due to the small acceptance of CRDC2 in the y direction it was not used to gate 10Be cuts some of the neutrons that receive a strong vertical kick in the center of mass from the decay of excited Be The thickness of the iron also reduces the overall neutron flux at MoNA by 4 due to scattering off iron nuclei at angles that miss MoNA This 4 loss in acceptance must be taken into account when determining MoNA s intrinsic efficiency All these acceptances were programmed and accurately into the ST mona simula tion code and used to adjust the detected count for the system efficiency calculation The MoNA acceptance as a function of decay energy is reflected in Figure 4 28 For higher decay energies the neutron acceptance dominates the losses while for lower en ergies the acceptance is cut uniformly by the steel blocker and the broad y distribution and are not dependent on decay energy 90 2000 ST mona 1600 _ N o o arbitrary units 00 S S O o 0 0 4 0 3 0 2 01 0 01 02 03 04 Focal plane y position m Figure 4 26 The y position at the focal plane thin scintillator is simul
27. HOME mona config export MONASETUP HOME mona config MoNA_setup_run tcl 143 export TREADOUT HOME tandem readout export TCONFIG HOME tandem spectcl export TSPECTCL HOME tandem spectcl export READOUT_SWEEPER HOME sweeper scriptedReadout export SPECTCL_SWEEPER HOME sweeper spectcl Add export EXP_HOME projects proj to the very top of the scr file Be sure to fill in the appropriate directory address and note that one can t begin an exported environment variable with a number but be creative with the EXP_HOME name to ensure it is not reused Edit all the following environment variables to begin with the name you choose for EXP_HOME instead of HOME This maybe the only executable you need to edit but follow a similar procedure for any others that may need it 144 Appendix B MONA SpecTcel Analysis Guide B 1 Introduction This guide is intended to give you an idea of how to use SpecTcl to analyze data that MoNA has collected This guide is written for the analysis of data taken from cosmic rays thus this may not be useful to you However it should give you an idea of what s involved in a fairly simple application of SpecTcl which is all it s intended to do Please read the NSCL documentation and general user guide 90 to familiarize yourself with the basic commands especially the spectrum and gate commands B 1 1 MONA Parameters MONA has 144 bars and 288 TDC 288 QDC chan
28. Pres 17 52 01 1911 mean orri 1501 4 ag 20 207 2 9 a annir bes 17 52 01 40 menn orr Aio 17 52 01 E gt _ Geometry Zoom Display a Display 7 Figure C 5 Tmean difference spectra 7 Look through the spectra in Xamine to make sure the data is usable i e that there is a distinct peak in each Tmean difference spectrum as shown in Figure C 5 8 Write all tmean diff spectra using the Write Tmean_offsets Spec button on the MONA SpecTcl window 9 Open a spice terminal window in directory mona contrib tmean_offset_cal and then open MoNA_Tmean_indie_offsets Note that before you run this ex ecutable you must delete or rename the file mona config MoNA_Tmean_indie _offsets tcl otherwise running the code will return an error This will open the executable that will calculate the Tmean independent offsets It calculates these by finding a gravity fit weighted average 0 3 ns to either side of the peak bin measured The program assumes the x axis in ns is symmetric about 0 i e 10 to 10 ns 185 For layer A the offsets for bar N are Offset Theory A8 AN Measured A8 AN For the cross terms e g A15 B0 the offsets for layer X are Offset Theory A15 X0 Measured A15 X0 Offset A15 A8 For all other layers the offsets for layer X and bar N are Offset Offset A15 X0 Theory X0 XN Measured X0 XN 10 Edit MoNA_setup_run tcl and save wit
29. Schulz S Thummerer S Torilov and A Tumino Nucl Phys A 734 345 2004 S D Pain Experimental Measurements of the N 8 Shell Breaking in the 1 Be Ground State PhD thesis University of Surrey 2004 D J Millener Nucl Phys A 693 394 2001 A Schiller N Frank T Baumann D Bazin B A Brown J Brown P A DeYoung J E Finck A Gade J Hinnefeld R Howes J L Lecouey B Luther W A Peters H Scheit M Thoennessen and J A Tostevin Submitted to Phys Rev Lett 2007 C Hoffman et al to be submitted 2007 A Horvath K Ieki A Kiss A Galonsky M Thoennessen T Baumann D Bazin C Bordeanu N Carlin M Csanad F Deak P DeYoung N Frank T Fukuchi Zs Flp A Gade D R Galaviy A Galonskz C Hoffman R Iysak W A Peters H Schelin A Schiller R Sugo Y Seres and G Veres Eur Phys J Ay 27 217 2005 G A Christian et al to be submitted W Rogers et al http physics westmont edu research cmda J Miller M Strongman L Elliott D B Hecksel M M Kleber P J Voss T Pike R Pepin A Ratkiewicz and W A Peters MoNA Calibration Guide Technical report MSU NSCL 2005 http www cord edu dept physics mona analysis html W A Peters Tandem SpecTcl Guide Technical report MSU NSCL 2006 http www cord edu dept physics mona analysis html R Fox SpecTcl User s Guide Technical report MSU NSCL 2003 http docs nscl msu edu daq spectcl
30. TDC channels that do not have valid QDC data The CHitParam code could be edited to require a QDC signal at each end of the MoNA bar but this will cut a non negligible fraction of events from the data and we use the ToF parameter to calculate neutron energy anyway 208 10 11 12 13 BIBLIOGRAPHY K S Krane Introductory Nuclear Physics John Wiley and Sons 1988 A Bohr and B R Mottelson Nuclear Structure volume 1 World Scientific New Jersey 1998 M Goeppert Mayer The Shell Model 1963 Nobel Lecture M Goeppert Mayer and J H D Jensen Elementary Theory of Nuclear Shell Structure Wiley New York 1955 J K Tuli Nuclear Wallet Cards National Nuclear Data Center Tth Edition April 2005 E K Warburton and B A Brown Phys Rev C 46 3 923 1992 M Thoennessen S Yokoyama A Azhari T Baumann J A Brown A Galon sky P G Hansen J H Kelley R A Kryger E Ramakrishnan and P Thirolf Phys Rev C 59 1 111 1999 I Tilquin Y El Masri M Parlog Ph Collon M Hadri Th Keutgen J Lehmann P Leleux P Lipnik A Ninane F Hanappe G Bizard D Durand P Mosrin J Peter R Regimbart and B Tamain Nucl Instr and Meth A 365 446 1995 Nuclear Enterprises Ltd Edinburgh Scotland UK P D Zecher A Galonsky J J Kruse S J Gaff J Ottarson J Wang F Deak A Horvath A Kiss Z Seres K Ieki Y Iwata and H Schelin Nucl Instr and
31. and J Hoefkens COSY INFINITY version 8 1 Technical Report MSUCL 1196 MSU NSCL 2001 http cosy nscl msu edu N Frank A Schiller D Bazin W A Peters and M Thoennessen Nucl Instr and Meth A submitted May 2007 H Scheit Simple Track for MoNA 2006 NSCL M B Chadwick et al Nucl Data Sheets 107 2931 2006 A Fass A Ferrari J Ranft P R Sala G R Stevenson and J M Zazula Fluka92 In Proceedings of the Workshop on Simulating Accelerator Radiation Environments 1993 P A Aarnio et al Fluka user s guide Technical Report TIS RP 190 CERN 1987 1990 R Madey F M Waterman A R Baldwin J Knudson J D Carlson and J Rapaport Nucl Instr and Meth 151 445 1978 R J Glauber Phys Rev 99 5 1515 1955 R H Stokes and P G Young Phys Rev 178 2024 1969 P G Hansen and B Jonson Europhys Lett 4 409 1987 T Otsuka M Ishihara N Fukunishi T Nakamura and M Yokoyama Phys Rev C 49 5 R2289 R2292 1994 T Nakamura S Shimoura T Kobayashi T Teranishi K Abe N Aoi Y Doki M Fujimaki N Inabe N Iwasa K Katori T Kubo H Okuno T Suzuki I Tanihata Y Watanabe A Yoshida and M Ishihara Phys Lett B 331 3 4 296 301 July 1994 N C Summers 2007 Private communication K L Yurkewicz D Bazin B A Brown J Enders A Gade T Glasmacher P G Hansen V Maddalena A Navin B M Sherrill and J A Tostevin Phys Rev C 74 2 024
32. be seen for the lowest and highest rows caused by the finite opening 14 cm of the Sweeper magnet s gap The data is taken from experiment 03048 Coulomb excitation of Be on a gold target at 90 MeV u 900 800 700 600 2 500 3 400 O 300 200 100 0 A 0 1 2 3 4 5 6 7 8 9 10 Neutron lab angle degrees Figure 4 13 The neutron angle relative to the beam axis has spikes due to the quan tized y parameter 76 8000 7000 6000 5000 S 4000 S 3000 2000 1000 MONA Layers Figure 4 14 Plot of total hits in each MoNA layer for neutrons from experiment 03048 The effective depth of each bar may be slightly less then the actual depth due to the dead layer effect This effect is caused by the charged recoil particle from the neutron collision not having a long enough path within the bar to deposit sufficient light to trigger the CFD with 10 mV threshold For a 2 MeV proton recoil this dead layer is less than 3 mm This effect is taken into account in the GEANT simulation and has little effect on the resolution of 5 cm for both the y and z directions A neutron that reacts within the small dead layer of a MoNA bar and the recoil proton travels into the next layer will record a wrong z position by no more than about 5 3 cm 4 2 4 MoNA Energy Resolution The velocity vn and kinetic energy Kn of the neutron are determined from the calculated reaction point within MoNA relative to the target and th
33. beam was directed into the N4 vault and onto a reaction target of Be with a thickness of 102 mg cm at the target position in front of the Sweeper magnet The Sweeper magnet focal plane detectors were used to identify and count the 80 600 500 A e 03038 data gt f g y ST mona o 400 Ly N 8300 7p 200 O O 100 0 0 5 1 1 5 2 2 5 Decay energy MeV Figure 4 17 The He decay energy is fitted with a Breit Wigner curve run through ST mona with peak energy at 0 425 MeV and I width equal to 0 18 MeV charged particle reaction products see Figure 3 2 MoNA was positioned 8 2 meters from the reaction target 4 3 2 Resolution Results Figure 4 17 shows the best reduced x fit Breit Wigner decay curve on top of the data experiment 03038 The resonant energy is 0 425 0 020 MeV and the T width is 0 18 0 04 MeV The uncertainties are calculated by the values needed to increase the reduced x fit by 1 0 The current results agree well with previous measurements from References 20 57 that report the ground state resonance at 0 43 0 02 MeV and a width of 0 16 0 03 MeV This confirms the individual resolutions used as an input for ST mona and the ability of the simulation to reproduce data 4 4 Measured MoNA Sweeper System Efficiency The Coulomb excitation of a nucleus from passing near another nucleus by exchanging a virtual photon 22 is well understood and calculable 23 and therefore is an ide
34. cut by the vertical limit from the drift time of CRDC2 at 100 mm Transmission is determined by integrating the Gaussian fit and is 834 target thickness yields 68 7 mb The largest uncertainties are from the fits to the acceptance regions of CRDC2 and the low total count of Be As displayed in Table 5 1 and plotted in Figure 5 6 this results in a reduction factor Rs of 0 66 0 07 This factor expresses the reduction of the single particle occupancy due to short range correlation effects Since the 0p3 2 neutron knockout Be 9Be 2Be X is the mirror process to the proton knockout in neutron deficient 9C 68 this measurement allows a comparison of single particle abundances for the same Ops 2 shell at two extremes of the chart of the nuclides Not surprisingly due to their near mirror relationship there are several similarities shared by the Be Be and 9C 8B systems Both reaction residues have no bound states and their AS values are both near 13 MeV C 8B Sp Sn equal to 12 96 MeV and 1Be 9Be Sn Sp equal to 12 8 MeV Comparing this new result with the Ops 2 proton knockout of C near the proton drip line reveals a decrease in the reduction factor from 0 82 0 06 to 0 66 0 07 Some differences 102 CS exp E Schol model p d and d p O e e p QO n knockout E p knockout 20 10 0 10 20 AS MeV Figure 5 6 The reduction factor for a variety of different reactions is plotted versus the diffe
35. do the same thing for the last cell Xpos_A15 in Xamine as you did for the first but use different points for the cut use the positive value for the second since you re trying to get a feel for how the ray travels through MoNA We will gate the middle bars to see the cosmic rays travel from top left to bottom right through layer A Finally you need to set up an and gate If you called the first gate for Xpos_A0 gatel and the one for Xpos_A15 gate2 then to create an and gate going to the TkCon shell and typing gate new andgate gatel gate2 155 Here gate new andgate tells SpecTcl that you are making a new gate called andgate the tells it that the gate is a logical and with gatel gate2 as the argu ments so that the gate is only true if both gate1 and gate2 are true This is the only way to apply more than one condition on a spectrum An and gate using can depend on many other gates just list all the ones you want to include inside the brackets B 3 6 Copying Spectra Now that you ve got your gates set up you want to make a copy of all the spectra youll be applying them to This is mainly for safety reasons you don t want to change your source data by gating it Go to the TkCon shell and type spectrum new xpos_a0_gatel 1 Xpos_A0 150 150 301 Here you re making a new spectrum named xpos_a0_gate1 from parameter Xpos_AO with a range of 150 to 150 cm and a resolution of 301 bins Repeat this for
36. filename tcl This will read the file and run the commands between each lt return gt as if typed one at a time as an in line command into the TkCon Window If there is a syntax error in the file the process breaks and all the commands after the error are not read in In that case just re edit the file comment out any commands before the error and source it again B 5 2 Creating Custom Pseudos In the course of your analysis you may find that you need to create a spectrum that s a calculation of two or more calibrated parameters or any calculation not done within SpecTcl already This technique will work for any reasonable arithmetic operation A pseudo parameter is really just a procedure implemented while filling the SpecTcl parameters Now you can finally tell SpecTcl to do whatever it was you wanted it to do It can output any value you choose into a new parameter that can be put into a spectrum like the regular parameters Three commands are involved Parameter First you need to define a new parameter It s a good idea to pick a high number for the id higher then 5000 as this command won t work properly and will cause problems down the road if you assign an id that is already in use Do not choose a number that is too high Every parameter id is created up to the highest number so extra large values will slow the analysis 160 Pseudo Now you need to define the pseudo The syntax here is a bit more complex
37. focal plane detector box to record the angle and position of the fragments after being deflected by the Sweeper magnet They each have 128 cathode pads spaced 2 54 mm apart in the dispersive plane The vertical position is measured from the drift time to the anode wire of the ionized electrons released by the charged particles through the gas The anode wire uses a nominal voltage of 750 V Both CRDCs share the same gas handling system and use 20 iso butane and 80 CF4 with an operating pressure of 50 150 Torr CRDC1 and CRDC2 are calibrated with a mask that is driven up in front of each CRDC After proper calibration the positions recorded by the CRDCs are accurate to within a millimeter The angular resolution depends on the separation between the CRDCs within the detector box and is 0 06 when one meter apart CRDC1 is fixed inside the front edge of the detector box and its position information is used when calculating the transformation matrix for fragment energy reconstruction 3 3 3 Ion Chamber The Sweeper ion chamber IC is a gaseous detector with 16 collection plates that get recorded by 16 peak sensing ADC channels Their sum is used as an energy loss dE measurement The chamber is filled with 100 200 Torr of P10 gas 90 argon and 10 methane The negative drift voltage is tuned for the charge range of particles being detected and is typically between 600 1200 V The 16 collection plates are generally held at a positive potential
38. hvfit directory also and outputs the QDC slope and offset values to the MoNA configuration directory So a third link is needed here gt rm spectclconfig gt ln fs mona config spectclconfig C 2 High Voltage Gain Matching The phototubes PMT s of each MoNA detector bar may vary in their sensitivity for a given voltage setting If one tube is more sensitive than another a standard flash of light emitted from varying places along the bar will not be detected with uniform efficiency If a weak light flash occurs nearer the more sensitive tube that tube has a good chance of detecting it However the other less sensitive tube may not detect it due to the fact that the light signal attenuates on its journey across the bar and therefore becomes even weaker This will cause low energy hits to be detected with non uniform efficiency across the length of the bar because both tubes must fire for an event to be considered good Therefore data taken in that particular detector bar will be skewed To solve this problem the voltage levels of the two PMT s of each MoNA bar must be gain matched Each tube must have its voltage level matched with the other in such a way as to ensure uniform detection efficiency across the bar Gain matching is done using a routine that finds the position of the cosmic peak from a particular run and determines and executes the best adjustment in the voltages of the tubes to properly gain match the detector Beca
39. ma bamse e my i sywe weri ves Unna ESOS ORR ER me oje sasara arwi tan mawmer mr i eraut siunt vat MA AINAN ARR ONO Figure 4 1 Neutrons black dot GEANT and y 3 2 1 simulation Reactions products include proton scatter blue dotted lines rays material as a function of the neutron energy reaction residue as a function of the released energy Cross Sect 10n 1 React ells A GEANT uses an extensive library of neutron reaction cross sections on a variety of along with the relative density of hydrogen and carbon in elements These are used BC408 to determine the neutron reaction cross section for one MoNA bar By using the FLUKA MICAP method within GEANT the neutron cross sections are determined H inelastic Helastic C inelastic C elastic 0 01 0 1 1 Neutron kinetic energy GeV Figure 4 2 Inelastic and elastic reaction cross sections of neutrons on carbon and hydrogen used by the GEANT simulation The FLUKA package cross sections are used above 20 MeV Cross sections taken from the evaluated nuclear data files ENDF 52 are used below 20 MeV 1 8 1 6 aa 10 fluka total fluka elastic b fluka inelastic 1 0 8 ss sectio 206 O 0 4 r 0 2 0 0 01 0 1 1 Neutron kinetic energy GeV Figure 4 3 Inelastic and elastic reaction cross sections of neutrons on BC408 MoNA plastic used by the GEANT simulation 65
40. matrix from the focal plane coordinates to target coordinates the newest inverse maps also inputs the forward tracked target position Directions to utilize this feature are described in section 4 The most important parameters calculated by this method are sweeper fp track ata bta yta sweeper im track xta yta ata bta sweeper fp track dta These are used to further calculate the energy of the fragment at the midpoint of the target parameter target e After I ve found a good_hit in the CHitParams cpp these calculations are performed m_fFragmass is the mass of the fragment in units amu double Famu m_fFragmass double amu 931 494013 MeV amu 199 Calculating energy from Brho mass charge values double Frag_betagamma_o m_fFragBrho 3 107 m_fFragQ Famu double Frag_gamma_o sqrt Frag_betagamma_o Frag_betagamma_o 1 0 Frag_KE_o is the central track energy in MeV u double Frag_KE_o amu Frag_gamma_o 1 0 set energy from delta ParamDT and central_energy in MeV u then add m_fTargeteloss target eloss to target e double Frag_KE double rEvent m_nParamDT 1 0 Frag_KE_o m_fTargeteloss rEvent m_nResultTE Frag_KE set target e in MeV u The target eloss variable m_fTargeteloss is the estimated energy the frag ment loses half way through the target in MeV u and it is added to the tracked energy to get the energy at the midpoint This is a decent
41. measured time resolution where the time difference between neigh boring bars is plotted for cosmic ray muons traveling straight down through them is plotted in Figure 2 15 The Gaussian fit shown has a standard deviation of 0 18 ns Since this data is self triggered and self stopped the time resolution of any external timing detector must be added in quadrature to this value for an accurate resolution of the neutron ToF yp The ToFy parameter is also effected by CFD walk for events that do not deposit 72 12000 Geant x x 10000 with dt spread 8000 Z 5 gt o 6000 2 4000 40 2000 0 10 8 6 4 2 O 2 4 6 8 10 X position resolution cm Figure 4 10 The neutron interaction point x minus the center of deposited energy xz is the intrinsic resolution of the MoNA plastic Calculated by GEANT it shows two trends The wider component of the dashed line that dominates the edges of the spectrum is from interactions off carbon that at first do not deposit enough energy to trigger the CFDs The central region shows the intrinsic position resolution for a scattered proton The dotted line includes effects from timing resolutions 0 18 ns of the signal and is fitted by a Gaussian distribution blue line with a standard deviation of 3 cm enough light in both PMTs to ensure proper CFD timing For events where the signal amplitude is close to the CFD threshold the CFD timing acts more like a leading edge discriminat
42. neutron knockout of 2Be to compare to previous works Chapter 6 details this experiment and the results 10 Chapter 2 Modular Neutron Array MoNA A collaboration of eight primarily undergraduate institutions along with Michigan State University and Florida State University separately requested and received Na tional Science Foundation grants to build and assemble the Modular Neutron Array MoNA 14 Undergraduate students built and assembled 16 modules from bars of plastic scintillator and tested them 15 Table 2 1 lists the founding institutions of the MoNA collaboration The array of nine vertical layers one layer from each school with 16 modules each was assembled at the National Superconducting Cyclotron Laboratory NSCL at MSU 2 1 Design MONA was designed for use with in flight fragmentation rare isotope beams produced by the CCF at the NSCL 31 Secondary beam energies are generally between 30 100 MeV u Neutrons from unbound states populated within the reaction target will have similar energies and are forward focused in the lab Reconstruction of the decay energy of the unbound states requires both the energy and position angle of the neutron see Section 3 6 1 With sufficient distance from the target the time of flight ToF can be used to calculate the velocity and energy while the position 11 Table 2 1 Founding institutions of the MoNA collaboration and their principle inves tigator for the NSF g
43. of neutron energies and subtracting a background the number of detected neutrons was deter mined for each energy range The number of detected neutron events above a software threshold for each energy range was divided by the GEANT simulation s efficiency for the corresponding threshold to yield the calculated count of incoming neutrons Fig ure 4 8 shows the calculated number of neutrons striking one MoNA module during this test run for four energy ranges and three threshold values Since the energy dist ribution of the neutrons was not flat the count for each 5 MeV bin does not need to be the same as the others but the three points for each bin should be consistent if the light response calculations in GEANT are correct The efficiencies used for each 69 2000 5 g 1800 0 Cc O 1600 5 cp 1400 z gt t 1 0 e t 1 5 t 2 5 Q 1200 1000 30 35 40 45 50 Neutron kinetic energy MeV Figure 4 8 The incoming neutrons per 5 MeV energy bin is calculated from the simulated efficiency for each threshold value plotted in Figure 4 9 o O w e w 0 R 0 25 o mb a One module efficiency o o a ho 20 25 30 35 40 45 50 55 60 Neutron kinetic energy MeV Figure 4 9 Efficiency curves as a function of neutron energies for one MoNA module The various simulated thresholds are labeled and the data points correspond to the relative efficiency for valid TDC events in MoNA using the incoming rate from Figure 4
44. off line analysis E Login as the experiment onto tapehost 2 gt cd projects proj 3 gt cp rp user H 4 Check that all subdirectories got transferred properly 142 A 6 4 Executables The executable files specifically those that end in scr use environment variables that are defined inside the user s bashrc file to navigate to the proper configuration files Once the experimental user account is deleted the user becomes you and not the experimental account This means that unless you only want to analyze one experiment you can t define these environment variables inside your bashrc file To overcome this limitation we must define the environment variables used for a specific executable directly in the file that sources it 1 Start by opening the tandem_spectcl scr for editing from the projects di rectory it was copied into 2 Comment out or delete the first couple lines that source etc profile and bashrc 3 Open the experimental account s bashrc file 4 Copy list of exported variables and paste them at the beginning of the scr file They include export SHARED_READOUT user mona shared readout export SHARED_SCALER user mona shared scaler export SHARED_SPECTCL user mona shared spectcl_shared export MONA_DAQ HOME mona daq export MONA_READOUT MONA_DAQ readout export MONA_SCALER MONA_DAQ scaler export MONA_SPECTCL MONA_DAQ spectcl export MONA_CONFIGDIR
45. oie ee Se ee osa 170 Os QDC Calibratio ac do a ee we ee ge BS he eS 171 C 3 1 Calibration Steps Vb toa ae e amp a ee eke E 171 G A ING Calibre mom a e ES AAA ELARG 173 C 4 1 Record Time Calibration Run 173 C 4 2 Running Calibration Code Ls a a a io 176 Gal Eile Names a a aa ia tarde ia 179 C 5 X Position Calibration 0 0 000 0 000000000084 179 CSL Record Cosmic RUN 2 e au bone a eee is 180 C 6 Independent Tmean Offsets 00000 ee eee 183 C 6 1 Finding Independent Offsets 183 Tandem SpecTcl Guide 187 Dap Getting Started dari eh ok Oe oe EOE Ak oe OE eRe EE 187 D 1 1 Standard Variables 2 5 lc A ae eke ee GBs Ala 187 D 1 2 Loading a Settings File aes Ae A ee ee a ey 188 de Tree Str ctute son eo ahi BIR ns te ae ae ce ed 189 LESS Sweeper Tree oo Sy Se ah We ae Ske See he Beg tir 189 D 22 User Ireen Solid to Ae a a A 190 D 2 3 Using the Tree Parameter GUI 190 D 3 SpecTcl Code Procedures 0 0 ee eee ees 192 D 3 1 Raw Sweeper Parameters o 192 D 3 2 Tree Calibrations y es as fh od 194 D 3 3 Third Level Parameters 00 el a Pee 196 Did MONA Hits do a sa ello A AA AS 197 Didios Valid Tandem Hit o ea e p a Sue he TE Be AL ee een a 197 D 3 6 Tracked Parameters o ak ot Bak ee 199 D 3 7 MoNA Tandem Parameters 204 200 D 4 Analysis Suggestions a eg Oe we eee 203 D 4 1 Tandem Control Buttons 2 0 0 4
46. plastic modules 10 by 10 by 200 cm arranged in an array of 9x16 to cover a large area and accept forward focused neutrons at energies greater than 30 MeV y axis Figure 1 4 shows a computer drafted image of the design for MoNA The charged particle residues from a neutron unbound state are deflected by a large gap dipole magnet called the Sweeper magnet 16 17 allowing the neutrons to pass through at zero degrees see Section 3 2 for details The Sweeper Magnet was built at the National High Magnetic Field Laboratory at Florida State University 1 4 Commissioning Experiments The first experiments for MoNA were performed to test the design goals of the system and quantify properties like resolution and efficiency To measure the resolution of MoNA a known resonant energy with a known width must be replicated and com pared to previous results To measure the system s efficiency a reaction with a known cross section for the production of a neutron fragment pair must be performed to cal culate the ratio of the known number of neutrons produced to the number of neutrons recorded by MoNA 1 4 1 Unbound He Ground State The ground state of He is unbound and an ideal choice to measure the energy resolu tion of the reconstructed decay energy for the MoNA Sweeper system This resonant state has been studied extensively and can be used for testing a neutron detector system The width of the He ground state resonance is known to be 1
47. proper reconstruction The comparison of the decay curve from ST mona 84 Focal plane x angle degrees 30 35 40 45 50 55 Fragment ToF ns Figure 4 19 Isotopic identification by the method discussed in Section 3 4 2 using the dispersive angle in the focal plane 0 and the fragment ToF The gates select from left to right Be Be and HBe For this experiment the separation did not require calculating ToF giq using the El cross section calculated through Equation 4 6 to the experimental data is shown in Figure 4 21 The close match between the experimental and simulated curves again confirms the correct simulation of the MoNA Sweeper system 4 4 4 Second Be Experiment for Efficiency Measurement Unfortunately the beam blocker installed for the 03048 experiment prevented an accurate measurement of the incoming rate and therefore a second Be Coulomb breakup experiment was performed The setup for 07503 was nearly identical except that the blocker was moved to accept a large portion of the distribution In addition the Sweeper magnet had since been tested to a higher magnetic setting sufficient to deflect the unreacted beam into the focal plane detectors for a beam rate calibration A disadvantage of 07503 was the limited acceptance of CRDC2 The drift voltage was 85 1800 mr 1000 m a 1600 F 03048 data l 03048 data 1400 800 ie ST mona l m
48. scattering events Events where the second hit is from the same neutron as the first hit are difficult to determine conclusively The energy deposited by scattering off a proton may be a simple relation Qi x cos 01 2 7 1 where 01 2 is the scattering angle between the first and second hit in MoNA and Q1 is the recorded deposited energy of the first hit But there is a high cross section for elastic and inelastic scattering off of carbon that does not follow this relation Nonetheless if the signature of proton scattered neutron events can be determined for reactions that only have one extra neutron in the system like the Coulomb excitation of Be to Be n the ratio of these proton scattered events to the total scattering events should be constant for a specific energy since the ratio of carbon to hydrogen in MoNA remains constant If the ratio of proton scattered event to the total is significantly different for a particular experiment the relative contribution from more than one neutron could be calculated Current efforts to create a robust gate for identifying proton scattered events include gating the inside of the causality cone mentioned above and looking at the energy versus scattering angle spectrum for events that correspond to Equation 7 1 One difficulty with calculating scattering angle is again the quantization of MoNA positions in the y and z directions A large scattering length gate is applied here as well that i
49. the first neutron that is simulated by the thermal distribution Equation 4 3 at 3 5 MeV with a peak energy near 0 5 MeV The MoNA Sweeper system acceptance for this distribution is simulated by ST mona and the resulting broad curve is illustrated in Figures 6 7 and 6 8 by the light blue line An improved feature of the current experimental setup over the previous exper iment is that by utilizing MoNA multiple neutrons can be recorded for one event The absolute efficiency of MoNA is near 75 and thus the efficiency to record two separate neutrons is about 50 In contrast the DeMoN array used in 30 has an absolute efficiency near 10 and thus the coincident two neutron probability is closer to 1 An effort is being made to positively identify two neutron events that can only come from the diffractive breakup of 12Be to get a more precise measurement of the shape and intensity for this decay channel thereby improving the fit to the remaining resonances This effort is discussed in more detail in Section 7 2 6 4 Conclusions The relative cross sections measured in the current experiment agree well with the pre vious measurements including the relative intensity for Ods 2 knockout and confirms the spectroscopic factor for the 1n knockout to the 5 2 state in 1 Be predominantly from the 0d 12 configuration in the ground state wave function of Be This spec 120 troscopic factor for the unbound decay channel does not increas
50. the directory containing the event files you wish to analyze maybe stagearea complete If they are not set or set incorrectly set them using the TkCon window set WorkDirectory mona daq spectcl set EventDirectory stagearea complete B 3 2 Creating Spectra Use the spectrum in line command in the TkCon window to create spectrum from any parameters To view a list of the parameters type parameter list Or press the List Parameters button on the bottom of the SpecTcl control window If you forget the syntax just type spectrum and the error message will display the syntax it s looking for When you ve made a spectrum of a parameter it must be bound to SpecTcl to view on Xamine so type the command sbind all There are a few pre set buttons to create and bind many of the commonly used spectra types These buttons are on the left side of the SpecTcl control window For viewing the X position of each bar you need to create position spectra do this by clicking the Create Pseudo Spec button on the SpecTcl Control window After you ve done this you can press the List Spectra button to list all the current spectra loaded into SpecTcl and verify that spectra with the group name Xpos exist 153 B 3 3 Configuring Xamine In the Xamine window click on the Geometry button in the lower left hand corner of the screen Change the configuration of the resulting pop up dialogue to 4x4 Then click the Display butt
51. the incoming velocity of the first hit in MoNA versus the velocity between the first and second hit and gating on the causality cone in distance and time from each first hit event Only a separate neutron or random background events triggers a hit outside of this causality cone The biggest challenge for implementing this analysis technique is the quantization of the MoNA position parameters A neutron that triggers two neighboring MoNA bars in either the y z directions will be recorded with a 10 cm distance between the two hits For events where the first hit was near the back edge 10 cm is an overestimation and vice versa for an event where the first hit was near the front face of the bar For these cases the velocity between the first and second hit has a large uncertainty To reduce this problem the data set should be limited if a sufficient number of counts are available to events where the distance between the two hits is at least 50 cm Indeed future 123 experiments using MoNA looking for two neutron coincident events are changing the configuration of MONA to include a large gap between layer D and E creating two walls for better resolution of the velocity for events where the first hit is in the front four layers A D and the second hit is in the second group of layers E I An additional way of analyzing two neutron events is by the relative intensity of total neutron events compared with events that determined to be one neutron
