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Nuclear Handbook - Berkeley Nucleonics Corporation

1. 19 1 15 2 Dead Layas ico pb Duende egi DET utes 19 1 15 3 Window 6 20 13 6 s DE ru ga ERE ea EPA 20 1 16 1 Preamplifier 21 1 17 Maximum Count Rate Determination 22 1 18 High Count Rate 22 T18 T Noise Effects s cte te e Ree RAO S RERO 23 1 18 2 Gated Integrator with TR 14 24 1 19 MICrOphORIGS nuire 25 1 20 Pulse Processing Electronics and Software 25 1 24 GtyOSLats peo x vesci 25 1 22 Detector Cool Down 27 POIPIOdUCIS oos dae 28 2 1 4422 4225 5 ihi fda EY hs 28 2 2 Ordering 28 2 2 1 Sample Order 28 2 3 Limited Liability Warranty 28 2 4 Selecting a Detector 29 2 5 Detector Specifications
2. LED nats Schmitt 9 inhibit Trigger ot pulse FET o HV output Crystal 77777 77777 Figure 1 18 Pulsed optical reset preamplifier The PGT TR 14 Transistor Reset Preamplifier p and n type is used with coaxial or large area planar detectors for gamma ray and high energy X ray applications The preamplifier shown in Figure 1 19 is designed for high energy rate applications with a maximum gt 800 000 sec In this type of preamplifier the charge accumulating on the feedback capacitor is periodically discharged through a suitably located transistor V Logic gt control 77777 Crystal C gt Figure 1 19 Transistor reset preamplifiers The PGT TR 1 Transistor Reset Preamplifier is used with low noise high resolution X ray detectors and incorpo rates a low capacitance FET with built in reset circuitry for optimum noise performance The PGT TR 14 p and n type Transistor Reset Preampli fier Figure 1 19 is designed for high energy rate applica tions with a maximum gt 800 000 MeV sec In this type of preamplifier the charge accumulating on the feedback capacitor is periodically discharged through a suitably located transistor 1 16 1 Preamplifier Characteristics A preamplifier may be characterized by its maximum count rate for a given energy range its max
3. 1 30 2 5 1 Duo 30 2 5 2 JT Cool Mechanically Cooled 32 2 5 3 High Purity Germanium Coaxial 33 2 5 4 N type Coaxial HPGe Extended Range Detectors 35 2 5 5 High Purity Germanium Well 37 2 5 6 High Purity Germanium Planar 39 2 5 7 N Type HPGe Planar Detectors 41 2 5 8 X ray Detectors 42 2 5 9 Sahara Silicon Drift 44 2 6 Endcap and Window Materials 46 2 7 GryOSIals utu dup eee Pee wea I IUE NW EIE is 47 2 7 1 Dipstick Cryostats 47 2 7 2 Unitary 48 2 7 3 Portable 51 2 7 4 Liquid Nitrogen Handling 53 2 8 Mechanical 55 2 8 1 11 000 26 55 2 9 Radiation 57 2 9 1 Model MPS 5 Radiation Shields 59 2 10 Low Background Materials
4. 60 2 11 Electronic Components for Gamma Spectroscopy with HPGe Detectors 406 Sa e s ee dw a 61 2 11 1 61 2 12 Nal Tl 63 2 13 Quadratic Compression Conversion The New Way Do Nal Gamma Spectroscopy 64 2 13 1 MCA 2100R Multichannel Pulse Height Analyzer 65 2 13 2 MCA 4000 Multichannel 67 2 13 3 System 4000 X Ray Spectrometer 69 2 13 4 MCA 8000 Multichannel Analyzer 72 2 13 5 System 8000 Gamma or X Ray 74 2 13 6 Quantum MCA Software for Windows 77 Appendix 1 Radionuclides for Energy Resolution 81 Appendix 2 Radionuclides for Marinelli Beaker Standard Sources 55 82 Appendix 3 Major y and X ray Lines for Various Radionuclides 83 Appendix 4 X ray Critical Absorption and Emission Energies in keV 87 Appendix 5 Glossary c Corp RUE 89 This page intentionally blank PRINCETON About Princeton Gamma Tech Princeton Gamma Tech founded in 1965 is an interna tional suppli
5. Figure 1 8 Determination of peak area 1 5 3 Quantitative Measurements Quantitative analysis determines the area of a peak peak integral in counts attributable to the nuclide in question In Figure 1 8 the background under the peak is assumed to be linear as shown by the shaded trapezoid The left and right sides of the peak are commonly defined by the full width half maximum FWHM of the full peak height or some multiple of it To relate the net counts in the peak A to the activity of the nuclide the detector efficiency must be known see Detec tor Efficiency on page 10 along with the half life and the branching ratio yield of the source An intensity calibration must also be carried out first The activity in microCuries uCi is given by time efficiency yield 3 7 107 Minimum Detectable Activity MDA is the activity when A lower detectability limit In addition for true quantitative analysis of spectra the col lection time must be known While the MCA is analyzing one pulse it cannot accept any new pulses for analysis This down time interval is known as dead time com pensate for dead time the actual analysis time is extended The MCA timer is turned off during dead time and is turned on again as soon as the pulse has been pro cessed and stored The sum of these times is the live time or the total time that the syste
6. 1 dewar 25598 Figure 1 13 Marinelli beaker configuration Sample tube LONG gate wire Sample outside inside well Blind Hole Well SHORT FET gatewire Through Hole Well Figure 1 14 Comparison of blind hole and through hole well detector design 1 7 1 6 Efficiency and Design of Well Detectors The usual well detector is a coaxial germanium crystal with a re entrant cavity well in the endcap that extends into the central hole within the detector element The sample holder is inserted into the well and the source is essentially sur rounded by active germanium As a result the well detec tor typically has a very high absolute efficiency With a high absolute efficiency the proportion of sum peaks also becomes relatively high A sum peak occurs when two gamma rays are coincident on the detector and the sum of their energies appears as a peak in the spec trum Standard sources specified by ANSI IEEE 325 1996 to measure the efficiency of a well detector are point sources lt 2 mm maximum diameter located 1 cm from the bottom of the sample hole One of the most commonly used standards is 90 When the 1173 2 keV line is coin cident with the 1332 5 keV line a sum peak appears at 2505 7 keV The true number of 1332 5 keV photons is therefore the count in the full energy peak
7. is emitted Figure 1 1 Schematic representation of gamma and X ray generation with a Bohr model of the atom The atomic number Z the number of protons in the nucleus determines the element The mass number A is the total number of protons and neutrons in the nucleus Protons and neutrons have nearly the same mass and contribute almost the entire mass of an atom Atoms hav ing the same atomic number but a different mass number are called isotopes In radioisotopes the proton neutron ratio is unstable and a stable configuration is achieved by emitting particle s gamma rays or both Radioactivity or the rate of decay of such a radioisotope is expressed as the number of disintegrations per second or the rate of change of the number of nuclei N with time EE N where decay constant 0 693 5 The decay constant is specific for each radioisotope and represents the probability of decay in the next second The half life To 5 is the time required for half the current num ber of atoms to decay The number of radioactive nuclides remaining after time t is then given by the equa tion N Noe Radiation may then react with matter to produce positively and negatively charged particles called ion pairs The three types of ionizing radiation are Photons gamma rays and X rays Charged particles protons electrons and alpha ticles Neutrons indirect ionizations
8. 21 3 25 Hel 3 724 MEA OBL Aged 4412 E FRE Figure 2 2 Representative spectra obtained from Eu with the Duo Detector The upper spectrum from the planar detector shows the 122 keV line Logarithmic display MDA 0 21 The lower spectrum is from the coaxial detector Linear display MDA 0 18 for the 688 keV line 31 2 5 2 JT Cool Mechanically Cooled Spec trometer PGT was the first manufacturer to link a mechanical cooler to an HPGe detector for continuous long term gamma ray spectroscopy without the inconvenience of maintaining liq uid nitrogen supplies PGT s first mechanical cooler the LAB COOLER has been in operation around the world for over eight years PGT now offers the JT COOL a compact system in which the compressor can be remote from the coldfinger and endcap In lung monitoring applications for example this means that there are no bulky LN dewars in the counting room This feature combined with the the five year mainte nance free operation makes the JT COOL an efficient alternative to systems cooled using LN Features Closed cycle cooler includes an air cooled compres sor and proprietary refrigerant mixture Lightweight compressor has smaller footprint than other mechanical coolers Flexible gas lines between the detector and the com pressor permit use of the detector in one room with the compressor in another Detec
9. 1 8 1 5 3 Quantitative 8 1 6 Timing and Coincidence Measurements 9 1 7 Detector Selection 10 1 7 1 Detector 10 1 7 1 1 Counting 10 1 7 1 2 Absolute 10 1 7 1 3 Relative Efficiency 10 1 721 4 intrinsic Efficiency 10 1 7 1 5 Efficiency of Marinelli Beakers 11 1 7 1 6 Efficiency and Design of Well Detectors 13 1 7 2 Detector Resolution and 14 1 8 Peak to Compton 14 1 9 System Noise and Microphonics 14 TICE Rango estansa rer natos Male has esate T PER 14 1 11 High Count 14 1 12 Window and Endcap 15 1 13 Low Background Spectroscopy 15 1 14 Crystal Types and 19 1 15 Crystal 1 19 1 15 1 Crystal
10. SP 22 entrance window well insert 4096 graphite dpm disintegrations minute typical 2 11 Electronic Components for Gamma Spectroscopy with HPGe Detectors The preamplifier and FET are the first in a series of elec tronic components required to convert the signal induced in the detector crystal to meaningful data 2 11 1 Preamplifiers PGT manufactures resistive feedback pulsed optical feed back and transistor reset preamplifiers The choice is usu ally based upon the count rate of the intended application The Model 352 low power preamplifier is available as an option For a resistive feedback preamp use of a lower value feed back resistor can yield a higher maximum energy rate but with a loss in resolution For higher count rates it is better to use either a pulsed optical or transistor reset system Some representative maximum energy rate products for various PGT detectors are shown in the following table Energy rate products refer to the total spectrum Note that count rate is also limited by the amplifier selected peaking time Options External configuration In line configuration Miniaturized versions for special applications While an in line preamp may fit into a smaller opening in shield or better meet other space requirements the exter nal preamp is out of direct line with the detector and there fore contributes less background radiation Pd m
