Model 460 Delay Line Amplifier Operating and Service Manual
Contents
1. ORTEC OATEC ORTEC PRECISION PULSER COUNT AMPLIFIER RATEMETER ORTEC LINEAR GATE IDELAYEDI INTEGRAL DISCRIMINATOR GATE amp DELAY GENERATOR Fig 6 6 Circuit Used to Measure Resolution Spread and Amplitude Changes at Various Count Rates 6 4 TROUBLESHOOTING PRECISION TIMING SINGLE PULSER AMPLIFIER CHANNEL ANALYZER INPUT INPUT c 1 QUTPUT POS OuTPUT 16018 Fig 6 4 Circuit Used to Measure Crossover Walk of the Amplifier and Single Channel Analyzer If the 460 is suspected of malfunctioning it is essential to verify such malfunctioning in terms of simple pulse generator impulses at the input The 460 must be disconnected from its position in any system and routine diagnostic analysis performed with a test pulse generator and oscilloscope It is imperative that testing not be performed with a source and detector until the amplifier performs satisfactorily with the test pulse detector The testing instructions in Section 6 3 of this manual and the circuit descriptions in Section 5 should provide assistance in locating the region of trouble and repairing the malfunction The two side plates can be completely removed from the module to enable oscilloscope and voltmeter observations with a minimal chance of accidentally short circuiting portions of the etched board The 460 may be returned to ORTEC for repair service at nominal cost Our st2. 4 04 1 1 2 SPECIFIOATIONS 2 Se TINS TAEEATION RA SAU RE RUNE 3 Sele GENERAL 2 55 usw I RU VC EVERIEEREUU EE IESU RENTES ete estar ote gaan 3 3 2 CONNECTION TO PREAMPLIFIER 2 3 3 3 CONNECTION OF TEST PULSE GENERATOR 4 3 4 CONNEGTION TO POWER hee t tt ttt t t centers 4 3 5 SHAPING CONSIDERATIONS 1 4 3 6 SELECTION OF PROMPT OR DELAYED OUTPUT 5 3 7 OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS 5 4 OPERATING INSTRUCTIONS tee tete a e ERR Rer ERR HEAR ERG 5 4 1 INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS 5 4 2 FRONT PANEL CONTROLS reu gene dee glee 6 4 3 FRONT PANEL CONNECTORS All BNC 6 4 42 REAR PANEL CONNEGTORS vu n e ERE E FE Es en 6 4 5 OPERATION WITH SEMICONDUCTOR DETECTORS 7 4 6 OPERATION IN NEUTRON GAMMA DISCRIMINATION SYSTEM WITH STILBENE AND EIQUID SCINTIEEATORS defe een ei aedes 9 4 7 NEUTRON GAMMA RAY DISCRIMINATION IN PROPORTIONAL COUNTERS 12
3. Gain stage A1 is an input buffer with a fixed gain of 2 It includes Q1 through Q7 and the gain is fixed by R1 R2 R3 and 15 This stage can be operated as either an inverting or a noninverting amplifier depending on the setting of the front panel switch S1 When the signal input polarity from the preamplifier matches the setting of the Switch the output from 07 is a negative pulse 036 045 Gain 2 5 0 2 DC Level The Q7 output is delay line shaped by DL1 and pole zero cancelled by R28 and applied to A2 08 through Q15 This stage operates in the differential mode providing an output that is the difference between the direct and delayed inputs The stage gain is either 2 or 5 depending on the setting of Coarse Gain switch S2 determined by R34 R35 and R23 to R26 R23 is factory adjusted for correct gain at the 10 and 20 settings of switch S2 to ensure that the pole zero cancellation is valid for all gain settings Feedback resistors R32 R33 R39 and R40 are also selected by the Coarse Gain switch to preserve a constant bandwidth Stage A3 Q16 through Q23 is noninverting and has a gain of 2 4 or 8 that is selected for various positions of switch S2 A selection of resistors R127 R81 R82 and R83 determines the gain for this stage Stage A4 Q24 through Q31 is a noninverting amplifier with a gain of 1 2 5 or 5 selected by switch S2 The gain resistors are R84 through R88 Gain selected by 52 f
4. 6 04 INPUT UNIPOLAR ADS BIPOLAR ORTEC MODEL 460 DELAY LINE AMPLIFIER 1 DESCRIPTION 1 1 GENERAL The ORTEC 460 Delay Line Amplifier is a nuclear pulse amplifier that provides delay line shaping for all output pulses It accepts input pulses of either polarity from the preamplifier and expands their amplitude by an adjusted gain factor within the range from 3 through 1000 An integrating time constant can be selected to shape the rise of the input pulse as desired Pole zero cancellation is adjustable 10 match the characteristic of the preamplifier output 1 2 DUAL OUTPUTS Two output pulses are furnished for each input pulse One is positive unipolar and is single delay line shaped it can be furnished as either a prompt or delayed output pulse The other is bipolar with positive polarity leading and is double delay line shaped Both of these output pulse shapes are available through front panel connectors with an output impedance of 10 and through rear panel connectors with an output impedance 01930 The main use for the unipolar output pulses is for energy measurements For this application the 460 provides high counting rate capabilities excellent overload recovery and dc adjustment of the output baseline The unipolar output is preferred for both single channel and multichannel analysis because of its low noise characteristic The main use for the bipolar output pulses is for tim
5. ORTEC ORTEC ORTEC ORTEC LINEAR GATE DELAY AMPLIFIER PREAMP ave am AMPLIFIER Linear Output to Muitichannel Analyzer ORTEC SCINTIL LATION PREAMP ORTEC ORTEC TSC ANALYZER AMPLIFIER 100330 Fig 4 16 Gamma Ray Pair Spectrometer ORTEC LINEAR GATE ORTEC ORTEC QR GATED BIASED AMPLIFIER PREAMP AMPLIFIER ORTEC DETECTOR MULTI CHANNEL pedi PULSE HEIGHT PICKOFF ANALYZER 300344 Energy Gated 15 ORTEC ORTEC OR PREAMP AMPLIFIER AMPLIFIER ORTEC DETECTOR MULTI CHANNEL SCA FOR E and or T PICKOFF ANALYZER ORTEC Other Gating Signals COINCIDENCE 200353 b Time Gated Fig 4 17 General System Arrangement for Gating Control 4 9 REFERENCES 1 F T Kuchnir and F J Lynch Time Dependence of Seintillations and the Effect on Pulse Shape Discrimination IEEE Trans Nucl Sci NS 15 9 107 1968 2 R V Hogg and A T Craig ntroduction to Mathematical Statistics 2d ed Macmillan New York 1965 Ronald Nutt A Study of a Scintillator Photo multiplier Timing System Ph D Thesis University of Tennessee March 1969 4 E F Bennett Gamma Ray Discrimination in a Proton Recoil Proportional Counter Neutron Dosimetry Pro ceedings of a Symposium Ha
6. 0408 12V Q44C 13V Q45C 7V 0498 12V 0518 13V 0528 12V Q56C 13V Q59C 13V 6 6 FACTORY REPAIR This instrument can be returned to the ORTEC factory for service and repair at a nominal cost Our standard procedure for repair ensures the same quality control and checkout that are used for a new instrument Always contact Customer Services at ORTEC 865 482 4411 before sending in an instrument for repair to obtain shipping instructions and so that the required Return Authorization Number can be assigned to the unit Write this number on the address label and on the package to ensure prompt attention when it reaches the ORTEC factory 22 Table 1 Bin Module Connector Pin Assignments For Standard Nuclear Instrument Modules per DOE ER 0457T Pin Function 1 3 V 2 3V 3 bus 4 Reserved bus 5 Coaxial 6 Coaxial 7 Coaxial 8 200Vdc 9 Spare 10 46V 11 6V 12 Reserved bus 13 Spare 14 Spare 15 Reserved 16 412V 17 12V 18 Spare bus 19 Reserved bus 20 Spare 21 Spare 22 Reserved 41 Function Reserved Reserved Reserved Spare Spare 24 V 24 V Spare bus Spare Spare 117 V ac hot Power return ground Reset Scaler Gate Reset Auxiliary Coaxial Coaxial Coaxial 117 V ac neutral High quality ground Ground guide pin Pins marked are installed and wired in ORTEC s 4001A and 4001C Modular System Bins