52. the pedestal peak is usually over a hundred times stronger than the count rate into the rest of the bins in the raw QDC spectrum Since these counts in the pedestal peak come from null value events and have no corresponding TDC data including them in the data stream can unnecessarily slow the readout process A hardware threshold can be set for each QDC channel such that channels with a digitized value less then the threshold will be ignored during readout The threshold bit of the CAEN V792 QDC modules can be set in multiples of 16 bins i e 0 16 32 64 80 96 112 128 144 This can cause insufficient pedestal subtraction when the pedestal peak for a given QDC channel is near any of these values Figure 2 9 shows the QDC response for background events when all 32 PMTs for a whole layer are turned on the width of the pedestal peak is about five bins Two possible threshold values are drawn as dotted lines at multiples of 16 If the pedestal peak value is just below one of the possible threshold values like PMT B 00 L left PMT for the first bar in the second layer shown in Figure 2 9 Setting the threshold to the nearest threshold value at bin 128 will still allow nearly half of the pedestal peak to be readout The relative magnitude between the allowed half of the pedestal peak to the rest of the raw spectrum will still be too great for efficient data recording of these channels Another situation is shown in Figure 2 10 for PMT B 02 L
53. where the pedestal 27 1000000 100000 10000 1000 arbitrary units 100 10 80 96 112 128 144 160 176 Raw QDC B 00 L bins Figure 2 9 The raw QDC pedestal peak for PMT B 00 L is too close to threshold value bin 128 to effectively reduce the null result count rate Both the simple and improved methods for setting the threshold value sets it to 144 for this QDC channel peak is a few bins below a possible threshold value Here setting the threshold at the next nearest possible value at bin 128 would be ideal to cut most of the pedestal peak intensity and cut a minimum of the overall spectrum but a consistent automated method for determining the best threshold value to use and a case by case basis is not simple Simple threshold cuts For the 12Be experiment the thresholds were set to the second nearest threshold value above the pedestal peak This cuts a minimum of 17 bins above the pedestal peak from the QDC response as is the case for PMT B 00 L and a maximum of 32 bins for channels where the peak is equal to a possible threshold value Using the same automated process to set the QDC threshold for channel B 02 L will unnecessarily cut into the portion of the non pedestal spectrum at bin 144 As discussed above the nominal calibration for the QDC response is 800 bins per 20 5 MeVee 0 025 MeVee per bin Therefore this method for setting the QDC thresholds results in minimum energy thresholds of 0 42 to 0 82 MeVee dependi
54. will execute all the necessary tcl code to create the proper pseudos make the straight down gates and apply them to the new parameters Then choose Attach Multiple and select all of the run files recorded in step 1 Or using the attach pipe cat command in the TkCon window manually type in all of the run files recorded in step 1 then select Start Analysis In Xamine select Window gt Read Configuration and pick one of the three win tmean_cal_x x win window settings to view the spectra Allow SpecT cl to analyze all the buffers to ensure sufficient statistics This may take overnight since the run was so long When the data is read in click Update All in Xamine 184 EJH Xamine juser 05034 mona daq spectcl win tmean_cal_a c win objects wi 4o ao i bal bal 20 bil IL br Ac rr dorar A E i E Pas 17 52 01 LATI mempr Afa 17 52 01 140 rummy prry Ans 17 52 01 119 mem prre Rast 17 52 01 1201 memar Afas 17 52 01 1217 mean prr Afas 17 52 97 1221 ll le sp Ao E saws iis ma Ease anseo L141 ma jas 11 52 eta L 4 Pe 5 le Windu Spectra Opticns Graph pa E f 19 mamar din ansi y mer o es E a HE 28 meme dos ansao 91 me Bs fen 20 y nor Hi 51 mean arrr Nnn i od ry 4 i F p 193 menar Beet 17 52 01 196 menor
55. within the CUser cpp file User Potscint RF XFP These are calibrated timing parameters that use their respective slope offset values to calibrate the corresponding raw Sweeper timing parameter Potscint for example user tof potscint cal sweeper tof pot user tof potscint slope potscint offset Note that the slope for each raw Sweeper timing channel might not be the same and should be negative since the trigger thin_ul is used in common start mode Set the offset for the potscint from a known beam through the Sweeper magnet to the thin plastic Be sure to calibrate and save the definition file before trying to use the third level parameters described below User Thin Time The timing channels for the four PMT s of the thin scintillator are calibrated and then averaged user tof thin_ul cal sweeper tof thin tul user tof thin_ul slope user tof thin_ul offset similar for all four PMT s user tof thin_time cal ul cal ur cal dl cal dr cal 4 thin_time slope thin_time offset 194 The offset for thin_ul should be set to place the spectrum peak at zero and the other three thin times at or near 1 ns The offset for the average thin time should be set to place the peak at about 0 5 ns The slope for the four individual thin PMT times should be positive and then set the average slope to negative 1 so it can be subtracted properly from the potscint time User Thin Thick e loss Thes
56. 0 Viewer Collimator e Target 1 Target 2 Target 3 front view side view Figure 3 4 The target chamber drive ladder contains 3 target positions along with a 7 mm steel collimator and a fluorescent aluminum viewer plate of the beam This target scintillator is used for ToF measurements and is 0 254 mm thick BC404 organic scintillating plastic It is connected to a PMT whose output is processed by a CFD within the Sweeper electronics rack before being used as the common stop for all MoNA TDC channels see Figure 3 6 for a diagram of the timing cables The second drive assembly has six positions and drives a target ladder that holds the primary reaction target and three other alternate 1 by 2 inch targets shown in Figure 3 4 The six drive positions are for the fluorescence viewer plate four tar get slots and a retracted position The side view of the target ladder in Figure 3 4 shows how the viewer plate is angled so the glow created by the beam impacting the fluorescence can be seen through a window by a camera above the target chamber Installed in the top alternate target position is usually a thick 7 mm steel block with a 1 mm bore through the center position This block is used both as a collimator for the beam and since it stops a majority of the beam to create a flash of prompt y rays to calibrate MoNA s time offset 41 3 3 2 CRCDs There are two Cathode Readout Drift Chambers CRDC inside the Sweeper
57. 1 Edecay MeV Width keV decay residue Opain Fexp 1 274 T 100 IBe g s 224 44 1 04 0 2 2 186 T 150 Begs 18 3 3 7 1 04 0 4 0 082 T 15 10Be 2 13 7 2 7 1 41 0 05 3 50 thermal 10Be g s 271 54 0 96 0 09 116 7000 Be 2 0 042 dj 0 069 9299 Payo 0 056 Thermal 083 Sum ae 03048 data Scale 1 09 1 08 1 1 Counts per 50 keV 0 0 5 1 1 5 2 2 5 3 3 5 4 Decay energy MeV Figure 6 7 Fit to resonances listed in Table 6 2 simulated by ST mona with cross section ratios as reported by 81 The solid black line is the sum of the four decay curves 0ds 2 violet 1p3 2 red decay to Be 2 green diffractive channel light blue The fit is optimized for energies between 0 2 and 3 5 MeV The only fit parameter returns 1 09 0 01 for the scale between the simulation counts and the data used in Figure 6 8 the WBP shell model calculations described in 6 that would decay roughly 90 to the 2 state in Be Reference 30 attributes this decay channel to at 5 27 state that decays 50 to the 9Be ground state a decay energy of 3 46 MeV and 50 to the 2 state in Be They cite Reference 82 that identifies the 3 96 MeV as a 5 27 state and the state at 3 4 MeV as 3 27 A resonance with 3 46 MeV decay energy is outside of the acceptance range for an accurate analysis in the current study But Reference 80 describes a nearb
58. 2 0 pow Frag_x 2 0 r vector squared double Frag_distance pow Frag_R2 0 5 in cm double Both_Product Distance first_count Frag_distance 201 solve for cos theta AxBx AyBy AzBz A B double cos_theta Both_Sum Both_Product rEvent m_nResultThe acos cos_theta 180 0 PI Here again first_count refers to the first neutron event greater than 50 ns in time of flight Decay Energy The energy of the fragment at the target calculated using an inverse map along with the Theta parameter and the neutron energy is used to calculate the invariant mass of the decay state The velocity difference parameter KE_vdiff is also calculated from their respective kinetic energies from KE MeV u to gamma with c 1 Vc 29 9792458 cm ns double Namu Nmass amu Neutron mass in amu 1 008665 double N_beta pow Nvel first_count Vc 2 0 squared double N_gamma sqrt 1 0 1 0 N_beta double Frag_gamma 1 00 Frag_KE amu double Frag_beta 1 0 1 0 Frag_gamma Frag_gamma setting KE_vdiff parameter to velocity difference rEvent m_nResultKV sqrt N_beta sqrt Frag_beta Vc double Pneutron Namu sqrt N_beta N_gamma double Pfrag Famu sqrt Frag_beta Frag_gamma Calculate M072 PMo 2 m172 m272 202 2 En Ef PnxPfxcos theta first convert KE into total E for N and Frag double Eneutron N_gamma Namu
59. 304 2006 V R Pandharipande I Sick and P K A deWitt Huberts Rev Mod Phys 69 981 1997 212 64 65 66 67 68 69 70 71 72 73 74 75 76 77 J R Terry D Bazin B A Brown J Enders T Glasmacher P G Hansen B M Sherrill and J A Tostevin Phys Rev C 69 5 054306 2004 A Gade D Bazin B A Brown C M Campbell J A Church D C Dinca J Enders T Glasmacher P G Hansen Z Hu K W Kemper W F Mueller H Olliver B C Perry L A Riley B T Roeder B M Sherrill J R Terry J A Tostevin and K L Yurkewicz Phys Rev Lett 93 4 042501 2004 A Gade D Bazin B A Brown C M Campbell J A Church D C Dinca J Enders T Glasmacher P G Hansen Z Hu K W Kemper W F Mueller H Olliver B C Perry L A Riley B T Roeder B M Sherrill J R Terry J A Tostevin and K L Yurkewicz Phys Rev C 69 3 034311 2004 A Gade D Bazin C A Bertulani B A Brown C M Campbell J A Church D C Dinca J Enders T Glasmacher P G Hansen Z Hu K W Kemper W F Mueller H Olliver B C Perry L A Riley B T Roeder B M Sherrill J R Terry J A Tostevin and K L Yurkewicz Phys Rev C 71 5 051301 2005 J Enders T Baumann B A Brown N H Frank P G Hansen P R Heckman B M Sherrill A Stolz M Thoennessen J A Tostevin E J Tryggestad S Typel and M S Walla
60. 40 higher relative cross section for this cross section from 81 leading to a cross section of 19 4 mb 130 Appendix A Experimental Startup A 1 Introduction The follow chapters describe how to manage a new MoNA Sweeper experimental account Many experimental codes run programs that reside in the user mona account like Readout and SpecTcl but are called with setup and hardware files from within the new experimental account Most of the following procedures can be done from a spice machine by logging in with the experiment user account A 2 Experimental Account A couple weeks before the experiment is scheduled to run a user account should be created by the computer group The user account name is set to the experiment number issued by the PAC like 03038 or 05124 When the account is made a standard password will be assigned 131 A 2 1 Password There are two passwords for every user The first is the Linux or DAQ password and must be changed to a custom one when you login the first time by using the gt yppasswd command It will ask you to enter the original password and then your new one twice The second password is for the Windows machines Go to the Data U and login into a Windows machine and it will notify you that the standard password has ex pired and you must enter a new one The password manager allows only ones that include capitals lower case and numbers All three groups must be represen
61. 60 30 keV with a resonance energy of 430 20 keV 19 20 By simulating the MoNA Sweeper configuration including a reaction model target properties and the beam properties the simulated physics parameters like energy and angle can be compared to measured parameters The individual detector resolutions measured by various methods can be programmed into the simulation to determine which parameters contribute the most to the experimental resolution of the reconstructed resonant energy 1 4 2 Be Coulomb Breakup The Coulomb breakup of Be was used to measure the absolute efficiency of MoNA Since the cross section for the release of a neutron is calculable the recorded neutron events counted in MoNA directly relates to the efficiency of the MoNA detector after effects due to acceptance are removed The Coulomb excitation is induced by a high Z reaction target of gold and the cross section is calculated using by the virtual photon method 21 23 and the continuum discretized coupled channels CDCC method 24 25 By adjusting reaction parameters in a Monte Carlo simulation for both the 10Be residue and the accompanying neutron to match the recorded distributions in the focal plane and MoNA detectors the system acceptance can be extracted Once this is completed a calculation reveals the efficiency of the MoNA detector to compare to design goals and GEANT simulations see Section 4 4 1 5 First Physics Results from MoNA Sweeper
62. 8 described in the text 70 energy range for the three threshold values is displayed in Figure 4 9 As a check the reverse process was used to confirm the relative threshold for the CFD TDC hardware without a software gate on Q By dividing the ungated counts in the MoNA bar for each energy bin by the mean value of the number of incoming neutrons from Figure 4 8 the efficiency for just the valid TDCs events in each energy bin can be calculated The results displayed in Figure 4 9 are consistent with the calibrated 0 65 MeVee CFD threshold determined in Section 2 3 3 4 1 4 MoNA Sweeper Layout Simulation The SIMPLE TRACK simulation ST mona 51 was designed to reconstruct the full kinematics of the decay of an unbound nucleus to a neutron and a residue It includes acceptance cuts and individual detector resolutions to resemble the recorded distri butions It uses a forward transformation matrix from COSY INFINITY 49 to track charged particle through the Sweeper magnet into the focal plane detectors The simulation starts with a user defined distribution of beam particles at a target set to match the parameters recorded by the experiment A choice of reactions is then simulated within the target For knockout reactions populating a neutron unbound state a Glauber model kick is applied 56 The decay energy distribution itself can be entered as a flat distribution a constant single value a Gaussian distribution or a Breit Wigne
63. A TDCs can be measured by the known muon speed through each MoNA layer Since cosmic ray muons travel nearly the speed of light actually 29 80 cm ns the time signature of vertically traveling muons in successive MoNA bars can be calculated from the nominal distance between them 10 27 cm 32 600 500 2 400 c J 300 200 40 100 0 20 15 10 5 0 5 10 15 20 teft tight BTT ns Figure 2 13 The calibrated times for each end are subtracted in this time difference spectrum for bar B11 The width at one third the average amplitude of the center region is calibrated to the full 200 cm of MoNA plastic illustrated by the dashed line A coincidence gate is applied to the transverse position for the top and bottom bars in one layer to make certain the muons travel straight down through the layer In addition a gate that only accepts events that strike all 16 bars in that layer have to be fulfilled The mean time tpar of the two calibrated TDC parameters for the left and right end of each bar is calculated and is independent of the position of the interaction thar ToFn Hert trignt 2 2 4 This mean time is also the time of flight ToF parameter for a neutron hit in MoNA when the TDC common stop signal comes from a thin scintillator at the target posi tion during an experiment The mean time for the top bar number 15 is subtracted from each successive 33 X position bar A15 cm a ome A
64. A y position rows Figure 4 27 The x and y positions are simulated by ST mona and agree well with the data from experiment 07503 The center of the x distribution at MoNA is not at zero and this agrees with the input angle required to simulate the focal plane data The y distribution in MoNA is cut by the Sweeper gap of 14 cm and agrees well with the angles used by the simulation 4 4 8 System Efficiency Integrating the total El cross section dg curve from the virtual photon method Equation 4 6 between 0 to 4 0 MeV returns a cross section of 1 21 barns for a 197 Au target This number is used along with the target thickness d in mass per area to determine the reaction rate for the Be beam and thus the number of neutrons Nn available for the system to detect Nn 0E1Npeam d m N A TjiveE MONA fpMoNA fp 4 11 where m is the molar mass of the target and Na is Avagadro s number Trime is the live time ratio of the DAQ system eMoNA fp MONA and np are the intrinsic efficiencies and geometric acceptances of MoNA and charged particle detectors that make up the total system efficiency During the production run 85 8x10 Be nuclei passed through the gold target resulting in 71633 Be neutron pairs A total of 9900 or 13 8 were detected with the necessary detector combination to identify the Be residue and reconstruct the decay energy spectrum When the live time Tliye 47 45 is accounted for the total 92
65. Element Identification eee ae a ie sa 44 3 4 2 Isotope Identification ea a A 44 2 SENES lA e a A aS A AA aaa S aa araa a aS 46 3 5 1 MoNA Sweeper Coupling ooa aa a 46 3 5 2 Coincidence Timing eo pda a ira a a 49 3 5 3 MoNA Level 1 Trigger bogies ua ca Ee Se 50 3 5 4 Level 2 Logia aa a da 52 30 5 o A Aig hey cis eRe cates ha dg 53 35 6 Auxiliary Inputs A A A Go e 57 3 5 7 Level 2 Trigger Conditions 58 3 6 Decay Energy Reconstruction ido a aaa ia eS 59 3 6 1 Invariant Mass aa a a de 59 3 6 2 Charged Particle Reconstruction 60 3 6 3 Energy and Angle of Neutrons 62 Performance 63 4 1 Neutron Detector Simulation es oy ss a oe 63 4 1 1 Reaction Cross Sections o e 64 AL Light Response ri a ie a 66 4 1 3 Simulated MoNA Intrinsic Efficiency 68 4 1 4 MoNA Sweeper Layout Simulation 71 4 2 Resolution Measurements ooa aa 72 4 2 1 MONA Time Resolution sarao a a ea ee 72 4 2 2 MONA X Resolution cada E sd 73 4 2 3 MONA Y Z Resolution 300 air a 75 4 2 4 MONA Energy Resolution oaa a 77 4 2 5 Focal Plane Resolutions 0 78 4 2 6 Simulated Resolution o 78 4 3 THe Resolution Test le oa lla Abe Y cedo rl Bogs Ged 79 4 3 1 Experimental Setup oaoa 80 4 3 2 Resolution Results 1 aida e So ee oe ee Fed Se 8 81 4 4 Measured MoNA Sweeper System Efficiency 81
66. Figure 4 23 shows the second gate on the dispersive light ratio from the thin scintillator and the fragment ToF parameter necessary to gate out the remaining Be 86 1200 FA e 03048 data mk Q Q o ST mona 800 arbitrary units O S H S O o 200 0 0 5 1 1 5 2 25 3 Decay energy MeV Figure 4 21 The decay energy data from 03048 is overlaid with the simulated decay energy curve after acceptance and resolution effects are added by ST mona The acceptance of the thin scintillator rejects almost all events where the Be exits the target at angles above 2 5 degrees This has the effect of selecting almost purely Coulomb excitation reactions as evident by the good agreement to just the El cross section of Equation 4 6 The neutron time of flight ToF is shown ungated and gated on 10Be in Figure 4 24 The gated spectrum dotted line is scaled up by a factor of two to demonstrate the lack of background events in the coincident spectrum 4 4 5 Measured Incoming Rate In order to calculate the system efficiency the incoming rate of Be onto the target must be measured This was done by calibrating the beam timing scintillator raw scaler rate to the Sweeper focal plane thin scintillator with the 14Be unreacted beam tuned to travel straight to the middle of the focal plane thin scintillator By taking into account the live time of the production runs the total number of incoming nuclei can be calculated and com
67. Fragmentation to Multiple Unbound States 126 7 3 4 Double Neutron Experiments 127 13 5 Cosmic Ray Survey on boy oe ath dk an aa ee ee 128 7 4 Scheduled Future Experiments 128 Conclusion 129 8 1 MONA Efficiency and Resolution 129 8 2 10Be Neutron Knockout o 129 8 3 12Be Ground State Wave Function o o o 130 Experimental Startup 131 AL troduction e AAA te aes Soe et ae See Tac Re 131 A 2 Experimental Account ah 6 a ka A RA he 131 AL PASS WO AAA A SA 132 ADD Group Members ass SARA AAA of gals 132 A A A i Res 133 Pas e A hk a 5 feed Ro a Re ok eg hod egy ce nde Roce 133 ALO Book Sy a a e ehn en ie 134 eG Bash Profile r a r SoS A ARA AAA A ale 134 A 4 Directory Structure unde os Sinko ly orp vaca debra ck ache degree So Rens 134 AAE Mona E A ce a ee oe ee ae Ore er oe ee ere 135 PA De Manden AA op HE Shen th ap Ya Bh ke ah Sky En Gn 135 A 4 3 Experiment AAA th Be oe Ne oe 135 A 4 4 Desktop A A SE ee Be 137 vill A 5 Running Experiment es apto tdci Pe te he dept ne 138 Awol Edit Settings Files Ia 4 0 oiva aau aanas a ES da 138 A 5 2 Orphaned Runs a A SAS OS 138 AVG Post Experiments 4 AA e a 140 A 6 1 Calibration Runs cada a a a SS 140 A02 Archive Tapes tai te A es be ne SG a Re GD SS 141 A 6 3 Analysis Space 00 God dane Gd edhe Re he SG eA A 142 PGA Exec utables sacara iaa eee 143 MoNA SpecTcl Analysis Guide 145 B
68. Level 1 If this condition is active then the logic will not issue a valid without receiving both signals otherwise every primary trigger enables a valid signal The second condition determines the minimum acceptable majority bit value A valid signal is not sent unless the majority value is larger than a user programmed set value If the first condition requires a coincidence the minimum majority bit must also be meet before a valid signal is issued The valid signal once sent is anded with the TDC veto signal from the Timer to make the computer go signal that starts the V262 I O module and DAQ process as described in Section 3 2 Self stop self trigger An alternate trigger condition setup overrides the requirement of the primary trig ger allowing the MoNA system to run in self stop and self trigger mode This override is usually only used during the MoNA calibration runs involving cosmic ray muons without an external time of flight detector or trigger In this mode the mona start from Level 1 is copied to the TDC common stop signal The absolute time is meaningless in this mode but the time difference between the two ends of a bar is still valid for calibrating the x position along the bar and the independent timing 58 offsets for each bar see Appendix C for its use 3 6 Decay Energy Reconstruction The energy of the unbound system is co
69. MoNA positioned 8 m or 14 m from the target MONA position t ns du cm ns 00 mrad 60 mrad 6 Kn MeV 8m 0 18 0 10 6 2 3 7 1 44 14m 0 18 0 05 3 6 2 1 0 72 78 10000 7 9000 E 8000 7000 E 6000 E 5000 4000 E 3000 E 2000 1000 E Counts 0 0 5 1 15 2 25 0 05 1 15 2 25 3 35 4 Decay energy MeV Decay energy MeV Figure 4 15 Each curve corresponds to a calculated decay energy using MoNA Sweeper detector resolution and simulated data by ST mona Part a shows the lower energy curves and Part b shows the higher energies For comparison the curve from a decay energy of 1 5 MeV is a solid black line in both parts The mass ratio for these simulations was 10 1 as is the case for Be Coulomb breakup Figure 4 15 shows the decay energy resolution for neutrons from the Coulomb ex citation of 1Be on a gold target and 90 MeV u Each curve was run with 100 000 fragment neutron coincident events The loss or total counts as the decay energy in creases are due to acceptance losses see Figure 4 28 The full width for a 900 keV decay energy is 400 keV The distributions in Figure 4 15 were each fit by a Gaussian and the standard deviation of these fit are plotted in Figure 4 16 The final decay en ergy resolution depends on the distance to MoNA the mass of the unbound nucleus and the thickness of the reaction target Other factors including the TDC range used for th
70. NA Level 1 trigger logic counts the number of coincident left right signals from the CFDs from each layer and the number of individual PMT channels fired Each CFD has two outputs one starts the correspond ing TDC channel and the other triggers the Level 1 logic A schematic diagram of the Level 1 logic is shown in Figure 3 7 The JTEC XLM72 logic modules described in Section 2 2 5 whose FPGAs are programmed as Level 1 perform a variety of primary functions There are nine Level 1 logic modules one for each layer A through I When a calculate signal is received from the MoNA Level 2 logic that will be discussed in the Section 3 5 4 Level 1 adds all the coincident left right pairs of MONA PMTs and a binary 2 bit majority channel is set according to the Table 3 1 The majority bits are read by the Level 2 Virtex XLM 2 2 6 logic module and used in determining whether to accept or reject the event In addition to setting a majority bit the Level 1 logic also sends out the inte gration gate to the 32 channel QDC for that layer as soon as the first MoNA signal arrives from a CFD This gate is made sufficiently long 120 ns to ensure the whole dynode signal from every PMT in that layer is integrated The first MONA CFD trig ger is transmitted to the Level 2 logic module as mona start to open the coincidence window The Level 1 logic modules have also been programmed to count the total number 50 mona start gt
71. QDC events in the recorded data This method was not used for the commissioning experiments but has 30 140 arbitrary units gt Q o P o o o o o N o 0 O 500 1000 1500 2000 2500 3000 3500 4000 Raw TDC spectrum bins Figure 2 12 The distinctive picket fence spectrum from a time calibrator connected to the TDC with a period 40 ns is used to calibrate this TDC channel been implemented since 2 3 4 TDC Calibration The only calibration that does not utilize cosmic ray muons is the TDC calibration As is standard for timing calibration a time calibrator module is used in conjunction with a CFD to create logic pulses at set time intervals The calibrator changes the start stop interval by a multiple of a selected time interval so that multiple time difference peaks appear in a raw spectrum The time calibration setting used for the MONA TDC calibrations was set to a range of 320 ns with 40 ns intervals The full range of the 12 bit TDC was set to 350 ns The distinctive picket fence spectrum shown in Figure 2 12 is recorded and fitted by a fortran code that finds the peak positions above a set count for each spectrum and fits the location of these bins with a linear function The slope is then used to convert the raw bins to nanoseconds 31 2 3 5 Position Calibration Once the TDC is calibrated the time difference between left and right TDC channels can be used to determine the interaction position within t
72. STUDY OF NEUTRON UNBOUND STATES USING THE MODULAR NEUTRON ARRAY MONA By William Alexander Peters A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physics and Astronomy 2007 ABSTRACT STUDY OF NEUTRON UNBOUND STATES USING THE MODULAR NEUTRON ARRAY MONA By William Alexander Peters The Modular Neutron Array MoNA at MSU NSCL was conceived and built by a collaboration of primarily undergraduate schools to perform neutron coincident experiments studying nuclear structure The purpose goals setup and results of the commissioning of MoNA utilizing the Sweeper magnet and its detectors to identify the charged particle residues in coincidence with the neutrons in MoNA are introduced Calibration techniques are detailed along with analysis procedures The first test experiments are presented and analyzed A measurement of the system resolution is made by comparing data from the one proton knockout of SLi to the known unbound resonance of He to detailed simulation of the MoNA Sweeper setup using a new Monte Carlo code SIMPLE TRACK The accuracy of the resolutions determined by calibration tests are confirmed by the final agreement with a He resonance at 0 425 0 02 MeV and a width of 0 18 0 04 MeV The absolute efficiency of the MoNA detector setup is determined from a Coulomb breakup experiment of Be This reac
73. TS TIDI 20 80 l 40 0 40 80 120 X position bar AO cm Figure 2 14 Muon tracks that travel straight down through bar AO and A15 de picted in Figure 2 6 will pass this two dimensional gate ensuring a minimum amount of spread in the time difference plots between neighboring MoNA modules used to calibrate their relative time offsets bar i runs from 0 to 14 creating 15 bar time difference spectra At t15 ti 2 5 Since the time offsets for each bar are determined relative to bar A8 tg is used as the reference instead of t15 for all of layer A as seen in the example for A7 A8 ToF parameters in Figure 2 15 These time difference spectra should correspond to the travel time between the two bars 0t 0 345 ns per bar The offsets for each calibrated mean time is set to ensure the difference spectra meet this condition Figure 2 15 shows the time difference between bars A7 and A8 The distribution shown will be fitted and offset to the proper 0 345 ns by the fitting program The offsets for the next layers are determined by first applying gates that include the diagonal track from the top of one row to the 34 2000 1500 arbitrary units gt o o 500 0 5 4 3 2 14 0 1 2 3 4 5 At Layer A ns Figure 2 15 The time difference At between A7 and A8 triggered by a fast muons in a downward track calculated per Equation 2 5 bottom of the next for example A15 to BO A slightly different dt 0 346 ns is used to ac
74. The MoNA collaboration has written two separate Monte Carlo programs to simulate the efficiency acceptance and resolution for MONA experiments The first is based on GEANT 3 2 1 43 and is used to determine the efficiency of a single MONA detector module and compounded for the whole 16 by 9 array The second program is SIMPLE TRACK and simulates the layout and acceptances and resolutions of the full MoNA Sweeper Magnet setup 51 When SIMPLE TRACK is configured for a MoNA Sweeper experiment it is referred to as ST mona Control experiments were performed to test the validity of these simulations With the efficiency acceptance and resolutions determined the simulations can be used to analyze experiments and optimize the design of future experiments 4 1 Neutron Detector Simulation The GEANT 3 2 1 based simulation was designed to determine MoNA s efficiency as a function of neutron energy and detection threshold The two most important com ponents of an efficiency simulation are the reaction cross sections of the detector 63 proach MoNA from 8 meters in this solid red lines and the light response curve for each 10ns 64 O ABI A a A eae dash lines ap an a rr ri ca tence a waat sare Pe SOAR A NA S ee a siaua yms wA oo ANSIA S WN SHV a N Jadian RUNES aja LAY ANSI NN UN i See w i ssaa wans sa NENA UNR ALE SSRIS AAA marsa ms Y graue vant Cy OAR CN 1 owas w
75. The disappearance of the N 8 magic number in neutron rich nuclei is evident in the beryllium isotopes where Be has a ground state that is an intruder 1 2 state due to a neutron in the 1s 2 shell The normal shell level ordering for stable nuclei would populate the 0pyy2 shell for the seventh neutron and the 1s 2 shell would start to fill with the ninth neutron In addition Be is a neutron halo nucleus and N 8 Li is a double neutron halo nucleus 26 further indicating a loosely bound N 8 neutron 1 5 1 One Neutron Knockout of Be The first experiment studying the beryllium isotopes concerns the population of the 0p3 2 shell of Be predicted by the shell model to contain a neutron single particle strength of 2 45 neutrons 27 By measuring the cross section of the one neutron knockout reaction to the 9Be ground state and comparing it to a theoretical knock out cross section calculated for that system by the eikonal model of fast reactions 28 an empirical reduction factor can be determined The reduction factor is a gauge of the shell model s accuracy in describing the system as an inert core with the last valence shell partially filled Since the shell model calculations do not include 3 body nucleon nucleon core short range interactions nuclei that experience such interac tions have single particle populations less than those predicted by the shell model and thus a reduction factor less than 1 In the case o
76. Total N E double Efrag Frag_gamma Famu Total frag E double Etotal Namu Namu Famu Famu A 2 0000x Efrag Eneutron Pneutron Pfrag cos_theta double Qamu sqrt Etotal Namu Famu in amu c 2 rEvent m_nResultEdecay Qamuxamu Tandem_e_decay in MeV c 2 Here Nvel is the neutron velocity for first_count Note that N_beta is v c and similarly for Frag beta that s why it is square rooted for many of the calcula tions D 4 Analysis Suggestions The following sections are written to help with some of the standard analysis pro cedures The Control window for Tandem SpecTcl is a little different than for the MONA version as shown by Figure D 2 D 4 1 Tandem Control Buttons For the most part the buttons on the Tandem SpecT cl Control window are the same as for the MONA SpecTcl 92 but for a few exceptions 203 Create Cal Spectra Create Pseudo Spec Create Hit Spec 2d Cal Spectra Si Help i s N l WorkDir itandem spectel 2d Pseudo Spectra SS A amt EvtDir Mome event_files 03038 Sweeper Map Ppacs Map t central_eo _set central_ eo Order Mass Charge Brho Order Mass Charge Brho gers I TT 0 1 0 fo 3 0 E MeV u P GeVic Inv Map E pees Eee 1D Raw List Variables 1D Cal 2D Spectra Source Run Number 0 Analyzed Buffers 0 Attach Online Attach to Files List Parameters