11. Specifications for standard IGC Series models are shown on the next page For other efficiencies different cryostats or options please contact PGT lithium diffusion layer typically 0 5 mm p type crystal Center core with p contact XL passivated surface Figure 2 4 P type HPGe Coaxial Detector Options Cryostat configurations to meet your needs Portable systems JT Cool mechanical cooler Ultra low microphonic QUIET ONE crystal mounting Low background materials Transistor reset preamplifiers Low power preamplifier Typical Applications Nuclear spectroscopy over the energy range of 40 keV to 10 MeV 100 70 50 30 20 Intrinsic Efficiency o Representative efficiency curve for a 20 p type coaxial germanium detector with an aluminum 2 endcap 1 12 2 10 30 50 100 300 500 1000 2000 Energy keV 33 34 Resolution FWHM Relative Peak Peak shape Model Number Efficiency 122 keV 1 33 MeV Compton FWTM FWHM eV keV IGC10175 1096 800 1 75 42 1 1 90 IGC10185 1096 850 1 85 39 1 1 95 IGC10200 1096 900 2 00 37 1 2 00 IGC15180 1596 800 1 80 47 1 1 90 IGC15190 1596 900 1 90 45 1 1 95 IGC15200 1596 950 2 00 42 1 2 00 IGC20180 20 825 1 80 52 1 1 90 IGC20190 20 900 1 90 49 1 1 95 IGC
12. 10 division Rear panel controls and connectors Power switch SHV female connector for detector bias 2 5mm power jack Fuse housing 9 pin D female preamp power conn 12V 24 HV shutdown GND 9 pin D male RS232 connector 15 pin D female pulse reset preamplifier interface 44 D female connector for multiple ROI output and aux I O RJ 11 connectors for RS485 Pole zero adjustment on off Pole zero oscilloscope monitor switch One potentiometer for PZ adjustment of each shaping time 3 total Input from detector preamplifier BNC Differential input from detector preamplifier BNC Amplifier output BNC ADC input BNC 0 10V unipolar or bipolar pulse ADC gate input BNC coin anti coin off CMOS TTL Pile up reject input BNC CMOS TTL Amp busy input for ext amp live time corr BNC CMOS TTL SCA output CMOS TTL Peak detect output BNC CMOS TTL ADC busy out BNC CMOS TTL External input for alarm and or auto shutdown CMOS TTL Weight 7 25 Ib 3 30kg Dimensions 10 5 in 26 7cm wide 12 5 in 31 8 deep 4 5 in 11 5cm tall Power requirements 10 18 VDC 18 watts external 12V universal AC supply provided Software 32 bit QuantumMCA compatible with Windows 95 98 NT 2000 XP Accessories QuantumGold software for quantitative analysis High purity germanium detectors LN fill system Selection of signal interface and detector bias cables 71 2 13
13. 5 9 e quu RO Externally mounted preamplifier Detector Preamp Maximum ee product IGC NIGC RG 11 70 NIGC PO 14B 250 IGP 500 mm RG 11 6 IGP gt 500 mm RG 11 12 IGP 2500 mm TR 14 400 standard 1000 optional Si Li IGX TR 1 200 Table 2 16 Maximum Energy Rates 61 62 11 352 14 TR 14 TR 1 Charge Sensitivity nomi 100 100 50 50 0 01 nal mV MeV Input Open Loop Gain 20 000 20 000 20 000 20 000 20 000 Input Pulse Polarity Output Impedance 930 930 500 500 500 Maximum Cable Length 30 6 30 30 30 m Integral Nonlinearity lt 0 05 lt 0 05 lt 0 05 lt 0 05 lt 0 05 Decay Time Constant 100us 200us Energy Rate Product 60 000 20 000 200 000 800 000 200 000 MeV sec Isolation VDC gt 5000 gt 5 000 gt 5 000 gt 5 000 gt 5 000 Power Requirements V 12 24 12 12 24 12 24 24 Connectors Input Hard wired Hard wired Hard wired Hard wired Hard wired Detector Bias SHV SHV SHV SHV using one 13 Timing Output BNC BNC CES zum pin connector Signal Output BNC BNC BNC BNC Test Pulse BNC BNC BNC BNC Inhibit Signal 9 Amphenol 9 Amphenol 9 Amphenol 9 Pin Amphenol Nominal Current Usage at 24V 12V 24V 12V 37 mA 6 4 mA 14 8 mA 3 8 mA 10 4 mA 3 7 mA 10 4 mA 3 7 mA 27 5 mA f 20 0 mA t 20 8
14. also the fewer counts per channel Using too many chan nels may produce a broad poorly defined peak Commonly used spectrum sizes are 4096 8192 or 16 384 channels 1 5 1 Peak Location Peak location can be done by looking for differences in successive channels that define a more or less Gaussian shape With a poorly defined low peak on a background this may be difficult to identify More commonly first or sec ond order or higher derivatives of the spectrum curves are used Since the spectrum is actually a histogram the curve is approximated from the gradient of adjacent channels The curve is smoothed by taking into account several channels at a time to eliminate some of the statistical scat ter The first derivative of the resulting curve changes sign at the centroid of a peak while the second derivative shows a minimum at the centroid Peaks may also be located by cross correlation with a search function such as a derivative of a Gaussian distri bution The spectrum data is digitally filtered to define a point in the peak with the background eliminated After a potential peak has been found its acceptability is determined by applying a threshold parameter to eliminate spurious peaks while ensuring that small real peaks are recognized The analytical software uses some multiple of the standard deviation to give the desired confidence level 1 5 2 Peak Measurement Once a peak has been located its energy is established by
15. beta 369 days Daughter 106p beta 30 4 seconds 0 512 20 6 0 616 0 7 0 622 9 9 0 874 0 4 1 050 1 5 1 128 0 4 1 562 0 2 Sodium Na b 2 60 years 0 511 Annihilation 1 275 99 95 Technetium 9 Tc beta 2 13 105 years 0 089 6x101 Thallium 201 electron capture 73 1 hours 0 035 0 22 0 032 0 22 0 135 2 65 0 166 0 16 0 167 10 0 0 068 0 082 Hg K X rays 95 Thorium 228Th alpha 1 913 years 0 085 1 6 0 132 0 19 0 167 0 12 0 216 0 29 Uranium 2380 alpha 4 49x10 years 0 048 6 Daughter 234TH beta 24 1 days 0 030 0 063 5 7 0 092 3 2 0 093 3 6 beta i 0 043 234 1 17 minutes Daughter Pa 0 767 0 2 0 810 0 5 beta 6 70 hours 1 001 0 6 Daughter 284 beta 0 053 0 19 Daughter 2340 y Xenon 133 beta 5 25 days 0 080 0 4 0 081 36 6 0 030 0 036 Cs K X rays 46 Zinc Zn Bt 243 8 days 0 345 electron capture 0 511 Annihilation 1 115 50 7 0 008 0 009 Cu K X rays 38 Zirconium 957 beta 64 0 days 0 724 44 5 0 757 54 6 86 6 hours 0 235 0 2 Daughter 95mwp 18 Appendix 4 X ray Critical Absorption and Emission Energies keV Element Kal 2 2 Kap Lol Lo LB1 Lp2 Lyi Liab Litab Liab Hydrogen 0 014 2 He Helium 0 025 3 Li Lithium 0 052 0 055 0 003 0 003 4 Be Beryllium 0 110 0 112 0 002 0 002 5B Boron 0 185 0 192 0 003 0 003 6C Carbon 0 27
16. correlating its centroid with the channel energy To do this a calibration spectrum is obtained For nuclear applica tions the source consists of nuclides which produce singlet peaks of known energy Usually two such points are suffi cient since energy calibration is nearly linear over most of the spectrum range For X ray applications the calibration source may be element samples which yield X rays of known energy when irradiated The energy of the located peaks is then matched with the known energies of gamma and X rays in a nuclide or ele ment library In most cases multiple peaks are produced by a given nuclide or element and it is this set of peaks and their relative intensities that pinpoint an identification Overlapping peaks may complicate the analysis and in such cases peak stripping or deconvolution must be per formed before the identification can be made In addition to the generalized searches that locate mea sure and identify all peaks as specific nuclides library directed searches can also be done Peaks of the nuclides or elements of interest are specified and the spectrum is searched in only the selected regions of interest ROls Although this type of search is faster than a generalized search it is more likely to miss an unexpected peak Select a search type based on the requirements of the specific analysis e P Full peak count Counts FWHM Half peak count Channels or energy
17. time is very short In pulsed reset systems preamplifier dead time coincides with the reset time and the maximum energy rate is primarily limited by the collection time per event Maximum energy rates in excess of 1000 GeV sec are common in reset type preamplifiers In the resistive feedback preamps events can be processed even during the decay time of previous events as shown schematically for high count rates in Figure 1 20 However as they pile up on one another the output level increases until it 21 energy absorbed reaches the maximum of the preamplifier dynamic range 23 3V for the RG 11B and 10V for the 352 The maxi mum energy rate is typically limited to 80 GeV sec Further if the time between events is less than 1 5x the peaking time of the main amplifier regardless of the type of preamplifier the pulses pile up and cannot be processed Main amplifier and ADC analog to digital converter dead times are the major contributors to system dead time 1 17 Maximum Count Rate Determi nation In dc coupled charge sensitive preamplifier there is a maximum value for the energy rate product energy x count rate above which the preamplifier will shut off As this maximum energy rate product is approached the detector system may exhibit severe resolution degradation and peak shifts For a given preamp the maximum count rate can be determined by dividing the measured maximum energy rate by the mean energy of the events
18. upper 105 full scale and lower 0 full scale in increments of 0 41 Zero adjustment via computer in increments of 0 41 Maximum throughput 75 000 cps Spectrum memory QCC mode 256 or 512 channels Linear mode 250 500 or 1000 channels Maximum counts per channel 224 1 i e 16 million Amplifier Bipolar shaping 2us fixed Built in dead time correction No pole zero adjustment required Coarse gain settings 1X 2X 4X 8X computer selectable Fine gain settings 1 to 2 5x computer adjustable in increments of 0 01 Counting presets Real time Live time Integral of all ROIs Integral of selected ROIs Gross ROI statistics Net ROI statistics Total system counts Total SCA counts Computer control by RS 232 with the following available baud rates 2400 9600 19200 38400 57600 and 115200 Maximum number of units connected to PC 8 total via RS 232 or Ethernet Digital stabilizer RJ 45 connection for Ethernet MCA2100R EN Software 32 bit QuantumMCA compatible with Windows 95 98 NT Accessories QuantumGold software for quantitative analysis Multiple port RS 232 card 14 pin tube base Selection of signal interface and detector bias cables Sodium iodide detectors 66 2 13 2 4000 Multichannel Analyzer Premium Performance at a Price You Can Afford 1000 2000 or 4000 channels of spectrum memory in a stand alone pac