7. 5 non overload pulse widths from X500 overload unipolar recovers in same time from X100 overload TIME JITTER 50 Amplitude En dv at FWHM 29 psec for a Gain 50 and E 10 V FWHM 2 9 psec for a Gain 50 and E 100 mV DELAY LINES 1 Us standard T 0 25 0 5 or 2 0 as T available Both delay lines have the same value CONTROLS FINE GAIN Single turn potentiometer for continuously variable gain factor of X0 3 to X1 COARSE GAIN 7 position switch selects gain factors of X 10 20 50 100 200 500 and 1000 INPUT POLARITY Slide switch sets input circuit for either Pos or Neg input polarity PZ ADJ Potentiometer to adjust Pole Zero cancellation for decay times from 25 Us to INTEG Slide switch selects an integration time constant of 0 04 0 1 or 0 25 Us for 0 04 Us setting amplifier rise time is 100 nsec DC ADJ Potentiometer to adjust the dc level for single delay line shaped unipolar output pulses DELAY IN OUT Slide switch on rear panel selects either 1 Us In or prompt Out timing for unipolar output pulses INPUT Accepts either polarity of pulses from preamplifier front panel type BNC UG 1094A U connector maximum linear input 3 3 V protected to 20 V Z 1 dc coupled OUTPUTS UNIPOLAR Prompt or delayed with full scale linear range of 0 to 10 V single delay line shaped baseline level adjustable to 1 0 V 2 1O dc coupled through front panel BNC UG 1094A U connector
8. Z 93O dc coupled through rear panel BNC UG 1094 U connector BIPOLAR Prompt output with positive lobe leading double delay line shaped with full scale linear range of 0 to 10 V Z 1O dc coupled through front panel BNC UG 1094A U connector Z 930 dc coupled through rear panel BNC UG 1094 U connector PREAMP Standard ORTEC power connector for mating preamplifier Amphenol type 17 10090 rear panel ELECTRICAL AND MECHANICAL POWER REQUIRED 24 V 90 mA 12 V 85 mA 24 V 90 mA 12 V 75 mA WEIGHT Shipping 4 25 Ib 1 9 kg WEIGHT Net 2 25 Ib 1 kg DIMENSIONS Standard single width module 1 35 by 8 714 in per TID 20893 Rev 3 INSTALLATION 3 1 GENERAL The 460 contains no internal power supply but is used in conjunction with an ORTEC 4001 4002 Bin and Power Supply and is intended for rack mounting therefore if vacuum tube equipment is operated in the same rack with the 460 there must be sufficient cooling by circulating air to prevent localized heating of the all semiconductor circuitry used throughout the 460 The temperature of equipment mounted in racks can easily exceed 120 50 unless precautions are taken 3 2 CONNECTION TO PREAMPLIFIER The preamplifier output signal is connected to the 460 through the BNC connector on the front panel labeled Input The input impedance is 1000 O and is dc coupled to ground therefore the output of the preamplifier must be either ac cou
9. both the interconnecting cable and 1000 resistive terminator Note that the signal span at the receiving end of this type of receiving circuit will always be reduced to 5096 of the signal span furnished by the sending instrument For your convenience ORTEC stocks the proper terminators and BNC tees or you can obtain them from a variety of commercial sources 4 OPERATING INSTRUCTIONS 4 1 INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS Refer to Section 6 for information on testing performance and observing waveforms at front panel test points Figure 4 1 shows some typical output waveforms E Peper Integ Time 0 04 usec Unipolar Prompt 22 EL EL A Integ Time 0 25 usec Unipolar Prompt Fig 4 1 Typical Effects of Integrate Time Selection on Output Waveforms taken with horizontal 0 5 and vertical 5 V cm 4 2 FRONT PANEL CONTROLS GAIN A coarse gain switch and a fine gain potentiometer select the gain factor The gain is read directly switch positions are 10 20 50 100 200 500 and 1000 and continuous fine gain range is 0 3 to 1 INPUT POLARITY Slide switch sets the input circuit for either Pos or Neg input polarity PZADJ Control to set the pole zero cancellation for optimum matching to the preamplifier pulse decay characteristics range 25 ps to infinity DC ADJ Potentiometer to adjust the dc level of unipolar output range 1 0 V DELAY Slid
10. position which satisfies these requirements if any The 460 provides both unipolar and bipolar outputs The unipolar output should be used in applications where the best signal to noise ratio resolution is desired such high resolution energy spectroscopy using semiconductor detectors Use of this output will also give excellent resolution at high counting rates when used with dc coupled inputs in the subsequent equipment The bipolar output should be used for time spectroscopy if the time signal is derived from a baseline crossover The bipolar output is also useful for energy spectroscopy in high count rate systems when noise or resolution is a secondary consideration and when the analyzer system is ac coupled 3 6 SELECTION OF PROMPT OR DELAYED OUTPUT The prompt unipolar output is obtained with the Delay switch set at Out This will normally be used for spectroscopy applications A delayed unipolar output is obtained with the Delay switch set at In and the pulses will be delayed by 115 for a time adjustment in a coincidence system or when gating logic isto be performed on the bipolar output before the unipolar pulse arrives at the gate 3 7 OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS There are three general methods of termination that are used The simplest of these is shunt termination at the receiving end of the cable A second method is series termination at the sending end The third is a combination of ser
11. the Coarse Gain switch to 1 K 6 Decrease the Fine Gain to 0 3 at which time the output should decrease by a factor of 3 3 Return the Fine Gain control to maximum Overload Tests Set the amplifier gain to maximum and adjust the pulse generator to obtain a 10 V amplifier output Increase the pulser amplitude by 500 to provide an overload Observe that the Unipolar and Bipolar Outputs both return to within 200 mV of the baseline within 15 us It will probably be necessary to vary the PZ Adj control on the front panel in order to cancel the pulser pole and minimize the time for the return to the baseline PZ Adi Calibration The correct setting of the PZ Adj control depends upon the characteristics of the input pulses that are furnished from the preamplifier during normal operation of the 460 Observe the amplifier unipolar output for a high gain setting 50 or more that will provide 8 to 10 V pulses for a monoenergetic signal from the preamplifier and adjust the PZ Adi control on the front panel to obtain the quickest return to the baseline following each pulse After the cancellation time has been minimized reduce the amplifier coarse gain to 20 and adjust R23 on the printed circuit to obtain the optimum Pole Zero cancellation at low gain settings Linearity The integral nonlinearity can measured by the technique shown in Fig 6 3 In effect the negative pulser output is subtracted from the positive amplifier output causing
12. 4 8 Mn aie 13 4 9 IREFERENGES e RR AUREUS 15 5 GIRGUITEDESGRIEPTIGON t ht ee tee 16 MAINTENANCE tac cde E er EK Ded BA Ded DAS DADA 18 6 1 TEST EQUIPMENT REQUIRED 7 2 1 18 6 2 PULSER MODIFICATIONS FOR OVERLOAD TESTS 18 6 32 PULSER e eu ER EE ERAS ENS EHE EE 18 6 4 TROUBLESHOOTING e emere EP 20 6 5 TABULATED TEST POINT VOLTAGES ETCHED BOARD 21 6 6 FAGTORY REPAIR isses ee ed et oes oe cate os RR doe Rx eee 21 SAFETY INSTRUCTIONS AND SYMBOLS This manual contains up to three levels of safety instructions that must be observed in order to avoid personal injury and or damage to equipment or other property These are DANGER Indicates a hazard that could result in death or serious bodily harm if the safety instruction is not observed WARNING Indicates a hazard that could result in bodily harm if the safety instruction is not observed CAUTION Indicates a hazard that could result in property damage if the safety instructio