77. V Stripping from the 0d 12 configuration leads to a 5 24 unbound state in Be at 1 78 MeV Figure 6 1 illustrates the various single particle wave function components and their decay paths for the stripping of one neutron There is also the possibility to knockout one of the non valence neutrons of 12Be leading to an excited hole state in Be The 0p3 2 shell level with four neutrons is a good candidate for just such a reaction The possibilities for exciting states not coupled strongly to a single particle state above 9Be or a hole from the 12Be ground state wave function are limited and not expected to contribute greatly to the Be n coincident data Although there may be core excited configurations that lead to the observed states in Be through 1n stripping that do not involve the paired neutron 109 Table 6 1 Summary of results from previous studies of the ground state wave function of Be The first experiment 29 could not measure neutron unbound states while results from the second experiment 30 agree well with the first for the bound states Ref Ebeam HBe j E MeV ae 29 78 MeV u 1 2 0 0 0 53 0 13 29 78 MeV u 1 27 0 32 0 45 0 12 30 39 3 MeV u 1 2 0 0 0 56 0 18 30 39 3 MeV u 1 27 0 32 0 44 0 08 30 39 3 MeV u 5 2 1 78 0 48 0 06 configurations in the unperturbed single particle shell model description of an inert core of Be in Be
78. a different speed through the beam optics The secondary auxiliary inputs have also been used with y ray detectors and a separate neutron de tector connected as Aux C input By enabling both the MoNA and Aux C secondary triggers one can record coincident events with the primary trigger for either of them Down scaler The down scaler logic unit is set to accept a fraction of the inputs connected to it The down scaled factors are set through the user interface in powers of two Any primary inputs that are enabled including the auxiliary inputs A or B that pass through the down scaler will be accepted as the primary trigger Down scaled data of an auxiliary input can be used to determine if there are any beam contaminants that do not strike all the focal plane detectors By connecting 97 the beam line scintillator to the Aux A input of the down scaler one can record a small fraction of the beam timing events relative to the target scintillator Since most secondary beam contaminants will have a different ToF through the beam line contaminants can be identified even if they do not reach the focal plane detectors 3 5 7 Level 2 Trigger Conditions The determination of whether to accept or reject an event is made within the Level 2 Trigger Condition logic and is controlled by a Tcl Tk user interface The first condition determines wether to require coincident events between a primary trigger and the majority output from
79. ach to File and select the run file recorded in step 1 In Xamine go select Window gt Read Configuration and pick one of the pseudowin Xpos win window settings Allow SpecTcl to analyze all the buffers to ensure sufficient statistics for the Xpos fitting program This may take over a half hour since the run was so long When the data is read in click Update All in Xamine Look through the spectra in Xamine to make sure the data is usable i e that the edges of the Xpos spectra look sharp Since the Xposfiited flag was set to false all the Xpos spectra will display the time difference a width of about 25 ns even though the spectra are still labelled with cm Select all the pseudowin Xpos win files to view all the Xpos spectra The spectra should look like Figure C 3 181 10 11 12 13 14 5 Xamine user 05034 mona daq spectcl pseudo_win XPOS_A win Modified File Window Spectra Options Graph_objects O A SO gt VO AA 0 SC i AO A 20 cm ass OS AO ives ia A Courts Figure C 4 X position AO spectrum Figure C 4 is an expanded view for module AO Once the file is done loading and the spectra look okay push the Write Xpos Spectra button in the SpecTcl Control window When the TkCon confirms the MoNAxposCosmics asc file is written press the
80. ajabali J Robertson W F Rogers S L Tabor M Thoennessen E Tryggestad R E Turner P J Van Wylen and N Walker Nucl Instr and Meth A 543 517 2005 A F Zeller et al Adv in Cyro Eng A 45 643 2000 M D Bird et al IEEE Trans Applied Superconductivity 15 1252 2005 T Baumann H Ikeda M Kurokawa T Nakamura M Miura Y Nishi S Nishimura A Ozawa I Tanihata T Sugimoto and M Thoennessen Nucl Instr and Meth A 505 25 2003 F Ajzenberg Selove Nucl Phys A 490 1 1998 M Meister K Markenroth D Aleksandrov T Aumann L Axelsson T Bau mann M J G Borge L V Chulkov W Dostal B Eberlein Th W Elze H Emling C Forssen H Geissel M Hellstrom R Holzmann B Jonson J V Kratz R Kulessa Y Leifels A Leistenschneider I Mukha G Munzenberg F Nickel T Nilsson G Nyman A Richter K Riisager C Scheidenberger G Schrieder H Simon O Tengblad and M V Zhukov Phys Rev Lett 88 10 102501 2002 K Alder and A Winther Electromagnetic Excitation North Holland Amster dam Oxford 1975 A Winther and K Alder Nucl Phys A 319 518 1979 C A Bertulani and G Baur Phys Rep 163 299 1988 J A Tostevin Nucl Phys A 682 320c 2001 N Austern Y Iseri M Kamimura M Kawai G Rawitscher and M Yahiro Phys Rep 154 125 1987 T Kobayashi O Yamakawa K Omata K Sugimoto T Shimoda N Takahashi and I Tanihata Phys Rev Lett
81. al 81 case to calibrate the efficiency of the MoNA Sweeper setup By Coulomb exciting llBe above its neutron separation energy of 0 504 MeV with a gold target the 9Be residue is deflected by the Sweeper Magnet into the focal plane detector box and the released neutron travels straight into MoNA The energy spectrum of virtual photons for a specific nucleus target combination can be calculated for a given beam velocity This spectrum along with the incoming rate of Be can be used to calculate the number of neutrons produced With the aid of the simulations the acceptance of the system can be divided by the number of recorded neutron events to reveal the intrinsic efficiency of the MoNA detector 4 4 1 Experimental Setup MoNA and the Sweeper Magnet were setup in the standard configuration with the reaction target just in front the Sweeper Magnet and MoNA 8 2 meters down stream The A1900 fragment separator with a 795 mg aluminum wedge at the dispersive image was used to purify the secondary beam of 90 MeV u 1 Be from a 0 primary beam at 120 MeV u impinging on a 1692 mg cm Be production target The Coulomb excitation occurs inside the 258 mg cm gold target positioned in front of the Sweeper Magnet Gold was chosen for its high proton number 79 A thick steel plate was installed inside the focal plane detector box to block the unreacted Be 4 4 2 Virtual Photon Calculations As the positively charged projectile passes near
82. al Tire A oh eto Bs ek ESO See Ee SSH 145 B 1 1 MONA Parameters 000000 pete 145 B 2 Configuration les out eek Ee DE ee PE oe BE AE 147 B 2 1 MONA Config Directory 200 148 Ba Running Sp cTel sn yl ana e 4d te Be ala GE Li TS an 150 Bid Open speclelias odia oad weg es as Fh od 150 B 3 2 Creating Spectra a sace ar Eo alae Pera 153 B 3 3 Configuring Xamine id a a ie Sep ame BY ees 154 B 3 4 Attaching Data 1 x s 4 6 dn ATAN 154 B 3 5 Debe Mp Gates oa oe te Ee A 154 B 3 6 Copying Spectra 2 a 4s ae Goto bal Ok eae A A 156 B 3 7 Displaying New Spectra xi a ee ee Baer 156 B 3 8 Applying Gates mail a a RS 157 Birds Asi Data E TAR Se sed 157 B 4 1 Exporting Data ia Gee bk od a BI ee SS 158 B 4 2 Importing into Excel 3 24 sta ak kd ane eee ed 158 Bio SIMmpuUyINE 2 224 4 Job athe amp a i arb da Sd we ere amp 159 B 5 1 Settmes Files syete ia Mob ne de gid eo 159 B 5 2 Creating Custom Pseudos ds ad aoa Bie as 160 B 5 3 Filtered Data A a ae her da dd 162 B 54 Useful Tips i a t ug ah AON a ada ida ad ad 163 MONA Calibration Guide 164 GP A a eed Be ad Sh 4 a AA 164 CEI PUG eR GTS e a doris aro vis Wey eS da Be en alee dO 165 C 2 High Voltage Gain Matching secs tapa a ee ee ae 166 Cadell Getting Started p saet whe eile Ta afoot dm afew wan 167 E 227 Wake Cosme Data ur bt a be a ee S Aa 167 C 2 3 Voltage Matching Codes coto 4 ech ae Gu Se bs 169 C 2 4 Setting New Voltages face ee
83. al voltage range for the XP2262B model is 1500 2400 Volts 15 External Stop Veto Level 2 MONA Start Y QDC gate MONA DAQ Overview Level 1 DAQ I O Q LL O o 3 E Z c lt 1 au O BSE S 5 2 SE ano 5S O o an Figure 2 2 The basic MoNA DAQ system The MoNA PMT anode signals are recorded by the TDCs while the dynode signals are recorded by QDCs The Level 2 logic Section 3 5 4 determines if the event is accepted computer go or rejected fast clear 16 There are two analog output signals for each PMT from the dynode and the an ode The PMT has a 12 stage dynode cascade following the photoelectron producing photocathode and the anode signal has a gain of about 10 with a transit time of 30 ns Each anode signal is transmitted to a CFD with a 16 foot 25 ns coaxial ca ble The positive dynode signal is taken from the next to last step in the multiplicative chain and is connected to a passive inverter with a 60 foot 90 ns coaxial 50 Q BNC cable and routed into a QDC 2 2 2 Digital Signal Conversion The standard MoNA setup uses 18 constant fraction discriminators CFDs to convert the analog anode signal from each PMT to a digital pulse The CAEN V812 CFDs have 16 negative polarity 50 Q LEMO inputs The internal timing delay chips are set to 3 ns which is about 80 the typical rise time for the raw anode signal from the PMTs The outpu
84. al 4095 The cat datetmp tzt is a date time stamp created by the code as a series of numbers MMD DYYHHMMSS to include in these file names gt More details about the script can be found in Ref 93 177 10 11 12 13 The 300 stands for the threshold If a channel contains more than 300 counts the program recognizes it as a peak Edit this value to one that is suitable for your run Make sure the exit command underneath the count threshold is commented out of the executable program file by placing the pound symbol in front of it Save your changes and exit the editor Run the tdc_calib f code by typing gt test sh in the spice window A long list of values and calibrating points will be printed to the screen you can scroll up through some of the bars but most shells don t scroll back far enough to see the fitting points for all 320 TDC channels If you are familiar with the viewer program TopDrawer try running it by using the td test tdr command Then don t touch anything To cycle through the graphs press enter Don t click on any of the windows You must be in the shell window to cycle through but can t overlap the black graphs because each graph needs to be viewed Verify that the points are evenly spaced by the specified increment and linear along the regression line The vertical axis is the channel number and the horizontal axis spans the range setting in nano
85. al above the CFD threshold also creating a mona start logic pulse TDC timing When an event occurs in a MoNA module the anode signal from each PMT is pro cessed by a CFD whose logic output signal is copied to two modules The first goes 47 common stop thin scintillator focal plane MoNA Sweeper Coupling neutron flight path 60 90 ns target scintillator Figure 3 6 The timing channels important for coincident events are shown along with the five cables described in the text used to couple the data acquisition electronics between the MoNA and the Sweeper systems Signal transit times are given for flight paths and signal cables Transit times for signals passed within the same rack mount straight arrows are less then 5 ns Double wide lines represent multiple signals passed through one ribbon cable 48 to a TDC as the start signal while the second goes to Level 1 to open the QDC integration window to be counted for the majority bit and copied to Level 2 as the mona start The TDCs are run in common stop mode and are stopped by the delayed target timing scintillator signal in cable E Therefore the raw TDC channels have a negative time slope which is taken into account when the left and right chan nels are calibrated and then averaged to get the time of flight from the target to each bar 3 5 2 Coincidence Timing The delays shown in Figure 3 6 are chosen to ensure all timing
86. al from CFD gt Cable E Sweeper Delay Ain signal from CFD gt Cable A Sweeper Delay ande signal from CFD gt Level 1 MONA TDC start 1 200_ QDC window opened Level 2 mona start o coincidence window opened Set Se le signal reaches MoNA QDCs ee tar pulse into Delay E i thin pulse into Delay A QDC window ends tean k in pulse after Delay A into Level 2 gt sweeper uo activates veto calculate target pulse after Delay E into Level 2 gt common stop i close coincidence window if no sweeper ie TDC veto ty if not valid fast clear duration is t then clear A in pulse out of Level 2 gt valid Cable D computer go ie thin pulse arrives at Sweeper TDC start lt _ Sweeper delay ends all Sweeper times into t 800 TDC stop Figure 3 10 The timing sequence is shown for a typical coincident event The scale on the left side is in nanoseconds so the entire sequence takes less then 1 us to accept or reject an event The readout of all MoNA and Sweeper modules may take a few ms and a rejected event is cleared by the fast clear signal tq in less than 800 ns Signal dependences and set times are described in Sections 3 5 1 to 3 5 5 59 Table 3 2 The five output signals from the Level 2 timer are determined by the three set values Output time Corresponding se
87. alibrated times For example user tof rf_pot cal user tof rf cal user tof potscint cal rf_pot slope rf_pot offset The respective slope offsets should not need to be other than 1 and 0 since the components are already calibrated User Pot_Thin Time Having the potscint and thin_time calibrated parameters don t tell you the time of flight of the fragments until you subtract the two The parameter for potscint thin_time as described above for the difference is constructed similarly here but with the added feature to adjust the time based on the tracking angle and position user tof pot_thin cal user tof potscint cal user tof thin_time cal sweeper fp track xfp sweeper tof potthinxfp sweeper fp track afp sweeper tof potthinafp To get the unadjusted tof just set these adjustment variables to 0 The first line of this calibration is saved as the frag_time in the code and used for the fragment s velocity This adjustment is useful for separating isotopes of the same element by rotating the time about the tracked dispersive position and angle to account for differing charge to mass ratios through the dipole 196 User Fragment Velocity Here the user tof pot_thin cal parameter is used without the adjustments de scribed above as frag_time along with user tof vfrag offset in centimeters to get the fragment velocity in cm ns The user tof vdiff cal parameter is the difference in cm ns between the neutr
88. ameters are in turn used to calculate the Hit parameters 146 Hit Parameters These parameters are not as useful as one would like since the code is written to scan the whole MoNA array starting with AO to 115 and labels the first event with two valid TDC channels as hit 1 and so on The Multi_hit parameter is the count of these valid hits for each MoNA event The list of hit parameters is X_hit Y_hit Z_hit TOF_hit KE_hit Q_hit Theta_hit Phi_hit Multi_hit Some pseudo parameters have been made to calculate the time ordered hits 91 and should be used for more advanced analysis B 2 Configuration files There are plenty of files sourced by the SpecTcl code when it begins Many are not to be adjusted in any way because they contain long lists of MoNA variable names and special tcl operations that are used by the underlying cpp code In general those files will get copied to your work space and never need to be adjusted or edited There are a few files that contain calibrated variables that get set once for each experiment and then a few that contain adjustable variables to set as you see fit to best analyze the data for a particular run number SpecTcIRC tcl Make sure that the directory that contains the spectcl scr file to launch SpecTcl also contains a SpecTc1RC tcl file and is edited to source the SpecTcl housed in a user mona mona spectcl_shared directory You may also set your WorkDirectory and EventDirecto
89. and other studies see Chapter 4 Two simulation codes are shown to accurately reproduce nearly all aspects of the MoNA Sweeper detector system MONA is well suited for moderate to high energy 30 200 MeV u radioactive beam reaction experiments because of the forward focusing of the decaying neutrons at such speeds But it can also be arranged off axis in the new vault configuration shown in Figure 7 1 to gain acceptance for higher decay energy resonances that emit neutrons at higher angles in the laboratory reference frame In addition the modular design capabilities of MoNA will be utilized in the future to increase the resolution for distinguishing multiple hit neutron events and two neutron events 7 2 Multiple Neutron Capabilities Given MoNA s high efficiency it has the capability to record multiple neutrons within one fragment coincident event However these events have to be identified and sepa 122 YZ Te na CEC ELEY EY a Figure 7 1 New vault configuration for the MoNA Sweeper system to be completed in the Summer of 2007 is a a Maximum angle position that will allow MoNA to accept neutrons at an angle up to 55 degrees relative to the beam axis This will greatly increase acceptance for higher decay energy resonances b Beam line position for MoNA showing the optional multiple wall configuration of the array rated from the multiple hits recorded from a single neutron events This is done by plotting
90. article strength in the 5 2 spectroscopic factor with roughly 25 still missing The result suggests equal parts for all three paired neutron configurations The current experiment attempts to confirm the results of the second experiment at over twice the beam energy and with the superior neutron efficiency of MoNA compared to the DeMoN array used in 30 6 2 Experimental Details A primary beam of 180 was accelerated through the Coupled Cyclotron Facility at the NSCL to 120 MeV u and impinged onto a production target of Be with a thickness of 1081 mg cm The secondary beam of 99 pure 12Be with 0 5 momentum spread was separated from the resulting cocktail by the A1900 fragment separator utilizing a 750 mg cm arcylic wedge installed at the dispersive plane see Figure 3 1 The secondary beam was directed into the N4 vault and onto a reaction target of Be with a thickness of 102 mg cm at the target position in front of the Sweeper magnet The Sweeper magnet focal plane detectors were used to identify and count the charged particle reaction products A thick steel plate was installed in front of the first CRDC to protect the CRDCs from the high rate of the secondary beam see Figure 3 2 The rigidity of the 2Be was too high to deflect it into the focal plane directly for a rate calibration and thus all measurements for the cross section to different decay channels are taken relative to each other and calculated by comparison to previous m
91. ated by ST mona The acceptance in the vertical direction of the thin scintillator is 0 2 m within the dotted lines 4 4 7 Simulation Input Parameters Since ST mona does not have a setting specifically for a Coulomb breakup reaction the input parameters must be set to reproduce the measured detector distributions as accurately as possible Figures 4 25 and 4 27 display the results of this effort In order to properly fit the dispersive parameters in the focal plane the incoming beam angle centroid was set off zero This setting is confirmed by the x distribution in MoNA Figure 4 27 The wide distribution in the y direction accounts for the largest acceptance cut in the focal plane detectors By not using CRDC2 the precise values for the input parameters have less an effect on the final acceptance of the thin scintillator as illustrated by Figure 4 26 The distributions for the x position and angle in the focal plane still did match exactly to the data as seen in the left panels of Figure 4 25 but they do not significantly effect the acceptance of the system 91 e 07503 data 175 J 600 E J F 150 E msot 125 F 3 lt a gt 400 E lt 100 E 4 lt g S 300 F J Dor 13 a so J 200 E e 07503 data J 25 100 E ST mona J 0 1 ti ee hed iio n 0 E n 08 at apri ap a r e ES AE 1 150 100 50 0 50 100 150 0 2 4 6 8 10 12 14 16 MoNA x position cm MON
92. atible modules and are manufactured by the same company CAEN 35 They are installed in three VME crates and are connected to a DAQ computer via fiber optic cables to control and read out all the VME modules needed for MoNA Section 3 5 details the sequence of functions for the Level 1 and Level 2 logic 2 2 1 Light To Signal Processing A total of 288 Photonis XP2262B 36 12 stage photo multiplying tubes PMT are coupled and bolted to the support flange The PMT window is lime glass with an index of refraction equal to 1 54 and is coupled to the acrylic BC802 light guide by optical grease The PMTs were selected to have a spectral response range that peaks at 420 nm and has a full range of 290 650 nm to closely match the scintillation light from the BC408 plastic that has a maximum intensity near 425 nm To counter the effect stray variable magnetic fields have on the electrons in the multiplying tube a mu metal shield 37 is also fixed to the flange surrounding the tube Each PMT is powered by a separate high voltage HV line that is set to yield a consistent light response to cosmic ray muons This gain matching process is discussed in detail in section 2 3 The HV power is supplied by two CAEN SY1527 supply controllers They are modular expandable and can be remotely controlled Eleven CAEN A1833BN 28 channel voltage banks are installed into the SY1527 controller that sets and monitors the negative voltages for the 288 PMTs The operation
93. beam optics with a focusing quadrupole triplet in front of the target and the dipole Sweeper magnet after the charged fragments traveling through the Sweeper magnet will be separated by their magnet rigidities A particles magnetic rigidity Bp measured in Tesla meters is related to a its charge q mass m speed v as described by Bp x mv q 3 1 For nuclei with the same magnet rigidity heavier ones will have a slower velocity and thus longer ToF Since the Sweeper focal plane accepts a range of nearly 18 in momentum other parameters must be used to correctly identify the magnetic rigidity of each particle After passing through a dispersive beam element like the dipole Sweeper magnet the rigidity of a particle depends on the dispersive position 44 dE MeVee ToF a u rigid Figure 3 5 Separation of carbon isotopes by their magnetic rigidities using the ad justed ToF 9 q parameter a dE versus calibrated ToF for many fragments and the gate used to select carbon b The gated carbon events after Equation 3 2 is applied with appropriate values separating the isotopes for identification and angle x and 07 By adjusting the fragment s ToF f Parameter we can further separate the particles by their rigidity The adjustment is made using two correction factors Cy and Cg to the dispersive positions and angles in the focal plane ToF gia 18 a ToF parameter of arbitrary units calculated by ad
94. ber for the orbital angular momentum for a harmonic oscillator is coupled to the spin 1 2 of the nucleon to create the nuclear shell levels In some cases this effect is so large as to create a new magic number for one shell like between 20 and 28 for the 1 f7 2 shell These shell levels are populated by up to 27 1 nucleons where j is the total angular momentum quantum number j l s The values on the right of Figure 1 1 are the maximum number of protons or neutrons each shell level can hold and the total number illustrating the magic numbers This nuclear model is called the spherical shell model and reproduces the nuclear structure of nucleons near stability 3 4 1 2 Neutron Rich Nuclei The shell model reproduces many of the observed qualities of nuclear structure par ticularly shell level populations but requires adaptation for nuclei not near the region of stability Figure 1 2 is a chart of the nuclides and shows the full known and unknown landscape of nuclei stable nuclei are displayed as black squares The red dashed lines mark the magic numbers for protons and neutrons Close to the drip lines the limit of binding energy where no more protons or neutrons can be bound within a nucleus by the nuclear potential some of these magic numbers no longer indicate stronger bind ing energies shell gaps disappear and new ones appear Sometimes a specific number of protons can bind many more neutrons than the neighboring element F
95. ce Phys Rev C 67 6 064301 2003 H P Blok G J Kramer and L Lapikas Nucl Phys A 679 267 2001 M B Tsang Jenny Lee and W G Lynch Phys Rev Lett 95 22 222501 2005 Jenny Lee J A Tostevin B A Brown F Delaunay W G Lynch M J Saelim and M B Tsang Phys Rev C 73 4 044608 2006 C K Gelbke et al Isotope Science Facility at Michigan State University Tech nical Report MSUCL 1345 NSCL MSU 2006 J A Tostevin J Phys G 25 735 1999 J A Tostevin 2007 Private communication U C Bergmann M J G Borge R Boutami L M Fraile H O U Fynbo P Hornshoj B Jonson K Markenroth I Martel I Mukha T Nilsson G Ny man A Oberstedt Y Prezado Alonso K Riisager H Simon O Tengblad F Wenander and K Wilhelmsen Rolander Nucl Phys A 692 427 2001 M Huhta P F Mantica D W Anthony B A Brown B S Davids R W Ib botson D J Morrissey C F Powell and M Steiner Phys Rev C 57 6 R2790 1998 G Gori F Barranco E Vigezzi and R A Broglia Phys Rev C 69 4 041302 2004 213 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 F M Nunes I J Thompson and J A Tostevin Nucl Phys A 703 593 2002 P G Hansen and B M Sherrill Nucl Phys A 693 133 2001 H G Bohlen R Kalpakchieva W von Oertzen T N Massey B Gebauer S M Grimes T Kokalova A Lenz M Milin Ch
96. clusion 8 1 MONA Efficiency and Resolution The absolute efficiency of MoNA was measured for 90 MeV neutrons from the Coulomb breakup of Be on a gold target to be 73 6 This confirms the GEANT Monte Carlo simulation s ability to reproduce the reaction cross section and light response for MoNA The Coulomb breakup cross section was calculated via the virtual photon method 21 23 The results of a Briet Wigner fit to the He data yields a peak at 0 425 0 02 MeV with a width T of 0 18 0 04 MeV consistent with previous measurements 20 57 The good agreement between Coulomb breakup data and re producing the unbound resonance of He confirms the ability to accurately model the MONA Sweeper experimental setup with the SIMPLE TRACK and GEANT Monte Carlo simulations 8 2 1 Be Neutron Knockout The first experiment involving just the Sweeper focal plane detectors measured the reduction factor Rs for the one neutron knockout reaction of Be to the ground state of Be Be has no bound excited states so the observance of Be in the Sweeper 129 focal place detectors uniquely determined the reaction channel The reduction factor the Ops 2 single particle spectroscopic factor in Be is determined to be 0 66 0 07 from a cross section of 68 7 mb This value follows the trend of the reduction factor versus AS the difference between neutron and proton separation energies of 10Be for values of AS near 13 MeV u This re
97. count for the diagonal distance Then the offsets within the next layer can be calculated as before from this one corrected mean time The whole MoNA array of 144 bars are calibrated relative to bar A8 which is centered on the beam axis Bar A8 s offset is set during each experiment using the y rays produced by stopping the beam in a thick target and the measured distance from the target to the center of bar A8 35 Chapter 3 MONA Sweeper Experimental Setup Combining MoNA and the Sweeper magnet along with the focal plane charged particle detectors to a single detector system completes an arrangement suitable for measuring the neutron unbound states of exotic nuclei near the neutron drip line with neutron kinetic energies above 30 MeV u The setup allows the neutrons from an unbound state created at the reaction target to be detected at zero degrees by MONA while the Sweeper magnet bends the charged particles into the focal plane detector box 3 1 Layout Figure 3 1 shows the Coupled Cyclotron Facility CCF 31 and the A1900 fragment separator 45 leading to the experimental vaults and the current position of MoNA The CCF accelerates the stable primary beam After impinging on a primary target the fragmented beam then travels through the A1900 to select the rare isotope of interest This secondary beam is then delivered to the experimental vault MoNA is currently placed behind the Sweeper magnet located inside the N4 vault o
98. ction 2 2 3 5 1 MoNA Sweeper Coupling The Sweeper DAQ system is interconnected to the MoNA DAQ system by five 120 ns 76 ft co axial cables labeled A B C D and E in Figure 3 6 These cables take a valid Sweeper event trigger through Cable A and a common stop target timing signal through Cable E The MoNA trigger logic sends back three signals to the Sweeper DAQ modules Cable A is the CFD logic signal from the upper left PMT channel of the thin scintillator in the back of the Sweeper focal plane This signal is passed to MoNA s logic as the sweeper signal input Cable B is the latched veto signal that prevents any incoming signals to all MoNA and Sweeper modules while the latch is activated This latch is opened by the Level 2 logic when a trigger is received and is released by either an end of event signal or with the end of a clear signal The veto latch remains on while the MoNA computer is busy reading out the DAQ modules Cable C is the fast clear signal from the MoNA Level 2 logic and is used to clear the Sweeper DAQ system The fast clear is also copied locally to the MoNA DAQ modules 46 Section 2 2 3 discusses this feature This signal is sent instead of the computer go for rejected events The fast clear and computer go signals are mutually exclusive Cable D is the master trigger or computer go output from the Level 2 logic to the V262 I O module to sta
99. ctor box If this acceptance cut is correlated to the parallel momentum which is true for the dispersive z plane the resulting distribution will not accurately represent the actual distribution of the Be fragments exiting the target Gating on a region within the angle versus momentum phase space that is not cut by the acceptance produces a distribution that accurately represents the true parallel momentum Figure 5 4 shows how the dispersive position distribution is cut by the edge of CRDC2 for run 2121 with a Sweeper setting corresponding to a central Bp of 2 9 Tm Figure 5 7 shows the gate on reconstructed dispersive angle 0z versus the reconstructed parallel momentum used to recover a portion of the true distribution of Be Run 2114 taken with the Sweeper magnet rigidity set to 3 1 Tm did not cut the distribution of the Be residue as shown by Figure 5 3 To increase the statistics the parallel momentum data from the higher rigidity setting run 2114 was scaled and grouped with the gated lower rigidity data from run 2121 In order to compare theoretical distributions with the data the theoretical 105 al o e run 2121 counts run 2114 scaled 40 0 fitsip Sa fitpa 2 gt O Trt Tree o 20 G 2 _ o 0 comica atl aE al ae BT tar 3000 3200 3400 3600 3800 4000 4200 Parallel momentum MeV c Figure 5 9 Parallel momentum distribution fitted with three theoretical curves The data and err
100. d MoNA is a high efficiency neutron detector Through measuring the position of the particle neutron or other particle it becomes possible to know the particle s path and thus extrapolate its energy In order to do this properly the X position parameter must be properly calibrated By noting the difference in time signals from 179 the photomultiplier tubes at each end of a certain MoNA bar we can produce a spectrum that displays the difference in the time signals in nanoseconds between the right and left sides of that bar By performing this calibration the user transforms the time difference spectrum in nanoseconds into a position spectrum in centimeters This is very useful in reconstructing events when analyzing data Another important reason for this is that the kinetic energy of the neutrons are calculated from KE 1 2 mn d t An accurate determination of the energy requires one to know the full 3d position of a hit in any given bar C 5 1 Record Cosmic Run Before any fitting code can find the correct X position slope and offset values an long cosmic ray run must be taken This new run requires the previous calibrations to be preformed first 1 Record an overnight 12 hours run of cosmic ray data with all detector bars Use MoNA multiplicity set to 1 fold and select self trigger and self stop on the XLM control Also be sure that you are using calibrated slope offset values for both the QDC and TDC parameters an
101. d ox File Window Spectra Options Graph_objects Help Spectrum x Geometry 1 Zoom Display Display Figure B 2 The Xamine startup window 151 Reading MoNA_setup_run mona Re writing param lists Done Direct or true visual with 24 total bits Pseudo visual with depth 8 Selected direct true with 24 bits Setting up Direct True red max 255 blue max 255 green max 255 Opening colortable in home dir user mona Xamine6 ctbl C Copyright Michigan State University 2008 All rights reserved iC Copyright Michigan State University 2008 All rights reserved C Copyright Michigan State University 2008 All rights reserved C Copyright Michigan State University 2008 All rights reserved C Copyright 1999 NSCL All rights reserved GatePackage cpp Filter command c 2003 N3CL written by Kanayo Orji inside shared RC Loading shared selectscript code Done Loading shared MoNA SpecDriver fui Done Loading state I 0 scripts Done Loading formatted listing scripts Done Loading gate copy script procs Done Loading TKCon console Figure B 3 The console shell Figure B 4 The Tkcon command window 152 Look at the right side of the SpecTcl Control window and find the WorkDir and EvtDir The first should be set to the current working spectcl directory usually mona daq spectcl The second should be set to
102. d it appears as a straight line in the logarithmic scale 10 When the last set has been viewed pressing Enter will close TopDrawer C 2 4 Setting New Voltages 1 Now you must apply the new high voltage settings by first going back to the spdaq16 terminal window and changing directories to mona hv_control 2 Now source the new voltage values into the HV channels by typing gt Vfitted scr Repeat Sections 2 2 2 3 and 2 4 until performing another iteration would not significantly change the voltages then move on to the QDC calibration procedure Usually twice is good enough if starting from voltages previously fitted for another experiment 170 C 3 QDC Calibration QDC calibration should only be completed after the high voltage channels are fitted following the High Voltage Gain Matching directions from section 2 It is important to know the light energy deposited by a scattered neutron event and also important to suppress the null result QDC pedestal events from swapping the Readout Since every QDC has 32 channels and each pedestal is a positive bin value all channels will readout if just one creates a valid trigger for that layer C 3 1 Calibration Steps 1 Edit and save MoNA_setup_run tcl with the QDC flag QDCfitted 2 Repeat the Take Cosmic Data section from Chapter 2 2 and make sure the recorded run in step 4 is brand new and was not used for voltage gain matching 3 You need to execute the calib s