19. 098 1 122 30 1 134 1 117 32 Ge Germanium 9 885 9 854 0 981 11 100 11 103 1 188 1 216 42 1 248 1 217 33 As Arsenic 0 543 0 507 1 725 11 863 11 867 1 282 1 317 529 1 359 1 323 34 Se Selenium 1 221 1 181 2 495 12 65 12 657 1 379 1 419 652 1 475 1 434 35 Br Bromine 1 923 1 877 3 290 13 465 13 475 1 480 1 526 794 1 599 1 552 36 Kr Krypton 2 649 2 597 4 112 14 313 14 323 1 638 93 1 727 1 675 37 Rb Rubidium 3 394 3 335 4 960 15 184 15 201 1 694 1 692 1 752 2 067 1 866 1 806 38 Sr Strontium 4 164 4 097 5 834 16 083 16 106 1 806 1 805 1 872 2 22 2 008 1 941 39 Yttrium 4 957 4 882 6 736 17 01 17 037 1 922 1 920 1 996 2 369 2 154 2 079 40 Zr Zirconium 5 774 5 690 7 666 17 969 17 998 2 042 2 040 2 124 2 219 2 302 2 547 2 305 2 220 41 Nb Niobium 6 614 6 520 8 614 18 95 18 989 2 166 2 163 2 257 2 367 2 462 2 706 2 467 2 374 42 Mo Molybdenum 7 478 8 373 9 600 19 964 20 002 2 293 2 290 2 395 2 518 2 623 2 884 2 627 2 523 43 Technicium 8 410 8 328 20 608 21 012 21 054 2 424 2 420 2 538 2 674 2 792 23 054 2 795 2 677 44 Ru Ruthenium 9 278 9 149 21 646 22 072 22 117 2 558 2 554 2 683 2 836 2 964 3 236 2 966 2 837 45 Rh Rhodium 20 214 20 072 22 712 23 169 23 224 2 696 2 692 2 834 3 001 3 144 3 419 3 145 3 002 46 Pd Palladium 21 175 21 018 23 816 24 297 24 347 2 838 2 833 2 990 3 172 3 328 3 617 3 329 3 172 47 Ag Silver 22 162 21 988 24 942 25 454 25 517 2 984 2 978 3 151 3 348 3 519 3 810 3 528 3 352 48 Cd Cadmium 23 172 22 982 26 093 26 641 26 712 3 133 3 127 3 316 3
20. 1 14 Crystal Types Geometries PGT selects the best high purity germanium HPGe sometimes called intrinsic IG and lithium drifted silicon Si Li crystals available for processing into detector crys tals The crystal size geometry type and contact layers are custom manufactured Note on nomenclature PGT has been an industry leader since the early days when the term intrinsic germanium was commonly used It is now recognized that high purity germanium or HPGe is a more appropriate term However PGT has retained the IG designation in its model numbers to eliminate confusion among models The crystals can be fabricated in various sizes and configu rations to cover the energy range count rate best suited for your particular applications Table 1 2 includes the basic crystal geometries and the applicable energy ranges NIGC n type HPGe Coaxial Detectors can mea sure photons from below 10 keV to 10 MeV with high efficiency They are less sensitive to neutron dam age than other coaxial detectors because electrons are the main charge carriers and these are not as easily trapped by the damage centers as are holes IGC p type HPGe Coaxial Detectors have an energy range of 40 keV to 10 MeV and are suitable for a wide variety of applications including portable Systems They have a long service life and can be stored warm for extended periods IGW p type HPGe Coaxial Well Detectors are useful in measuring low
21. 10 665 180 40 1 1 90 NIGC10190 10 715 1 90 39 1 1 95 NIGC10200 10 735 2 00 38 1 2 00 NIGC15185 15 675 1 85 44 1 1 90 NIGC15190 15 715 1 90 42 1 1 95 NIGC15200 15 735 2 00 40 1 2 00 NIGC20190 20 690 1 90 48 1 1 90 NIGC20195 20 750 195 46 1 1 95 20200 20 790 2 00 44 1 2 00 NIGC25190 25 690 1 90 50 1 1 90 NIGC25195 25 760 195 48 1 1 95 NIGC25200 25 790 2 00 46 1 2 00 NIGC30190 30 715 190 54 1 1 90 NIGC30200 30 825 2 00 52 1 2 00 NIGC30210 30 850 210 48 1 2 00 NIGC35195 35 775 1 95 55 1 2 00 NIGC35210 35 830 210 52 1 2 00 NIGC35220 35 900 220 50 1 2 00 NIGC40195 40 800 1 95 59 1 2 00 NIGC40210 40 850 2 10 54 1 2 00 NIGC40220 40 925 2 20 52 1 2 00 NIGC45200 45 825 2 00 60 1 2 00 45210 45 950 210 57 1 2 00 45220 45 975 2 20 55 1 2 00 NIGC50220 50 860 2 20 58 1 2 00 NICG50230 50 1000 2 30 56 1 2 00 NIGC55220 55 900 2 20 60 1 2 00 NIGC55230 55 1000 2 30 58 1 2 00 NIGC60220 60 1100 220 60 1 2 00 NIGC60230 60 1200 2 30 58 1 2 00 NIGC70230 70 1100 2 30 60 1 2 00 NIGC70240 70 1200 2 40 58 1 2 00 Table 2 4 NIGC Series Detectors 2 5 5 High Purity Germanium Well tors PGT germanium well detectors use the through hole technology to minimize microphonics and provide higher resolution performance This is a true coax design in which the crystal is less than 5 mm from the face of the endcap and the sample can be placed deeper within the detector The soli
22. 10 mm active areas LNe free rapid Peltier cooling usually within 30 sec onds and automatic temperature control within 1 C for high detector stability Options 5 or 10 mm active areas Be window or proprietary ultra thin window for light element sensitivity Adaptable detector housing design Typical Applications X ray fluorescence with the advantages of small size high resolution and high count rate e Clean rooms where LN is prohibited Any situation where LNs is convenient or benefi cial Any application where high count rate is an advan tage 45 2 6 Endcap and Window Materials transmission curves for the various materials The endcap portion of the cryostat protects the crystal within the vacuum chamber and is the interface between the incident radiation and the crystal itself If the endcap material absorbs the incoming photons a window of higher transmission material is needed Endcap Material Applications Standard endcap for most applications useful down to 20 keV Aluminum Low background aluminum available including Pechiney aluminum for example for well detector inserts Oxygen free high conductivity copper OFHC Low background applications most useful above 40 50 keV Stainless steel Low background applications and where easy decontamination is important for example for lung monitors or MPS portable spectrometers Table 2 9 Endc
23. 14 57 1000 0 5 15 30 122 10 000 5 8 16 30 20 000 9 10 18 31 50 000 17 16 22 34 100 000 20 23 28 38 55 1000 0 10 30 60 5 9 keV 10 000 5 13 31 60 20 000 9 15 34 62 50 000 17 22 38 65 100 000 20 28 44 70 Figure 1 23 Noise contributions pulsed reset preamplifiers because 1 f noise is also smaller the resolution degrada tion at short time constants is less than that for resistive feedback preamps For a given shaping time high count rates can lead to the possibility of pulse pile up in which pulses arrive at the MCA almost simultaneously The MCA treats such a dou ble pulse as a single pulse of greater amplitude and energy This leads to the following types of distortion in the spectrum Extra high energy counts Fewer counts in the photopeak Increase in the FWHM for the full energy peak This spectrum degradation becomes significant when the product of input count rate and pulse processing time exceeds 0 5 and it is a dominant factor when this value is gt 1 Decreasing the pulse processing time of the main amplifier by decreasing the shaking time reduces the spectrum dis tortion but with a loss in resolution as shown in Table 1 4 A pile up rejector can also be used if it is compatible with the MCA 24 These figures are meant as a general guide and assume the use of a suitable main amplifier pile up rejector and multichannel analyzer Table 1 4 Resolu
24. 2 x2 weight 2500 Ibs Designed for vertical dipstick cryostats Interior cavity 11 16 to accommodate a variety of detector configurations and Marinelli beakers Detector plug sized to coldfinger Rigid steel support stand with leveling pads Clamshell lid for access to sample holder Swing open front access e Weight 2500 Ibs Optional Configurations and Accessories Custom shield for NPR cryostats Available with 2 thick bulk lead Sample geometry stands Support table leveling device for fine adjustment at table top level Dewar leveling stand May be ordered as stackable plates Copper tin lining available Applications Low activity gamma analysis when it is necessary to minimize ambient background Cosmic rays Environmental contaminants M p Preamp and dewar components g 57 20 5 A Hinged lid for sample access Low background virgin lead 10 cm Graded lining Cd 0 05 cm with 2 Cu surface 0 163 cm Low carbon steel casing 1 25 cm Cavity 16 high x 11 diameter Y Table 24 x24 Overhead view of clamshell access for sample A f 27 30 zl 6 pewar 212 1 8 eveling 5 stand 24 YS Adjustable table pads Model 411 SD with standard dipstick Model 411 NPR w
25. 33 HPGe Planar Detectors 39 HPGe Well Detectors 37 intrinsic efficiency 10 ionizing radiation types 3 J JT Cool Mechanically Cooled Spectrometer 32 55 L liquid nitrogen handling devices autofill systems 53 diagram 54 gravity feed systems 53 low background spectroscopy 15 materials 16 27 60 table of specifications 17 Marinelli beakers 11 configuration 12 MCA 2100R Multichannel Pulse Height Analyzer 65 MCA 2100R specifications 66 MCA 4000 Multichannel Analyzer 67 MCA 4000 specifications 68 MCA 8000 Multichannel Analyzer 72 MCA 8000 specifications 73 MCAs MCA 2100R Multichannel Pulse Height Analyzer 65 MCA 4000 Multichannel Analyzer 67 MCA 8000 Multichannel Analyzer 72 microphonics 14 25 Model MPS 5 radiation shields 59 N noise 14 in high count rate systems 23 N type Coaxial HPGe Extended Range Detectors 35 N type HPGe Planar Detectors 41 pair production 4 peak location 8 peak to Compton ratio 14 photoelectric effect 4 portable cryostats 51 preamplifier characteristics 21 types 61 pulsed optical reset 20 resistive feedback 20 transistor reset 20 Q quadratic compression conversion 64 quantitative analysis about 8 Quantum MCA software 77 R radiation detectors see detectors radiation shields 57 model MPS 5 59 radioactivity basic principles of 3 relative efficiency 10 resolution detector 14 5 sensitivity detector 14 spectroscopy system steps in assembling 28 spectrum an
26. 528 3 716 4 019 3 727 3 538 49 In Indium 24 207 24 000 27 274 27 859 27 937 3 287 3 279 3 487 3 713 3 920 4 237 3 939 3 729 50 Sn 25 270 25 042 28 483 29 106 29 190 3 444 3 435 3 662 3 904 4 131 4 464 4 157 3 928 88 Element Kal 2 2 Kap Lol Lo 1 2 Lyl Liab Litab Liab 5150 Antimony 26 357 26 109 29 723 30 387 30 491 3 605 3 595 3 843 4 100 4 347 4 697 4 381 4 132 52 Te Tellurium 27 471 27 200 30 993 31 698 31 809 3 769 3 758 4 029 4 301 4 570 4 934 4 613 4 341 531 Iodine 28 610 28 315 32 292 33 016 33 170 3 937 3 926 4 220 4 507 4 800 5 190 4 856 4 559 54 Xe Xenon 29 802 29 485 33 644 34 446 34 579 4111 4 098 4 422 4 720 5 036 5 452 5 104 4 782 55 Cs Cesium 30 8970 30 623 34 984 35 819 35 983 4 286 4 272 4 620 4 936 5 280 5 720 5 358 5 011 56 Ba Barium 32 191 31 815 36 376 37 255 37 443 4 467 4 451 4 828 5 156 5 531 5 995 5 623 5 247 57 La Lanthenum 33 440 33 033 37 799 38 728 38 932 4 651 4 635 5 043 5 384 5 789 6 283 5 894 5 489 58 Ce Cerium 34 717 34 276 39 255 40 231 40 440 4 840 4 823 5 262 5 613 6 052 6 56 6 165 5 729 0 833 59 Pr Praseodymium 36 023 35 548 40 746 41 772 41 998 5 034 5 014 5 489 5 850 6 322 6 846 6 443 5 968 0 883 60 Nd Neodymium 37 359 36 845 42 269 43 298 43 571 5 230 5 206 5 722 6 090 6 602 7 1