13. Amplifier and SCA With the setup of Fig 6 4 obtain a 10 V amplifier output at an amplifier coarse gain of 50 Attenuate the pulser by X10 using only the pulser attenuator switches The shift in the SCA should be less than 2 nsec The Walk Adj trim potentiometer on the SCA must be adjusted properly in order to make this measurement Crossover Walk with Amplitude Amplifier Only The crossover walk of only the amplifier can be measured with the setup shown Fig 6 5 421 Integral Discriminator or any other leading edge discriminator and the ORTEC 416 Gate and Delay Generator are used to delay the trigger of the oscilloscope so that the crossover of the amplifier can be viewed on the shortest time scale of the oscilloscope 10 nsec cm Two identical high frequency attenuator pads must be used for this measurement the ORTEC 419 Pulser attenuator can be used if the attenuator of another 419 Pulser is used for the other attenuator The pulser and the amplifier gain are adjusted so that there is 3 to 10 V bipolar output at the oscilloscope with the first attenuator having X20 attenuation and the second attenuator having no attenuation Observe the crossover on the oscilloscope and remove the X20 attenuation from the first and add it to the second attenuator The crossover walk under these conditions should be less than 1 nsec ORTEC PRECISION PULSER ORTEC INTEGRAL IDISCRIMINATOR ORT
14. EC GATE amp DELAY GENERATOR TRIGGER DIRECT INPUT INPUT ORTEC SELECTABLE AMPLIFIER Fig 6 5 Circuit Used to Measure Crossover Walk of the Amplifier Only Counting Rate Changes Resolution spread and amplitude changes with counting rate can be measured with the setup shown in Fig 6 6 Pulser pulses are mixed at the amplifier input with prearnplifier pulses from a Cs source and the delayed mixed output is fed to an ORTEC 442 Linear Gate A 421 Integral Discriminator and a 416 Gate and Delay Generator are used to open the linear gate at the proper time to accept a shaped 20 pulser pulse from the amplifier delayed output Adjust the Amplifier gain so that Cs peak will store at about the 7096 level approximately channel 2900 in a 4096 Analyzer in the pulse height analyzer and then adjust the pulser amplitude to store at the 84 level approximately channel 3450 in a 4096 Analyzer Change the Cs source position until the counting rate as measured by the ratemeter is approximately 50 000 counts sec Two spectra are then accumulated one with the Cs source present and one with the Cs source removed Using a 1 Us shaping time constant the pulser peak in the presence of the 13705 source should be shifted no more than 0 2 seven channels for 4096 Analyzer as compared to the pulser only spectrum ORTEC 3 SCINTILLATION PREAMPLIFIER 131C SCINTILLATION SOURCE COUNTER
15. ICKOFF CONTROL ALTERNATE 1 1 i ee ad Ls 4 Linear Output to Multichannel Analyzer UNIPOLA OuTPUT PULSE SHAPE ANALYZER ORTEC 427A DELAY AMPLIFIER ORTEC 458 Fig 4 13 Neutron Gamma Discrimination System with Proportional Counter 14 ORTEC ORTEC ORTEC TSC ANALYZER PREAMP AMPLIFIER ORTEC FAST COINCIDENCE UNIT ORTEC SILICON SURFACE LINEAR GATE BARRIER DETECTOR Linear Output to Multichannet Analyzer Source Li DRIFTEO GERMANIUM ATE amp DELAY mene ie DETECTOR DISCRIMI GENERATOR 1 NATOR ORTEC Gate amp Delay 1 Generator TIME PICKOFF ALTERNATE CONTROL ORTEC TIMING ess FILTER AMPLIFIER ORTEC ORTEC ORTEC 7 ORTEC PREAMP AMPLIFIER DELAY Preamp amp AMPLIFIER TIME PICKOFF 200328 UNIT Fig 4 15 Gamma Ray Charged Particle Coincidence Experiment ORTEC ORTEC ORTEC Gate amp Delay TIME PICKOFF SCINTIL Tse CONTROL nerator LATION AMPLIFIER ANALYZER PREAMP ALTERNATE ORTEC ORTEC Preamp Amp DISCRIMI NATOR FAST COINCIDENCE UNIT GENERATOR Ge Li DRIFTED DETECTOR ORTEC TIMING FILTER AMPLIFIER
16. Printed U S A Model 460 Delay Line Amplifier Operating and Service Manual ORTEC Part No 733320 Manual Revision C 1202 Advanced Measurement Technology Inc a k a ORTEC a subsidiary of AMETEK Inc WARRANTY ORTEC warrants that the items will be delivered free from defects in material or workmanship ORTEC makes no other warranties express or implied and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ORTEC s exclusive liability is limited to repairing or replacing at ORTEC s option items found by ORTEC to be defective in workmanship or materials within one year from the date of delivery ORTEC s liability on any claim of any kind including negligence loss or damages arising out of connected with or from the performance or breach thereof or from the manufacture sale delivery resale repair or use of any item or services covered by this agreement or purchase order shall in no case exceed the price allocable to the item or service furnished or any part thereof that gives rise to the claim In the event ORTEC fails to manufacture or deliver items called for in this agreement or purchase order ORTEC s exclusive liability and buyer s exclusive remedy shall be release of the buyer from the obligation to pay the purchase price In no event shall ORTEC be liable for special or consequential damages Quality Control Before being approved for shipment each ORTEC instrument must pas
17. a null point that can be measured with high sensitivity The pulser amplitude must be varied between 0 and 10 V using an external voltage source for the pulser and the amplifier gain and pulser attenuator must be adjusted to give zero voltage at the null point with a 10 V output The variation in the null point as the pulser is varied from 10 V to zero is a measure of the nonlinearity Since the subtraction network also acts as a voltage divider this variation must be less than 10 V full scale x 0 05 max nonlinearity x 2 for divider network 52 5 mV max null point variation 19 PULSE ENERATOR AMPLIFIER UNDER ATTENUATED OUTPUT VERTICAL INPUT Fig 6 3 Circuit Used to Measure Nonlinearity Output Loading With the same setup as in Linearity adjust the amplifier output to 10 V and observe the null point change when the output is terminated in 1000 The change should be less than 5 mV Noise Measure the noise at the amplifier output at maximum amplifier gain and 0 25 Us Integrating time constant using the RMS Voltmeter The noise should be less than 20 UV x 1000 gain 1 13 17 7 mV for single delay line outputs and 35 UV x 1000 gain 1 13 31 0 mV for double delay line outputs The 1 13 is a correction factor for the average reading voltmeter and would not be required for a true rms voltmeter Both inputs must be terminated in 100 for this measurement Crossover Walk with Amplifier
18. alyzer Probably the most convenient method of making resolution measurements is with a pulse height analyzer as shown by the setup illustrated in Fig 4 5 The amplifier noise resolution spread can be measured directly with a pulse height analyzer and the mercury pulser as follows 1 Select the energy of interest with an ORTEC 419 Pulse Generator and set the Amplifier and Biased Amplifier Gain and Bias Level controls so that the energy is in a convenient channel of the analyzer 2 Calibrate the analyzer in keV per channel using the pulser full scale on the pulser dial is 10 MeV when calibrated as described in Calibration of Test Pulser 3 Then obtain the amplifier noise resolution spread by measuring the FWHM of the pulser spectrum The detector noise resolution spread for a given detector bias can be determined in the same manner by connecting a detector to the preamplifier input The amplifier noise resolution spread must be subtracted as described in Detector Noise Resolution Measurement The detector noise will vary with detector size and bias conditions and possibly with ambient conditions ORTEC ORTEC ORTEC LINEAR AMPLIFIER BIASED AMPLIFIER PREAMP E L DETECTOR ORTEC oRTEC ORTEC PULSE PULSE GENERATOR AMPLIFIER STRETCHER i GATED BIAS i 1 L 290091 MULTI CHANNEL PULSE HEIGHT ANALYZER Fig 4 5 System for M