103. d below between 0 to 5 cm The Gaussian fit has a standard deviation of 2 2 cm 4 2 3 MONA Y Z Resolution In both the longitudinal and vertical directions z and y the interaction position of a neutron event can only be known to a precision of the depth and height of each MONA bar 10 cm The y and z resolutions are simply 5 cm Figure 4 12 shows the x y distribution of neutrons in MONA from the Coulomb excitation of Be on a gold target at 90 MeV u The effect of the quantized y position can be seen in lab angle 9 of the neutrons displayed in Figure 4 13 Each subsequent spike in the 6 spectrum is due to neutrons striking the next row above or below Figure 4 14 shows the same neutron data from the side of MoNA through the nine layers The increase in counts for the second layer is due to the fact that some highly scattered protons can travel a couple centimeters and react in both the first and next layer The ST mona simulation randomizes the actual position of the neutron hit within the bar while the reconstruction always uses the center of each bar and therefore is quantized in 10 cm steps The z axis uncertainty adds to the velocity uncertainty along with the time resolution 75 Y position in MONA row 120 80 40 0 40 80 120 X position in MONA cm Figure 4 12 Plot of z versus y MONA positions The z direction is plotted in 4 cm bins while the y position is quantized to the 10 cm bar height A decrease in intensity can
104. d by the calibration code Select all the win TDC win files to view all the raw TDC spectra Pay special attention to some of the inner most MoNA bars like D7 to G9 and see if any are double peaked A suitable threshold value must be less than any double peaked count The fitting code will take any channel above threshold preceded by a channel below threshold and fit it to the next incremental period Running the code with a threshold that runs through a double peaked spike will cause the fitted slope to be very wrong Figure C 2 is a sample spectrum with the delta time set to 40 ns and a range of 350 ns Select Write Any Spectra in the SpecTcl Control window From the pop up window open Spectrum List and select all the TDC data spectra there should be 320 total Click Accept and Close Name the spectra file including the range and period you ve chosen Make sure that the ASCII is selected Click Write Spectra 175 tJ Xamine user 05034 mona daq spectcl win T_I_R win ax File Window Spectra Options Graph_objects Help 00 3000 3500 400 Counts 0 Geometry F Zoom Update All Expand Harker Cut Display Update Selected Un xpand Summing Region E Display Info J Log J Map Integrate Figure C 2 Calibrated TDC Xamine spectra C 4 2 Running Calibration Code Running the tdc_calib f code by sourcing the test sh
105. d check that the calibration flags in MoNA_ setup run tcl QDC_thres_flag QDCfitted TDCfitted 2 Open MoNA SpecTcl 92 in the spice terminal window or from a Data U machine 3 In the SpecTcl Control window click Create Pseudo Spec 4 In order to avoid any time walk that may occur with near CFD threshold events you must apply a high Qmean gate from 8 to 120 MeVee to each Xpos spectra 180 E Xamine user 05034 mona daq spectel pseudo_win XPOS_A win Modified File Window Spectra Options Graph objects Help Im thy 1007 SO zom ay 50 omia O 2 14341 xpos at 17 49 29 1 on 100 th h i T 50 s0 50 aal 0 i 0 do EJ 0 A y 0 y 14431 xpos 24 17 49 48 eS 14441 xpos AS 17 49 48 4451 xpos A6 17 49 48 4461 xpos A 17 49 48 100 i yay by nen TE o 50 Sar E sob 0 A o E a ar a ag 14471 xeos A87 17 49 48 14481 xpos AF 17 49 48 E 14361 xpos AL 17 49 48 100 L 100 ty Eo WM p 100 e 50 s50 50 sob Geonetry Zoom Update All Expand Harker Cut Display Update Selected UnExpand Sunming Region and Display Info Loo F Hap Integrate tontos Figure C 3 X position Xamine spectra Do this by clicking Apply Qgate to Xpos See Ref 94 for a detailed discussion on the CFD walk issue Then choose Att
106. d to the yoke to reduce the Sweeper magnet s significant fringe field which effect the magnetically sensitive detectors nearby 3 3 Charged Particle Detectors Figures 3 2 and 3 3 show schematic diagrams of the charged particle detectors in the MoNA Sweeper setup The target chamber contains a thin target scintillator used for the both the fragment and neutron timing The Sweeper magnet detector box contains two position sensitive detectors two energy loss detectors one gas one plastic a thin timing detector and a total energy detector Details of the Sweeper focal plane electronics and DAQ modules can be found in Nathan Frank s Ph D Dissertation 47 The Sweeper focal plane detectors are designed to accurately identify the charge and mass of the reaction residues and their position and angle relative to the Sweeper 38 neutron detector array 5m o D 55D 5 Osa TE it 5 0 ou 8 2 0 ce oe 2 E O ER Ss E OU 3 E g ta O o sweeper magnet quadrupole triplet Figure 3 2 The MoNA Sweeper setup includes charged particle detectors in the Sweeper focal plane detector box The target timing detector is used for the time of flight measurements for both the neutrons to MoNA and the charged particles to the focal plane thin scintillator dE An optional blocker is installed to limit the count rate to the rate sensitive CRDC detectors x y Original image from Reference 46 39 Target
107. delay of 75 ns before the TDC veto asserts The final set time is the duration of the clear window to ensure any fast cleared modules are ready for the next event Figure 3 10 details the sequence signals from the target reaction to the computer go or fast clear signals The delays for the external cables A through E are adjusted for the specific exper imental setup Such factors as distance between the target to MoNA and the speed of the charged particle residues are taken into account to make certain the timing signals come within the valid window set by the TDC range and the timing overlaps of the Level 2 timer 93 jnpow oIBo euJajul eubis pajebau JOJ99uu09 indino yndul puebe 7 lt do s uow O I ZIZAN Jea 3 ll lt dojs jas ae lt 9 91929 183 9158 q alqeo lt od ondas Corn dar lt g alqeo OBA to pep euour lt UOHIPUOD aBn L ex Amofew lt Ue primary welbeg 21607 Z 2497 J jeoS umoq de ojan lt y a1qeo Jadaams Figure 3 9 The Level 2 logic programmed into the Virtex XLM controls the accep tance or rejection of an event 54 Standard timing sequence a a eee in target and target scint lt ___ fragment reaches focal plane thin scint E neutron reaches MoNA t 100 target sign
108. described in the text The distribution is slightly different and the integrated cross section for the CDCC curve is 1 26 barns and 1 21 barns for the virtual photon cross section reduces the number of events as per Figure 4 28 by more than the increase due to the total cross section The resulting MoNA efficiency is higher than the virtual photon method results 78 compared to 73 95 Chapter 5 One Neutron Knockout of Be 5 1 Introduction A secondary beam of 99 pure Be used for detector calibration of the 12Be exper iment where the reaction residue is 1 Be was utilized further to perform a measure ment of the inclusive single neutron knockout cross section to 9Be to compare with theory Using the shell model the shell level configuration and the spectroscopic factor for the valence nucleons can be calculated These single particle calculations along with the eikonal reaction model 24 can calculate the cross section for the single neutron knockout reaction of Be to Be The eikonal approach assumes a sudden straight line trajectory for the nucleon s constituents and has been shown to be valid at the intermediate energies of radioactive beam production at NSCL 62 These calculations do not include repulsive short range 3 body nucleon nucleon hard core interactions 63 and experimental cross sections rarely match the theoretical cal culations for many systems where the short range effects cannot be ignored The
109. ding the two x and x correction terms to the original fragment time between the target scintillator and the focal plane thin scintillator ToF p When optimal values are chosen for Cy and Cg this first order adjustment will effectively separate particles with the same magnetic rigidity in time of flight as if the Sweeper focal plane momentum acceptance was very small After gating on a specific element the adjusted ToF y g spectra can be used to identify the isotopes Figures 3 5 a and b are examples of separating various carbon isotopes by their magnetic rigidities The gate shown in part a is applied to part b after Cy and Cg are set to optimize the separation For most experiments a combination of x or 0 versus ToF g q and the TKE signal 45 will effectively separate the mass number for a selected element 3 5 Trigger Logic When MoNA and the Sweeper magnet are used in coincidence mode all the data acquisition DAQ modules are routed through one VME I O CAEN V262 mod ule connected to the MoNA computer All the DAQ modules of the two setups are connected by five cables and the MoNA Level 2 logic discriminates between events to readout and those to clear An accepted event results in reading the DAQ modules and an end of event signal produced by the MoNA computer and routed to all modules through the VME bus A rejected event is fast cleared to reset the DAQ modules An overview of the MONA DAQ electronics is shown in Se
110. e primary start to accept or reject an event and send the corresponding signals to the Sweeper electronics through cables B C and D Figure 3 9 is a schematic drawing of the Level 2 logic programmed into 52 the Virtex XLM 3 5 5 Level 2 Timer The XLM72 internal clock runs at a frequency of 80 MHz All outputs and logic conditions are set by the end of a clock cycle and are therefore discretized by 12 5 ns Because of this all the delays used for and gates with coincident logic signals must have at least 13 ns overlap to ensure proper logic conditions These internal delays are set through a Tcl Tk program to interface with the XLM unit before each recorded run There are three values to set in units of clock cycles Set Seta and Set3 These values along with the trigger conditions are used to set the process times for each of the five output channels of the Level 2 logic Timer ta tp te tq and te The delay times are as indicated by Table 3 2 The delay time for t is equal to Seta if the primary signal starts the Timer and equal to the sum of Set and Seta if the secondary signal comes first This is to allow more time for a coincidence between MONA and the primary trigger condition when MoNA is used in tandem mode along with the Sweeper detectors Typical values for Set Seta and Setz are 18 6 and 60 respectively This cor responds to a coincidence window of 225 ns after the timer starts and a
111. e MoNA and the sweeper TDCs and the separation between the CRDCs in the Sweeper focal plane detector box also play a role but are not as important All these factors are simulated by ST mona and can be adjusted on a case by case basis 4 3 He Resolution Test To directly compare the simulated MoNA Sweeper system using GEANT and ST mona a study of the known unbound resonance of the ground state of He was performed A secondary Li beam was stripped of a proton by a Be reaction target 79 350 _ 300 3 x 250 Oo 5 200 Cc O 150 O 100 ab 50 0 0 05 1 15 2 25 3 35 4 Decay energy MeV Figure 4 16 Standard deviations of the resolution curves shown in Figure 4 15 plotted versus the decay energy and He n coincident events were recorded by MoNA and the Sweeper focal plane detectors Inputing the experimentally determined resolutions into SIMPLE TRACK and adjusting the energy and width of the He resonance to match the data the result is then compared with previous works 4 3 1 Experimental Setup A primary beam of 180 was accelerated through the Coupled Cyclotron Facility 31 at the NSCL to 120 MeV u and impinged onto a production target of Be with a thickness of 3526 mg cm The secondary beam of 99 pure Li with 0 5 momentum spread was selected from the resulting cocktail by the A1900 fragment separator 45 utilizing a 825 mg cm Al wedge installed at the dispersive plane see Figure 3 1 The secondary
112. e bar The other 30 QDC channels will have a null result and indeed the count rate of the pedestal peak for any given QDC channel is usually two or three orders of magnitude stronger than the rest of the raw spectrum see Figure 2 7 The QDC collects charge from the internal pedestal current for the duration of the integration gate and compiles a non zero value that depends on the pedestal current and the width of the integration gate The pedestal current and integration gate is adjusted to place the pedestal peak near bin 100 in the 12 bit 4096 bins raw QDC spectra see Figure 2 9 2 3 2 QDC Calibration Once the PMTs are properly gain matched the QDCs are calibrated using the same light response curve of cosmic ray muons used to gain match the PMTs The raw QDC spectra are fitted with a Gaussian plus an exponential background to the muon peak as shown in Figure 2 8 The pedestal peak is used as the zero point for each QDC calibration The average energy loss for cosmic ray muons per centimeter of BC408 26 plastic is 2 0 MeV for MoNA plastic 42 As determined by GEANT simulations 43 using the angular flux of cosmic ray muons and the geometry of MoNA the Gaussian fitted muon peak is set to 20 5 MeVee This linear calibration has been checked with y ray sources energies near 1 MeV for a few bars on the outer layers and found to be correct within 0 075 MeVee 2 33 QDC Thresholds As mentioned in section 2 3 1 the count rate of
113. e crashes during a run the automatic copying and transferring of settings and event files will not happen properly A properly recorded run creates a run folder experiment run that contains the two settings folders and a link to the actual evt file in user event complete To get the links and the Readout program back to working order after a crash first check to see if spdaq16 needs to be rebooted gt ping spdaqi6 Type CONTROL C to quit pinging If there is no response you must go into the N6 area and reboot spdaq16 directions for rebooting are on orange tape on the machine If the pinging worked or after rebooting spdaq16 make sure there are no Readout codes running The following command lists the current programs containing eadout 138 gt ps axuwwlgrep eadout Then kill any programs still running by using the procedure number listed gt kill Rebooting spdaq16 will also kill stray procedures but requires the user to restart many control programs after Follow this check list before continuing with the next run 1 Restart Readout and manually increase the run number 2 Start and then stop a run without recording 3 Use the gt ls la command in the experiment directory to look for a run folder run made for the interrupted run 4 Look for copied mona_settings and sweeper_settings folders within the the run folder 5 If needed copy the settings folders into the interrupted run fo
114. e front is labeled F9 The array is assembled on a stand that is adjusted so that the beam axis is aligned to center of the ninth bar from the bottom bar A8 Figure 1 4 shows the final design configuration for the 144 modules into one array 12 Table 2 2 Dominant neutron reactions for hydrogen and carbon in plastic scintillators at 90 MeV 32 The Q value for the reaction is also listed for specific cases The total cross section for 90 MeV neutrons with carbon is reported to be 500 mb 33 with about half from elastic scattering Reaction a at 90 MeV mb Q value MeV TH n n p 80 0 0 Cain CO 250 0 0 2C n 2n C 22 18 72 2C nn 2C y 14 4 43 12C n p B Xn 95 12 59 12C n d B Xn 24 15 96 120 n n 30 10 7 26 120 n a Be 3 5 71 12C n X 2a 28 n a 12C n X Li 40 n a 2 1 1 Detection Method As is the case for all plastic neutron detectors the dominant interaction for detection is elastic scattering of the neutrons off the protons in hydrogen atoms Since protons have a mass so close to the mass of the neutron they are especially effective at absorbing energy when they scatter neutrons For this reason it is beneficial to use a plastic with a high hydrogen density Bircon BC408 11 used for the MoNA bars has a hydrogen to carbon mass ratio of 1 104 and a total density of 1 032 g cm In addition there is a significant contribution from inelastic reactions with carbon atoms producing a variety o
115. e neutron ToF Un 4 12 y2 22 ToFy 4 4 TT Kn y Mn Mn 4 5 Where y is the relativistic Lorentz scaling factor 1 4 1 vn2 c2 such that the total energy E is equal to ymn The farther MoNA is stationed away from the target along the z axis the better the velocity and also energy resolution becomes because the 5 cm resolution for each bar in the z direction becomes a smaller percentage of the total distance Resolution for various parameters for Ky 70 MeV or 11 cm ns neutrons are listed in Table 4 2 4 2 5 Focal Plane Resolutions The energy and angle of the charged particle fragments are reconstructed from the position and angle measured by the CRDCs in the Sweeper focal plane detector box The position resolutions for these are measured using a steel mask with 0 5 mm holes The recorded distributions are analyzed to determine the resolution in both the z and y directions This is covered in more detail in Reference 47 The CRDC resolutions are determined to be 1 6 mm This corresponds to an angular resolution of 1 7 mrad when the CRDCs are separated by their maximum distance of 1 82 m 4 2 6 Simulated Resolution By including all the individual detector resolutions and running ST mona for different decay energies the overall decay energy resolution for the system can be simulated Table 4 2 Resolutions given as the standard deviations for various MoNA parameters for Ky 70 MeV neutrons with
116. e parameters are analogous to the timing channels Here each thin thick Sweeper raw ADC channel is calibrated and then the four are averaged In addition the two averaged energy loss parameters are added together to form user e total cal Sweeper Positions and Angles Variables can be set to calibrate the gain and pedestal values for each CRDC pad The x position is calibrated by taking the weighted average of all the pads above threshold and then using the slope 2 54 mm per pad is converted to millimeters Using a mask to calibrate the y direction from the drift time these positions can have a precision of better than one millimeter The angles are then calculated from these positions and the distance between them sweeper fp gap Furthermore you can set the track zfp variable and and get the calculated x y positions at this z point in front or behind CRDC1 These two extra x y parameters are called track xfp and track yfp These two tracking parameters will become important later Sweeper Ion Chamber Each pad for the IC has it s own slope and offset variables and then the overall e loss fp ic de parameter has a slope and offset 195 D 3 3 Third Level Parameters Many of the calibrated parameters are still not at the level of being useful for a true physical analysis of the reaction of interest The third level parameters are used to calculate some useful ones All the other user tof parameters are differences of two c
117. e the random background rate does not overload our detectors compared to coincident events with a correlated external stop signal It also allows for the use of less delay cables for the 288 TDC channels In common stop mode just one delay is used for the stop trigger from the thin target scintillator see Section 3 3 1 Fast clear capabilities One desirable feature of the CAEN TDCs is their fast clear capabilities This feature allows the user to send a logic signal to clear all digitized channels and buffers and prepare for the next start signal These modules take only 600 ns to complete the full fast clear cycle and to be ready for the next event If the trigger logic discussed in Section 3 5 4 rejects the current event the TDC can be fast cleared before the module is finished digitizing and even before a common stop signal has arrived This saves many microseconds and dramatically increases the live time ratio of the system compared to not using the fast clear option Without this fast clear capability the DAQ system would have to wait for the module to digitize and then issue a standard sequence of end of event and clear signals before the module clears its buffers for the next possible event The MoNA trigger logic holds the fast clear signal level for 800 ns to ensure all TDCs and QDCs modules are cleared before releasing 18 2 2 4 Light Amplitude Processing MONA uses 9 CAEN V792 charge to digital con
118. e the summed spec troscopic factor of the three paired neutron states dominated by the stripping of one paired neutron to the two neutrons in these states predicted by the unperturbed single particle shell model description of an inert core of Be in 12Be There may be higher shell configurations adding to the ground state wave function not yet ex plored or the simple assumption of two neutrons above an inert 9Be core might be inaccurate and the contributions from core excitations cannot be ignored The reliability of the current results rest on the relative intensities of the 2 69 MeV 3 27 resonance state in Be and the total non resonant background Close analysis sug gests the previous experiment did not have consistent efficiency for the low relative energy zero lab angle neutrons from the decay to the 2 excited state in 9Be and undercounted this decay channel The current measurement finds 40 higher relative cross section for the decay to the 2 excited state in Be from Reference 81 leading to a cross section of 19 4 mb Further theoretical study is needed to determine the configuration of this 3 96 MeV 3 27 state in Be including its overlap to the 2 state in 9Be and the likely mechanism from the 2Be ground state to populate this second 3 27 state in Be 121 Chapter 7 Outlook 7 1 Evaluation of Design The design goals for MONA have been achieved by the performance shown through the analysis of the test experiments
119. ear Spectra button Now re attach your data file SpecTcl will start analyzing the data Now s a good time for a coffee break a typical run can have over 1 000 000 buffers to analyze When it s done the Spectra will look something like Figure B 5 Notice the peaks seem to move from one side to the other as you look at successive bars Most of these event are muons that pass through the left side of bar A15 through the right side of bar AO So the overall pattern will look like a diagonal path through layer A 3Note that it s very important to clear spectra whenever you make a change to the spectra or the gates 157 File Window Spectra Options Graphobjects Help 1B 4 H1E a 7 5 15801 xpos A0 caf 16 57 24 15871 xpos al annie 16 57 24 isegi xpos a2 aire 16 57 24 E E E E h N ved HULL ee E o A I A O 15901 xpos a4 amoil re 16 57 24 1so1 xpos as awt me 16 57 24 E z E E E E Spectrum 593 X 150 50 Y Counts 0 Update Selected UnExpand Summing Region Ean Info F Log F Map tontoa Update All Expand Marker Cut Figure B 5 Gated x position Xamine window B 4 1 Exporting Data When SpecTcl has finished analyzing the data you might want to export it for later use Go to the SpecTcl Control Window and click the Write Any Spectra button on the left Select the spectra you
120. easurements of Ref 30 Since the common stop signal used in the 12B6 experiment was the focal plane thin plastic dE detector for all MONA TDCs and Sweeper channels instead of the tar get scintillator the ToF measurement of the neutron was calculated by subtracting the target scintillator time from the average left and right MoNA times This additional step adds to the uncertainty of the ToF measurement Using the resolution of the thin plastic dE scintillator 0 2 ns yields a total of standard deviation 0 4 ns 111 N o N 4 o T T T T T iy 1 o T o Focal plane angle degrees a T o T o T 2 90 3 E as oo a 50 S5 e a u TOF igid TOF igid a u Figure 6 2 Isotope identification with a two dimensional gate a Gates are applied to select from left to right 9Be Be and Be b The same plot in coincident with a neutron event in MoNA for the neutron time of flight ToFan 6 3 Analysis Beryllium residues were gated by energy loss dE through the focal plane thin plastic scintillator Since the beam was also beryllium a nearly all inclusive gate is made to the dE TKE spectrum and applied to the angle ToF plot for isotope identification This is completed by using the ToFigiq method as discussed in Section 3 4 2 Figure 6 2 shows the gates used to select difference reaction residues Part b of the figure confirms the identification of Be not o
121. edestal peak value 29 2500 V N Q Q o 1500 QDC minimum ke S S al Q o 0 10 20 30 40 50 60 CFD threshold mV Figure 2 11 The threshold for the CFDs were calibrated by recording the calibrated QDC spectrum edge one half amplitude for a range of different CFD thresholds in mV The linear fit crosses 10 mV at 0 65 MeVee and then setting the threshold to the nearest possible value above this bin the newer technique only cuts a maximum of 19 bins and a minimum of 3 bins above the pedestal peak This minimum of 3 bins is sufficient to cut most of the pedestal peak and reduce the over abundance of pedestal values by a few orders of magnitude compared to the uncut peak This new method would apply the QDC threshold at bin 144 for both PMT B 00 L and at bin 128 for B 02 L since the peak is four bins below 128 By applying the proper calibration the improved threshold cut to B 02 L Figure 2 10 the minimum energy recorded is 0 1 MeVee compared to 0 51 MeVee with the simple method This difference is even more pronounced for QDC channels where the pedestal is right at a possible QDC threshold value 0 41 MeVee with the improved method compared to 0 82 MeVee before The full range of possible QDC thresholds for this improved method corresponds to minimum energy cuts of 0 08 0 475 MeVee Since these cuts are at or below the CFD threshold of 10 mV about 0 65 MeVee in this mode there are nearly the same number of valid TDC and
122. edges of the spec trum is from interactions that scatter before depositing enough energy to trigger the CFDs The central region of the dashed line shows the intrinsic position resolution for a scattered proton The dotted line includes effects from timing resolutions 1 5 cm and is fitted by a Gaussian distribution blue line with a standard deviation of 3 cm Figure 4 11 shows the recorded distribution of cosmic ray muons through MoNA bar B1 second from the bottom gated by 0 5 cm gates on the bars above and below it The Gaussian fit in Figure 4 11 has a standard deviation of 2 2 cm This resolution should be slightly less than the resolution for neutrons since muons have a negative charge and interact directly with the scintillating material These x resolution studies only apply for the first MoNA hit Subsequent hits in MONA could be highly scattered events from the first hit When MoNA was being assembled by undergraduate students some of them per formed a neutron shadow bar test to check the position resolution of an individual MONA module The data analysis was presented in a poster they made about their work on MoNA and clearly identifies a x resolution of less than 3 cm 1 Available through the MONA Collaboration website http www cord edu dept physics mona 74 20 15 10 5 0 5 10 15 20 X position MONA bar B1 cm Figure 4 11 Calibrated x position spectrum of cosmic ray muons paths in MoNA bar B1 gated above an
123. ee eee 152 Gated x position Xamine window 00004 158 Raw QDC Xamine spectra ies ta ko RAS BSH id oe 168 Calibrated TDC Xamine spectra o a 176 X position Xamine spectra sais B44 we Bald weed a 181 X position AQ spectrum 5 6 8 pA ase phe A aS 182 Tmean difference spectra sis See Go ee pe amp Garp ae Ger She 185 Tree parameters user window 2 0 000 eee 188 Tandem oped Lel control window 2 Yok sda ted rs Hae eS 204 Images in this dissertation are presented in color xlv 1 1 2 1 2 2 3 1 3 2 3 3 4 1 4 2 4 3 5 1 6 1 6 2 LIST OF TABLES Comparison of existing major neutron detectors Founding institutions of the MoNA collaboration Dominant neutron reactions in plastic for 90 MeV neutrons Level 1 Majority bits ea ah peers ha eh a el Bas Level 2 timer delay times o o Cosy or traditional transformation matrix parameters Light response coefficients for GEANT Resolutions for MONA at 8 m and 14 m positions Detector efficiencies and acceptances for 075038 Cross section and spectroscopic factor for 1n knockout of 9Be Summary of results from previous studies of 2Be Relative intensities of 2Be decay compared to previous work XV 12 13 50 56 61 68 78 93 103 110 116 Chapter 1 Introduction 1 1 Magic Numbers and the Shell Model Much effor
124. em SpecTcl This Tree Parameter GUI has four tabbed pages Spectra Parameters Variables Gates These will be discussed in detail in section 2 3 The other main visual difference is that the SpecTcl Control Window has two graphics in the center and a few extra buttons to track forward and do inverse tracking to the target These extra features will be discussed in section 4 D 1 1 Standard Variables In the Tandem version the Tandem_spectcl tcl file replaces the MoNA_spectcl _run tcl file and also creates a couple tandem parameters and sets the tandem 187 Figure D 1 Tree parameters user window variable target eloss This is the extra energy to add to the fragment energy for e loss through half of the reaction target in units of MeV u As covered in the Mona SpecTcl Guide 92 the MoNA_Z_pos variable is set in the MoNA_setup_run tcl file within the mona config directory This sets the distance in centimeters from the target to the center of bar MoNA bar A8 The tmean offset variable is also set in the MoNA_setup_run tcl file D 1 2 Loading a Settings File The front page of the Tree Parameter GUI is shown in Figure D 1 The button Load in the upper left corner can be used to load a file a definition file containing all the spectra gates and variable settings and values Using the Cumulate option will overwrite only the values set in the new configuration file So if you set a variable and then load a
125. equire the beam line detectors Now an appropriate inverse map must be made inv extension and sourced with the nv map button A good check to see if it is working is to source a collimator run with a known beam and known energy The positions at the target should be centered near zero and the energy should match D 4 4 MONA Timing For proper MoNA timing the potscint signal should be routed as the common stop for all TDC s During the experiment be sure to take a few self triggered runs with some thick stopping material in place of the target This will create a lot gamma rays streaming toward MoNA Applying a gate to the front of MoNA or to bar A8 will fix the distance they travel to be equal to the variable MoNA_Z_pos in centimeters The tmean_offset variable should then be set to move gamma peak to the time light takes to travel to the front of MONA MoNA_Z_pos divided by 29 98 Click the List Variables button to display current values in the TkCon window D 4 5 Isotopic Separation The best technique for separating isotopes is to gate a particular proton number using the calibrated Ion Chamber fp ic de parameter and apply this gate to a 2d de tof spectrum Use the adjustable user tof pot_thin cal parameter for the x axis and set the sweeper tof potthinafp potthinxfp variables to shift the time based of the tracked positions and angles These are not the forward tracked or the inverse tracked parameters These parameters have n
126. ermined by using of a barium fluoride BaF detector installed next to the production target in front of the A1900 Figure 3 1 It is not inserted into the beam path but measures the radiation produced at the 9Be production target The 98 Dispersive angle degrees 50 55 ToF ns rigid Figure 5 2 Dispersive 1 angle versus fragment ToF The two gates select Be left and Be right count rate of the BaF is proportional to the primary oxygen beam intensity which in turn is proportional to the secondary beam rate of 9Be The BaF scaler count calibrated by deflecting the Be beam directly into the Sweeper focal plane thin scintillator was used to determine the cross section for the production runs Even though the Sweeper magnet was set to accept the Be some 9Be from a low momentum tail of the initial secondary beam distribution reaches the Sweeper focal plane These two isotopes must be separated and identified as described in Section 3 4 2 Figure 5 2 shows the adjusted ToF j9iq versus the dispersive angle in the Sweeper focal plane detectors clearly separating Be and Be While trying to optimize the Sweeper magnet two different settings were recorded The first setting at 3 1 Tm clearly accepts nearly the whole distribution of the Be residue as shown in Figure 5 3 but also accepted much more 9Be beam requiring stricter limits on the incoming beam rate to avoid quenching the CRDCs that should 99
127. estimate for the fragment s energy assuming the reaction occurs at the target s midpoint D 3 7 MoNA Tandem Parameters The Tandem MoNA code calculates some useful parameters as well The Tandem_vdiff hit parameters are miss named and are actually just the velocity for that MoNA hit in cm ns and not a difference at all It is calculated from the ToF hit parameters and the MoNA_Z_pos variable The KE_hit parameters are calculated form the velocity and the mass of a neutron A good practice is to gate this parameter on the neutron peak from the ToF_hit parameter The following calculations are also done within 200 the CHitParam cpp code KE_neutron This is actually the first tandem parameter to be set after verifying that MoNA recorded a hit with a valid neutron time greater than 50 ns Check if good_hit set to true if good_hit 4 if so set result KE_neutron to MoNA KE hit of first_count rEvent m_nResultKEn KEarray first_count The index first_count refers to the first neutron event greater than 50 ns in time of flight Theta The angle between the fragment and the neutron is calculated from the fragment tracked angles and the neutron angle using vector analysis This value goes into the Theta parameter First add both vectors double Both_Sum Frag_x Xarray first_count Frag_y Yarray first_count Frag_z Zarray first_count double Frag_R2 pow Frag_z 2 0 pow Frag_y