27. CE energy is exceeded are normally photoelectric events 1 2 3 Pair Production In pair production an incident photon in the field of the nucleus of an absorber atom gives up all its energy to pro duce an electron positron pair Unlike the photoelectric effect and Compton scattering which are possible at all energies pair production has an energetic threshold equal to the combined positron electron rest mass 1 022 MeV Above this threshold the cross section for the event Compton effect E 1 E 1 cos0 511 14 511 2bE E energy of incident photon keV E energy of scattered photon keV T kinetic energy of the scattered electron scattering angle Compton edge when 180 Figure 1 2 Compton scattering increases rapidly with Z of the absorbing material up to about 10 MeV beyond which it decreases because of screening effects The entire photon energy E is con verted to the kinetic energy of the positron electron pair i e E 1 022 MeV plus the rest mass of the pair The positron is annihilated by an atomic electron producing two 0 511 MeV photons emitted at 180 to each other None one or both of these photons may escape resulting in a spectral distribution that includes a full energy peak FEP a single escape peak SEP and a double escape peak DEP as shown in Figure 1 3 FEP Eg m 180 scatter from inactive material DEP 180 Coun
28. MCA the channel 3 Incident photon corresponding to the given energy is incremented by one The familiar spectrum display is essentially a histogram of the probability density of energies of the detected radiation or a plot of the number of counts in each channel against the energy in the channel In addition to counting and stor ing the data the MCA provides the mechanisms for dis playing printing and analyzing the information The pulses arrive at the main amplifier at random time intervals At higher count rates the system is unable to dis criminate between pulses if the time between events is less than 1 5x the peaking time of the main amplifier The pulses pile up and cannot be processed resulting in peak broadening This spectrum degradation becomes significant when the product of input count rate and pulse processing time exceeds 0 5 and it is a dominant factor when this value is gt 1 Decreasing the pulse processing time of the main ampli fier by decreasing the peaking time reduces the spec trum distortion but produces a loss in resolution To compensate a pileup rejection module is frequently included in the circuitry and the ADC live time is extended to account for the time that the system is unable to process pulses A typical PGT nuclear detector system is illustrated sche matically in Figure 1 7 The components shown include A germanium detector with an external preamplifier and standard d
29. and electronics Please include specifications with your request 1 Choose the type of detector crystal based on energy range activity level count rate efficiency resolu tion and cost 2 Select a preamplifier appropriate to the expected count rate 3 Consider a beryllium window for low energy gamma rays or a light element window for X rays 4 Select the cryostat that is suitable for your holding time requirements available space low background and portability needs A mechanically cooled detec tor be preferable to a standard LNo cooled detector PGT has extensive experience manufactur ing non microphonic mechanically cooled detectors 5 Add any special requirements such as lead shields or low background materials 6 Select the required electronics For information on various options see the sections listed below or con tact a PGT employee for assistance e MCA 4000 Multichannel Analyzer page 67 e System 4000 X Ray Spectrometer on page 69 e MCA 8000 Multichannel Analyzer on page 72 28 System 8000 Gamma or X Ray Spectrome ter on page 74 MCA 2100R Multichannel Pulse Height Ana lyzer on page 65 Quantum MCA Software for Windows on page 77 7 Select any other required accessories such LNo autofill systems and dewar supports 8 Contact the PGT Nuclear Sales Department for addi tional information on customized options price quotes and or
30. are thus especially suitable for suppression of Compton scattering to reduce background The main charge carriers in n type detectors are electrons which are less susceptible to traps created by neutron damage This makes them ideal under conditions of high neutron flux PGT NIGC detectors have proven themselves in space and high altitude applications The detector flown on the Mars Observer annealed itself in space and sent back data on solar flare induced gamma ray activities Fur ther a neutron damage repair kit allows you to repair these detectors in your own lab if damage does occur PGT NIGC detectors have a long service life and can be stored warm for extended periods of time Features n type high purity germanium with ion implanted exterior surface and lithium diffusion center contact Vertical dipstick cryostat Standard 32 liter dewar Aluminum endcap with beryllium window 100 70 30 20 1 NO Intrinsic Detector Efficiency percent ON oo 2 r Beryllium window P ion implant layer 0 3 n type crystal Aluminum endcap Center core with N lithium diffusion layer typically 0 5 mm Passivated surface 20 mil beryllium windo pre Figure 2 5 N type HPGe Coaxial Detector RG 11 B C resistive feedback preamplifier 12 ft bias signal and power cables Unlimited temperature cycling without loss of resolu tion Options Portabl
31. both problems by having the channel width of the 64 converter at a particular energy be proportional to the energy resolution of the system at that energy In a QCC Nal Tl spectrum all peaks have the same FWHM expressed in channels independent of energy QCC tech nology can cover the entire energy range of interest with sufficient resolution to provide accurate spectral analysis while providing enhanced minimum limits for identification 2 13 1 2100R Multichannel Pulse Height Analyzer MCA bias supply amplifier and preamplifier all in one small package Patented Quadratic Compression Conversion greatly improves performance Easy installation and setup No internal slots or reserved memory required Includes 32 bit QuantumMCA software PGT has incorporated the latest in modern electronics in the MCA2100R to provide a complete gamma spectrome ter for Nal The MCA2100R features a fast dual mode ADC and two standard modes of operation either as a stan dard 1000 channel MCA in linear mode or as a 512 chan nel MCA in QCC mode What is QCC QCC is Quadratic Compression Conversion PGT s pat ented signal processing technique that delivers spectra with uniform channel peak widths from 20 to 2000 keV This powerful technique employs a pulse processing algo rithm that converts a 16k spectrum to a 512 channel spec trum in real time The peak to background ratio of the converted spectrum is significantly
32. continuum background regions Automatic peak labeling with ROI names or associated nuclides Reports Graphic spectrum printout reformats screen view for high resolution printer output All markers display settings and annotations are included By channel data report single or multi column ROI summary report spectrum plot with ROI data ROI detail report Peak identify report Quantitative analysis reports by nuclide or by ROI QuantumGold only 79 80 Appendix 1 Radionuclides for Energy Resolution Radionuclide Half Life Energy 55Fe 2 74 years 5 9 keV 241 am 433 years 59 54 keV and 26 3 keV X rays 109 4 463 days 22 2 keV X ray doublet 88 0 keV 129 1 5 107 yrs 40 0 keV 57 272 days 122 1 keV and 136 5 keV 137 30 3 years 661 7 keV 31 8 32 2 36 4 keV from daughter 56 22Na 2 60 years 511 keV 1274 5 keV 60C9 5 24 years 1173 2 keV 1332 5 2087 1 91 years 583 keV 2614 5 keV 229 source 1526 13 3 Multiple lines 121 1408 keV prominent lines include 121 8 keV 344 3 778 9 964 1112 1 1408 0 and X rays preferred for energy resolution measurements TPreferred for coaxial detector specification measurements 81 Appendix 2 Radionuclides for Marinelli Beaker Standard Sources MBSS Radionuclide Half Life Energy P RN 10964 462 7 88 0 k
33. cps Maximum energy rate products for these systems are limited by the amplifier and ADC rather than by the preamplifier itself 1 19 Microphonics Microphonics essentially refers to mechanically generated noise that impacts spectral resolution Within detector cry ostats noise can be introduced by the mechanical vibration of internal components relative to surfaces at different potentials Such oscillations may be from The bubbling of liquid nitrogen The vibration of other equipment in contact with the cryostat Environmental noise such as heavy equipment in the vicinity of the detector Even a change of capacitance between the FET gate and high voltage of only 5 x10 picofarad is sufficient to gener ate a microphonic signal equivalent to that of a 10 keV X ray Microphonic deterioration of signals will appear on the MCA as a broadened peak or in severe cases as a phan tom peak or a double peak PGT has developed an ultra low microphonics mounting system THE QUIET ONE M with a Microphonic Rating MR of 0 1 at 90 db over the range 100 Hz 10 kHz MR is a measure of the increase in noise level at the detector endcap due to acoustic noise PGT QUIET ONE mountings are available for most PGT high purity germanium detectors They are particularly use ful for Low activity measurements requiring well defined peaks High resolution analysis of complex spectra with multiple isotopes Environmental an