19. andardized procedure requires that each repaired instrument receive the same extensive quality control tests that a new instrument receives Contact our Customer Service Department 865 482 4411 for shipping instruction before returning the instrument 6 5 TABULATED TEST POINT VOLTAGES ON ETCHED BOARD The following voltages are intended to indicate the typical dc voltages that can be measured on the etched circuit board In some cases the circuit will perform satisfactorily even though due to component variation some voltages may measure different from the listed values Therefore the voltages should not be taken as absolute values but rather are intended to serve as an aid in troubleshooting All the voltages listed below were measured with no input signal and with the front panel controls set at about their mid ranges When an input signal is furnished to the 460 the normal signal polarity is shown for each of 7 test points in the measurement 21 MM _______ Location Voltage Signat Polarity 1 lt 100 Negative TP2 350 mV Positive TP3 130 mV Positive 4 lt 20mv Negative TPS Adjusted by R118 to 1 V Positive TPG lt 50 mV Bipolar leading 7 lt 500 Q3B 12V 4 13V 058 12V 098 12V Q11B 13V 0128 12V Q18B 12V 0198 13V 0208 12V Q26B 12V 0278 13V 0288 12V Q33B 45V Q34B 45V Q378 12V 0398 13V
20. ble coaxial cable type RG 62 U or RG 71 U is recommended 3 3 CONNECTION OF TEST PULSE GENERATOR Connection to the 460 Through a Preamplifier The satisfactory connection of a test pulse generator such as the ORTEC 419 or equivalent depends primarily on two considerations the preamplifier must be properly connected to the 460 as discussed in Section 3 2 and the proper input signal simulation must be applied to the preamplifier To ensure proper input signal simulation refer to the instruction manual for the particular preamplifier being used Direct Connection to the 460 Since the input of the 460 has 10000 input impedance the test pulse generator will normally have to be terminated at the amplifier input with an additional shunt resistor If the test pulse generator has a dc offset greater than 1 V a large series isolating capacitor is also required since the input of the 460 is dc coupled ORTEC Test Pulse Generators are designed for direct connection When any of these units are used they should be terminated with a 1000 terminator at the amplifier input or be used with at least one of the output attenuators set at In The small error due to the finite input impedance of the amplifier can normally be neglected Special Considerations for Pole Zero Cancellation pole zero cancellation network in the 460 is factory adjusted for a 50 Us decay time to match ORTEC FET preamplifiers When a tail pulser is connected directl
21. con Detector Back Current vs Bias Voltage Preamplifier Main Amplifier Gain Adjustments as a Function of Input Particle Energy With the input energy at a constant or maximum known value the following method is recommended for adjusting the total system gain of the preamplifier and main amplifier to an optimum value 1 The primary design criterion for the preamplifier is the best signal to noise ratio at the output therefore operate the preamplifier with the gain switch in its maximum gain position This will result in the best signal to noise ratio available and at the same time the absolute voltage amplitude of the preamplifier signal will be maximized 2 Since the fine gain control of the 452 is an attenuator set it to as near maximum as possible by manipulating the coarse gain 4 6 OPERATION IN NEUTRON GAMMA DISCRIMINATION SYSTEM WITH STILBENE AND LIQUID SCINTILLATORS The single delay line shaped output pulses from the ORTEC 460 are suited ideally to the input requirements of the ORTEC 458 Pulse Shape Discriminator When these instruments are included in the system neutron gamma discrimination can be effected such that the amplifier output pulses can also be routed into a multichannel analyzer with the gamma spectrum stored in one half of the analyzer and the neutron spectrum stored in the other half of the analyzer Theory Neutrons and gammas produce light scintillations NE 213 NE 218 and Stilbene detect
22. e maximum pulse height dial reading 1000 divisions is equivalent to 10 MeV loss in a silicon radiation detector The procedure is as follows 1 Connect the detector to be used to the spectrometer system i e preamplifier main amplifier and biased amplifier 2 Allow particles from a source of known energy alpha particles for example to fall on the detector 3 Adjust the amplifier gain and the bias level of the biased amplifier to give a suitable output pulse 4 Setthe pulser Pulse Height potentiometer at the energy of the alpha particles striking the detector e g for a 5 47 MeV alpha particle set the dial on 547 divisions 5 Turn on the Pulser and use the Normalize potentiometer and attenuators to set the output due to the pulser for the same pulse height as the pulse obtained in step 3 Lock the Normalize dial and do not move again until recalibration is necessary The pulser is now calibrated the Pulse Height dial reads in MeV if the number of dial divisions is divided by 100 Amplifier Noise and Resolution Measurements As shown in Fig 4 2 the preamplifier amplifier pulse generator oscilloscope and a wide band rms voltmeter such as the Hewlett Packard 400D are required for this measurement Connect a suitable capacitor to the input to simulate the detector capacitance desired Use the following procedure to obtain the resolution spread due to amplifier noise 1 Measure the rms noise voltage Ems a
23. e characteristics Gain 10 Rise time 100 nsec Input equivalent noise Av 70 x 10 V The rise time noise is given approximately by At 2 42 G 2 35 Av v tg 5 where is rms noise at the input v is the signal level of interest and t4 is the rise time The V2 factor exists because of two level measurements and the 2 35 converts the rms value to FWHM For the example above the time resolution at the minimum pulse height of 20 mV is At 2 10 2 35 70 x 1075 20 x 102 100 x 107 11 5 nsec FWHM Many delay line amplifiers have good noise characteristics for high gain butthe noise increases very rapidly as the gain is lowered From the above example it becomes evident that the amplifier must be operated at minimum gain and must have good noise characteristics before neutrons and gammas can be separated over the entire range of 20 mV to 10V The ORTEC 460 furnishes these characteristics The 458 should be operated in the X0 1 V input discriminator range for the 400 1 dynamic range In this position 1000 divisions is equivalent to 100 mV at the input to the 458 The 458 input discriminator control should be set above the input noise but not lower than 100 divisions on the control The Walk Adj should be adjusted for optimum walk over the entire dynamic range of interest A typical block diagram for a neutron gamma ray discrimination system is shown in Fig 4 10 The 458 Pulse Shape Analyzer PSA time wi
24. e jth photoetectron out of a total of R photoelectrons is given by the statistical order equation git 1 atri Dr 1 R The following analysis is based first order approximation of the pulse shape If more exact results are desired refer to the work of Kuchnir and Lynch Assuming effective exponential for the scintillation permits one to obtain a better understanding of how the three parameters affect the neutron gamma separation The mean time for the jth photoelectron is given by 1 in j R j T T F 2 where F is the ratio or the fraction The variance in time of the jth photoelectron is given by 1 s 3 k 0 10 The width of the time distribution varies directly with T and the photoelectron level j but inversely with R the total number of electrons Therefore as the fraction at which the time information is derived increases toward unity the separation of the neutron and gamma increases but the time resolution is poorer The object is to choose a photoelectron level that will minimize the overlap of rise time of the neutron and gamma ray signals Kuchnir and Lynch by using the measured distributions and a more general order equation predicted the optimum separation to exist when the fraction of pulse height used is between 0 8 and 0 9 The ORTEC 458 was designed to take advantage of the optimum trigger point Consider a