128. f the Sweeper The contour illustrates the gate used to recover a portion of the true distribution 5 3 2 Parallel Momentum Comparisons An additional check of the knockout process in the parallel momentum distribution The angular momentum quantum number l of the stripped nucleon will determine the relative spread of residue s momentum distribution A value of l equal to 1 cor responding to the stripping of a p shell nucleon will result in a parallel momentum distribution that is wider than that for L 0 but narrower than l 2 This is due to an effect of the uncertainty principle where the larger spacial distribution of the lower angular momentum states will result in a smaller energy distribution Since the ground state of Be is 0 and the state of Be is the 3 27 ground state the momentum distribution of the residue should match well with a Ops 2 shell neutron Fragments that exit the target at large angles will strike the frame of the Sweeper magnet detector box or miss the active region of the charged particle detectors and 104 0 3500 3550 3600 3650 3700 3750 3800 3850 3900 Parallel momentum MeV c Figure 5 8 Parallel momentum distribution of the unreacted Be beam through the target The Gaussian distribution with a standard deviation of 13 1 0 8 MeV c was folded into the eikonal model momentum calculations used to fit the data in Figure 5 9 fail to reach the thin scintillator trigger at the back of focal plane dete
129. f Be the decay channel is uniquely identified as a Op 2 neutron knockout by the Be residue since Be has no bound excited states and does not require the use of MoNA Chapter 5 details the experiment using the Sweeper magnet and the focal plane detectors to measure the reduction factor for Op 2 neutron knockout of Be 1 5 2 Ground State Wave Function of Be The second experiment continues the study of the evolution of the lower neutron shell levels in beryllium isotopes at the neutron drip line The standard order of filling the nuclear shell levels for stable nuclei is already broken by the neutron halo nucleus H Be so the mixture of neutron pair correlations in the 0 ground state wave function for 12Be is predicted not to be just a simple combination of 1sy or 0p 2 paired neutrons built on a 9Be core Indeed the first experiment to measure the populations of these configuration found about half of the total neutron single particle population missing 29 suggesting a strong add mixture of 0d 12 neutron pair wave function More recently a second experiment including the ability to measure the neutron unbound levels in Be confirmed the hypothesis 30 by observing the 5 2 level in 1 Be by stripping one of the 0d 2 paired neutrons from 12Be Using MoNA a third experiment was performed with higher statistics enabled by MoNA s high efficiency for fast neutrons focusing on the neutron unbound exit channels from one
130. f possible charged particles or y rays Table 2 2 lists the major contributing reactions of an organic hydrogen and carbon plastic scintillator including their energy thresholds Reactions emitting alpha particles have minimum required energies Q value of at least 5 7 MeV and account for a noticeable increase in total cross section with plastic for neutron energies near 30 MeV Since alpha particles do not induce as much scintillation light due to their mass reactions that produce alpha particles do not add significantly to the detection efficiency unless the detector threshold is relatively low less than 3 MeV electron equivalent MeVee 13 light guide gt PMT scintillation light neutron Figure 2 1 Diagram of one MoNA module and illustrates production of scintillation light dotted lines by charged particles released from neutron reactions see Table 2 2 The light is captured by the two PMTs coupled to the bar with light guides 2 1 2 Light Propagation When a charged particle passes through the lattice of a plastic scintillator 1t excites the large organic molecules that subsequently de excite via release of a photon in the visible range The number of photons released by this scintillation process is pro portional to the energy lost by the charged particle through Coulomb interactions with the lattice and depends on the charge mass and speed of the particle BC408 is organic scintillating plastic that has an i
131. f the NSCL 36 MONA Sweeper Magnet iy l h A IN SS f 1 jes ey o E Eg BS SE ag vu Do 7 s Hs Im x o gt b h o e E 3 Dv oom E 2 y Qs E 3 ie 6 A Ay NS e J Figure 3 1 The Coupled Cyclotron Facility CCF provides the beam for the MoNA Sweeper setup The A1900 fragment separator selects the nucleus of inter est from the resulting cocktail of fragments created at the production target behind the K1200 cyclotron at velocities of nearly half light speed Image from Reference 44 37 at MSU The distance between the target and MoNA must be optimized for each experiment to balance velocity resolution and angular acceptance 3 2 MSU FSU Sweeper Magnet The Sweeper magnet was built by the National High Magnetic Field Laboratory at Florida State University 16 17 Its superconducting coils are made of niobium titanium for a maximum magnetic filed of 4 Tm requiring a large 10 foot iron return yoke The magnetic field is controlled to deflect the charged particles into a focal plane detector box at 43 in the horizontal dispersive plane x In order to allow neutrons to pass through the Sweeper magnet has a large 14 cm gap sealed with a thin 0 25 inch steel plate at zero degrees This thin steel neutron window scatters 4 of the high energy neutrons from the target and seals the vacuum of the beam line and focal plane Two copper resistive trim coils are attache
132. g Region Ean Display Info F Loo 1 Map Integrate Lentes Figure C 1 Raw QDC Xamine spectra In the SpecTcl Control window click Create Raw Spectra Then choose Attach to File and select the run file recorded in step 1 In Xamine go select Window gt Read Configuration and pick one of the win Q_x_x win window settings Allow SpecTcl to analyze all the buffers to ensure sufficient statistics for the cosmic peak fitting program When the data is read in click Update All in Xamine Look through the spectra in Xamine to make sure the data is usable i e that there is a cosmic peak in each of the spectra Select all the win QDC win files to view all the QDC raw spectra The spectra should look like Figure C 1 with a pedestal peak near channel 100 and a cosmic muon bump three orders of magnitude smaller near channel 900 If there is a problem with one of the bars double check that the voltage is on and that the inverter box is getting a good dinode signal from the PMT then inverting it for the QDC 168 11 In the SpecTcl window choose Write Cosmic Spectra to perform an swrite command on all raw QDC spectra This also reads in the last Cosmic_Volts tcl file and labels each spectra with the proper high voltage channel 12 In the spdaq16 terminal window change directories gt cd mona contrib hvfit C 2 3 Voltage Matching Code 1 Now you run the high voltage fitting code 93 by typ
133. gate2 using the name xpos_a15_gate2 and for the middle 14 spectra Xpos_A1 to Xpos_A15 with _andgate in the name because we will apply the new andgate to them all Next you need to bind them using the sbind all command as noted above B 3 7 Displaying New Spectra In the Xamine window use the Display button to view all the new spectra you ve just bound At this point it s a good idea to save your configuration name it some thing unique and save it You ve just saved the setup that s currently in Xamine you have not saved the spectra names or the gates so if you ve done a lot of work or feel like you might want to revisit the these settings for this experiment now might be a Tt is nice to select a bin number that is a multiple of the range you ve selected plus one so the bin edges line up with the values 156 good time to go to the TkCon shell press h and copy paste the result to a text file See Section 5 B 3 8 Applying Gates Go the TkCon shell and type apply gatel xpos_a0_gatel to tell SpecTcl that you re applying gate1 to the spectrum called xpos_a0_gate1 Now repeat to apply gate2 to the xpos_a15_gate2 spectrum The apply command can have a whole list of arguments so to apply the andgate to all the middle 14 Xpos spectra you just made you only need one line apply andgate xpos _al _andgate xpos _a2 _andgate B 4 Analyzing Data Go to the SpecTel Control window click on the red Cl
134. ground state wave function of 12Be 118 6 3 2 Diffractive Breakup and Two Neutron Decay The relative intensities of the fitted resonances depend on the shape and intensity of the non resonant background curve The diffractive breakup of 2Be to Be n leading to Be 2n or directly to Be 2n is accepted by the gate used in Figure 6 2 and is a large contribution to the non resonant background in both Figure 6 7 and 6 8 The precise shape of the cross section spectrum for this decay channel is not known but was modeled by the diffractive channel leading to bound 1 Be n in Ref 30 The acceptance for Be reaction residue in the current study was severely cut and would not lead to a reliable estimate of the shape of the diffractive decay spectrum The current analysis was made using a thermal Maxwell distribution with a temperature of 3 5 MeV per Equation 4 3 and closely matches the diffractive curve used by Ref 80 One piece of evidence supporting the choice of modeling the non resonant breakup decay is that the two regions of the spectrum that are dominated by only this channel near 0 5 and 2 7 3 5 MeV are fit very well by the 3 5 MeV thermal distribution Although it is clear that the large uncertainty in the relative intensity of the 3 27 state at 2 1 MeV in Table 6 2 is largely due to the uncertainty in the non resonant curve and the lower acceptance as decay energy increases Analyzing the decay energy curve for even
135. ground data a strong cosmic ray muon peak corresponding to 23 Cosmic ray muons Figure 2 6 Side view of MoNA showing cosmic ray muons that travel through MoNA and are used to calibrate many properties of MoNA The time offsets for the whole array relative bar A8 highlighted are set from muons that go straight down one layer or cross to the neighboring layer as shown 20 5 MeVee appears in the QDC spectra as seen in Figure 2 7 The voltages of all channels are adjusted until the difference between the pedestal peak null value and the muon peak is about 800 bins out of a 12 bit 4096 bins raw QDC spectrum This not only ensures the PMT signals are matched but also sets the QDC full range to about 100 MeVee This procedure provides an approximate gain matching to set the thresholds consistently and to ensure similar PMT response times but it does not substitute for proper calibration of the energy deposited within the bar see Section 233 Adjustments to the voltages are done by fitting the muon peak portion for the 24 1000000 100000 10000 1000 100 arbitrary units 10 hi O 500 1000 1500 2000 2500 3000 3500 4000 Raw QDC C 03 R bins Figure 2 7 Raw QDC spectrum for PMT C 03 R the right PMT dynode signal of the forth bar in the third layer The dominance of the pedestal peak in the lowest channels is clearly seen followed closely by the self triggered CFD threshold that appears only as a shoulde
136. h Tmean_indie_offset set to true to read the MoNA_Tmean_indie_offsets tcl file during next start up 11 If you now restart SpecTcl and repeat steps 3 7 the peaks in each spectra should show up right at the theoretical values listed in the file Tmean_offsets _theoretical In between steps 3 and 4 you must reread the independent offset file you just made since the first line of source tcl reads in a blank set of offsets source env MONA_CONFIGDIR MoNA_Tmean_indie_offsets tcl 12 If you would like to redo the Tmean independent offsets you must delete or rename the file config MoNA_Tmean_indie_offsets tcl before executing the code again Double check that all the calibration flags in MoNA_setup_run tcl mentioned in Chapter 1 are set to true For future runs MoNA is now calibrated with data specific for the experiment 186 Appendix D Tandem SpecTcl Guide D 1 Getting Started The tandem version of SpecTcl for the Sweeper MoNA setup is a complex and large set of files compiled to form a complex and powerful analysis tool It unpacks all the raw channels and converts many of them to calibrated parameters and even some to very useful physics parameters Please familiarize yourself with the Mona Spec Tcl Guide 92 and the online SpecTcl User s Guide 90 before proceeding Concepts in those documents will not be reviewed One of the most noticeable differences is that an extra control window is used with the tand
137. h shell script to perform the calibration To do this make sure you are in the mona contrib hvfit directory 4 Run the calib sh program by typing the gt calib sh command 5 When the code is finished information about each channel will displayed As on the screen from left to right the seven numbers correspond to the following 1 HV Channel 2 Muon Peak bin 3 Pedestal bin 4 Diff 2 3 5 QDC Threshold 6 QDC Slope 7 QDC Offset 6 Note that the QDC calibration code is QDC_Cal QDC_raw QDC_offset QDC_slope 171 so the QDC offset is in units of raw bins and the QDC slope is in units of MeVee bin This is fitted to set the muon peak at 20 5 MeVee and the pedestal to zero 7 Make sure that the numbers in column 4 are all about 800 and match column 2 minus column 3 8 Check that the QDC threshold values are about QDC Threshold Pedestal bin 3 16 1 9 Check that the QDC offset values are the same as the Pedestal Peak values 10 Check that the QDC slope values are all about 0 028 11 If the preceding checks are not confirmed then the High Voltage Gain Matching directions must be re done 12 This program also saves the new slope offset data in mona config and links to QDCfittedTHRE tcl and QDCfittedSLOOFF tcl 13 Enter the mona config directory and check to see that there are current threshold and slope offset files based on the date and time of completion by using the command gt
138. he bar Again using cosmic ray muons and their uniform flux with respect to the MoNA bar axis the width of each bar can be calculated in nanoseconds Figure 2 13 shows the time difference spectrum used to calibrate the horizontal position of MoNA bar B11 A cut is made in the respective QDC channels above 8 MeVee to ensure there is no y ray background and the gated time difference spectrum is calibrated to 200 cm and the center is offset to zero While the distribution of muons through the bar is uniform the recorded distribution is not Some muons that strike the corners of a MoNA module may not pass through enough plastic to deposit enough light such that both left and right CFDs fire This effect is modeled by a Monte Carlo simulation and determines the width of the time difference distribution at 1 3 the maximum plateau corresponds to the actual 200 cm width of the MoNA bar The nominal calibrated conversion from time difference in nanoseconds to centimeters for the MoNA bars is approximately 8 cm ns 2 3 6 Time Offsets Even after the TDC response is calibrated to nanoseconds the time relative to a common stop signal cannot be determined with out knowing the individual time offsets for each channel In yet another way of using the cosmic ray muon flux through MoNA the small differences in the amplification time for the individual PMTs and the differences in the cable lengths for the TDC common stop signal that is daisy chained to all MoN
139. he strong peak near 0 0 is from the highly excited 3 96 MeV state in Be decaying to the 2 state of Be E 3 87 MeV with the surrounding rainbow shape produced mostly by decay of the 5 27 1 274 MeV state This spectrum is an alternate way of displaying the pertinent kinematic parameters used for the calculating the decay energy with Equation 3 7 To account for acceptance cuts that may affect the resonant shape of the final decay energy spectrum the MoNA Sweeper Monte Carlo simulation SIMPLE TRACK 113 O 20 40 60 80 100 120 140 160 180 200 Neutron kinetic energy MeV Figure 6 4 The neutron kinetic energy has a much larger range due to its small mass is again utilized configured as ST mona with MoNA Sweeper detectors It is run with the known widths and energies of the three resonant peaks populated with sufficient intensity with this setup plus one thermal background curve simulating both the non resonant neutrons and the diffractive breakup channel with two neutrons The input beam properties were adjusted to reproduce the angles and positions of the residues in the focal plane Although the beam line tracking detectors were not used they have little effect on the final decay energy spectrum since most of the kinematic properties are carried by the lighter neutron After the simulation folds in the various detector resolutions for MoNA and the focal plane detectors which in turn translate to target angle and energy resolution
140. hin the Sweeper magnet s 14 cm curved gap 47 These measurements cover the whole operational range of the magnet and a permanent reference Hall probe was used to extrapolate to the field strength used during an experiment Once a reference Hall probe value is recorded for an experiment a magnet field map is generated by IGOR PRO 48 using the archived series of measurements The field is calculated for the mid plane of the 14 cm gap and then imported to COSY INFINITY 49 along with the desired particle s mass and charge to yield a transformation matrix from the target position in front of the Sweeper magnet to the position of CRDC 1 inside the focal plane detector box The matrix relates the particle s horizontal and vertical angles and positions at CRDC 1 to the angles and energy at the target Table 3 3 shows the parameters related by the transformation matrix This matrix is inverted to output the parameters in the right column using the left column as the input The relative energy de is the ratio of the charged particle energy to the nominal energy of the central track calculated by COSY INFINITY 61 Incoming tracking One drawback of this inverse matrix is that it in order to calculate the relative en ergy de it must assume the dispersive x position at the target is zero As shown in the figure of the experimental layout 3 1 there are two position sensitive detectors upstream from the target These were not used in the 12Be or
141. hough it is a true proton scattered neutron Considering the efficiency of each vertical MoNA layer is about 25 this could occur about 5 of the time Despite these challenges progress is being is being made on both positively iden tifying two neutron events and generating a standard ratio of single neutron proton scattered events to total single neutron events The ratio will be used to calculate the relative two neutron component in a particular data set for relative cross section measurements while positively identifying the two neutron subset of data will be used for calculating di neutron decay energies 125 7 3 Other Completed Experiments 7 3 1 Oxygen Isotopes In two separate experiments the MoNA collaboration studied neutron unbound states for three Oxygen isotopes 2924230 The first experiment used a 2 Ne secondary beam and produced the first excited states neutron unbound in both 240 and 220 though 2p and 2p n knockout reactions respectively 83 The second experiment used a 26p secondary beam and was designed to study the unbound ground state of 250 through the 1p knockout 84 It also produced significant amounts of highly excited 240 decaying to unbound 230 with a final residue of 220 Some of the two neutron identification techniques are being applied to these data 7 3 2 SLi Coulomb Breakup This experiment was performed to study the validity of nuclear astrophysical models by comparing relative intensities
142. ht c the value of 29 8 cm ns is used as the speed of the muons in calculations So if we look at the Tmean values for these events between two bars we can calculate the proper time offset of these two bars relative to each other If we gate on only muons travelling nearly straight down the time difference is 0 344 ns for a 10 cm bar 10 26 cm is used as the dimensions of the bar because of tape and gaps between bars If we use bar A8 as our reference A8 offset is set to 0 the whole MoNA array each bar can then be set to have the proper time offsets The Tmean differences between bars are calculated through pseudo parameters and the values read by a code from their spectra C 6 1 Finding Independent Offsets Before any offset values can be calculated a long cosmic ray run must be taken This new run requires the all previous calibrations to be preformed first 1 Record an overnight 12 hours run of cosmic ray data with all detector bars 183 Use MoNA multiplicity set to 3 fold cosmics and select self trigger and self stop on the XLM control Also be sure that you are using calibrated slope offset values for both the QDC and TDC parameters and check that the calibration flags in MoNA_setup_run tcl QDC_thres_flag QDCfitted TDCfitted Xposfitted Open MoNA SpecTcl 92 in the spice terminal window or from a Data U machine From the TkCon window type source mona contrib tmean_offset_cal source tcl This
143. ing the gt hv sh com mand This runs a shell script that executes the program fit_mona spectra f 2 When the process completes there will be a listing of information about each channel and the changes that have been made The six numbers are left to right 1 HV channel 2 Muon Peak bin 3 Pedestal bin 4 Difference 2 3 5 Current HV setting 6 New HV setting The process also saves the new high voltage settings and links them to hv_files QDCfittedHV tcl 3 By just carefully viewing the listed numbers from the output of the fit_mona spectra code we can determine if everything went smoothly without Top Drawer 4 Make sure that the numbers in column 4 are all about 800 and match column 2 minus column 3 5 Check that the new voltages settings in column 6 are not too different from those in column 5 169 6 If you are familiar with the program TopDrawer try the next four listed items otherwise you re done with this part 7 Try to open TopDrawer by typing gt td spectratest tdr in the spice terminal window 8 Press Enter each time you wish to change to the next set of 8 plots displayed Each time you do this the word pause will appear in the spice window Note There are 288 spectra so there will be over 30 TopDrawer screens to look through 9 Look for a peak that appears around bin 800 and 2 white fit lines one a gaussian fit to the peak and the other an exponential fit to the backgroun
144. ingly After I am assured of at least one good hit the code then scans the hits for the lowest time value and saves it s index The rest of the Tandem parameters continue to use only that hit index including the KE neutron and Tandem_e_decay parameters The code to find the first hit greater than 50 ns is here First check that the MoNA array counter had at least one hit if Counter gt 1 initialize temp variable double temp 0 0 array place of ToF first hit initial value for hit 1 count 0 int first_count 0 MONA hit ToFarray first_count initial value to hit 1 double ToF_first ToFarray 0 condition set true when ToF has hit greater than 50 ns bool good_hit false loop through the ToF to find earliest and set first_count to index of earliest for int j 0 j lt Counter j 4 Check if MoNA ToF array has a hit with time great than 50 ns if ToFarray j gt 50 0 4 set good_hit true is there is one good_hit true 198 continue to look for earliest ToF that is greater than 50 ns temp ToFarray j if temp lt ToF_first ToF_first temp Set first_count to array index of earliest hit first_count j D 3 6 Tracked Parameters By using an inverse map the SpecTcl code calculates not only the position and angle of the fragment at the target but also the relative energy to the magnet s center track An inverse map is just a transformation
145. inux Data U machine login in with the experiment account and follow these commands gt cd 7 gt chmod 0750 gt rm rf ssh gt mkdir ssh gt cd ssh gt chmod 0700 gt ssh keygen t dsa P f id_dsa gt mv id_dsa pub authorized_keys gt mv id_dsa identity gt chmod 0600 identity gt chmod 0640 authorized_keys gt cd A 2 4 Event Space When the account was created the computer group should have also issued space on an event disk for recording event files Create a link called stagearea to this issued directory address 133 gt cd gt In s user event3 05124 stagearea Replace event3 and 05124 with the proper assigned values issued by the computer group A 2 5 Log Book Log books are provided by the NSCL and one should be taken from the main level copy room Put the date and the experiment number on the cover Inside Cover I like to use the inside cover to record the list of collaborators and the password A 3 Bash Profile Similar to the ssh directory some of the programs refer to the standard direc tory structure outlined in the next chapter and are given environment variables within the bashrc file The standard bash files can be copied from the user mona Bash files directory After logging in with the experiment account follow these commands gt cd 7 gt cp rp user mona Dot _files gt cp p Dot _files bash A 4 Directory Structure
146. ion 740 North Thomas Drive Bensenville IL 60106 USA http www magnetic shield com IL Karsh A Bohm K Th Brinkmann L Demirors and M Pfuff Nucl Instr and Meth A 460 362 2001 Jan Toke User s Manual Systems JTEC Instruments 32 Thompson Rd Rochester NY USA December 2002 Revision B W Rogers et al 2007 Westmont College CA USA Private communication R Madey J W Watson M Ahmad B D Anderson A R Baldwin A L Cas son W Casson R A Cecil A Fazely J M Knudson C Lebo W Pairsuwan P J Pella J C Varga and T R Witten Nucl Instr and Meth 214 401 1983 J M Paul Nucl Instr and Meth 96 51 1971 GEANT CERN library long writeup Technical Report W5013 CERN 1994 T Baumann 2007 NSCL design drawings Private communication D J Morrissey B M Sherrill M Steiner A Stolz and I Wiedenhoever Nucl Instr and Meth B 204 90 2003 211 46 47 48 49 50 51 52 53 54 59 56 57 58 59 60 A Schiller T Baumann D Bazin J Brown P DeYoung N Frank A Gade J Hinnefeld R Howes R A Kryger J L Lecouey B Luther W A Peters J R Terry M Thoennessen and K Yoneda volume 831 page 92 AIP 2006 N Frank Spectroscopy of Neutron Unbound States in Neutron Rich Oxygen Isotopes PhD thesis Michigan State University 2006 Wave Metrics IGOR PRO 5 0 1 0 10200 SW Nimbus G 7 Portland OR USA M Berz
147. lder gt cd experiment gt cp rp current mona_settings run gt cp rp current sweeper_settings run 6 Now look for a linked evt file Within the run folder look for a linked evt file pointing to the actual evt file in one of the stagearea subdirectories Look for a linked evt file in the experiment orphans or current direc tories 7 Find the actual evt file in stagearea complete or current or orphan di rectories 139 8 Move the actual evt file for the interrupted run into stagearea complete 9 Fix links to the evt file for the interrupted run within the experiment run folder to link to the actual file now located in the stagearea complete direc tory gt cd experiment run gt ln s stagearea complete run 4096 evt 10 If needed delete old links from the experiment orphans or current directo ries If all goes well the next run can now be recorded Be sure to make a note in the log book during which run the Readout program halted A 6 Post Experiment As the experiment time is completed there a few prudent procedures to perform to ensure the data is capable of being analyzed properly A 6 1 Calibration Runs Before turning MoNA HV off take a couple cosmic background runs for future cali bration checks One long run 6 hours with MoNA self triggered stopped and multi plicity set to 1 fold and then another long run again self triggered a
148. les some linked files and directories are installed In general the whole mona directory tree is copied from the preceding experiment and includes the wrong directory links and old calibration values They must be checked to ensure they link to the proper destination The command gt 1s la can be used to double check if the links are set properly The following commands should be done when first setting up a new experimental account and to correct any old or mislabelled links TDC Calibration Links In the mona contrib tcal directory the TDC calibration code looks for the TDC spectra written after reading a time calibration run A link to the spectcl spectra directory is used gt rm monatcaldata gt ln fs mona daq spectcl spectra monatcaldata The code then saves the TDC slope values to the MoNA configuration directory so a link needs to made to it gt rm spectclconfig gt ln fs mona config spectclconfig HV and QDC Calibration Links In the mona contrib hvfit directory the high voltage gain matching code needs to input the MoNArawQDCcosmics asc file created in SpecT cl from a cosmic background run A link needs to be set gt rm monacosdata gt ln fs mona daq spectcl cosmics monacosdata 165 The gain matching code also needs to output the new voltage file to right directory gt rm hvfiles gt ln fs mona hv_control hv_files hvfiles The QDC calibration code runs from the mona contrib
149. ll the full breadth of MoNA magnitude is more than enough to compensate the production rate This experiment had a slightly different layout than the standard MoNA Sweeper configuration and is shown if Figure 7 2 By placing the reaction target in front of the quadrupole triplet focusing magnet we were able to focus the fragments by their charge to mass ratio or Bp and more easily separate mass and proton number for a large range of reaction residues Acceptance loses due to the bore radius of the triplet magnet in between the target and MoNA was not too restrictive to reduce the rates for many nuclei of interest The analysis is still being completed but there are over 500 neutron fragment coincidences for at least a dozen identified nuclei 86 7 3 4 Double Neutron Experiments In an effort to further test the capabilities to separate and analyze experiments with more than one neutron an experiment to reconstruct the unbound ground state resonances for 2Li and Li was completed They were produced by knockout from secondary beams of 4B 2 protons and 4Be 1 proton respectively using the standard MoNA Sweeper configuration 121 is unbound by more than 1 MeV while 127 131i is unbound via two neutron decay by about 3 MeV and likely decays through a 121 resonance on the way to a HLi 2n 7 3 5 Cosmic Ray Survey MoNA collaborators at Westmont College in Santa Barbara California have built the Cosmic Muon Detector Ar
150. ls la 14 Edit and save MoNA_setup_run tcl with the QDC flags QDC_thres_flag You are now ready to run an experiment with voltage matched PMT s and cali brated QDC parameters The next time you take data the QDC s will ignore values less than the threshold so no pedestals are read The energy of lost events due to the 172 pedestal suppression will be between 4 to 19 channels which is less than 0 5 MeVee Also the QDC calibrated spectra will be fitted for 20 5 MeVee at the muon peak and zero for the where the pedestal was C 4 TDC Calibration MoNA uses time to digital converters TDC s to set timing coincidences for events that occur in the array In a sense they are fancy stop watches for the detector When a TDC channel receives a pulse from the anode of a PMT of a particular detector bar it begins charging a capacitor When the delayed logic stop occurs the capacitor stops charging and the amount of charge on the capacitor corresponds to the time the TDC was charging However each TDC does not charge at exactly the same rate as another so the rate at which two different TDC channels charge will give different times for identical time events This presents a problem that must be overcome with a calibration The time calibrator NIM box which is physically daisy chained to each of the TDC channels at the beginning of the process gives precise signal spikes at equal and adjustable intervals over a predetermined a
151. luorine Z 9 for example is bound to at least N 22 while oxygen is only bound until N 16 5 Furthermore phenomenon like neutron and proton halo nuclei are found to exhibit strange properties that cannot be modeled by nucleons in a simple potential well Studying the evolution of these shell levels constrains theoretical explanations and predictions The level structure of neutron rich nuclei can change dramatically from one nucleus to the next due to interactions that are not observed near the valley of stability because of the different proton and neutron configurations of rare nuclei Discoveries like these drive current efforts of nuclear structure experimentation and shell model theory 6 and the undiscovered region of the chart of the nuclides in Fig ure 1 2 is mostly neutron rich where neutron detectors are likely to play an important role in their study 1 2 1 Neutron Unbound States Some of the most important nuclear structure quantities include the nuclear popula tions within shell levels and the level structure binding order of shell level within the nucleus for nuclei far from stability Near the neutron drip line methods for studying energy levels are limited to neutron spectroscopy experiments Figure 1 3 illustrates the extent of nuclei where other methods would not be sufficient to record the energy levels of these nuclei Nuclei whose excited states are unbound cannot be studied by using y ray detectors This cove
152. m calculated by the eikonal reaction model successfully re produces the expected 0ps 2 neutron knockout distribution for the Be Be Be X reaction The calculated reduction factor of 0 66 0 07 is slightly less than other 1n knockout systems near AS 13 MeV It is also slightly less than the mirror system of 0p3 2 proton knockout in a neutron deficient C nucleus with the 2C C 8B X reac tion 68 with Rs equal to 0 82 0 06 To the extent that this difference is significant the proton halo property of 8B might lead to less short range correlations Some com parisons between 9C s true mirror nucleus Li made in references 68 75 76 suggest other unexpected properties exist for 9C which might account for the differences 107 Chapter 6 Ground State of 12Be 6 1 Introduction As discussed in the previous chapter spectroscopic factors from knockout reactions are used as a diagnostic tool to study the single particle occupancy of nuclear shells The experiment described in the previous chapter focused on the 0p3 2 shell level population of 9Be The experiment detailed in this chapter is more complex and ex plores the relative single particle occupancies of a few different shell levels comprising the ground state of 2Be 2Be is at the neutron drip line and the supposedly magic number N 8 This shell gap is known to break down away from the valley of stability at the neutron halo nucleus MBe that has a 1 2 151 2 ground state 19