34. dewars are available in several standard bucket sizes as well as special portable models The basic con struction is shown in Figure 2 1 on page 27 Features Rugged aluminum construction Standard volumes of 7 5 15 and 30 liter buckets Options Stainless steel construction Low background materials Liquid Nitrogen Auto fill System Pressurized LN mother dewar for filling portable models Endcap configurations are shown on the next pages 48 Vacuum and molecular sieve Preamp Endcap B Cold finger Figure 2 13 Schematic of unitary cryostat con struction Model Designation Cryostat Configuration Crystal Type Dewar Volume Coaxial Coaxial Aluminum Down looking DT Germanium 7 5 liter 15 liter 30 liter Coaxial Horizontal HT MTE Stainless 1 Steel 15 liter Planar Planar Aluminum Down looking DT Germanium 7 5 liter 15 liter lt 500 mm 30 liter Planar 1000 mm Horizontal HT 1500 2000 mm Stainless Steel 15 liter Planar Si Li 10 30 60 mm Low Background Coaxial Aluminum NPR Germanium 15 liter Planar Germanium 30 liter 500 mm 1000 mm Stainless Steel EL 1500 2000 mm 15 liter 406 mm 16 std 20 liter or as specified Swivel Head Low Coaxial Aluminum Background Germanium 15
35. eral factors that should be considered 16 An external preamplifier is generally better than an in line preamp because the naturally occurring residual radioac tive materials found in the circuit board are not in direct line of sight with the detector The molecular sieve getter which may have a slightly higher residual radioactivity than activated charcoal is sig nificantly more effective in adsorbing contaminants and maintaining the vacuum The NPR cryostat with or without a lead shield is a better way to keep the getter from iradiat ing the detector PGT recommends the low background beryllium entrance window rather than magnesium because the latter is much more readily corroded A Vespel window is also available For the same window thickness Vespel has a lower energy transmission 71096 at the 14 4 keV line of 57 However it is less costly Material Application Pertinent Data Oxygen free high conductivity copper OFHC endcaps 4 and 8 mounting cup pedestal unit and nut cooling rod clamp and coldfinger 0 24 dpm kg 208 0 78 dpm kg 214 Bi 15 2 dpm kg Ultra low background Pechiney aluminum 1ppb Th endcap and crystal holder well insert 96 Al 4 Si lt 150 parts per trillion U Th 50 mm virgin lead internal shield 8 endcap copper clad 50 mm tungsten internal shield Ultra low background beryllium IF I and IF
36. improved by using energy channels where they are needed the most Conse quently the resolving power of the system is greatly improved 1 Ww In the figure above the lower peaks were taken from a con ventional 1000 channel linear spectrum of Co60 These are the 1173keV and 1333keV peaks Notice how the peaks are broad and cover many channels The upper portion shows the same Co60 peaks taken in QCC mode In this example the 1333keV peak of in the linear spectrum is spread over 75 channels whereas the same peak in the QCC spectrum is defined by 28 channels Most important the peak to background ratio of this peak in the QCC spectrum is 5 2 while it is only 2 8 in the linear spec trum This is almost a factor of two improvement For low energy peaks the opposite occurs The number of chan nels per peak is increased relative to the number that would be used in a linear spectrum QCC uses channels where they are needed PGT Quantum MCA2100R SS gt MCA2100R features include Two MCA modes 512 channels max and linear 1000 channels max 3 5us successive approximation ADC Complete computer control Stand alone operation no slot required in the PC Internal preamplifier for use with Nal detectors Bipolar pulse shaping amplifier PC communication methods RS 232 and Ethernet MCA2100R EN Easy setup and energy calibration via QuantumMCA software The MCA21
37. item reports Click in the list to highlight the peak on the display and bring it into view if necessary The image at the right shows some of the many hardware con trols available to PGT instruments Whether you are setting peak search sensitivities deciding what lines to use to identify isotopes or displaying mark ers you can choose the fully automated feature or take over control yourself Your investment in QuantumMCA software will always be a good one With lifetime technical support and a liberal free update policy you can be assured your software will remain as state or the art as when you first purchased it Energy Intensity 173 2 99 90 1332 5 99 98 0 1342 5 Emo TEE TER Come OR Quantum Gold is the premier MCA software package for analysis of spectra It provides all of the features of QuantumMCA plus the capability for quantitative analysis Accurate detector efficiencies are essential for good quan titative analysis QuantumGold provides a sophisticated detector model which accurately accounts for the effects of detector size and window absorption Accuracy can be fur ther enhanced by measuring single or multi isotope stan dards and fitting the results to the residuals of the calibration function The rapid scan analysis algorithm automatically searches the spectrum for peaks sets ROIs does a cross correla tion analysis to identify the isotopes and performs a quanti tative
38. mA t 1 6 mA t Available as an option BNC unless otherwise specified T Negative TR 14B Table 2 17 PGT Preamplifiers 2 12 Nal Tl Detectors PGT offers a variety of sodium iodide detectors for your unitswhich include the photomultiplier tube PMT Our spectroscopy needs All Nal Ti detectors are integral products are listed in the following tables Model Number Description SN15x20PMT1 5 1 50 x 2 0 Nal TI crystal on 1 5 12 pin PMT SN20x20 PMT2 0 2 0 D 2 0 Nal TI crystal on 2 0 14 pin PMT SN30x30 0 3 0 D x 3 0 1 crystal on 3 0 14 PMT Table 2 18 Standard Detectors Model Number Description WN15x20APMT1 5 1 5 D 2 0 Nal TI crystal with 0 625 x 1 5 deep well on 1 5 12 pin PMT Table 2 19 Well Type Detectors Model Number Description SN15x20TB 1 5 D x 2 0 Nal TI crystal on 1 5 PMT with rugge dized water tight housing and integrated tube base SN20x20TB 2 0 x 2 0 crystal on 2 0 PMT with rugge dized water tight housing integrated tube base and carrying handle SN30x30TB 3 0 D x 3 0 Nal TI crystal on 3 0 PMT with rugge dized water tight housing integrated tube base and carrying handle Table 2 20 Ruggedized Detectors with Integrated Tube Base 63 2 13 Quadratic Compression Conversion QCC The New Way To Do Nal Gamma Spectroscopy Nal Tl spectroscopy has always b
39. monitor installations Field deployment for monitoring waste or accident sites 55 56 vacuum housin Diam 114 3 m 4 57 55 6 455 mm 365 mm 281 mm 9 gt 17 5 x 14 37 x 11 06 21 8 kg 48 Ibs Detectors Coaxial or planar Germanium Si Li Aluminum endcap Laboratory stand for all attitude operation Table 2 15 JT Cool 2 9 Radiation Shields Low level counting as in environmental and contamination sampling requires that ambient background radiation be eliminated The type of shielding material and the thickness needed to screen the detector depend on the background environment The most commonly used materials are lead and steel pre World War 1 Generally 4 bulk lead is suffi cient to stop 1 MeV gamma rays Above 5 in thickness there is increased probability of interaction of cosmic rays within the shield to give Pb K X rays Where this may bea problem a graded Z liner is used Cadmium and copper are frequently the materials of choice The Cd liner absorbs the Pb X ray and emits a lower energy secondary X ray which is in turn absorbed by the Cu which then produces a 8 keV X ray Features Low carbon steel outer jacket 3 8 1 2 thick Cast virgin low background lead bulk shield 4 thick Graded liner of cadmium or tin 0 02 and soft cop per 0 064 Floor footprint
40. noted that the count rates are those observed in the total spectrum Once the maximum energy rate of a given system is known count rates for other spectra can be calculated For example in the system above with a maximum energy rate of 60 GeV sec the maximum total count rate for 13765 662 keV line with a mean energy of 0 5 MeV is 120 000 counts sec Using a lower value feedback resistor can yield a higher maximum energy rate but with a loss in resolution For high count rates and high energies the use of a transistor reset preamp is much better Count rate is also limited by the pulse pair resolving time which is a function of the amplifier selected peaking time Some representative maximum energy rates for various PGT Preamp Detector systems are shown in Table 1 3 Max energy Detector Preamp rate GeV sec IGC NIGC RG 11 15 70 IGP RG 11 15 6 lt 500 mm IGP RG 11 15 12 gt 500 mm IGP PO 14B 200 lt 500 mm IGC NIGC IGP TR 14 400 standard 1000 Si Li GX TR 1 200 Table 1 3 Maximum Energy Rates 1 18 High Count Rate Systems The main amplifier shaping time may have to be decreased at higher count rates Energy resolution at shorter shaping time becomes worse however because of increasing noise attributed to the FET component of the preamp and the detector capacitance At longer shaping time the sys tem noise will again increase particularly with resistive feedback preamps becau
41. of the start stop time intervals gives a peak in the spectrum The timing resolution of the system is described in terms of FWHM and sometimes FWTM for the peak See Detector Resolution and Sensitivity on page 14 for additional information The time pick off unit which produces an output logic pulse precisely related to the occurrence of an event is crucial to these measurements Among the sources of error in the time pick off measurements are amplitude walk and timing jitter Amplitude walk refers to the time movement between the input and output pulses of the unit due to differences in shape and amplitude of the pulses coming from the detec tor It is usually the most important factor in semiconductor detectors Timing jitter is primarily due to the statistical fluc tuations in the signal from the detector and is more impor tant in scintillator photomultiplier systems A constant fraction discriminator CFD is commonly used to reduce walk and jitter In this device the leading edge of the input pulse crosses through a discriminator with a threshold that is a constant fraction of the signal amplitude This original pulse is added to a delayed inverted and amplified version of that pulse to give a zero crossover which is independent of rise times or amplitudes Timing resolution is very dependent on the entire electron ics system Figure 1 9 is a diagram of the system used to measure the timing resolution of some PGT p type co