25. e switch selects either 1 Us delay in or prompt Out output of the unipolar signals INTEG 3 position switch selects integrate time constants of 0 04 0 1 and 0 25 Us 4 3 FRONT PANEL CONNECTORS All Type BNC INPUT Positive or negative with rise time 10 to 650 nsec decay time must be greater than 25 Us for proper pole zero cancellation Input impedance is 10000 dc coupled Maximum linear input signal is 3 3 V with a maximum limit of 20 V OUTPUTS Two BNC connectors with output impedance of lt 1Q Each output can Provide up to 10 V and is dc coupled and short circuit protected Unipolar The dc level is adjustable for offset to 51 0 V The unipolar pulse shape is determined by a 1 Us delay line Linear range is 0 to 10 V Bipolar Bipolar pulse is prompt with positive lobe leading and the Pulse is double delay line shaped Linear range is 0 to 10 V The crossover walk of this output is lt 2 5 nsec for 100 1 dynamic range 4 4 REAR PANEL CONNECTORS OUTPUTS The unipolar and bipolar pulses are brought to the rear panel on BNC connectors The specifications of these outputs are the same as those for the front panel connectors except that the output impedance is 930 at these connectors PREAMP POWER Standard power connector for mating with ORTEC preamplifiers 24 V and 12 V 4 5 OPERATION WITH SEMICONDUCTOR DETECTORS Calibration of Test Pulsor The ORTEC 419 Pulser or equivalent is easily calibrated so that th
26. easuring Resolution with a Pulse Height Analyzer Current Voltage Measurements for Silicon and Germanium Detectors The amplifier system is not directly involved in semiconductor detector current voltage measurements but the amplifier serves well to permit noise monitoring during the setup The detector noise measurement is a more sensitive method of determining the maximum detector voltage that should be used because the noise increases more rapidly than the reverse current at the onset of detector breakdown Make this measurement in the absence of a source Figure 4 6 shows the setup required for current voltage measurements The ORTEC 428 Bias Supply is used as the voltage source Bias voltage should be applied slowly and reduced when noise increases rapidly as a function of applied bias Figure 4 7 shows several typical current voltage curves for ORTEC silicon surface barrier detectors Whenitis possible to float the microammeter at the detector bias voltage the method of detector current measurement shown by the dashed lines in Fig 4 6 is preferable The detector is grounded as in normal operation and the microammeter is connected to the current monitoring jack on the 428 Detector Bias Supply DETECTOR Normal MICRO BYPASS ORTEC BA 030 007 300 ORTEC 025 050 100 ORTEC 025 100 100 ORTEC 030 200 100 045 450 100 Back Current 4A Bias Voltage Fig 4 7 Sili
27. ies and shunt termination where the cable impedance is matched both in series at the sending end and in shunt at the receiving end The most effective method is the combination but termination by this method reduces the amount of signal strength at the receiving end to 50 of that which is available in the sending instrument Touse shunt termination at the receiving end of the cable connect the 10 output of the sending device through 93O cable to the input of the receiving instrument Then use a BNC tee connector to accept both the interconnecting cable and a 1000 resistive terminator at the input connector of the receiving instrument Since the input impedance of the receiving instrument is normally 10000 or more the effective instrument input impedance with the 1000 terminator will be of the order of 930 and this correctly matches the cable impedance For series termination use the 930 output of the sending instrument for the cable connection Use 930 cable to interconnect this into the input of the receiving instrument The 10000 or more normal input impedance at the input connector represents an essentially open circuit and the series impedance in the sending instrument now provides the proper termination for the cable For the combination of series and shunt termination use the 93O output in the sending instrument for the cable connection and use 930 cable At the input for the receiving instrument use a BNC tee to accept
28. ig 1 1 Delay Line Clipping Without Pole Zero Cancellation T VE X Fig 1 2 Single Delay Line Shaped Pulse with Pole Zero Cancellation E FofTolEolt Tp 2 SPECIFICATIONS PERFORMANCE GAIN RANGE 7 position Coarse Gain selection from 10 through 1000 and single turn Fine Gain control from 0 3 through 1 total gain is the product of Coarse and Fine Gain settings SHAPING FILTER Front panel switch permits selection of integration time constant with T 0 04 0 1 or 0 25 15 40 100 or 250 nsec INTEGRAL NONLINEARITY lt 0 05 NOISE lt 20 UV rms referred to input using 0 25 Us Integrate and maximum Gain of 1000 lt 25 UV for Gain 50 lt 60 UV for Gain 10 1 TEMPERATURE STABILITY Gain 0 01 C 0 to 50 C DC Level lt 0 mV C 0 to 50 C CROSSOVER WALK For constant gain walk lt l nsec for 20 1 dynamic range x2 nsec for 50 1 lt 2 5 nsec for 100 1 Crossover shifts lt 4 nsec for any adjacent Coarse Gain switch settings COUNT RATE STABILITY A pulser peak at 8596 of analyzer range shifts less than 0 296 in the presence of 0 to 10 random counts sec from a 13705 source with its peak stored at 75 of analyzer range Checked in accordance with methods outlined IEEE Standards No 301 USAS N42 2 IEEE Transactions Vol NS 16 6 December 1969 OVERLOAD RECOVERY Bipolar recoversto within 296 of rated maximum output in less than
29. ing measurements using baseline crossover as the timing indication Double delay line shaping provides a precision time at the baseline crossover point that is independent of the pulse amplitude 1 3 POLE ZERO CANCELLATION Pole zero cancellation is a method for eliminating pulse undershoot after the first differentiating network The technique employed is described by referring to the waveforms and equations shown in Figs 1 1 and 1 2 In an amplifier not using pole zero cancellation the exponential tail on the preamplifier output signal usually 50 to 500 5 causes an undershoot whose peak amplitude is roughly undershoot amplitude differentiated pulse amplitude differentiation time preamplifier pulse decay time For a 1 differentiation on time and a 50 preamplifier pulse decay time the maximum undershoot is 2 and decays with a 50 Us time constant Under overload conditions this undershoot is often sufficiently large to saturate the amplifier during a considerable portion of the undershoot causing excessive dead time This effect can be reduced by increasing the preamplifier pulse decay time which generally reduces the counting rate capabilities of the preamplifier or compensating for the undershoot by using pole zero cancellation single delay line shaping differentiation is accomplished by subtracting a delayed replica of the signal as shown in Fig 1 1 The droop in the input signal during the delay