153. made map extension and sourced with the Ppacs map button A good check to see if it is working is to source a collimator run with a known beam and known energy The positions at the target should be centered near zero D 4 3 Sweeper Inverse Tracking Inverse tracking can only be completed after the CRDC s have been calibrated for position from mask runs The Inv map button is used in conjunction with the Order Mass Charge Brho input frames to calculate the energy of the fragment at target from information from the focal plane CRDC detectors These inputs should corre spond to the mass and charge of the fragment you wish to track through the Sweeper magnet The Order should be set to 3 or higher if the inverse map was made to a higher order The Brho input should correspond to the Brho value setting of the Sweeper magnet before the run Check the experiment s logbook for this number This number is also needed to make the inverse map so you can check with the person who calculates the inverse maps as well Once the input frames are filled with the appropriate values the sweeper fp track 3This button is used with both beam line tracking PPAC s or CRDC s 205 map maxparameters variable should be set to 4 if you wish to use the old inverse maps that do not require the beam line detectors or to 5 for the new inverse maps that take into account the x position at the target from the forward tracking map described above that r
154. matches very well for the whole fitting region In Figure 6 8 the relative intensity of each curve is a treated as a free parameter but the absolute scale for the data was fixed at 1 09 The only resonance not consistent with the previous measurement is the highly excited Be decay to the 2 state in Be This apparent discrepancy of 40 can be accounted for by considering the efficiency and acceptance issues of low relative 115 Relative angle degrees Relative velocity cm ns Figure 6 6 The relative angle and the relative velocity neutron minus fragment contains all the kinematic information used to calculate the decay energy energy zero lab angle neutrons for the experimental setup of Ref 30 The efficiency for the lowest decay energies is less than the rest of the spectrum due to the lack of a large gap dipole to deflect the charged particles off beam axis in the DeMoN setup This low energy decay channel is likely caused by knockout of a non valence neu tron in Be leading to a highly excited state in Be where the spin and parity of this excited single particle state decays predominantly to the 2 state in Be This core neutron is thought to be in the Op3 g shell as calculated by B A Brown 27 using Table 6 2 Decay energies and widths used by SIMPLE TRACK for 2Be decay simula tion and relative comparisons ferp taken from Figure 6 8 to the measured cross sections reported in Steve Pain s Ph D thesis 8
155. meters On the second page you can change the default settings for any parameter These are the same limit values that are displayed when a parameter is selected for a spectrum as described above 1 First click the designation button for an empty row It will turn red 2 Select a parameter using the Parameter label drag down menu 3 The default values will be displayed 4 Edit the values for High Low Bins Unit 5 Select Set to make the changes or Load to revert back to previously set values 6 Select Change Spectra to apply changes to all spectra containing that parameter Changing Variables Changing tree variables on the third page of the Tree Parameter control window is done analogous to changing parameter values as in the previous section 1 First click the designation button for an empty row It will turn red 191 2 Select a variable from the Variable drag down menu 3 The default values will be displayed 4 Edit the values for Value Unit 5 Select Set to make the changes or Load to revert back to previously set values Changing Gates The forth page in the Tree Parameter GUI deals with gates Gates can be made by using in line commands in the TkCon window 92 or by using Contour or Cut buttons in Xamine If any gates have been made you can double click the name of any gate and view its dependencies and type You can then edit the values or delete the gate Compound gates can be made by using the in line comma
156. meters and then calibrate them with user defined variables Branches of this tree include tof rf xfp potscint and thin timing also fragment velocity e thin and thick e loss These branches hold parameters that can be calibrated and manipulated within the CUser tree code D 2 3 Using the Tree Parameter GUI Making Spectra The following directions apply only to sweeper and user tree branches For MoNA spectra use the TkCon window or the pre set buttons on the SpecT cl Control window 92 MONA spectra will indeed be displayed in the spectra tab of this GUI and can be edited once created D Bazin has written some excellent documentation about using the Tree Parameters 95 1 In the upper left hand corner of the window select the type of spectrum you wish to create For information about the different types see Ref 90 2 Next select the X Parameter label to use the drag down menu and move cursor to find the tree parameter you want 3 The default parameter limits will be displayed to the right of the name 4 Edit the parameter limits Low High Bins as desired 190 5 Select Create Replace and your spectrum will be displayed in the columns be low 6 Double click any spectrum to edit any of the limit values and then repeat pre vious step 7 Apply any gate that is made by selecting the Gate drag down menu and then Apply 8 Save time by saving definition file using Save button Changing Para
157. n Change directories to the evtdata space provided by the computer group gt cd evtdata Read the files from the tape gt tar xvf dev st2 When the reading is completed check that the entire experiment directory was copied including actual evt files not links 141 11 Eject tape and label it with the date experiment number and runs included If all the experiment run folders were repaired properly if Readout crashed the actual evt files should have been copied correctly If they were not copied correctly find the run folders for the missing evt files and rewrite the link to the actual evt file Then delete the files you just wrote to the evtdata space and start over from step 4 Since this process copies each evt file inside their respective experiment run folders it is not possible to attach multiple files when analyzing the date with SpecT cl 89 A useful trick is to make a new folder within the evtdata space that contains links to all the evt files 1 gt cd evtdata 2 gt mkdir evt_links 3 gt cd evt_links 4 gt for i in experiment run evt do ln s i done 5 Check that all evt files have a link in this folder A 6 3 Analysis Space Along with an evtdata space the computer group also should have provided a projects space to copy the analysis files The projects area can be accessed from the high speed spice machines and should be used for all
158. n a certain part of the tube For this example choose for this bar the region between 80 0 cm and 60 0 cm Move the cursor to 80 cm on the 154 spectrum in Xamine and click once then move to 60 cm and click again This will fill the coordinates into the appropriate box in the Cut pop up window Select the name box and label the gate gate1 and then select Ok to accept Cuts can also be declared with the gate in line command in the Tk Con window see Ref 90 for details MONA is set into a right handed coordinate system with positive z in the direction of the moving beam and positive y as the up direction toward ceiling This means positive x is to the left when looking at the front of MoNA layer A Xamine displays spectra from lower value to higher value so the range 150 150 301 will have the correct coordinates but left and right will be reversed on the screen Just image you are viewing the Xpos of a bar from behind MoNA where spdaq16 sits This way positive x is to the right of the viewer since you are looking in the negative z direction In the TkCon shell type gate list to verify that the gate has been created Note that if you ve made a mistake in gate definitions you can use the gate delete gatename command to zero out the gate This command does not remove the gate from SpecTcl it just gets rid of all its arguments This is handy it allows you to change gates at the last minute without changing much else Now
159. n and plastic scintillator 12 and takes up a volume of 3 cubic meters The NEUT detector at RIKEN Japan 13 has only two layers of scintillating plastic limiting its total efficiency The total array has 30 bars 15 in each layer Each bar is 6 1 cm thick z axis and tall y axis and 214 cm wide z axis The Modular Neutron Array MoNA 14 15 assembled at NSCL at Michigan State University in 2003 was designed to detect neutrons at energies consistent with experiments utilizing rare isotope beams from in flight fragmentation as currently done at the NSCL about 30 100 MeV u It is also capable of running with pas sive iron converters similar to LAND in between the last six layers to increase the efficiency for higher energy neutrons gt 100 MeV It has 90 cm of active plastic scintillator when arranged in its current configuration of 9 layers z axis of 16 rows Table 1 1 Specifications of various neutron detectors including the original design goals for MoNA 18 Efficiencies are listed for a representative energy within the normal range of neutron energies for each detector Detector Lab Material Neutron energies Efficiency NEUT RIKEN Plastic 40 200 MeV 14 DeMoN GANIL NE213 5 50 MeV 10 Neutron Walls NSCL NE213 10 100 MeV 30 LAND GSI BC408 100 1000 MeV 90 MoNA NSCL BC408 30 200 MeV 70 Figure 1 4 Computer generated image of the original MoNA design including 144
160. n gate on muon tracks for time offsets Time difference At between two bars triggered by a muon track Drawing of Coupled Cyclotron Facility CCF MoNA Swe per setup 9 44 L 94 a epee ee Drawing of Sweeper detector box 0 0 0004 Target ladder diagram e ts gee Be Example of adjusted ToFyigjg isotope separation oo xl 3 6 Diagram of MoNA Sweeper coupling and timing 48 3 7 MONA Level 1 logic diagram 0 a la a 51 3 8 Diagnostic scaler display from Level 1 logic modules 52 3 9 MONA Level 2 logic diagram e 54 3 10 Signal times for typical coincident event 55 4 1 Drawing of GEANT 3 2 1MoNA setup with neutrons 64 4 2 Hydrogen and carbon neutron cross sections used in GEANT 65 4 3 Neutron reaction cross sections for MoNA plastic used in GEANT 65 4 4 Measured light response curve for 35 40 MeV neutrons 66 4 5 Neutron kinetic energy spectrum for 80 100 MeV neutrons 67 4 6 Measured light response curve for 80 100 MeV neutrons 68 4 7 Simulated total intrinsic efficiency for MONA 69 4 8 Incoming neutron count calculated by efficiency simulation 70 4 9 CFD hardware threshold analysis o 70 4 10 Resolution of x position in MoNA calculated by GEANT 73 4 11 Calibrated x position of muons gated above and below 75
161. ncreases resolution but reduces the total count Another problem that 124 involves using the Q parameter as calculated by Equation 7 1 to restrict the possible scattering angles off a proton is the path length an energetic proton has in MoNA Energy loss calculations yield a path length of about 3 cm for 90 MeV protons in BC408 plastic That means that nearly 30 of the highly scattered neutrons off a proton will not deposit all their energy in the first bar and punch through to deposit their remaining energy in the neighboring bar This will lead to a calculated scattering angle that is less than the actual one In an attempt to compensate for these punch through hits the Q parameters for the second hit if it is the neighboring bar is added to the first hit Q for a value that is much closer to the actual energy deposited The third hit is then analyzed as the second hit for the purpose of determining the scattering angle This analysis is complicated by the non zero probability that the neutron actually scatters three times twice in two neighboring bars and again in a third bar Since the first two proton collisions are independent of each other the twice scattered neutron could end up at zero degrees again with reference to the beam angle But by using the analysis procedure as described above the energy of the first two hits would be added and the result from Equation 7 1 will be a scattering angle too large to accept the event even t
162. nd or selecting the And type D 3 SpecTcl Code Procedures D 3 1 Raw Sweeper Parameters The Sweeper code does not calibrate any timing parameters but does indeed have many other parameters that are very useful The most important code for the Sweeper parameters deals with the four tracking detectors The two beam line trackers PPAC s or CRDC s and the focal plane CRDC s are read in through an XLM module and a large chunk of data is taken for each valid hit Gas tracking detectors have many par allel wires that collect the ionizing charge from the gas as a particle passes through There is also a time channel to determine the drift time usually the y direction of the ionized electrons Another gas detector the Sweeper code reads is the Ion Chamber This works in a similar fashion as the CRDC s but is not used to determine the position It has 192 16 charge collecting pads that are used to get a precise measurement of energy loss through the gas The thin and thick plastic scintillators at the end of the focal plane are used for timing and e loss measurements These two each have four PMT s and are recorded by eight QDC and TDC channels The cyclotron RF and the A1900 extended focal plane timing detector xfp along with the pot scintillator potscint finish off the sweeper timing channels Each time is common started by the Sweeper trigger which is a logic delayed signal from the upper left PMT on the thin scintillator S
163. nd adjustable range These signals give a standard by which to calibrate the TDC s to ensure proper timing for events that occur in MoNA Since the same TDC channels are used from one experiment to the next this calibration is not needed for every experiment C 4 1 Record Time Calibration Run Before any fitting code can find the right TDC slope a run must be recorded using the Ortec NIM Time Calibrator module connected through a NIM threshold discriminator and then to the test inputs of the MoNA CFD s This setup has been connected and only needs the time calibrator module installed to run again 1 In the directory mona config open the file MoNA_setup_run tcl and edit and 173 save the desired range for the width of the TDC window in nanoseconds under Global Settings where you find the command set range The range is the total time that spans all 4095 channels it can be set between 140 and 1200 ns Also make sure the TDCfitted flag is set to false Set both the range and the increment in the time calibration module model 462 in the NIM crate to the correct settings and turn it on The increment period or delta t is how often the TDC records a spike The range should be set equal to or close than the range set in step 1 Give a meaningful name to TDC calibration the run in the Readout window For example TDC cal Trange 350ns Tdelta 40ns Plug the start output of the time calibrator into the CFD test in
164. nd impinged onto a production target of Be with a thickness of 1222 mg cm The secondary beam of 99 pure Be with 0 5 97 momentum spread was separated from the resulting production target cocktail by the A1900 fragment separator utilizing a 750 mg cm acrylic wedge installed at the dispersive plane see Figure 3 1 The Be beam was directed into the N4 vault and onto a reaction target of IBe with a thickness of 102 mg cm at the target position in front of the Sweeper magnet The Sweeper Magnet focal plane detectors were used to identify and count the reaction products The basic setup is shown in Figure 3 2 with the only change being that the blocker was moved out of the active range of the CRDCs The focal plane acceptance was measured at nearly 18 momentum spread Since the inclusive cross section was being measured the electronics were run in Sweeper singles mode thereby recording all events that reach the Sweeper focal plane 5 3 Analysis 5 3 1 Cross Section Calculations The reaction cross section was calculated with oe Nbeam d m Na 5 1 where d m is the target thickness in mass per area divided by its molar mass With a 102 mg cm 9Be target and Na Avogadro s number the target nuclei per millibarn for this experiment was 6 8x10 The number of Be nuclei measured No in the focal plane was adjusted for the efficiency and the incoming beam count Npeam Was adjusted for live time Nbeam Was det
165. nd stopped with multiplicity set to cosmics 3 fold The first one can be used to double check the QDC and Xpos calibration 88 The second run is used to set the Tmean independent offsets for each bar 88 140 A 6 2 Archive Tapes When all the experiment runs and the additional calibration runs are completed the event files must be copied to tape and then read off the tape into the evtdata disk space The NSCL provides a nice manual for copying data onto tapes called Perparing to Close your Experimental Account I will not cover all the directions contained in that manual so it should be read as well I will go through the most common steps and address common problems that have arisen in the past 10 Acquire a DTL or similar digital tape from the Computer help room Double check that all run folders within the experiment directory contain proper links to actual evt files in the stagearea complete directory Login to the tapehost machine currently in the Data U 2 cubicle with the experimental account Change directories to the experiment directory gt cd experiment Identify the tape drive you are using Maybe dev st2 or dev st0 It is used as the third argument in steps 6 and 9 Record entire experiment directory onto tape gt tar cvhf dev st2 Wait for entire directory to be recorded onto the tape it may take a couple hours The terminal window should display all items writte
166. ndex of refraction equal to 1 58 and an atten uation length of about 2 3 meters for the scintillation light as determined by MoNA student experiments and Reference 34 with a maximum intensity at a wavelength of 425 nm This attenuation length becomes important for light response calibration see Section 2 2 4 It is important to note that charged particles within the scintillating plastic are necessary to produce any light and register an event Even y rays produced in these interactions are only indirectly detected through compton scattering with an electron The cross section for photo peak absorption is related to the proton number Z of the material to the fifth power and therefore carbon Z 6 has an extremely low probability to absorb the entire y ray energy compared with other elements Figure 2 1 is a diagram of a MoNA module illustrating how a neutron reacts within the scintillating plastic and releases light that travels to the ends of the bars where a light guide passes it into a photo multiplying tube PMT 14 2 2 Electronics Figure 2 2 shows the basic data acquisition DAQ configuration for MoNA The MONA setup utilizes a variety of digital electronic modules to process and record the light response from the plastic including photo multiplying tubes PMTs constant fraction discriminators CFDs and time and charge digital convertors TDCs and QDCs The digital electronic modules are all IEEE 1014 standard VME comp
167. ne data for experiment 07503 Data from CRDC2 is also shown to ensure the y angles and positions match the real distributions It was not used in the calculation of the efficiency or isotopic identification since fitting such a restrictive distribution leads to large uncertainties The large angular spread needed to match the focal plane detectors causes some of the acceptance to be cut by the limit of the thin focal plane scintillator which is 200 cm in both the x and y directions This acceptance cut is illustrated in Figure 4 26 with simulated data and the 200 cm cuts are shown This cut reduces the acceptance by 23 Including the geometric acceptance of CRDC1 and the blocker an additional 13 misses the focal plane detectors In addition to the acceptance cuts of the 9Be residue the neutrons are collimated by the edge of the 0 25 inch steel neutron window at the back wall of the Sweeper Magnet vacuum cavity This opening is 14 cm in the vertical y axis direction and 89 1600 1000 1400 e 07503 data J e 07503 data 7 800 1200 _ Simona 4 ST mona 9 2 gt 800 F q e v S 3 600 15 400 oO 400 nin 200 200 4 o 0 60 40 20 0 20 40 60 10 0 10 20 30 40 50 Focal plane x angle mradians Focal plane y angle mradians 4000 7 T J 600 T T T T x 3500 F e 07503 data 500 El e 07503 data 3000 E ST mona 4 Ceri isd ST mona 2 Lao
168. ne data 4 4 9 CDCC Cross Section Calculations An alternative to calculating the cross section with the virtual photon method is the continuum discretized coupled channels CDCC method 24 25 This method includes contributions and interferences between the many possible excitation levels and the small nuclear diffractive decay channel is accounted for The results of the calculation 61 are compared to the virtual photon decay curve and plotted in Figure 4 30 The total integrated cross section for the CDCC calculation is 1 26 barns a little higher than the 1 21 barns calculated using the virtual photon method This method also yields a three dimensional differential cross section that includes the angles and relative energies of the neutron and the 10Be residue in the lab frame Figure 4 29 plots the CDCC calculated differential cross section as a function of 10Be angle folded by the spread of the incoming beam used by ST mona to fit the target out focal plane data The angle used by ST mona to fit the 07503 data is also plotted When this CDCC cross section curve from Figure 4 30 is put into ST mona the lower geometric acceptance of the higher decay energy events above 2 0 MeV 94 E Virtual Photon S 1 2 S y CDCC lt 2 c 0 8 Q D 0 6 199 2 0 4 O O 0 2 0 05 1 15 2 25 3 35 4 Decay Energy MeV Figure 4 30 The calculated cross sections using the CDCC and virtual photon meth ods
169. nels Raw and Cal Parameters There are 576 raw and 576 calibrated parameters The names of the raw parameters are a little confusing but not needed that often The raw QDC parameters and spectra are named Portions of this guide where originally written by MoNA Collaboration undergraduate student A Ratkiewicz 145 A_QDC 00_L or A_QDC OO_R The raw TDC parameters and spectra are named differently TDC_OL 00_A or TDC_1R 00_A The calibrated parameters an spectra are named with _CAL appended to the raw name The raw and calibrated TDC parameters are backwards in time since the TDC s are stopped in common stop mode by the potscint signal that comes before the CFD fires at MoNA Bar parameters These are then used to calculate a few parameters for each of the 144 bars Xpos Tmean KE Qmean The Tmean bar parameters in ns are calculated by the average of the two calibrated TDC parameters A negative slope is used to put the time in the correct direction Tmean TDC_OL OO_A_CAL TDC_1R 00_A_CAL 0 5 The Qmean bar parameters in MeVee are calculated by the geometric average of the two calibrated QDC parameters Qmean sqrt A_QDC OO_L_CAL A_QDC OO_R_CAL The Xpos bar parameters in cm are calculated by the difference of the two calibrated TDC parameters And the KE bar parameters in MeV are calculated from the Tmean parameters the MoNA_Z_pos variable and the mass of a neutron These bar par
170. new configuration file that also sets a value for that 188 variable the value will be overwritten It is wise to have a standard configuration file that only has variables set so others can make their own spectra and then set the variables using that standard file with the Cumulate option The current settings for all spectra parameters variables and gates that can be edited using the directions in the next section can be saved by using the Save button These files should be stored in the settings directory This first page of the Tree Parameter GUI also is where the spectra can be created for sweeper and user tree parameters only D 2 Tree Structure The Sweeper and some MoNA variables and parameters are defined in a tree struc ture The two base tree labels are sweeper and user D 2 1 Sweeper Tree This tree contains all the sweeper parameters and variables written by D Bazin including fp CRDC s thin and thick scintillators IC im beam line tracking tof rf xfp potscint timing trigger tigger channels These branches hold parameters like CRDC beam line tracking positions and an gles Ion Chamber energies thin and thick scintillator energies and various timing channels 189 D 2 2 User Tree This tree contains calibrated parameters created by W A Peters Many of the Sweeper parameters cannot be calibrated without major changes to the code so this tree was made to input many raw Sweeper para
171. ng on the location of the original 28 1000000 100000 10000 1000 arbitrary units 100 10 5 80 96 112 128 144 160 176 Raw QDC B 02 L bins Figure 2 10 The raw QDC pedestal peak for PMT B 02 L is a few bins below a possible threshold value 128 The simple method for setting the threshold value places it at bin 144 for this QDC channel while the improved method sets it to 128 pedestal peak in the raw spectra The CFD adjustable threshold for the anode signal that triggers the QDC gate was set to 10 mV which was calibrated at 0 65 MeVee as shown in Figure 2 11 The CFD calibration was performed with a known y ray source by recording the value in a calibrated QDC spectrum that the intensity drops by half while adjusting the CFD threshold Having as low a threshold as reasonably possible is important for increased efficiency of detecting neutron scattering interactions because events that deposit less than 4 MeVee outnumber high energy events where the neutron transfers almost all of its kinetic energy to a recoil proton Using this simple QDC threshold procedure the QDC threshold may be above the CFD TDC threshold and many events may be recored with no associated QDC information Improved threshold cuts Following the commissioning experiments a new automated method was found for setting the QDC threshold that corresponds to a minimum energy cut of less than 0 5 MeVee for all channels By first adding three bins to the p
172. ng scripts 91 use 20 hit parameters as inputs into the pseudos MONA hardware run tcl This file sources the MoNA_setup_run tcl file and creates the scriptable data packets and commands to configure the VME modules TDC s QDC s and Scaler s Differ ent QDC threshold lists are sourced if the QDC_thre flag is set to true This file should not need adjusting unless the MoNA hardware changes like adding neutron cans MoNA_dynamic_var_run tcl This file sources all the default variable settings and then the calibrated or fitted ones if the appropriate flags are set in MoNA_setup_run tcl This file also creates all the non raw MoNA parameters from large lists that are defined in MoNA_Param_run tcl It does not need editing MONA_spectcl_run tcl This file is directly sourced by the scr script file that launches SpecTcl It s main function is to define the data packets to unpack in SpecTcl that are defined in the hardware file for example unpack add mona unpack add bitpattern It does this by first sourcing the MoNA_hardware_run tcl file and the MoNA_dynamic variables files It also sources the MoNA_Param_run tcl file to create all the raw parameters from it s lists This file is replaced by Tandem_spectcl tcl for the Tandem version of SpecTcl 89 149 MONA readout_run tcl This file is similar to MoNA_spectcl_run tcl but tells the Readout code which packets to fill for example readout add mona
173. nly by its angle through the focal plane de tectors but also its relative rate of coincident neutrons compared with other beryllium isotopes Reconstruction of the target angles and position for the charged particles in the focal plane is then completed using the process described in Section 3 6 2 without the use of the beam line tracking detectors due to their inefficiencies for low Z beams The reconstructed energy and angles of the residues at the target are combined with 112 12000 10000 8000 6000 Counts per MeV u N D gt Q Q Q Q o o 0 e 50 60 70 80 90 100 110 120 130 140 Fragment energy MeV u Figure 6 3 Reconstructed energy spread of the Be residue in coincidence with a neutron in MoNA the corresponding parameters for the neutrons in MoNA to determine the relative en ergy and opening angle between them Figures 6 3 and 6 4 plot the measured kinetic energies for the coincident Be residue and neutrons respectively Subtracting the neutron velocity from the reconstructed fragment velocity yields the relative velocity spectrum shown in Figure 6 5 The similarity in spectrum shapes for the neutron kinetic energy and the relative velocity illustrate that most of the kinematic re sponse of the reaction is carried by the neutron due to it being 1 10 the mass of the fragment Data shown in Figure 6 6 illustrates the relationship between relative velocity and opening angle for the Be n coincident data T
174. nt for the rectangular shape of the array The muons that reach the surface are traveling at 29 8 cm ns nearly the speed of light The muons will lose energy through a material based on its density and thickness For 10 cm BC408 this energy loss is an average of 20 5 MeV and they take 22 North 3000 2500 2000 1500 1000 500 1583 6 0 20 10 0 10 20 30 South Figure 2 5 Cosmic ray muon flux through MoNA in degrees from the zenith The plot was completed by MoNA undergraduate students at Westmont College 40 0 345 ns to traverse each detector bar Since the flux per volume is constant the full width of every bar will be illuminated Figure 2 6 illustrates a couple of possible muon paths through MoNA The beam axis is marked in front of bar A8 by a blue arrow This procedure has been used for other plastic neutron detectors 41 2 3 1 Gain Matching the PMTs Since the timing and rise time of the PMTs can change depending on the voltage applied to ensure comparable values for each detector bar the voltages must be adjusted to gain match the PMTs to a standard light response The voltages for the PMT channels are chosen to place the peak associated with cosmic ray muons at the same relative position for all the raw QDC spectra This technique will ensure consistent dynode signal intensity because the QDC integra tion gates and pedestal currents are the same for all QDC channels By recording a day long run of back
175. nverted to kinetic energy of the reaction residues Both the fragment and the neutron get equal momentum kicks and since the neutron is often 10 times lighter or more it gets a much larger velocity kick compared to the fragment By measuring the velocities and angles of both reaction residues in the center of mass reference frame the relative energy between the two can be calculated by determining the Lorentz four vector P with the unit less convention D pe E Px Py Pz E p 3 3 for both the fragment and the neutron E is the total energy of the particle equal to the mass if at rest The decay energy of the unbound system can be calculated by the invariant mass method independent of the reference frame 3 6 1 Invariant Mass Because the square of any Lorentz four vector is equal to the square of mass of the particle P P P m the kinematic equation of the unbound system before and after the decay reduces to quantities that can be measured in the lab frame PY PP Ph 3 4 where 7 denotes the pre fragment unbound system The subscripts f and n refer to the reaction residue fragment and the released neutron in the lab frame Since the left side of Equation 3 4 is just the total initial mass of the system including decay energy 59 Equation 3 4 expands to Edecay Mp mn y m j me 2 E En ppn cos 0 3 6 including the masses of the fragment mg the neutron my
176. o the thin_ul_time raw parameter has the same spectra as the raw sweeper trigger parameter Every timing channel immediately subtracts this sweeper trigger raw tdc value from itself in the code to get ride of the logic unit s time jitter when it delays the PMT signal The subtraction looks like this in the code thin tul thin time_ul sweeper trigger similar for all four PMT s pot pot sweeper trigger rf rf sweeper trigger xfp xfp sweeper trigger The actual raw tdc values for RF xfp and potscint times are lost while for those for the eight thin thick times are not because a new raw parameter is used for the subtracted values These raw parameters can not be adjusted by any slopes or offsets For this reason gates applied to these parameters are rather robust If you can separate the desired events from these spectra then using a gate with these will make sure you don t need to reset the gates once the all the calibrations are made within the user tree Subtracting un calibrated raw time parameters is not wise but these timing channels are all on the same TDC and have very nearly the same slope to nanoseconds 193 D 3 2 Tree Calibrations The Sweeper code does not calibrate the timing channels but is does have a calibrated energy loss parameter for the lon Chamber IC and calibrated position and tracking parameters The User code calibrates the timing channels and also the thin thick e loss done
177. of 100 V to attract the free electrons pushed by the negative drift voltage 42 3 3 4 Thin Thick Plastic Scintillators Both thin and thick BC404 organic plastic scintillators 11 have four PMTs mounted close to the corners that are connected to a TDC through a fast CFD with a delay time set to 3 ns The linear average of the four calibrated timing spectra from the thin scintillator is used for the ToF parameter for the fragments If less than four PMTs fire for one detector the correct time can be recovered by calculating the position of interaction from the CRDC data and then taking a weighted average of the remaining TDC parameters The 5 mm thin scintillator is used primarily as a timing detector and a second dE measurement The thick plastic scintillator is 15 cm thick which is enough to stop all the fragments and yield a total remaining kinetic energy TKE signal These parameters are determined by routing each PMT signal to a peak sensing ADC and taking a position corrected average of the four signals for the thin or thick scintillators for the dE and TKE measurements respectively To gain match the light response of the raw ADC channels the Sweeper magnet is tuned to direct a small spot of the secondary beam collimated by a thick steel collimator to the center of the focal plane The eight thin thick voltages are tuned to match their raw spectra Typical voltages are 1500 2100 V The beam is then swept across the active region