42. on one surface usually by boron ion implantation or gold metalli zation The thickness of this layer is about 0 3 um The other surface is a thicker N layer 0 5 mm formed by lithium diffusion When a bias voltage is applied to the crystal incident radi ation creates charge carriers that are swept toward the oppositely charged contacts For IGW and IGC detectors the applied voltage is positive and holes are the primary carriers For detectors with a P layer on the face a negative bias is applied In this case electrons become the main charge carriers Such crystals are less sensitive to neutron damage For silicon detectors the p type silicon crystals are counter doped with Li ions to achieve the required impurity level by a lithium drifting procedure 1 15 1 Crystal Shape PGT does not use the bullet shape for its detector crys tals The variation in the electric field in the crystal which such a shape supposedly avoids is minor The straight across design of PGT crystals allows for better clamping of the crystal in the endcap which results in lower micro phonics and therefore better resolution 1 15 2 Dead Layers The term dead layer refers to a thin layer of inactive material on the surface of the semiconductor detector crys tal through which the incident radiation passes before reaching the active material Any radiation absorbed by this layer is lost that is does not contribute to the signal in
43. produced in the detector MO 5 1 6 x 10719 Coulomb Q x MeV sec Ip 2 98eV of charge x charge per x rate at which current carriers per charge carrier energy IS induced absorbed in detector detector feedback test point current resistor Voltage ER max countrate E spectrum energy rate at max of spectrum For example in a germanium detector with a resistive feedback preamp 1 MeV of energy falling on the detector produces a charge of 0 53 x 1013 coulombs Thus if 1 GeV sec is detected the current generated is 0 053 nAmps This current flowing through a 10GQ feedback resistor raises the voltage at the preamplifier test point by 0 53V As the energy rate is increased to 44 GeV sec the test point voltage increases to gt 23 3 V at which point the preamplifier shuts down Therefore for this example 44 GeV sec is the maximum energy rate ERma that the detector preamp assembly can handle The maximum count rate is determined by dividing this value by the mean energy of the spectrum In this particular system the maxi mum count rate for 57 would be approximately 440 000 counts sec 22 For a coaxial detector the feedback resistor value cold is typically 5 10 GQ The average 7 5 GQ resistor gives a maximum energy rate of 60 GeV sec For the Co spec trum with a mean energy of 0 8 MeV the maximum count rate is 70 000 counts sec It should be
44. purchased from a distributor please contact your distributor prior to con tacting the factory A RMA number is required for returns and repairs SUCH WARRANTIES ARE IN LIEU OF OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE WITH RESPECT TO THE SOFTWARE AND THE ACCOMPANYING WRITTEN MATERIALS IN NO EVENT WILL PGT BE LIABLE TO YOU FOR DAMAGES INCLUDING ANY LOSS OF PROFITS LOST SAVINGS OR OTHER INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF YOUR USE OF OR INABILITY TO USE THE PROGRAM EVEN IF PGT OR AN AUTHORIZED PGT REPRESENTATIVE HAS BEEN ADVISED OF THE POSSI BILITY OF SUCH DAMAGES PGT WILL NOT BE LIABLE FOR ANY SUCH CLAIM BY ANY OTHER PARTY This limited warranty gives you specific legal rights Some states provide other rights and states do not allow excluding or Imiting implied war ranties or limiting liability for incidental or consequential damages As a result the above limitations and or exclusions may not apply to you Furthermore some jurisdictions have statutory consumer provisions which may supersede this section of the Agreement GENERAL If any provision of this Agreement shall be unlawful void or for any reason unenforceable then that provision shall be deemed severable from this Agreement and shall not affect the validity and enforceability of the remaining provisions of this Agreement This Agreement is governed by the laws o
45. severe cases the energy peaks may even be considerably misshapen or double peaks may appear In contrast in through hole well detectors the center con tact extends the full length of the crystal A very short gate lead is needed from the back of the crystal to the FET consequence PGT well detectors have outstanding resolu tion 1 7 2 Detector Resolution and Sensitivity The detector resolution is a measure of how accurately a detector system can discriminate the energy of each pulse Energy resolution determines how well the spectral lines are separated in the MCA display The energy resolution for PGT coaxial germanium and well detectors and sometimes large planars is defined as the Full Width at Half Maximum FWHM for the full energy peak of the 1 33 MeV line of Co expressed in keV All coaxial detectors are also tested at the 122 keV line of Co The narrower the peaks the less overlap con volution there will be with other spectrum lines and also the fewer background counts will be included in the peak integrals FWHM of the 122 keV line of 57 or the 5 9 keV line of 55 is used with planar detectors and with coaxials for lower energy radiation Detector resolution is further refined by determining the Full Width at Tenth Max FWTM and Full Width at Fiftieth FW0 02M of the 1 33 MeV line The peak shape ratio FWTM FWHM is lt 1 9 for a very good detector while the ratio FW0 02M FWH
46. stem Mother Dewar Capacity 30 liters Stand Aluminum 36 high or as specified 54 Table 2 14 Liquid Nitrogen Handling Devices 2 8 Mechanical Coolers PGT was the first to offer a mechanical cooler for use where liquid nitrogen is unavailable too expensive or inconvenient PGT s leadership in low microphonic assem blies is proven in these systems Even where the detector is mounted against a vibrational surface gamma spec troscopy resolution remains high There are now several types of mechanical coolers avail able to suit your particular requirements Use of a mechan ical cooler eliminates the need for LN storage and transfer facilities PGT will also retrofit LNo detectors to a mechanical cooler as well as repair the detector itself 2 8 1 JT Cool The JT Cool features an AC powered air cooled compres Sor which is attached to the cold head by flexible gas lines that have self sealing fittings at each end It is designed for continuous maintenance free operation The JT Cool compressor operates with a proprietary refrig erant that is CFC free The system is capable of operating at ambient temperatures of 10 35 C Higher temperatures may lead to gain changes so it is recommended that the ambient temperature be controlled within the above bound aries The smaller footprint and the lighter weight of the compres sor ensure more flex
47. sub female connector for ROI output ADC input BNC 0 10V unipolar or bipolar pulse ADC gate input BNC coin anti coin off CMOS TTL Pile up reject input BNC CMOS TTL SCA output CMOS TTL ADC busy out BNC CMOS TTL External input counter BNC CMOS TTL Weight 4 06lb 1 85kg Dimensions 10 4in 26 4cm wide 12 3in 31 2cm deep 2 75 7 0cm tall Power Requirements 10 18 VDC 9 6 watts external 12V universal AC supply provided Software 32 bit QuantumMCA compatible with Windows 95 98 NT 2000 XP Accessories QuantumGold software for quantitative analysis High purity germanium detectors Nal detectors Selection of cables Dc ROWAUX oput 21 a Tech 1010 Commerc Park Dr Ste Ridge TN 37830 2 13 3 System 4000 X Ray Spectrometer Premium Performance at a Price You Can Afford MCA bias supply amplifier all in one package Fast 2 7us ADC ROI AUX IO with up to 15 fast TTL ROls definable in the software No slots or reserved memory required in the PC Includes 32 bit QuantumMCA software The System 4000 is a complete spectrometer in a single integrated package It is designed to make X ray spectros copy easy The System 4000 is configured with 4000 chan nels of spectrum memory a 0 to 1 kV bias supply and an analog pulse processor with 2us 1245 and 2445 shaping times for X ray spectrometry The System 4000 has onboard Ethernet and
48. sure that the detectors are not handled inappropriately Mechanical shock can cause internal damage IG detectors requiring a beryllium entrance window are delivered with a protective cover for the endcap The beryllium window is very fragile and its accidental breakage is not covered by this warranty 2 4 Selecting a Detector The choice of detector for a particular application is based on Energy range of interest Efficiency Resolution Count rate Cost Table 2 1 lists different types of applications and the type of detector appropriate for each one Type of Application Suggested Detector Large samples for example environmental samples in Marinelli beakers with complex spectra IGC Series of p type coaxial HPGe Small samples IGW well detectors with the optional NPR cryostat and low background materials Particle accelerators with Compton suppression Systems or other high flux situations NIGC extended range n type coaxial HPGe with transis tor reset preamp for high count rates Spectroscopy of transuranic elements and mixed gamma and X ray samples IGP planar detectors Body burden assessment and lung monitoring NIGP n type planar crystals in detectors mounted in low background NPR style cryostats or portable MPS cry ostats Non LNe cooled systems are available High resolution spectroscopy in areas of high vibration for example truck mounted laboratories or ind
49. 0 to 90 of its final value CHARGE SENSITIVE PREAMPLIFIER An amplifier pre ceding the main amplifier in which the output signal ampli tude is proportional to the charge injected at the input COAXIAL DETECTOR cylindrical crystal with a hole bored partially or completely through the crystal coaxial with its longitudinal axis The outer surface of the crystal is one contact and the surface of the inner hole is the other COMPTON CONTINUUM Continuous electron energy distribution due to elastic scattering when a photon interacts with a bound electron COMPTON EDGE CE Compton scattering in which the photon is backscattered along its original path and maxi mum energy has been imparted to the electron COMPTON SCATTERING Elastic collision between an incident photon and a bound electron CRYOSTAT Vacuum enclosure which includes the end cap with the detector crystal preamplifier FET and coldfin ger by which the crystal is maintained at its operating tem perature CRYOSTAT DIPSTICK cryostat whose vacuum is completely separate from that of the dewar CRYOSTAT UNITARY cryostat whose vacuum is inte gral with that of the dewar DEAD LAYER The layer in a semiconductor detector of ten at the contact region in which none of the energy lost by ionizing radiation contributes to the resulting signal DEAD TIME Time during which the electronics are busy processing pulses and no new pulses can be measured DECAY The di