30. istors Q32 through Q35 Gain Stage A7 Q48 through Q59 accepts both the prompt and the delayed SDL pulses This stage operates in the differential mode providing an output that is the difference between the prompt and delayed inputs and this difference is the bipolar double delay shaped output pulse The gain of the stage is fixed at 2 5 the same as the gain for A6 and thus the overall gains for the two output shapes are equalized The output impedance 17 through the front panel connector is less than 10 It is isolated from the front panel test point by R209 The signal also passes through series resistor R210 for the 930 characteristic output impedance through the rear panel connector Coarse Gain factors of 10 through 1000 are obtained by various combinations of selected stage gains The selections in A2 A3 and A4 are shown in Table 5 1 together with the fixed gains in Al and in either A6 for unipolar outputs or in A7 for bipolar outputs Any of these selected gain factors is also subjected to the attenuation selected by the Fine Gain control A trim potentiometer R187 is provided on the printed circuit board for a calibration adjustment to balance the areas of positive and negative polarities in the bipolar output signals When these areas are equal the dc coupled output will provide a high counting rate without any baseline shift This potentiometer is factory adjusted and should not require any recalibration under
31. n is not observed Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product In addition the following symbol may appear on the product ATTENTION Refer to Manual DANGER High Voltage Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product SAFETY WARNINGS AND CLEANING INSTRUCTIONS DANGER Opening the cover of this instrument is likely to expose dangerous voltages Disconnect the instrument from all voltage sources while it is being opened WARNING Using this instrument in a manner not specified by the manufacturer may impair the protection provided by the instrument Cleaning Instructions To clean the instrument exterior Unplug the instrument from the ac power supply Remove loose dust on the outside of the instrument with a lint free cloth Remove remaining dirt with a lint free cloth dampened in a general purpose detergent and water solution Do not use abrasive cleaners CAUTION To prevent moisture inside of the instrument during external cleaning use only enough liquid to dampen the cloth or applicator Allow the instrument to dry completely before reconnecting it to the power source ER 27771 ey e on O AMPLIFIER FIME GAIN g DELAY IN COARSE GAIN 199 200 OUT ELA PREAMF
32. ndow is set on the gamma peak and above any extraneous peaks in the time spectrum caused by amplitude saturation of the main amplifier A UL logic pulse is generated for all events with rise times greater than the UL control setting PULSE SHAPE ANALYZER OUTPUT GAMMA ROUTING NEUTRONS 5 ENERGY SIGNAL 200571 Fig 4 10 Block Diagram for a Typical Neutron Gamma Separation Experiment 12 NEUTRON GAMMA DISCRIMINATION EXPERIMENT NEUTRON ENERGY 3 0 5 MeV GAMMA ENERGY 600 COUNT RATE 25 000 cts sec _ GAMMA NEUTRON 03 Fig 4 11 Neutron Gamma Rise Time Spectrum Figure 4 11 is a typical spectrum of the 458 output with a plutonium beryllium source 4 7 NEUTRON GAMMA RAY DISCRIMINATION IN PROPORTIONAL COUNTERS Gamma ray discrimination proton recoil proportional counters has been accomplished by several experimenters Recently Obu reported excellent separation of neutrons and gammas at energies of 10 keV and lower The basic principle is that the proton recoils from the neutrons produce a very short ionization path whereas the electrons produced by the gammas will occur over a relatively long path in the chamber Thus the rise time associated with the neutrons will be less than and also better defined than the rise time of the gamma event This is illustrated in Fig 4 12 The suggested block diagram for the proportional counter system for
33. neutron gamma discrimination is shown in Fig 4 13 The 460 delay line shaped amplifier should have 2 Us shaped line for optimum performance The Lower Level control of the window should be set just below the peak corresponding to the neutron rise time see Fig 4 12 and the UL control should be set just above the neutron peak The majority of the events causing a window output will correspond to neutrons and the events causing a UL output will correspond to gamma rays 13 NEUTRON EVENT Pai GAMMA RAY EVENT NUMBER OF EVENTS 7 20057 290874 04 1 0 20 RISE TIME usec Fig 4 12 A Typical Neutron and Gamma Rise Time Spectrum from a Proton Recoil Proportional Counter 4 8 OTHER EXPERIMENTS Block diagrams illustrating how the 460 and other ORTEC 400 Series module can be used in experimental setups are given in Figs 4 14 4 17 ORTEC SCINTIL LATION PREAMP ORTEC OATEC TSC ANALYZER AMPLIFIER P M BASE TUBE ORTEC LINEAR GATE ORTEC CFT DISCRIMI NATOR 77 Ge Li DRIFTED DETECTOR GENERATOR ORTEC TIMING FILTER AMPLIFIER ORTEC ORTEC TIMING DELAY FILTER AMPLIFIER AMPLIFIER AMPLIFIER 200329 Fig 4 14 Gamma Gamma Coincidence Experiment ORTEC 459 HIGH VOLTAGE POWER SUPPLY PROPOR TIONAL COUNTER ORTEC ORTEC 109 460 PREAMP AMPLIFIER ORTEC TIME P
34. normal conditions Both of the output circuits are protected against shorts For the unipolar output the protection is furnished by 046 and 047 and for the bipolar output it is furnished by Q58 and Q59 Table 5 1 Coarse Gain Factors 10 2 1 2 1 2 5 20 2 1 4 1 2 5 50 2 5 2 1 2 5 100 2 5 4 1 2 5 200 2 5 8 1 2 5 500 2 5 8 25 2 5 1000 2 5 8 5 2 5 6 6 1 TEST EQUIPMENT REQUIRED In order to adequately test the specifications of the ORTEC 460 the following equipment should be utilized 419 Precision Pulse Generator Tektronix Model 547 Series Oscilloscope with a Type plug in or equivalent Hewlett Packard 400D RMS Voltmeter 6 2 PULSER MODIFICATIONS FOR OVERLOAD TESTS The 460 incorporates variable pole zero cancellation factory adjusted to approximately 50 Us Therefore when either the ORTEC 419 or 204 Pulse Generator is used to check overload it should be connected as shown in Fig 6 1 and the pole zero cancellation adjusted to compensate for the fall time of the pulse generator ORTEC PULSE GENERATOR 1002 DIRECT OUTPUT FOR RC 50 usec C 05 F AMPLIFIER OUTPUTS BIPOLAR UNIPOLAR Fig 6 1 Pulse Generator Modifications If the pulser output is fed into a charge sensitive preamplifier such as the ORTEC 109A 120 124 or 125 through a small capacitor to simulate the output of a semiconductor detector the decay time of the pulser will cause an additional p
35. oise Referred to Input u V 100414 Fig 4 3 Noise as a Function of Gain and Integrating Time Constant in the ORTEC 460 Delay Line Amplifier Detector Noise Resolution Measurements The same measurement just described can be made with a biased detector instead of the external capacitor used to simulate the detector capacitance The resolution spread will be larger because the detector contributes both noise and capacitance to the input The detector noise resolution spread can be isolated from the amplifier noise spread if the detector capacity is known since where Nota is the total resolution spread and Nin is the amplifier resolution spread with the detector replaced by its equivalent capacitance The detector noise tends to increase with bias voltage but the detector capacitance decreases thus reducing the resolution spread The overall resolution spread will depend upon which effect is dominant Figure 4 4 shows curves of typical total noise resolution spread versus bias voltage using ORTEC BA 030 007 300 025 050 100 ORTEC 025 100 100 ORTEC BA 030 200 100 ORTEC 045 450 100 RMS Noise 100159 9 25 50 75 100 125 Bias Voltage Fig 4 4 Noise as a Function of Bias Voltage the data from several ORTEC silicon surface barrier semiconductor radiation detectors BIAS VOLTAGE Amplifier Noise and Resolution Measurements Using a Pulse Height An