178. of the detectors to ensure the ADC spectra are not saturated when the fragment nears the corners and to position correct the average of the four raw signals An absolute energy calibration is often not necessary to separate or identify the reaction fragments 3 4 Reaction Residue Identification The detectors mounted in the Sweeper focal plane detector box are designed to aid in the identifying and analyzing the charged particle residue in coincident with a neutron in MoNA The residual fragment from the neutron unbound state must be positively 43 identified to reconstruct the corresponding decay energy The Sweeper magnet sepa rates these residues from beam contaminants and other reaction products not related to the nucleus of interest 3 4 1 Element Identification The element number of the charged fragments is identified from the dE signal recorded by the thin scintillator detector or the IC Energy loss is proportional to the Z of a charged particle and the dE parameter is calibrated by the known secondary beam often one or two elements higher than the nucleus of interest This process is de scribed in more detail in Reference 47 3 4 2 Isotope Identification Although the TKE signal in the thick focal plane scintillator is related to the mass of the charged particle residue sometimes the resolution is not sufficient to accurately separate the isotopes and a more powerful method must be utilized Given the design of the
179. of the Coulomb excitation of SLi at different energies The decay products were also measured as a function of the scattering angle related to the impact parameter Since the astrophysical inverse reaction n y has been measured and studied a detailed study of the Coulomb dissociation or y n reaction can serve as a check to the assumptions used to determine the astrophysical properties of a reaction that cannot be studied directly Preliminary analysis of this experiment were reported in Reference 85 7 3 3 Fragmentation to Multiple Unbound States By taking 48Ca directly to our reaction target this experiment populated neutron unbound states directly from the fragmentation of the primary beam Even though the cross section to produce nuclei near the drip line is much smaller than from single or double nucleon knockout reactions the beam flux increase of many orders of 126 diamond timing detector reaction target quadrupole triplet sweeper magnet t dE neutron detector charged particle NOE array W detectors vault shielding Figure 7 2 Alternate configuration of the reaction target placed in front of the fo cusing quadrupole triplet magnet to increase isotope separation by ToF A high rate diamond detector was used for the target timing signal The total distance to MoNA is extended to 16 5 meters because the neutron acceptance is so small after passing through the bore of the triplet that they do not fi
180. on and use the Apply command in the pop up window to add desired spectra to the Xamine cells Using the Okay command will close the pop up window after inserting the selected spectra You can save any Xamine configurations by selecting Write Configuration from the Window menu on top be sure to save it as a win file in the win directory You may also read in previously saved configurations but you must be sure the included spectra have been bound to SpecTcl first For this example select the configuration file pseudo _win Xpos A win to display all the Xpos spectra for layer A B 3 4 Attaching Data In the SpecTcl Control window click on Attach to File and select a run to read in Once this is done SpecTcl will begin analyzing the data Let it run for a short while so that you have an idea where the peaks and valleys in your data will be For the example procedures that follow you need to source a cosmic background run preferably one with the MoNA trigger set for 3 fold cosmic coincidence If you do not need to read in the whole event file and when you ve got an idea where the peaks and valleys in your data are click on the Stop Analysis button B 3 5 Setting up Gates Back in Xamine double click on first cell the cell in the upper left hand corner of the window to zoom in on it This should be Xpos_A0 Now click the Cut button in the lower right hand corner Here we are going to tell SpecTcl that we want gate on events that hit i
181. on velocity calculated from hit 1 and the fragment velocity it s slope and offset should be 1 and zero respectively D 3 4 MONA Hits The code to fill the hit parameters is processed as each bar is calibrated and so hit_1 is the first valid one the code calibrates as it parses through all 144 bars making the Bar parameters 92 starting at AO and ending at 115 These hit parameters are not ordered by time and should only be used as approximate checks during run time See Ref 91 for ways to time order all the hits The Multi_hit parameter is the number of valid hits for that MoNA event defined as two valid raw TDC channels for one bar The hit parameters include X_hit Y_hit Z_hit TOF_hit KE_hit Q_hit Theta_hit Phi_hit Multi_hit D 3 5 Valid Tandem Hit In the CHitParam cpp code I have written a process to find the first MoNA hit based on time of flight I first exclude events that are too fast to be neutrons by taking asking if the time is greater than 50 ns for all hits This is required to avoid calculations using hits from a gamma ray created at the target 50 nanoseconds is 2You should follow the directions form section 2 3 and change the units for vfrag offset to cm and the units for the vfrag cal and vdiff cal to cm ns 197 the time a gamma ray takes to travel 15 meters If MoNA is placed further than 14 5 meters away from the target CHitParam cpp should be edited and this value should be increased accord
182. on walls They comprise two walls of liquid NE213 filled glass bars The coverage area is 2 by 2 meters and it is primarily used for neutron energies less then 40 MeV 10 The Large Area Neutron Detector LAND at GSI Germany is a large array of 0 5 cm thin BC408 11 plastic scintillator plates sandwiched between 0 5 cm thin passive iron plates The sandwich is repeated 10 times for a 10 cm thick A 50 A 40 20 Ca n K S PEET Ar 2 Drip line A 30 UI Cl z s A P Si A 20 Al x Mg xO Na 10 Og Ne Bl nls N F A oonkin NM o wN Y gt AS C E Stable ws Sw B Bound Me h da e p Be s Not populated O First excited x He 2 by beta decay state unbound 0 H 0 10 20 30 40 Neutrons Figure 1 3 Many nuclei near the neutron drip line can not be adequately studied by methods other than neutron spectroscopy Populating unbound resonances by 8 decay cannot be done for nuclei without a feeder nucleus marked be arrows Also nuclei with no bound excited states swirls cannot be studied by y ray spectroscopy Measuring the resonant energy of the ground state for any unbound nucleus beyond the drip line also can only be done with neutron spectroscopy 200 cm long bar and then all ten plastic scintillators are coupled to one PMT at each end The full array has ten layers of criss crossed bars with a total of 50 cm of both iro
183. ona 2 1200 2 5 S 600 3 J gt 1000 gt 800 400 x 2 600 o oO Oo J 400 200 L 4 200 z 0 a f f fi f f 0 fi fi fi Va 70 60 50 40 30 20 10 0 10 20 80 60 40 20 0 20 40 60 80 100 120 Focal plane x position mm Focal plane y position mm 4000 r 1200 E 4 J 3500 j 03048 data 1000 L 03048 data A 3000 ST mona 7 N p E 800 ST mona z 2500 Ai E 5 5 gt D 4 S 2000 18 600 E E J 0 5 1500 is 400 1000 4 z t 200 500 F 2 J A 0 ds tenses 0 A 40 30 20 10 0 10 20 100 80 60 40 20 0 20 40 60 Focal plane x angle mradians Focal plane y angle mradians Figure 4 20 The relevant focal plane parameters for the Be Coulomb experiment 03048 are fit by the ST mona simulation code not large enough to collect all the electrons and this caused it to miss more than 50 of the events and seriously cut into the distribution Thus the analysis of the data was performed without CRDC2 To identify the isotopes in this experiment the ratio of light deposited into the four PMTs on the focal plane thin scintillator substituted for a second dispersive position measurement along with CRDC1 The identification plot is shown in Figure 4 22 The horizontal axis is the log of the ratio of light deposited in the two left PMTs to the two right PMTs Here also some of the unreacted Be reaches the focal plane and tracks a large positive angle through the detectors
184. ons and a Texas Instruments digital signal processor TMS320C6711 running up to 900 Mflops for the numerical operations The external interface has 72 ECL ports that are hardware configured as either inputs or outputs The interface with the VME bus is made through 32 bit and 16 bit data transfer rates up to 40 Mbytes per second The XLM72 20 also features two banks of asynchronous static random access memory ASRAM of 2 Mbytes each and enough flash memory to store up to four FPGA configuration files Each XLM72 is programmed to serve as a Level 1 logic unit for each of the nine layers of MONA bars Here each CFD outputs for all the PMT signals in that layer are cabled to the ECL input ports in the front of the XLM72 The Level 1 logic counts the number of coincident left right signals accumulated and forwards it to the next level in the trigger logic These processes are described in more detail in Sections 3 5 3 and 3 5 4 The raw CFD signal count is also read by the VME bus by a tcl tk program to display the live rate of all the input channels from 288 CFD channels for diagnostic purposes 2 2 6 Level 2 Logic Module The Level 2 logic is contained in one JTEC model Virtex XLM module The exterior design and ECL ports are the same as the XLM72 model The Virtex XLM has increased memory and FPGA logic capabilities by using the high performance high capacity Xilinx Virtex model FPGA chips All trigger discrimination and Level 2 logic proce
185. or and the output logic pulse timing is dependent on the signal amplitude This effect is mostly canceled for the time difference parameter used for the x position calibration but is magnified by two for the ToF parameter and is in addition to the intrinsic CFD resolution The CFD walk was measured to be less than 0 1 ns for signals less than 2 MeVee and is nearly non existent above 4 2 2 MONA X Resolution For the x axis the position is determined by the difference between the two timing parameters from each end of the module As mentioned before 2 3 5 the conversion from the time difference parameter to centimeters along the bar is nearly 8 cm ns 73 Using this slope and the intrinsic time resolution detailed in the previous section the intrinsic z axis resolution becomes 1 5 cm This does not account for effects from neutrons interacting in the plastic The GEANT simulation code calculates that the point of interaction of a neutron within the plastic is not always equal to the position of the deposited energy This is true for reactions that release y rays since they can scatter significantly while exciting electrons that then create the scintillation light For carbon scattering interactions the neutron s path can change dramatically before depositing energy by a second interaction Figure 4 10 shows the intrinsic resolution from the GEANT simulation dashed line The wider component of the dashed line that dominates the
186. or bars from run 2114 are scaled to match run 2121 The s p and d wave knockout fits are individually scaled curve must be folded by with the parallel momentum of the incoming beam and boosted to the lab frame by multiplying the center of mass theoretical distribution by the Lorentz scaling factor 1 08 of the beam The resulting distribution is then offset to match the centroid of the data The unreacted beam s momentum distribution is plotted in Figure 5 8 and the Gaussian fit to this data has a standard deviation of 13 1 0 8 MeV c Figure 5 9 shows the overlay with three parallel momentum calculations corre sponding to the knockout from three different spin states used for the ground state of Be 1 0 1 and 2 calculated by the eikonal approach 74 The calculations for the 0 and 2 curves were calculated as if the ground state of Be was from a 51 2 and ds 2 shell level respectively even though the Be ground state is known to be P3 2 The parallel momentum of the 9Be residue is calculated from the reconstructed energy using the inverse transformation matrix described in Section 3 6 2 Since the magnitude is also a free parameter the three curves were then each scaled indepen dently to illustrate that the P3 2 curve is indeed the best match to the data The 106 discrepancies at low momenta is common for these types of fits and reported to be caused mostly be diffractive breakup 24 5 4 Conclusions The parallel momentu
187. or the current study confirms the reported results of the previous measurements Differences in the decay energy spectrum with previous measurements concerning the cross section to populate the 9Be 2 state are noted and likely due to limited efficiencies at forward angels for the previous work Finally a discussion of MoNA s capabilities is presented and experiments com pleted to date are summarized Plans for the future of MoNA are also introduced MONA analysis and calibration guides are included in the appendices My efforts are inspired by my friends family and my dear wife Nicole ACKNOWLEDGMENTS I would like to specifically thanks members of my advising committee Michael Thoennessen B Alex Brown Carl Schmidt Wayne Repko Thomas Glasmacher and Filomena Nunes Their guidance and has been a source of focus and very much appreciated I only hope to do as well as job as they did for me to others someday Their knowledge was ever present and ever giving Michael Thoennessen in particu lar was nurturing and strict with wonderful equanimity I would also like to thank God for making the universe so complex and exponen tially incomprehensible that after thousands of years of trying there is still a lot a physics left to discover The environment at MSU has been wonderful especially Debbie and Laura with out whom I would have paid more money to MSU in fees They have been guides in some ways on life and academics many times
188. osition of the reaction in 19 o T Right QDC response MeVee Eh o 98aA9 N suods DUO 427 ol 80 X position along MoNA bar cm 80 Figure 2 3 The center frame shows the geometric mean of the left and right QDC responses in the neighboring frames by Equation 2 3 The background due to low energy y rays dominate the lower bins of the spectra while the cosmic ray muons are calibrated to 20 5 MeVee the bar The center frame shows that the Q parameter is flat for the whole length of the bar There is a second order effect to the attenuated light not recovered through this treatment from the reflected light that travels a full bar length extra Due to the geometric shape of the MoNA bars and the large attenuation length A the effects from the reflected light for MoNA are not more than 1 as seen by the position in dependence of the Q parameter in Figure 2 3 Furthermore effects from the reflected light for less elongated scintillation volumes are generally less than 5 and mostly effect interactions at the ends of the bars for energies just above threshold 38 2 2 5 Level 1 Logic Modules The basic logic processes for each layer of 16 modules utilize JTEC model XLM72 universal logic modules 39 These are versatile and programmable modules that interface with VME systems and use Xilinx XCS40XL Field Programmable Gate Arrays FPGA that run on a 80 MHz clock cycle for logic operati
189. ot been transformed from the focal plane 4The new inv maps use as an input the x position at the target sweeper im track xta calculated from the forward mapping 206 coordinate system They are just tracked to a z position in front negative or behind positive CRDC1 using the sweeper fp track zfp variable It is also good practice to display the tracked sweeper fp track afp or sweeper fp track xfp parameters versus the adjustable time to help you choose the best values With some luck you ll find some settings for the three variables that really separate the isotopes For detailed directions on this subject see Ref 96 D 4 6 Decay Energy The Tandem_E_decay parameter incorporates the angle between the neutron and the fragment and when the all the tracking and calibrations are completed it is the best calculation we have to get the decay energy of neutron unbound states D 4 7 Multiple Neutrons Since MoNA is so large and it s depth is considerable 90 cm often a single neutron will react more than once inside it s volume and be recorded as more than one hit in the hit parameters The most likely case is where the neutron strikes a proton in one bar the proton travels out the side of the bar into a neighboring bar thereby causing two hits from one neutron The most interesting case is where there are indeed two neutrons entering MoNA and each reacts with a different bar to cause two hits These different scenarios a
190. oupling spin orbit interactions leads to groupings and gaps corresponding to the experimentally known magic numbers from Reference 3 The numbers in brackets on the right side refer to the number to fill each shell level and the total number to that point The notation for shell levels in this figure starts at 1s 2 while the prevailing current notation and used within this thesis starts at 051 9 120 Proton number Z Qo pu oO de ta 0 20 40 60 80 100 120 140 160 180 Neutron number N Figure 1 2 Chart of the nuclides the full nuclear landscape as proton number Z versus neutron number N Regions that are yet undiscovered but predicted to exist are shown in green The magic numbers are marked by dashed red lines more photo multiplying tubes PMT to convert the light response from an interacted neutron to time and amplitude signals The time of flight ToF of the reactions relative to a target timing detector are used to determine the neutron s velocity Table 1 1 lists neutron detectors at major fragmentation facilities The DeMoN array in GANIL France 8 is an array of liquid NE213 9 detectors mounted on stands that can be easily rearranged and placed at large angles relative to the beam axis The efficiency of this detector is only about 10 The first large neutron detector at the National Superconducting Cyclotron Laboratory NSCL Michigan State University USA consists of the neutr
191. pared to raw rate of the beam line scintillator The raw scaler rates between the focal plane thin scintillator and the beam line scintillator indicate they are over 99 coincident 87 80 UN g any ay E ron Ay eet e DN ho TORE 5 ae E j ir HN ie INE A Ma Hal Pal AN d i yo ob Mt fA fi I o 0 N iti H i Y id W Hh iy i I x i y al i 4 Y 1 oa i py EA in y we Al W ty y 1 Q 1 i ll 4 I Q ri A y e i x O 40 thin log lieft lrigm A U Figure 4 22 The ratio of light between the left and right sides of the thin scintillator is plotted against the dispersive position in CRDC1 to gate 9Be residues for the Coulomb breakup experiment 07503 0 75 0 75 thin 10g left lrigrt a u 1 5 46 48 50 52 54 56 58 60 62 ToF ns Figure 4 23 A second gate on ToF versus light ratio is used to reject a small contam ination of unreacted Be that passes the first gate 88 Ungated Gated x2 Counts 50 0 50 100 150 200 250 300 Neutron ToF ns Figure 4 24 The background seen in the ungated ToFy parameters nearly completely disappears when gated on a coincident 9Be residue A smaller peak near 30 ns in the ungated spectrum is due to prompt y rays induced by the beam on the reaction target 4 4 6 Detector Acceptances Again ST mona is used to simulate the focal plane acceptances and match to the focal plane parameters Figure 4 25 shows the simulated curve with the focal pla
192. ppropriate square well potential ro 58 is set according to Reference 59 to 4 0 fm S is the spectroscopic factor 83 1 2 El barns g i dB E1 dE e fm MeV Cc 5 0 8 pra gt n E1 keV Sos 5 0 4 0 1 2 3 4 5 Excitation energy Mev Figure 4 18 The calculated cross section for El excitation of Be from 1 Au at 90 MeV u calculated from Equation 4 6 is shown by the solid curve The dashed line is the number of virtual photons per keV as calculated by Equation 4 7 The dotted curve is the El transition probability as calculated from Equation 4 10 Figure 4 18 shows the energy spectrum for the number ng w of virtual photons dashed line from 90 MeV u Be passing Au along with the transition probability dotted and the total cross section solid This calculation is nearly identical to Reference 60 for Be on a lead target at 40 MeV u instead of a gold target at 90 MeV u 4 4 3 Experimental Comparison The energy dependent El cross section solid line of Figure 4 18 can be included in ST mona and the simulation and then compared to the data from experiment 03048 The isotopic identification of the 9Be residue is shown in Figure 4 19 The tail of the unreacted Be distribution tracks a large positive angle through the focal plane due to its high magnetic rigidity compared to the Be residues Figure 4 20 shows various focal plane parameters used to restrict the input of the simulation and to ensure
193. put discrimi nator channel on the left of the NIM crate and double check that this signal is routed to all CFD test inputs Plug the stop output of the time calibrator into the TDC test input discrimi nator channel on the left of the NIM crate and double check that this signal is routed to all TDC common inputs Make sure all the CFD s are running by checking their output OR lights to see them blinking fast Record a short 10 minute run with all detector bars Use MoNA multiplicity set to 1 fold and select self trigger on the XLM control Do not select self stop the time calibrator must send the both the start and the stop signals Open MoNA SpecTcl 92 in the spice terminal window or from a Data U machine 3Traditionally we have used 350 ns for the TDC full scale 174 10 11 12 13 14 15 16 17 In the SpecTcl Control window click Create Raw Spectra Then choose Attach to File and select the run file recorded in step 1 In Xamine go select Window gt Read Configuration and pick one of the win TDC win window settings Allow SpecTcl to analyze all the buffers to ensure sufficient statistics for the TDC fitting program When the data is read in click Update All in Xamine Look through the spectra in Xamine to make sure the data is usable i e that there are evenly spaced spikes in each of the spectra Each spike must have more than 300 counts to get recognize
194. r a couple decades less intense right next to it The cosmic ray muon peak is set 800 bins above the pedestal peak to gain match the PMT voltages spectra with a Gaussian and an exponential Figure 2 8 is a close up view of the spectrum in Figure 2 7 for PMT C 03 R right PMT of the fourth bar in the third layer fitted by the exponential Gaussian combination on a linear scale The difference between the pedestal and the muon peak is calculated and compared to 800 The voltage is adjusted accordingly using an algorithm that takes into account the 12 multiplicative steps of the MoNA PMTs Another day long MoNA run is recorded and another iteration is performed and so on until a the pedestal muon differences are consistent with 800 bins such that another iteration would not improve the result This usually occurs after two or three iterations Pedestal peak Since all 32 channels of each QDC share a common integration gate all events with less than 16 coincident left right PMT hits will have some QDC channels with no signal Most events in MoNA are 1 fold events or a single left right coincidence for 25 100 y ata my a PAB arbitrary units 300 500 700 900 1100 1300 1500 Raw QDC cosmic spectrum bins Figure 2 8 The region near the muon peak is fitted by the sum of an exponential decay and a Gaussian solid line The center or the Gaussian fit is used for both gain matching the PMTs and latter to calibrate the QDCs on
195. r distribution given by r do dE 4 2 ES Ea a or a thermal Maxwell distribution do dE x E al 4 3 where Eg and T are the resonant energy and width of the unbound state respectively 71 and T is the temperature of the Maxwell distribution all units MeV A custom distribution for the decay can also be implemented The acceptances and detector resolutions of a particular experimental setup are determined either by the information from the beam line tracking detectors or by matching the focal plane detector distributions After configuring the input parame ters for ST mona the positions and angles of the fragments at the point of the reaction are reconstructed through the inverse matrix This information is then combined with the neutron parameters as per Equation 3 7 to yield a simulated decay energy curve to compare directly with experimental data 4 2 Resolution Measurements 4 2 1 MoNA Time Resolution The intrinsic resolution of each TDC channel corresponds to the TDC range divided by the number digitization bins 4096 for a 12 bit TDC For a TDC range of 350 ns this is 0 085 ns per bin The resolution of the CFD logic output from the raw anode signal of the PMTs is estimated to be about 0 1 ns 35 The neutron time of flight parameter ToF is calculated by the average of the left and right TDC channels for a given MoNA module Equation 2 4 The resolution for this parameter is about 0 18 ns Evidence of the
196. ram One column fills with the calibrated values and then the following ones are the same data re histogramed with x2 and higher compression factors B 5 Simplifying B 5 1 Settings Files Now you can repeat the same gates and commands you just did for layer B However you re not going to do all that tedious typing again Instead you re going to put the bulk of your commands in a text file and source the file from the TkCon shell This will save you time if we ever want to revisit the analysis Open a text editor use Kwrite or emacs Emacs is prefered by people with a strong Unix background If you are not entirely comfortable with it use Kwrite Kwrite s a lot like notepad so you shouldn t have any problems When your text editor opens go to the TkCon window type h and then highlight the commands you used to create and apply the gates for layer A Now select Copy from the TkCon Edit menu In the editor select Paste then edit the commands for layer B instead of layer A You must delete the line numbers that the h command 159 inserts in front of the lines Don t forget to type sbind all at the end of the file if you create any spectra within This is also a good place to save the in line commands to create the gates you use they must be created before they can be applied Save the file in the settings directory as a tcl file To source the file and run the commands go back in the TkCon window type source settings
197. rants Institution Principle Investigator NSF grant Ball State University Indiana R Howes PHY 0132367 Central Michigan University Michigan J Finck PHY 0132532 Concordia College Minnesota B Luther PHY 0132725 Florida State University Florida K Kemper amp S Tabor PHY 0132434 Hope College Michigan P DeYoung amp G Peaslee PHY 0132405 Indiana University South Bend Indiana J Hinnefeld PHY 0132567 Michigan State University Michigan M Thoennessen PHY 0132434 Millikin University Illinois J Brown PHY 0132507 Western Michigan University Michigan P Pancella PHY 0132438 Westmont College California W Rogers PHY 0132641 Now with Marquette University Wisconsin Now with Wabash College Indiana can be determined by the individual detector hit within a larger array With these considerations in mind MoNA was designed with 144 detector modules and assembled in an array Because each MoNA bar measures 10 cm by 10 cm by 200 cm the full array takes up a volume of 2 88 cubic meters The array can be moved by an overhead crane to center it 8 to 14 meters downstream of the reaction target leading to solid angles covering 0 574 to 0 205 steradian respectively By assembling MoNA nine layers in depth the estimated efficiency of about 20 for one bar is compounded 9 times Each layer has 16 modules labeled 0 through 15 the nine layers are labeled by letters A through I For example the tenth module of the sixth layer from th
198. ratio between the corresponding spectroscopic factors C2S is known as the reduction factor Rs The reduction factor represents a physically meaningful property when the shell model calculations remain a consistent reference for comparing a variety of 96 se de p d and d p O e e p O n knockout E p knockout 20 10 0 10 20 AS MeV C Sexp C Schell model Figure 5 1 The reduction factor for a variety of different reactions is plotted versus the difference of nucleon separation energies AS equals Sy Sp for neutron spectroscopic factors and Sp Sy for protons Figure reprinted from Reference 72 data originally compiled by Lee et al 71 see text for list of References different systems Rs has been shown to follow a trend as a function of the differ ence between the neutron and proton separation energies AS for proton and neutron knockout 64 68 e e p 69 and calcium transfer reactions 70 for energies ranging from 50 2000 MeV u 71 see Figure 5 1 This is the first measurement of the 0pzy2 neutron knockout Be 1 Be 9Be X in a neutron rich nucleus and is the mirror process to the 0p3 2 proton knockout in neutron deficient C 68 This measurement will allow a comparison of single particle abundances for the same Ops 2 shell at two extremes of bound nuclei 5 2 Experimental Details A primary beam of 180 was accelerated through the Coupled Cyclotron Facility at the NSCL 31 to 120 MeV u a
199. ray 87 using smaller versions of MoNA detector modules They record muon flux per solid angle of the sky over long periods of time Recently in an effort to utilize MoNA in between experiments the FPGA logic modules were modified to record high multiplicity self triggered events in MoNA to compare the cosmic ray muon flux from two opposite sides of the continent Both detectors are synchronized to sidereal time time relative to the stars in the cosmos not the sun A unique analysis code is used to account for MoNA s rectangular shape to get the angular flux 7 4 Scheduled Future Experiments Scheduled to run in the fall of 2007 is the di neutron decay of Be Unlike the two neutron decay of 1Li the ground state resonance of Be is predicted to have a two neutron separation energy of about 1 5 MeV compared to about 1 8 MeV for the one neutron separation energy for 15Be This experiment will be the first to run in the new vault configuration and MoNA will also be separated into four walls two layers in each of the first three walls and layers G I in the last wall Each wall will be separated by 0 5 m This setup should increase the resolution for identifying two neutron events A study of the unbound ground state of 2 C has also been approved This exper iment will utilize y ray detectors near the target chamber as an auxiliary trigger to distinguish the ground state from excited states of the 2 C residue 128 Chapter 8 Con
200. re difficult to distinguish Using the time ordered pseudo parameters 91 we can make a good attempt to separate these events When the hits are sorted by time of flight we can look at the distance between two hits to see if they are neighboring bars The velocity of the second hit should be less than the first if the same neutron reacts twice There are also other more advanced calculations and parameters that can be made to determine the number of incoming neutrons including the energy deposited by the first hit versus the scattered angle between two hits 207 D 4 8 Limitations The Tandem_E_decay code does not require any signal in the respective QDC param eters so a careful simulation code must accompany any final analysis to account for some soft neutron events near the edges of MoNA that don t deposit enough light to be seen by both CFD s at each end of the bar This will induce a slight under counting of events at ends of the MoNA bars and should be mimicked in a simulation like GEANT The threshold for the QDC s are set about 10 channels above the pedestal by the QDC fitting program to ensure the pedestals are not read out for all MoNA events and thereby swamping the data acquisition with 288 meaningless values In practice this corresponds to an energy of about 0 5 MeVee and is a bit higher than the 10 mV setting for each CFD that triggers the TDC channels Therefore we get plenty of MoNA events with a valid pair of
201. readout add bitpattern B 3 Running SpecTcl There must be a SpecTcl executable created that can be run from your user account or an experimental account These executables have been traditionally housed in the user mona spectcl_ shared directory and accessed through the local mona daq spectcl script files that source the local mona config directory filled with relevant settings and calibration factors B 3 1 Open SpecTcl Open SpecTcl by either clicking the button on a DAQ machine display of a current experimental account or executing the script by typing gt run_spectcl scr or the equivalent script file in the mona dagq spectcl directory You will see four windows pop up B 1 B 2 B 3 and B 4 The TkCon window should have listed many configuration settings including which fittings flags are set and whether or not you are using calibrated slope offset values for QDC TDC Tmean and Xpos parameters This listing of settings finishes with Done Done The code also lists the data packets it recognizes like maybe Level2 when the bitpattern data packet is used 150 E Create Raw Spectra Create Cal Spectra Create Pseudo Spec Create Hit Spec 2d Cal Spectra 2d Pseudo Spectra lol x Ezy WorkDir projects proj6 05033 monafdag specte EvtDir fevtdata 05033 complete Source Run Number 0 Analy Figure B 1 The MoNA SpecTcl Control window JH Xamine Unname
202. rence of nucleon separation energies AS The green point is added for the current measurement of the 1n knockout of Be at AS 12 8 MeV between the two systems include the magnitude of the WBP shell model spectroscopic factors 0 94 protons for 9C compared to 2 45 neutrons for Be where the extreme single particle shell model would place 1 proton and 3 neutrons in the Ops 2 shell respectively Another difference is that Be is one neutron from removed a neutron halo state while the 8B residue is considered a proton halo 68 The large effective radius of a halo nucleus could lead to less short range correlations expressed by the reduction factor Table 5 1 Theoretical calculations for the 1n knockout and diffraction nuclear breakup channels of Be to the ground state of Be The total theoretical cross section calculated per Equation 5 2 is compared to the current measurement to de termine the reduction factor Rs Ostr Odi f cs Oth Cexp Rs 30 3 mb 8 0 mb 2 45 104 mb 68 7 mb 0 66 0 07 103 3 st ye Ye MO i E i n ni i l l hen om 40 Te ot 3 i i i nm y 0 Z ad i S 40 fa ih eD kahi 2 t 7 Hi l 2 O 80 3000 3250 3500 3750 4000 4250 4500 Parallel momentum MeV c Figure 5 7 The reconstructed dispersive xz angle of the IBe residue plotted ver sus the parallel momentum The distribution is cut by the geometric acceptance o