50. 0 03 increments Zero adjustment in increments of 0 41 PC adjusted Maximum throughput 180 000 cps Spectrum Memory MCA 4001 250 500 and 1000 channels MCA 4002 250 500 1000 and 2000 channels MCA 4004 250 500 1000 2000 and 4000 channels maximum counts per channel 2 1 i e 2 1E9 Digital Stabilizer Internal ADC zero and gain stabilization PC controlled time constants Balanced channel and ROI centroid modes Gain 12 5 range Zero 1 25 range Multichannel Scaling Input Rate 5 MHz Dwell Time 10 ms to 2 1E7 seconds Dead time 35 between passes and 3us between channels Signal sources internal SCA any ROI external input Counting Presets Real time Live time Integral of all ROIs Integral of selected ROIs Gross ROI statistics Net ROI statistics Total system counts Total SCA counts Linearity Differential lt 1 over top 99 of range Integral lt 0 05 over top 99 of range Battery backup for Spectrum Setup parameters Clock memory Computer Control RS232 baud rates 2400 9600 19200 38400 57600 115200 Max number units connected to PC 8 Ethernet connection 68 Front Panel Indicators LEDs for Acquire Event Serial Com AUX 1 in power 3 color LED array for dead time Rear Panel Controls and Connectors Power switch 2 5mm power jack Fuse housing 9 pin D male RS 232 connector 44 pin D
51. 0 7 0 329 21 0 432 3 3 0 487 45 0 752 4 496 0 816 2396 0 868 5 596 0 920 2 596 0 925 6 9 0 950 0 6 1 597 95 6 2 348 0 9 0 2522 3 3 Lead 210 alpha 22 3 years 0 046 4 beta 0 009 0 017 Bi K X rays 21 Manganese 312 5 days 0 835 100 0 0055 Cr K X rays 25 Molybdenum 99 beta 66 2 hours 0 041 1 2 0 141 5 4 0 181 6 6 0 266 1 4 0 740 13 6 0 778 4 7 0 823 0 13 0 961 0 1 Daughter 99 6 02 hours 0 141 83 9 Neptunium 237 alpha 2 14x108 years 0 029 12 0 087 13 0 186 0 08 0 118 0 18 0 131 0 09 0 134 0 07 0 143 0 44 0 151 0 25 0 155 0 10 0 169 0 08 0 193 0 06 0 195 0 21 0 212 0 17 0 238 0 07 233 0 075 1 3 Daughter 233 27 0 days 087 508 0 104 0 7 0 300 6 5 0 312 38 0 340 4 3 0 375 0 7 0 398 1 3 0 0416 1 7 Plutonium 238Pu alpha 87 7 years 0 043 I C 0 011 0 022 UL X rays 13 0 094 0 115 UK X rays 2 1X104 85 86 Nuclide Type of Decay Half Life Photon Energy MeV Yield Radium 226Ra alpha 1600 years 0 186 3 4 214 beta 26 8 minutes 0 053 Daughter 0 242 67 0 295 16 9 0 352 32 0 alpha 19 8 minutes 0 273 5 3 Daughter Bi beta 0 609 41 7 0 769 5 3 1 120 14 3 1 238 5 0 1 378 4 8 1 764 15 9 2 204 5 3 ds allpha 1 62X104second 0 046 4 Daughter lt Pb beta 0 009 0 017 Bi L X rays 21 Ruthernium 1 8
52. 0 is a complete spectrometer in a single integrated package It is designed to make gamma or X ray spectroscopy easy The System 8000 has configurations with 8000 or 16 000 channels of spectrum memory Each has a 0 to 5kV bias supply and an analog pulse processor with 2us 45 and 8us shaping times All configurations of the System 8000 have onboard Ethernet and RS 232 inter faces for easy connection to the PC or network High Performance The System 8000 gamma spectrometer has been engi neered to give optimum performance in a wide range of applications with HPGe and Si Li detectors The three computer selectable time constants offer choices for high throughput applications standard operation and highest possible resolution The shaping amplifier features 8th order triangular and Gaussian filters for minimum series noise and optimum resolution Automatic noise discrimina tors and a gated baseline restorer with rate adaptive resto ration give the ultimate in stability even at the highest count rates To provide the best possible pile up rejection even at the lowest energies the fast channel has adaptive time constants which ensure maximum possible sensitivity This translates into the best possible performance from your detector system Computer control of all hardware func tions complements the power and flexibility of the system Analytical Software For qualitative analysis the System 8000 includes QuantumMCA software at no addit
53. 00R is packaged as a peripheral to the PC It does not require any internal PC interface slots or special memory reservations This avoids problems in upgrading to the newer PCs and operating systems The MCA2100R communicates via the RS 232 port Simply connect a serial cable to one of the COM ports on the PC and the other end to the RS 232 connector on the MCA 2100R and you are ready to go To connect multiple units to the PC use a mul tiple port RS 232 interface or select the optional Ethernet connection The MCA2100R includes QuantumMCA software for quali tative analysis All hardware setup and calibration functions are made through the software It is not necessary to set internal jumpers or switches to configure the unit For ease of setup the MCA2100R with the QuantumMCA software can perform an automatic adjustment of the detector bias coarse gain and fine gain Simply place a Cs137 source near the detector and press one software button The unit performs all hardware adjustments For a more precise energy calibration the system can perform a quadratic energy calibration and resolution calibration based on a Eu152 spectrum In minutes the MCA2100R is ready to use For applications that require quantitative analysis the pow erful and user friendly QuantumGold software is available 65 2100 Specifications 3 5us successive approximation 14 bit resolution Discriminators computer adjusted
54. 1 15 illustrates some typical transmissions Another useful measure is the thickness of the total window meaning in this case the detector dead layer cryostat mount and entrance window A window thick ness index may be defined as the ratio of the peak areas of the 22 and 88 keV lines of 99 For thin windows the thickness index is based on the X ray fluorescence of a standard glass consisting of oxides of Si Ba Ca Li Mg Zn and B When the glass is fluoresced with an 55 source X ray lines are produced in the 1 5 keV range The peak area ratios of these lines to that of the coherently backscattered 5 9 keV line of the source can define the window thickness index 1 13 Low Background Spectros copy For very low activity spectroscopy in particular for environ mental analyses and Minimum Detectable Activity MDA determinations it is frequently necessary to eliminate background radiation This interfering radiation may come from the naturally occurring radioactive impurities in the detector cryostat materials or from cosmic sources Figure 1 16 shows the effects of background radiation and various steps taken to eliminate it The data were obtained with a PGT detector 15 10 1 10 2 10 3 10 4 10 5 Counts keV Minute 10 6 10 7 10 8 0 1200 2400 Energy keV 3600 4800 6000 Typical cryostat assembly 10 cm thick lead shield Cryostat assembly rebuilt
55. 1 nAmp at cryogenic temperatures Figure 1 4 is a simple diagram of a detector When the reverse bias is applied the intrinsic region i is created by depletion of charge carriers The detector crystal has a lithium diffused N layer about 0 5 mm thick on one surface and a thinner P layer formed by boron ion implantation or metallization on the other surface V applied 1 high voltage P layer W crystal depth i intrinsic region E electric field Figure 1 4 Schematic of photon semicon ductor interaction In this type of semiconductor radiation detector a photon interacts within the depletion region to release electrons and holes which move to the contacts of opposite polarity along the lines of the electric field E established by the applied high voltage The resulting charge is integrated by a charge sensitive preamplifier to produce a voltage pulse with height amplitude proportional to the incident photon energy 1 3 1 Photon Semiconductor Interactions Not all pulses produced by a mono energetic photon source will have the same amplitude Line broadening occurs due to statistical fluctuations and electronic noise Also some of the electron hole pairs are trapped and do not reach the detector contacts thus producing smaller sig nals which cause tailing on the low energy side of the peak Additionally many of the interacting gamma rays are not completely absorbed in the det
56. 20200 20 975 2 00 46 1 2 00 IGC25185 25 850 1 85 55 1 1 90 IGC25195 25 950 1 95 53 1 1 95 IGC25200 25 1000 2 00 50 1 2 00 IGC30185 30 860 1 85 58 1 1 90 IGC30195 30 950 1 95 56 1 1 95 IGC30200 30 1000 2 00 54 1 2 00 IGC35190 35 875 1 90 60 1 1 90 IGC35200 35 1000 2 00 58 1 2 00 IGC40190 40 875 1 90 62 1 1 90 IGC40200 4096 1000 2 00 58 1 2 00 IGC45195 4596 900 1 95 64 1 1 90 IGC45200 4596 1000 2 00 60 1 2 00 IGC50195 50 950 1 95 65 1 1 90 IGC50200 50 1000 2 00 63 1 2 00 IGC55195 55 1000 1 95 67 1 2 00 IGC55210 55 1200 2 10 64 1 2 00 IGC60195 60 1000 1 95 70 1 2 00 IGC60210 60 1200 2 10 66 1 2 00 IGC70200 70 1000 2 00 754 2 00 IGC70215 7096 1200 2 15 70 1 2 00 IGC80220 80 1200 2 20 70 1 2 00 IGC90220 9096 1400 2 20 74 1 2 00 196100230 100 1400 2 30 74 1 2 00 Table 2 3 Series Detectors 2 5 4 N type Coaxial HPGe Extended Range Detectors PGT n type germanium coaxial detectors are useful down to 3 keV since they have a standard beryllium entrance window and a thin 0 3 um P face In contrast p type detectors with their thick lithium diffusion outer contact and aluminum endcap are opaque to energies below about 40 keV The NIGC extended range detectors are therefore the best choice for applications involving both X ray and high energy gamma ray spectroscopy in the same sample These detectors exhibit excellent timing characteristics and are appropriate with anti Compton shielding They
57. 232 baud rates 2400 9600 19200 38400 57600 115200 Maximum number of units connected to PC 8 Front panel indicators LEDs for Acquire Event Serial com AUX I O in use Power 3 color LED array for dead time Rear panel controls and connectors Power switch 2 5mm power jack Fuse housing 9 pin D male RS232 connector 25 pin DB female connector for ROI output 15 pin D sub high density female auxiliary I O connector Ethernet interface connector RJ 45 ADC input BNC 0 10V unipolar or bipolar pulse ADC gate input BNC coin anti coin off CMOS TTL Pile up reject input BNC CMOS TTL Amp busy input for ext amp live time corr BNC CMOS TTL SCA output CMOS TTL ADC busy out BNC CMOS TTL Peak detect output BNC CMOS TTL Weight 4 06 Ib 1 85kg Dimensions 10 4 in 26 4cm wide 12 3 in 31 2cm deep 2 75 7 0cm tall Power requirements 10 18V DC 9 6 watts external 12V universal AC supply provided Software 32 bit QuantumMCA compatible with Windows 95 98 NT 2000 XP QuantumGold software for quantitative analy sis 73 2 13 5 System 8000 Gamma or X Ray Spectrometer Premium Performance at Price You Can Afford MCA bias supply amplifier all in one package Configurations for gamma and X ray spectroscopy Easy installation and setup No slots or reserved memory required in the PC Includes 32 bit QuantumMCA software The System 800