36. ole in the transform equation of the preamplifier output This additional pole will degrade any overload measurements In order to eliminate the pole the pulser must be pole zero canceled as shown in Fig 6 2 6 3 PULSER TEST PULSE GENERATOR CHARGE SENSITIVE PREAMPLIFIER 4 Le T 200312 Fig 6 2 Pole Zero Cancellation of a Pulser Output Functional Checks Before making functional checks of the 460 set the controls as follows Coarse Gain 1K Fine Gain 1 Input Polarity Pos Integ Time Constant 0 04 Delay Out 1 Connect a positive pulser to the 460 as shown in Fig 6 1 and adjust the pulser to obtain 10 V at the 460 Unipolar Output This should require an input pulse of 10 mV The Bipolar Output should also be 10 V 2 Place the Delay switch to the In position The Unipolar pulse should be delayed 1 is from its original position Return the Delay switch to Out 3 Change the Input Polarity switch to Neg and then back to Pos while monitoring the outputs for a polarity inversion 4 Monitor the Unipolar Output dc level and ensure that the output will vary at least 1 0 V with the DC Adj Reset to zero volts See IEEE Standards No 301 USAS N42 2 IEEE Trans Vol NS 16 6 December 1969 5 Obtain 10 V output with maximum gain Decrease the Coarse Gain switch stepwise from 1 K to 10 and ensure that the output amplitude changes by an appropriate amount Return
37. or A2 and 4 VE Unipolar e Output Bipolar Output Js Fig 5 1 Block Diagram of 460 Delay Line Amplifier A Fine Gain control R60 is used between 2 A3 as a continuously variable attenuator with a range of 0 3 through 1 A selectable Integration time constant uses switch S4 resistors R84 and R85 and capacitors C24 and C25 to determine the rise time for an input pulse The effect of the integration is applied between A3 and A4 The single delay line shaped pulse from A4 is furnished directly to one input of A7 to Delay Line DL2 and to the Out position of the rear panel Delay switch S3 If switch S3 is set at Out the prompt SDL pulse is furnished to A6 If switch S3 is set at In the same SDL pulse is furnished into A6 after the 1 Us delay in 012 Gain stage A6 includes Q36 through 045 This stage has a fixed gain of 2 5 and furnishes the unipolar output through both the front and rear panel connectors The output impedance through the front panel connector is less than 10 The signal passes through series resistor R198 for the 930 characteristic output impedance through the rear panel connector test point on the front panel connector A test point on the front panel is isolated by R197 The output of A6 is fed back through A5 to be used as a differential input to This circuit seeks the adjusted dc level set by R118 as the quiescent unipolar output level Stage A5 uses trans
38. ors with significantly different decay characteristics The 10 to 90 rise time f of the integrated light from the scintillators is approximately 130 nsec when excited with neutrons and approximately 10 nsec when excited with gamma rays The scintillation is not a simple exponential as is illustrated by Kuchnir and Lynch but consists of a combination of at least four components as illustrated by their results shown in Table 4 1 Nuclear Enterprises Ltd San Carlos California 3See References at the end of this section Table 4 1 Photoelectrons per keV Energy Loss Scintillator Stilbene 0 1 405 33 270 2 3 213 1 66 316 323 270 17 NE 213M 1 34 5 41 30 5 285 19 NE 218 1 76 358 365 288 20 Anthracene 36 Nal TI 8 8 3 For energy transfer from solvent to solute First 3 components by the light output in organic scintillators CRepresents loss in the scintillator whan coupled to an RCA 8575 photomultiplier with good light collection Three parameters determine the ability to distinguish between gammas and neutrons the total number H of photoelectrons produced at the cathode for a given energy of excitation the shape f t of the light scintillation for both neutrons and gammas and the photoelectron level j at which the pulse shape information is deduced If one assumes that the neutron and gamma can be characterized with an effective single decay time the probability distribution function for th
39. pled or have approximately zero dc voltage under no signal conditions The 460 incorporates Pole zero cancellation in order to enhance the overload characteristics of the amplifier This technique requires matching the network to the preamplifier decay time constant in order to achieve perfect compensation The network is variable and factory adjusted to 50 us to approximately match all ORTEC FET preamplifiers If other preamplifiers or more careful matching is desired the adjustment is accessible from the front panel Adjustment is easily accomplished by using a monoenergetic source and observing the amplifier baseline with an oscilloscope after each pulse under overload conditions Adjustment should be made so that the pulse returns to the baseline in a minimum of time with no undershoot Preamplifier power of 24 V 12 V 24 V and 12 V is available on the preamplifier power connector When using the 460 with a remotely located preamplifier i e preamplifier to amplifier connection through 25 ft or more of coaxial cable care must be taken to ensure that the characteristic impedance of the transmission line from the preamplifier output to the 460 input is matched Since the input impedance of the 460 is 1000Q sending end termination will normally be preferred i e the transmission line should be series terminated at the output of the preamplifier All ORTEC preamplifiers contain series terminations that are either 93O or varia
40. rwell December 14 1962 International Atomic Energy Agency Vienna 1963 5 Sayres and M Coppola He Neutron Spectrometer Using Pulse Risetime Discrimination Rev Sci Inst 35 4 431 1964 6 J M Cuttler 5 Greenberger and S Shaley Pulse Risetime Discrimination for He Counters Nucl Instr Methods 75 309 11 1969 7 G R Ricker Jr Pulse Risetimes in Proportional Counters Rev Sci Instr 40 2 227 1969 8 E Mathieson and T J Harris Pulse Shape Discrimination in Proportional Counters Theory of Electronic System Nucl Instr Methods 88 181 92 1970 9 M T Ichimori and Shirakata Gamma Ray Discrimination in a Proton Recoil Spectrometer for a Fast Reactor Spectrum Measurement Nucl Instr Methods 89 131 39 1970 LINEAR GATE IGATED BIASED PULSE HEIGHT 16 5 CIRCUIT DESCRIPTION Figure 5 1 is a block diagram for the ORTEC 460 Delay Line Amplifier In this diagram the circuits are divided into 7 functional groups and the transistors that comprise each group are defined Use this figure and the schematic 460 0101 51 at the back of the manual to aid in understanding the circuits The 460 consists of five gain stages Al through A4 are all in series The output from A4 is processed through A6 for a unipolar output and through A7 for a bipolar output The function of A5 is to maintain a quiescent adjusted dc level for the unipolar output
41. s a stringent set of quality control tests designed to expose any flaws in materials or workmanship Permanent records of these tests are maintained for use in warranty repair and as a source of statistical information for design improvements Repair Service If it becomes necessary to return this instrument for repair it is essential that Customer Services be contacted in advance of its return so that a Return Authorization Number can be assigned to the unit Also ORTEC must be informed either in writing by telephone 865 482 4411 or by facsimile transmission 865 483 2133 of the nature of the fault of the instrument being returned and of the model serial and revision Rev on rear panel numbers Failure to do so may cause unnecessary delays in getting the unit repaired The ORTEC standard procedure requires that instruments returned for repair pass the same quality control tests that are used for new production instruments Instruments that are returned should be packed so that they will withstand normal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the designated ORTEC repair center The address label and the package should include the Return Authorization Number assigned Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the sender s expense and it will be the sender s responsibility to make claim with the shipper Instruments not in warranty