203. rs a large number of nuclear states near the drip line that require neutron spectroscopy to study 7 In addition nuclei that are at the drip line cannot be populated by S decay experiments that require a N 1 Z 1 feeder nucleus Neutron spectroscopy involves detecting neutrons from an unbound resonance that are forward focused from fast beams greater than 10 MeV per nucleon MeV u about zero degrees in coincidence with the residual nucleus 13 Neutron Detection Tools Neutron detectors for energies between 10 and 100 MeV are generally made of an organic scintillating material A volume of scintillating material is coupled to one or w ai 115 2 16 184 184 SM real neem 3d a7 8 Sho A le i M 2 12 even 9 A 3d45 2 6 pl 11 13 2 19 126 126 39 2 I a _ _ _ _ _ _ _ _ _ 2 A Shw E 21 Tje 8 0000 j P in9 2 10 sl Las Ml ma 12 82 82 e a e 4 hw A ee 8 64 sis A 2452 68 19 19 9 2 10 50 50 2018 14 3hw p pa it 5 2 16 38 odd Gy ee esl 72 8 28 28 2hw 28 id 3 2 4 20 20 id lt 2 2s 2 6 hs a e fl y 0 2 8 8 Ary Ip ip 3 2 4 6 re 5 ee 15 2 2 2 Figure 1 1 Level diagram using a Woods Saxon potential for nuclei and c
204. rt the readout of all the modules connected to the VME bus It is also used by the Sweeper electronics as a common start for the TDCs since it is precisely timed from the incoming Cable A signal thin scintillator upper left The Level 2 logic takes 337 4 ns to process the event and issue this master trigger The total transit time for the thin scintillator s signal is illustrated in Figure 3 6 and all Sweeper timing signals into the Sweeper TDC are delayed to wait for it Cable E carries the CFD output of the target timing scintillator The thin target scintillator is positioned just in front of the reaction target and is used as the common stop for all MoNA TDCs after appropriate delay is manually added This time along with the measured distance to each bar in MoNA is used to calculate the velocity and thus the energy of each neutron detected in MoNA While these five signals are shared by the MoNA and Sweeper systems those internal to the Sweeper s digital logic are described in more detail in Reference 47 QDC gating The positive dynode signal from each MoNA PMT is delayed by a 95 ns 60 ft cable and then inverted by a passive inverter chip before going into the QDC modules Each CAEN V792 QDC processes all 32 channels form one layer in MoNA The delay is chosen such that by the time the raw dynode signal arrives at the QDC an integration gate has already been opened by the Level 1 logic for every layer with a valid anode sign
205. ry at the end of this file The SpecTcl_Driver tcl file is sourced 147 from this file The Driver runs the Tk graphical user interface that displays the buttons and such we call the SpecTcl Control Window B 2 1 MONA Config Directory The mona config directory contains many of the files that control the configuration settings for SpecTcl The most import ones are MoNA setup_run tcl This file contains many permanent lists and a few fitting flags and variables The most important parts are the TDC and QDC setup lists that get read into the scriptable SpecT cl code to configure the Readout and SpecTcl codes It also has the CFD lists of addresses and configuration file names for all 18 CFD s The top of the file has variables that can be edited for each experiment Here we have a series of fitting flags QDC_thres_flag QDCfitted TDCfitted Xposfitted Tmean_indie_offset These are set to true after the appropriate calibration or fitting code is com pleted 88 The tmean_offset variable is a global time offset for all Tmean parameters of all bars and should be set from a MoNA gamma timing run or to some reasonable value to start like 333 0 ns The MoNA_Z pos variable should be set to the distance from the center of the reaction target position to the center of MoNA bar A8 in centimeters 148 The MoNA_hits variable is read in to create that many hit parametes and spectra The default is 20 because the time sorti
206. s the final decay energy simulation is calculated and plotted on top of the data in Figure 6 7 6 3 1 Comparisons to Previous Results Due to the high energy of the 2Be beam 91 MeV u and the position of the steel blocker in front of the Sweeper focal plane the unreacted beam could not be deflected into the focal plane detectors for a beam rate calibration as was done for the one 114 5000 W 4000 3000 2000 s per 2 cm ns 1000 Count 5 4 3 2 14 0 1 2 3 4 5 Relative velocity cm ns Figure 6 5 The relative velocity neutron minus fragment looks very similar in shape to Figure 6 4 and is slightly asymmetric due to the greater acceptance of forward emitted neutrons neutron knockout of Be in Chapter 5 By simulating the reaction through the ST mona code a relative comparison of the intensities and by extension the cross sections of the four curves can be made and compared to previous work Using the relative cross sections of the four decay channels in Table 6 2 reported by Reference 81 a fit to the current data taken is shown in Figure 6 7 The individual resonances are drawn and listed with their corresponding relative intensity i e 0 069 is 6 9 of the integrated cross section less than 3 5 MeV is accounted for by the 1 274 MeV 5 27 state The fit is a least x fit between energies 0 2 and 3 5 MeV for the scaling factor The data from the current experiment are shown with statistical error bars and
207. s and the folder that contains all the cfd settings that might change during the experiment gt cd mona_settings gt ln s user mona config MoNA_scaler_setup tcl gt ln s user mona config MoNA_setup_run tcl gt ln s user mona config MoNA_dynamic_var_run tcl gt ln s user mona config MoNA_readout_run tcl gt ln s user mona config MoNA_spectcl_run tcl gt ln s user mona config MoNA_hardware_run tcl gt In s user mona config QDCfittedTHRE tcl gt ln s user mona config QDCfittedSLOOFF tcl gt ln s user mona config MoNA_Param_run tcl gt ln s user mona config Xpos_cal tcl gt ln s user mona fpga xlm_values dat gt ln s user mona hv_control hv_files Vout_current tcl gt ln s user mona cfd 136 Daniel Bazin should fill the current sweeper_settings folder with the proper Sweeper related files or one could try to copy them from a previous experimental account and then he can edit them as needed Daniel does not use links but instead sources the settings files from this folder directly when configuring the Sweeper DAQ Complete The scaler files are saved each time Readout is ended in a subdirectory of experiment This makes it easier to transfer all the relevant data to tape after the experiment is finished A new subdirectory called experiment complete must be made gt cd experiment gt mkdir complete
208. script will save a slope offset _datetime tcl file in the contrib and mona config directories It will also automat ically link the latest one to MoNA_TCAL dynamic_var tcl to get used when running SpecTcl The offset values for the TDC parameters are not very meaningful and set to 100 channels 1 Log onto a spice machine as the experimental account with SSH Secure Shell and type gt cd mona contrib tcal monatcaldata 2 Use the 1s la command to reveal your spectra file most likely among several others 3 Type cd to back up a directory 176 4 Now open to edit the test sh script It should look similar to this bin sh tdc_calib lt lt EOF monatcaldata Tcal_run1002_350_40 asc n test tdr 40 1 3840 300 EOF ln sf slope_offset_ cat datetmp txt tcl slope_offset_latest tcl exit cp slope_offset_ cat datetmp txt tcl spectclconfig ln sf slope_offset_ cat datetmp txt tcl spectclconfig MoNA_TCAL_dynamic_var tcl exit 5 On line 3 of the script change the filename after the monatcaldata directory to the one you desire to calibrate the filename should correspond to the name of the file you just checked in step 2 6 The first number under test tdr should be changed to the calibration period or delta t that the run was taken with in nanoseconds On the next line the 1 stands for the first channel and 3840 refers to the number of usable bins 255 less than the tot
209. seconds If a linear fit line seems to deviate from the line of points you may need to start over with recording a new time calibration run 178 14 You can check the slopes by opening the slope_offset_latest tcl file and seeing if the slope values are close to range in ns 4096 A range of 350 ns should have a slope near 0 08 9 ns channel 15 If the fitted slope are not near the range divided by 4095 you may need to start over with recording a new time calibration run or re running the fitting code with a different threshold value C 43 File Names As you can see the calibration file is saved in mona config with no easy name to describe what it contains and the MoNA_TCAL dynamic _var tcl link always points to the latest calibration created You may want to reset this link to a file run earlier and or rename calibration files to ones with meaningful labels using the 1n sf or cp commands Make sure the MoNA_TCAL_dynamic_var tcl link points to the correct file for your experimental runs Now you can reopen MoNA_setup_run tcl and edit the TDCfitted flag to true C 5 X Position Calibration The X position calibration may be done after an experiment is finished as long as a sufficiently long recorded run is taken at the end of the experiment but some position and energy spectra during the experiment may look strange if this is not done before hand MoNA must be gain matched and the QDC and TDC slope offset values must be fitte
210. signals are within the TDC s range The delay times depend on the speed of the secondary beam the distance from the target to MoNA and the TDC full range For most MoNA experiments the TDCs are set to 350 ns full range to accept the prompt y rays from the target the full neutron time distribution and a significant window for background events The delay for Cable E target scintillator used as the common stop is set to place the neutron peak near the middle of the raw TDC spectrum The y rays appear about 30 ns in the calibrated spectrum depending on the distance and the neutron peak is between 60 90 ns depending on the beam energy This leaves sufficient time in front of the y ray peaks for recording random background events and sufficient time for slower neutrons to arrive within the TDC range To accomplish this the delay time for Cable E is generally near 100 ns The delay for Cable A is generally around 80 ns Here the sweeper signal must arrive within the coincident window defined by one of the set times for Level 2 as described in Section 3 5 4 49 Table 3 1 The majority bits are set based on the number of coincident left right pairs of CFD channels in one layer coincident pairs majority bits Zero 00 one 01 two 10 three or more 11 3 5 3 MONA Level 1 Trigger Logic Each MoNA layer contains 16 detector modules with 2 PMTs each leading to 32 CFD TDC and QDC channels The Mo
211. ssing are done in the JTEC Virtex XLM as described in Sections 3 5 4 and 3 5 7 A diagram of the internal routing architecture in the Virtex FPGA unit is shown in Figure 2 4 2 3 Calibration The detailed process of calibrating MoNA for an experiment is explicitly presented in Appendix C The light response and position calibration for each MoNA module is performed with cosmic ray muons cosmic ray muons are produced high in the atmo sphere from very fast charged particles permeating deep space Due to the thickness of the Earth s atmosphere the muon flux I relative to the the zenith at any point on the surface is a function of the cosine of the zenith angle squared Figure 2 5 21 a8 a AAAA AAA ae ae baobab 4444444 Se an Oo e644 e 5554 5444 2883558383 E E E Bjs sasassasa 5 224444424488 A S4444 4444444484 pajae eeS5 444856444 w Figure 2 4 The internal routing map between logic gates for the Virtex FPGA is displayed for a sample Level 2 logic code One input and the pathways that signal takes is highlighted in red shows actual muon flux data taken from MoNA over the course of a few weeks The intensities of each 90 in the N S and E W directions are adjusted for the angular coverage to accou
212. sult is slightly less than the reduction factor for the mirror nucleus C proton knockout from the Op3 2 Shell 68 8 3 2Be Ground State Wave Function The relative cross sections measured in the current experiment confirms the spec troscopic factor for the 1n knockout to the 5 2 state in l1Be predominantly from the Od 12 configuration in the ground state wave function of 12Be of 0 48 from Reference 30 This spectroscopic factor for the unbound decay channel does not in crease the summed spectroscopic factor of the three paired neutron states 0s 12 Opi and 0d5 2 dominated by the stripping of one paired neutron to the total two neutrons predicted by the unperturbed single particle shell model description of an inert core of Be within Be There may be higher shell configurations adding the to ground state wave function not yet explored or the simple assumption of two neutrons above an inert 1 Be core might be inaccurate and contributions from core excitations may be important There is evidence for a significant increase in the reported cross section for the knockout reaction to 3 87 MeV 3 27 state in Be 80 that decays predominantly to the 3 96 MeV 2 excited state in 9Be Close analysis suggests the previous ex periment did not have consistent efficiency for the low relative energy zero lab angle neutrons from this decay energy which is only 82 keV and undercounted this decay channel The current measurement finds
213. t is put toward studying the evolution of magic numbers in atomic nuclei especially in the neutron rich region Characteristics of magic nuclei include a sharp decrease in the nucleon separation energy when one or two neutrons or protons are added to a magic number nucleus 1 2 These discontinuities in the separation energy are a consequence of gaps in the binding energy between shell levels at a magic number of protons or neutrons for the next nucleon Magic nuclei with an even number of both protons and neutrons have a much higher first excited state 2 than non magic nuclei The transition probability to this first excited state is much lower in neighboring even even nuclei due to the lack of collectivity since strongly bound ground states are highly spherical and take a lot of energy to excite to the 2 excited state Quantum mechanical approaches developed to account for these magic numbers reproduce the proper gaps in binding energy for these particular numbers of nucleons by using a Woods Saxon potential Vws r Vis 1 1 with an additional spin orbit coupling term V The spin orbit coupling lowers the potential energy of s where lis the orbital angular momentum quantum number and s is the spin of the nucleon always 1 2 for fermions The effect is opposite for s states Figure 1 1 displays the results of Equation 1 1 from Reference 3 The vertical scale represents relative binding energy The quantum num
214. t response equation 4 1 with coefficients aj 4 set according to Table 4 1 and E is the energy loss for the charged particle calculated in small steps of path length through the plastic The curves closely reproduce the MoNA data from both experiments Figures 4 4 and 4 6 4 1 3 Simulated MoNA Intrinsic Efficiency Figure 4 7 shows the intrinsic efficiency for MoNA as calculated by GEANT for a wide range in neutron energies and several light response threshold values in MeVee A software gate applied to the calibrated Q parameter defined in Section 2 2 4 is needed to accurately identify a position independent threshold for comparison with Table 4 1 Light response coefficients used by GEANT in Equation 4 1 The values are taken from Reference 55 charged particles a as a3 a4 protons 0 95 8 0 0 1 0 9 alphas 0 41 5 9 0 065 1 01 68 t 0 65 t 2 0 t 10 t 30 20 40 60 80 100 120 140 160 180 200 Neutron kinetic energy MeV Figure 4 7 Simulated total calculated intrinsic neutron efficiency for MoNA with threshold values of 0 65 1 0 2 0 and 3 0 MeVee simulations Due to the difficulty of producing a calibrated beam of neutrons at the NSCL an alternate method was used to compare with simulation Neutrons produced by stopping an argon beam on a thick collimator at the target position provided a broad range of neutron energies at MoNA By gating on a small range
215. t values clock cycles ta Seti ty Seti te Seta or Set Seto t te 6 cycles te Set1 Seta Setz 6 cycles For a normal coincident event during a production run the entire logic system has been cleared from the previous event and awaits a start Usually a mona start signal comes from Level 1 to start the timer Then a primary signal enters the timer before the end of the coincidence window and the veto latch is activated and copied to cable B for the Sweeper electronics A computer go signal is then asserted that is anded with the valid signal from the Level 2 trigger condition logic Along with this computer go signal the Timer also sends out the TDC veto to close the TDC inputs near the end of the TDC range If no valid signal is received from the Trigger Condition logic then a fast clear signal is issued to clear all QDC and TDC modules and is copied to cable C for the Sweeper electronics This is followed by a clear signal that resets the logic modules and closes the veto latch to accept the next start If a valid signal is sent before the coincidence window closes the computer go signal activates the readout of the QDCs then the TDCs modules This signal is also sent back to the Sweeper modules as a common start through cable D for the delayed Sweeper timing channels The MoNA QDC modules are done digitizing before the TDCs
216. ted in the password The Linux machines do not have this restriction but it is advised to choose one that can be used for both A 2 2 Group Members Contact a member of the computer group or send a e mail to add the users mona and sweeper to the experiments user group Also ask that the new account be added to the mona and sweeper groups This is to ensure that when we login as the new account we can copy over the necessary files from the user mona directories You must also ask to add your personal account to the experiments user group along with other collaborators of your research team You can view the members of a group by the following command gt ypmatch monag group Substitute monag with 4444 4Hg or any group name you wish to query You can also find the list of groups a user account is a member of The following is an example for the user mona gt groups mona 132 A 2 3 SSH Many DAQ codes are called from the Data U machine but actually run on another machine usually spdaq16 Since the codes are trying to communicate with the spdaq machine it will ask for the password before continuing This pause in the action will usually cause the desired program call to fail By setting up a proper ssh directory you can then call these programs without providing a password There are directions in the Data U for setting up the ssh directory to ssh without passwords but I will cover them here as well From a L
217. the positively charged target nucleus they repel each other through the Coulomb force and exchange a virtual photon 21 This photon excites the projectile through an El transition Both the cross section for an El transition and the energy spectrum of the virtual photons can be calculated by the virtual photon method The virtual photon method uses the charge of the target nulcei Z and speed 82 of the projectile v to determine the number of virtual photons for a given target nucleus shown is Figure 4 18 The formal calculation of the total breakup cross section is given by dog _ 1 El pa Ce 4 6 The density n w g1 of El photons is calculated by for relativistic speeds y gt gt 1 23 with a the fine structure constant and modified Bessel functions of order zero Ko and one K 2 bra mog 4 7 ngr w Z a EK0K1 Faz Ai KO 4 7 as a function of the virtual photon s frequency w where E hw and E 12 wR oes 4 8 2 4 8 where R is the sum of the radii for the projectile 1Be and the target 197 Au calculated by A1 3x1 2 fm and is set to 8 fm The cross section for the El photons dB E1 9 c a pa one 4 9 is calculated with the transition probability dB E1 dE 2kro 252 n272 ENS dB El g 3h e Z y Es Ez Es 4 10 dE 1 kromp A El Here k y2puEs h where u is the reduced mass of residue and the neutron Es is the separation energy of Be 0 504 MeV The radius of an a
218. tion is chosen because the decay energy and the cross section can be calculated through both the virtual photon method and the continuum discretized coupled channels method The data agree very well with the calculated decay curves and the total system efficiency is determined MoNA s absolute efficiency is deduced to be 73 6 for 90 MeV neutrons This is above the original design goal and agrees with MoNA GEANT simulations The first two physics experiments for the MoNA Sweeper system are presented The first is a measurement of the one neutron knockout cross section from 9Be to the ground state of Be Because Be has no bound excited states the observance of Be in the Sweeper focal place detectors uniquely determines the reaction channel The reduction factor the Ops 2 single particle spectroscopic factor in Be is determined to be 0 66 0 07 The results are compared to other spectroscopic factors near the same AS neutron minus proton separation energies The second experiment concerns the population of different paired neutron wave functions in the ground state of Be 1512 Op 2 and 0d 2 The relative cross section to the different single particle states in 1Be can be used to determine relative admixture abundance of the corresponding neutron pair wave function in Be above a Be core The relative cross section to the unbound 5 27 in HBe is measured by a neutron knockout reaction using MoNA The decay energy curve f
219. ts are a fan out of two ECL 110 Q impedance 17 pin ribbon cables whose logic pulse width is controlled from 15 to 250 ns One side of one MoNA layer is connected to each 16 channel CFD and then routed to half of a 32 channel TDC through the ECL inputs The other ECL ribbon output is connected to the XLM72 logic module for Level 1 trigger logic control see section 3 5 3 Each CFD channel has its own rejection threshold set in 1 mV steps from 0 to 255 mV The standard operating CFD threshold is set to 10 mV Each CFD also has an OR output LEMO port that is activated for any valid CFD channel This output is used as a diagnostic counter When an additional CFD is used with auxiliary detectors this OR output is used as an auxiliary trigger signal see Section 3 5 6 17 2 2 3 Timing Signal Processing The time to digital converters TDCs are CAEN model V775 with 32 ECL input channels each For consistent and symmetric cabling of the CFDs each side of MoNA uses 5 TDCs for 288 total channels The full scale of each TDC can be set from 140 to 1200 ns For MoNA s standard configuration the range is set to 350 ns representing about 0 085 ns for each bin in the 12 bit digitized spectrum These TDCs can be run in common start or common stop mode The standard configuration runs in common stop mode where the neutron interaction within the MoNA bar acts as the individual start for the corresponding TDC channel This mode is used sinc
220. ts with two neutrons in the decay chan nel is different than for those with one neutron Since the two neutrons in this case may not to be correlated with each other and the decay energy is calculated from the energy and angle of the first valid hit in MoNA the resulting decay energy spectrum would have a wider spread of energies then the actual reaction energy of the decay For example given an uncorrelated two neutron decay from a state 500 keV above the two neutron separation energy the sum of two decay energy calculations using the same energy and angle of the charged particle residue would equal 500 keV but for just the first neutron the calculated decay energy spectrum would be a curve between 0 0 and 500 keV not including resolution effects Furthermore the first 119 neutron is not necessarily the neutron with the most decay energy in the center of mass reference frame since the initial reaction plane could project a fast neutron backwards in the lab frame while the slower one reaches MoNA first and is used for the decay energy calculation In the current experiment the actual reaction energy for the diffractive breakup to two neutrons is not a distinct state but instead a broad distribution caused by the overlap of the target nucleus onto the neutron wave func tion of 12Be 56 The calculated decay energy for the first of two released neutrons would be less than the total reaction energy It is this calculated decay energy of
221. uires a special SpecT cl code that uses the filtered file as an input and has the filtered parameters defined For more information about this see Ref 90 162 B 5 4 Useful Tips e In a unix shell or the TkCon window the up arrow key will display the last command pressing the up arrow twice will display the command before the last etc e In a unix shell or the TkCon window typing h will give you a history of past commands e Typing the command with no arguments will display an error message illustrat ing the expected syntax for example gate 163 Appendix C MONA Calibration Guide C 1 Introduction The follow chapters describe how to prepare the MoNA detector for an experiment using a suite of fitting programs and procedures The MoNA setup file called MoNA_setup_run tcl in the mona config directory contains the important flags to set to true after each successive calibration or fitting procedure is finished They are QDC_thres_flag QDCfitted TDCfitted Xposfitted Tmean_indie_offset Start by opening MoNA_setup_run tcl and editing these flags to false then saving Portions of this guide where originally written by MoNA Collaboration undergraduate students including J Miller M Strongman L Elliott D B Hecksel M M Kleber P J Voss T Pike R Pepin and A Ratkiewicz 164 C 1 1 Proper Links Since the fitting codes run in a different directory from the configuration fi
222. use these adjustments are 166 the program s best guesses multiple iterations of the gain matching process must be completed before the PMT voltages are accurately matched C 2 1 Getting Started 1 Open up two terminal windows one to a spice machine and another connected to spdaq16 2 In the spdaq16 terminal go to the mona hv_control directory 3 To make sure all of MoNA is turned type gt Vallon scr C 2 2 Take Cosmic Data 1 Let the voltages settle for a few minutes 2 Be sure you are in the hv_control directory of the spdaq16 terminal by using the command gt pwd 3 Now you must read out the current voltages into hv_files Vout_current tcl and copy them into hv_files Cosmic_volts tcl file by the commands gt Vout scr gt Vcopy scr 4 Record a two hour or longer run of cosmic ray data with all detector bars Use MoNA multiplicity set to 1 fold and select self trigger and self stop on the XLM control 5 Open MoNA SpecTcl 92 in the spice terminal window or from a Data U machine 2This must be a new recorded run for each iteration 167 10 EJ Xamine user 05034 mona daq spectcl win Q_A_L win Ja File Window Spectra Options Graph_objects Help Geonetry Zoon Update All Expand Marker Cut Display Update Selected UnExpand Summin
223. ussian fit to the neutron kinetic energy data is used as an input for GEANT to compare the light response shown in Figure 4 6 of neutrons within the BC408 plastic Two separate experiments were performed to test the simulation s light response for MoNA at two different energy ranges and two different situations The first pro duced a wide range of neutron energies by stopping most of a 40 MeV u argon beam in the thick steel collimator at the target position The resulting neutron distribu tion covered energies between 25 60 MeV 35 40 MeV Neutrons were gated by their time of flight ToF and a 12 5 cm wide area near the center of one bar to compare with GEANT For the second experiment neutrons were produced by the Coulomb breakup of Be on a gold target at 90 MeV u 10Be coincident neutron data from the whole array were used to compare to simulation The Gaussian fit of the distribution of neutron energies shown in Figure 4 5 was used as the input distribution in GEANT for the comparison plotted in Figure 4 6 The light response curve is calculated as per Reference 55 by l a E as 1 exp a3E 4 1 67 1000 x MONA 100 A Geant Madey QD y E 5 10 nee PL Ne LN FALDA 0 1 LESS el O 10 20 30 40 50 60 70 90 100 Deposited light MeVee Figure 4 6 Measured light response curve for the neutron data from Figure 4 5 into the full MoNA array compared to GEANT simulation using the Madey ligh
224. verters QDCs with 32 ECL input channels each for all 288 PMT dynode signals In the standard MoNA configuration all 32 dynode signals of a 16 module layer are connected to one QDC Channels 0 15 for the left side PMT dynodes and channels 16 31 for the right The QDCs use negative current integrating ribbon cable inputs from the passive dynode inverter boxes The module accepts a logic integrating gate that is set in compliance with the module s maximum integrated charge of 400 pC As with the CAEN TDCs the QDCs also have fast clear capabilities The scintillation light from a charged particle reaction in a MoNA bar is attenuated as it passes to the ends of the bar to the light guides The rate of attenuation for the light ti the left and right PMTs are exponentials given by by lee 2 2 1 lr lofe 2 420 2 2 with zo corresponding to the x position measured within the MoNA bar between negative 100 and positive 100 cm and A is the attenuation length about 3 meters for BC408 Because of this attenuation the final signal recorded by the QDC is less than the actual light produced as a function of the distance away from the end To recover an even distribution for the light deposited within the bar independent of the position the geometric mean is calculated Q Vile 2 3 Figure 2 3 illustrates the effectiveness of this equation where the left and right in dividual QDC spectra are displayed versus the horizontal p
225. would like to export and don t forget to give it a unique name The default format is ascii which works well with Excel You may select any format you want to use This will then save the swrite file in the spectra directory B 4 2 Importing into Excel Open Excel click on Data go to Get External Data and select Import Text File Change the file type option to all files and select your ascii file In the first page select delimited then next In the following box check both the space and other delimiter boxes In the other box type a closed parentheses This will turn every space and closed parentheses read in by Excel into a new column space which makes life much easier for you Now click finish and select the first cell to start the 158 import Next if you ve only imported one spectrum per Excel sheet and you want to auto matically turn these columns into calibrated and compressed columns you must first set your macros security to medium Do this by selecting the tools gt options gt security gt macro security menus and then setting the macro security to medium Now open the Excel file projects proj1 mona docs spectcl read macro_calibrate xls that has the correct macros in it and select the Enable Macros option Once this file is opened in Excel go back to your data sheet and you can run the macro test2 on your imported data This will create many new columns and fill any missing zero s from the original histog
226. x acceptance of Be residue for run 2114 5 4 Sweeper focal plane x acceptance of Be residue for run 2121 5 5 Sweeper focal plane y acceptance of Be residue 5 6 Reduction factor versus nucleon separation energies with 9Be 5 7 Reconstructed target angle acceptance of 9Be residue o 5 8 Momentum distribution of Be beam through the reaction target 5 9 Parallel momentum distribution of Be residue compared to p wave fit 6 1 Diagram of decay channels for 12Be neutron knockout 6 2 Isotope identification for the 2Be ground state experiment 6 3 Be residue kinetic energy form the 2Be ground state study 6 4 Neutron kinetic energy from the 2Be ground state study 6 5 Relative velocity for the 12Be ground state study 6 6 Opening angle versus relative velocity for the Be ground state study 6 7 2Be experiment fit to data fixing cross sections to previous work 6 8 12Be experiment fit to data allowing individual amplitudes to adjust 7 1 Future vault configuration for MoNA Sweeper setup 7 2 Alternate setup for direct fragmentation experiment xiii 93 94 95 112 113 114 B 1 B 2 B 3 B 4 B 5 C 1 C2 C 3 C 4 C 5 D 1 D 2 The MoNA SpecTcl control window 000 151 The Xamine startup window oa cuca a Pe 151 Theconsolesshelli eu todo de deg dete tt deg Hae eid ERAN 152 The Tkcon window 2 ad tele a oe ea be
227. y 5 27 state at 3 90 MeV separate from the 3 27 state at 3 96 MeV that could account for this discrepancy Considering the other 3 27 state at 2 69 MeV could also come from stripping a neutron out of the Ops 2 117 9000 8000 7000 6000 Be 2 5 2 3 2 Thermal 1 41 1 36 1 46 1 04 0 857 1 24 1 04 0 622 1 56 0 958 0 874 1 05 Sum 03048 data al o o o gt 4000 Counts per 50 keV w o o o 2000 1000 0 0 5 1 1 5 2 25 3 3 5 4 Decay energy MeV Figure 6 8 Same as Figure 6 7 with overall scale fixed at 1 09 while all four individual decay curves are adjusted relative to the reported cross section measurements 81 used for Figure 6 7 to find the best fit to the data The fit range for this plot is 0 0 to 3 5 MeV The fit values represent the ratio of our data to the cross sections reported by 81 The only resonance that is not consistent with the previous measurement is the highly excited 3 96 MeV 3 2 state in 11 Be decaying to the 2 state of Be shell further shell model analysis is needed to determine the coupling to the various states and their coupling to the 2 state in Be and the role core excitation plays in the initial 12Be The other three decay curves fit very well with the previous measurement and confirm the spectroscopic factors to the 5 2 state in HBe reported in reference 30 that is produced mostly by stripping of one of the 0d 12 neutrons in the

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