42. s and are presented here to illustrate the effect of various parameters on the neutron gamma separation pas Gammas Neutrons Counts Channel Gammas Neutrons Counts Channel Fig 4 8 Calculated Response for a 100 keV and b 7 keV Electron Equivalent Energies Deposited in NE 213 11 Proper Application of the 458 and 460 The 458 Pulse Shape Analyzer measures the 90 10 fall time of the linear signal presented to its input To obtain the best time resolution use the fast unipolar delay line shaped output from the 460 The rise time of the unipolar delay line shaped pulse should not be greater than 100 nsec for best results and the amplifier should have low noise characteristics and be operated at low gain Figure 4 9 shows the process by which a delay line shaped pulse is produced Notice that the time information is inverted in the process of producing the trailing edge of the pulse The time information that occurs at the 1096 point on the input signal occurs at the 9096 level on the trailing edge and the time information occurring at the 90 level on the input signal is transformed to the 10 level on the trailing edge Input To Main Amplifier Delayed and Inverted Signal OL Shaped Signal Out of Main Amp Fig 4 9 Single Delay Line Shaped Signal Consider the effect of amplifier noise on the neutron gamma separation for a wide dynamic range of operation Assume the following amplifier nois
43. should follow the same procedure and ORTEC will provide a quotation Damage in Transit Shipments should be examined immediately upon receipt for evidence of external or concealed damage The carrier making delivery should be notified immediately of any such damage since the carrier is normally liable for damage in shipment Packing materials waybills and other such documentation should be preserved in order to establish claims After such notification to the carrier please notify ORTEC of the circumstances so that assistance can be provided in making damage claims and in providing replacement equipment if necessary Copyright 2002 Advanced Measurement Technology Inc rights reserved is a registered trademark of Advanced Measurement Technology Inc All other trademarks used herein are the property of their respective owners CONTENTS WARRANT Y sexe REX ii SAFETY INSTRUCTIONS AND SYMBOLS 4 iv SAFETY WARNINGS AND CLEANING INSTRUCTIONS qk DESCRIPTION e A A ee eR e I au eg 1 T4 GENERAL ath ath 1 1 22 DUAE OUTPUTS gic 222 t het atta 1 1 3 POLE ZERO
44. t the amplifier output 2 Turn on the ORTEC 419 Precision Pulse Generator and adjust the pulser output to any convenient readable voltage E as determined by the oscilloscope The full width at half maximum FWHM resolution spread due to amplifier noise is then FWHM 2 88 Erms diat gms o where Eja is the pulser dial reading in MeV and 2 66 is the factor for rms to FWHM 2 34 and noise to rms meter correction 1 13 for average indicating voltmeters such as the Hewlett Packard 400D A true rms voltmeter does not require the latter correction factor ORTEC OSCILLO SCOPE RMS VOLTMETER Fig 4 2 System for Measuring Amplifier and Detector Noise Resolution PREAMP AMPLIFIER DETECTOR OR Ter ORTEC PULSE GENERATOR if 100161 Figure 4 3 shows the amplifier noise generated by the 460 It is a function of both the integrating time constant and of the gain setting The portion of the curves between a gain of 3 3 and a gain of 10 reflects variations in settings of the Fine Gain control while the Coarse Gain is set at 10 All of the remaining portions of the curves reflect the Coarse Gain switch while the Fine Gain control remains at maximum Wherever possible the Fine Gain control should be set within the upper portion of its range in order to minimize the amplifier noise Fine Gain agend O Unipolar Output Bipolar Output RMS N
45. time makes this subtraction imperfect and a long under shoot is produced A pole zero cancellation eliminates this undershoot by adjusting the amplitude of the delayed signal as shown in Fig 1 2 Total preamplifier amplifier pole zero cancellation requires that the preamplifier output pulse decay time be a single exponential decay and matched to the pole zero cancellation network The variable pole zero cancellation network allows accurate cancellation for all preamplifiers having decay times of 25 Us or greater The network is factory adjusted to 50 Us which is compatible with all ORTEC FET preamplifiers Improper matching of the pole zero cancellation network will degrade the overload performance and cause excessive pileup distortion at medium counting rates Improper matching causes either an under compensation undershoot is not eliminated or over compensation output after the main pulse does not return to the baseline and decays to the baseline with the preamplifier time constant The pole zero adjust is accessible from the front panel of the 460 and can easily be adjusted by observing the baseline with an oscilloscope while a monoenergetic source or pulser having the same decay time as the preamplifier under overload conditions is being used The adjustment should be made so that the pulse returns to the baseline in the minimum time with no undershoot Egll Emax 627 E gt 7 Eglt Tp F
46. typical example where Eqs 2 and 3 can be used to predict the separation of neutrons and gamma rays Assume the following experimental conditions 1 The neutron pulse height is equal to the gamma ray pulse height equivalent of 100 keV electron energy or 500 keV neutrons 2 The scintillator is 213 on an RCA 8575 photo multiplier producing 1 7 photoelectrons keV of electron energy 3 The effective decay of NE 213 is 130 nsec for neutrons and 10 nsec for gamma rays The variance for the neutron rise time is calculated by 2 g 2 2 n 910 090 0090 1 2 4 H K In Eq 4 Ris 1 7 x 100 keV 170 j 0 9 x 170 or 152 i 7 amp 56 x 1077 5 0 Substituting the values of R Eq 4 yields o 56 x 10 80 61 a 56x10 x 022 122 At 235 x 12 2 20 nsec FWHM 1 2 z k 0 0 7 45x10 x 0 22 0 95 ds 4 5 x 109 At 0 95 x 2 35 225 nsec FWHM The mean separation would be a ty 120 nsec The calculated results are shown in Fig 4 8a with the shapes assumed to be approximately Gaussian Figure 4 8b illustrates what happens to the ability to separate the neutrons and gamma rays at approximately 350 keV neutron energy or 70 keV equivalent electron energy The assumptions used to obtain Eqs 1 and 2 are representative of first order approximation
47. y to the amplifier input the PZ Adj should be adjusted if overload tests are to be made other tests are not affected See Section 6 2 for the details If a preamplifier is used and a tail pulser is connected to the preamplifier test pulse input similar precautions are necessary In this case the effect of the pulser decay must be removed i e a step input should be simulated Details for this modification are also given in Section 6 2 3 4 CONNECTION TO POWER Turn off the Bin Power Supply when inserting or removing modules The ORTEC NIM modules are designed so that it is not possible to overload the Bin Power Supply with a full complement of modules in the Bin Since however this may not be true when the Bin contains modules other than those of ORTEC design check the Power Supply after inserting the modules The 4001 4002 has test points on the Power Supply control panel for monitoring the dc voltages 3 5 SHAPING CONSIDERATIONS The rise time of the output pulses from the 460 will be a function of the rise time furnished from the preamplifier and of the setting of the front panel Integ switch When the switch is set at 0 04 Us the rise time for a step input from the preamplifier will be less than 100 nsec The 0 1 and 0 25 Us switch settings will provide proportionately longer rise times Check the input specifications for the instrument into which the 460 output pulses will be furnished and set the Integ switch at the
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