58. 35 0 198 1 709 1 809 75 Re Rhenium 61 131 59 707 69 298 71 220 71 662 8 65 8 584 0 008 0 273 11 684 12 522 11 955 0 531 1 774 76 Os Osmium 62 991 61 477 71 404 73 393 73 860 8 910 8 840 0 354 0 596 12 093 12 965 12 383 0 869 1 842 771 Tridium 64 886 63 278 73 549 75 605 76 108 9 173 9 098 0 706 0 918 12 509 13 413 12 819 1 211 1 914 2 041 78 Pt Platinum 66 820 65 111 75 736 77 866 78 379 9 44 9 360 1 069 11 249 12 939 13 873 13 268 1 559 1 978 2 122 79 Au Gold 68 794 66 980 77 968 80 165 80 723 9 71 9 625 1 439 11 582 13 379 14 353 13 733 1 919 2 048 2 206 80 Hg Mercury 70 821 68 894 80 282 82 526 83 113 9 987 9 896 1 823 11 923 13 828 14 841 14 212 2 285 2 120 2 295 81 Tl Thallium 72 860 70 820 82 558 84 904 85 529 10 266 0 170 2 210 2 268 14 288 15 346 14 697 2 657 2 195 2 389 82 Pb Lead 74 957 72 794 84 922 87 343 88 014 10 549 0 448 2 611 2 620 14 762 15 870 15 207 3 044 2 268 2 484 83 Bi Bismuth 77 097 74 805 87 335 89 833 90 521 10 836 0 729 3 021 2 977 15 244 16 393 15 716 3 424 2 342 2 579 84 Po Polonium 79 296 76 868 89 809 92 386 93 112 11 128 1 014 3 441 3 338 15 740 16 935 16 244 3 817 2 418 85 As Astatine 81 525 78 596 92 319 94 976 95 740 11 424 1 304 3 873 3 705 16 248 17 490 16 784 4 214 86 Rn Radon 83 800 81 080 94 877 97 616 98 418 11 724 1 597 4 316 4 077 16 768 18 058 17 337 4 618 87 Fr Francium 86 119 83 243 97 483 00 305 01 147 12 029 1 894 4 770 4 459 17 301 18 638 17 904 5 028 88 Ra Radium 88 485 85 466 100 136 03 048 03 927 12 33
59. 4 8000 Multichannel Analyzer 8000 16 000 channels of spectrum memory stand alone package Easy installation and setup via Ethernet 10 100 base T or RS 232 No slots or reserved memory required in the Includes 32 bit QuantumMCA software The MCA8000 is PGT s latest multichannel pulse height analyzer Designed to provide outstanding performance and value at an economical price its features make pulse height analysis a pleasure to perform Packaged as a stand alone unit it offers total computer control excellent performance and flexibility There are two ways to connect the MCA 8000 to the computer Ethernet and RS 232 The MCA 8000 is available in two configurations 8000 chan nels of spectrum memory and 16 000 channels Each unit also comes with QuantumMCA software for Microsoft Win dows and it is compatible with the quantitative analysis software package QuantumGold The MCA 8000 features 8 12 us successive approxima tion ADC With hardware add one to memory and an on board 20 MHz processor there is processing power to spare Differential non linearity is less than 1 percent over the top 99 of the range and integral non linearity is less than 0 05 over the same range Digital stabilizers are provided for both the gain and offset Data is stored as 31 bits per channel with an additional 8 bits for ROI informa tion Flexible live time correction is provided with a choice of simple busy Low
60. 44 6 727 6 215 0 929 61 Pm Promethium 38 687 38 160 43 945 44 955 45 207 5 431 5 408 5 956 6 336 6 89 7 448 7 018 6 466 0 978 62 Sm Samarium 40 124 39 523 45 400 46 553 46 846 5 636 5 609 6 206 6 587 7 180 7 754 7 281 6 721 63 Eu Europium 41 529 40 877 47 027 48 241 48 515 5 846 5 816 6 456 6 842 7 478 8 069 7 624 6 983 1 081 64 Gd Gadolinium 42 983 42 280 48 718 49 961 50 228 6 059 6 027 6 714 7 102 7 788 8 393 7 940 7 252 1 131 65 Tb Terbium 44 470 43 373 50 391 51 737 51 998 6 275 6 241 6 979 7 368 8 104 8 724 8 258 7 519 1 185 66 Dy Dysprosium 45 985 45 193 52 178 53 491 53 789 6 495 6 457 7 249 7 638 8 418 9 083 8 621 7 850 1 340 67 He Helium 47 528 46 686 53 934 55 292 55 615 6 720 6 680 7 528 7 912 8 748 9 41 8 920 8 074 1 293 68 Er Erbium 49 099 48 205 55 690 57 088 57 483 6 948 6 904 7 810 8 188 9 089 9 776 9 263 8 364 1 347 69 Tm Thullium 50 730 49 762 57 576 58 969 59 376 7 18 7 135 8 102 8 472 9 424 10 144 9 628 8 652 1 405 70 Ytterbium 52 360 51 236 59 352 60 959 61 313 7 414 7 367 8 401 8 758 9 779 10 486 9 977 8 943 1 462 71 Lu Lutecium 54 683 52 959 61 282 62 946 63 306 7 654 7 604 8 708 9 048 10 142 10 867 10 345 9 241 1 521 72 Hf Hafnium 55 757 54 579 63 209 64 936 65 313 7 898 7 843 0 021 9 346 10 514 11 264 10 734 9 556 1 581 73 Ta Tantalum 57 524 56 270 65 210 66 999 67 400 8 145 8 087 9 341 9 649 10 892 11 676 10 130 9 876 1 644 74 Tungsten 59 310 57 973 67 233 69 090 69 508 8 396 8 333 9 670 9 959 11 283 12 090 11 5
61. 5 1 pate 0 032 0 038 BaKXrays 7 83 Nuclide Type of Decay Half Life Photon Energy MeV Yield Cobalt 56 bt 78 0 days 0 511 Annihilation electron capture 0 847 99 97 0 977 1 4 1 038 14 0 1 175 2 3 1 238 67 6 1 360 4 3 1 771 15 7 2 015 3 1 2 035 7 9 2 599 16 9 3 010 1 0 3 202 3 0 3 254 7 496 3 273 1 8 3 452 0 9 Cobalt 57 electron capture 271 7 days 0 014 9 5 0 122 85 5 0 136 10 8 0 692 0 16 0 006 0 007 Fe K X rays 55 Cobalt Co beta 5 27 years 1 173 99 86 1 333 99 98 Europium 152 beta 13 3 years 0 122 28 2 Bt 0 245 7 4 0 344 26 3 electron capture 0411 2 29 0 444 3 196 0 779 12 8 0 867 4 1 0 964 14 4 1 086 10 0 1 090 1 7 1 112 13 6 1 213 1 495 1 299 1 696 1 408 20 6 Gold 198 beta 2 696 days 0 412 95 45 0 676 1 06 1 088 0 23 lodine 125 electron capture 60 0 days 0 035 7 0 027 0 032 Te K X rays 138 lodine 129 beta 1 57 107 years 0 040 7 5 0 030 0 035 Xe K X rays 69 lodine 1311 beta 8 04 days 0 080 2 4 0 284 5 9 0 364 81 8 0 637 7 2 0 723 1 8 Daughter 131MXe 12 days 0 164 2 Iron Fe electron capture 2 69 years 0 0059 0 0065 Mn K X rays 28 Krypton 85 beta 10 73 years 0 96 second 0 514 0 43 Daughter 5 Rb Nuclide Type of Decay Half Life Photon Energy MeV Yield Lanthanum 1401 beta 40 27 hours 0 131 0 8 0 242 0 6 0 266
62. 5 5 0 27 94 1 100 IGP213190 200 16 0 13 0 190 200 490 495 5 0 IGP505330 500 25 2 5 0 330 345 550 560 5 0 IGP507315 500 25 2 7 0 315 330 545 555 5 0 IGP510305 500 25 2 10 0 305 320 540 550 5 0 27 94 1 100 IGP513305 500 25 2 13 0 305 320 540 550 5 0 IGP1005400 1000 35 7 5 0 400 610 15 0 IGP1010380 1000 35 7 10 0 NA 380 NA 595 15 0 43 18 1 700 IGP1013360 1000 35 7 13 0 360 585 15 0 40 Table 2 6 IGP Series Detectors 2 5 7 Planar Detectors PGT s n type semi planar germanium detectors offer the best low noise and high resolution capabilities at low to moderate energies The capacitance of these detectors with a wrap around P contact and a small center N con tact is much less than that of a true planar of similar size This results in lower noise and better resolution than achieved by any other detector geometry at energies of 3 keV to 1 MeV Also because the cylindrical walls are charge collecting and because there are virtually no dead germanium layers beyond the active region these detec tors exhibit better count rate performance and peak to background ratios As with all HPGe detectors they are temperature cyclable and can be stored indefinitely at room temperature Standard Features n type high purity germanium with P ion implanted entrance window Vertical dipstick cryostat Standard 32 liter dewar Aluminum endcap and beryllium window RG 11 B C resistive feedback preampli
63. 50 14 40 1 30 2 20 IGW5023 14 50 14 40 1 30 2 30 IGW7521 10 75 10 40 1 20 2 10 IGW7522 10 75 10 40 1 20 2 20 IGW7522 14 75 14 40 1 30 2 20 IGW7523 14 75 14 40 1 30 2 30 IGW10022 10 100 10 40 1 20 2 20 IGW10023 14 100 14 40 1 30 2 30 IGW12022 10 120 10 40 1 20 2 20 IGW12023 14 120 14 40 1 30 2 30 IGW12025 16 120 16 40 1 35 2 50 IGW14023 14 140 14 40 1 30 2 30 IGW14023 16 140 16 40 1 35 2 30 Table 2 5 IGW Well Detectors 2 5 6 High Purity Germanium Planar Detectors PGT p type germanium planar detectors have high effi ciency in the lower energy ranges making them the ideal detectors for transuranic materials and mixed gamma and X ray samples The combination of the thin entrance layer with a beryllium endcap window allows detection down to 3 keV The IGP detectors are available in sizes from 25 mm to 1000 mm to meet your needs for economical small area counting at low to intermediate energies P type planar detectors retain their high resolution up to 1 MeV With the optical feedback or transistor reset preamplifiers energy count rate product limits are 200 and 400 GeV sec respec tively These rugged detectors have a long service life and can be stored warm for extended periods of time Some intrinsic efficiency curves for planar detectors are listed on page 12 Features p type high purity germanium with very thin metal lized entrance window Vertical dipstick cryostat Standard 32 liter d
64. 7 0 283 0 002 0 002 7N Nitrogen 0 392 0 400 0 008 0 008 80 Oxygen 0 525 0 531 0 009 0 009 9F Fluorine 0 677 0 687 10 Ne Neon 0 849 0 874 0 048 0 022 0 022 11 Na Sodium 1 041 1 067 1 072 0 055 0 034 0 034 12 Mg Magnesium 1 253 1 295 1 303 0 063 0 050 0 049 13 Al Aluminum 1 486 1 486 1 553 1 559 0 087 0 073 0 072 14 Si Silicon 1 740 1 739 1 832 1 840 0 118 0 099 0 098 15 Phosphorus 2 014 2 014 2 136 2 142 0 153 0 129 0 128 16S Sulfur 2 308 2 306 2 464 2 470 0 193 0 164 0 163 Chlorine 2 622 2 621 2 815 2 820 0 238 0 203 0 202 18 Ar Argon 2 957 2 955 3 192 3 203 0 287 0 247 0 245 19K Potassium 3 313 3 310 3 589 3 608 0 341 0 297 0 294 20 Ca Calcium 3 691 3 688 4 012 4 038 0 341 0 344 0 399 0 352 0 349 21 Sc Scandium 4 091 4 085 4 460 4 496 0 395 0 399 0 462 0 411 0 406 22 Titanium 4 510 4 504 4 931 4 964 0 452 0 458 0 530 0 460 0 454 23 Vanadium 4 9452 4 944 5 427 5 464 0 511 0 519 0 604 0 519 0 512 24 Cr Chromium 5 414 5 405 5 946 5 9887 0 573 0 581 0 679 0 583 0 574 25 Mn Manganese 5 898 5 877 6 490 6 537 0 637 0 647 0 762 0 650 0 639 26 Fe Tron 6 403 6 390 7 057 7 111 0 705 0 717 0 849 0 721 0 708 27 6 930 6 915 7 649 7 709 0 776 0 790 0 929 0 794 0 779 28 Ni Nickel 7 477 7 460 8 264 8 328 8 331 0 851 0 866 015 0 871 0 853 29 8 047 8 027 8 904 8 976 8 980 0 930 0 948 1100 0 953 0 933 307 Zinc 8 638 8 615 9 571 9 657 9 661 1 012 1 032 200 1 045 1 022 31 Gallium 9 251 9 234 0 263 10 365 10 368 1
65. 8 2 194 5 223 4 839 17 845 19 233 18 481 5 442 89 Ac Actinium 90 894 87 681 102 846 05 838 06 759 12 650 2 499 5 712 5 227 18 405 19 842 19 078 5 865 90 Th Thorium 93 334 89 942 105 592 08 671 09 630 12 966 2 809 6 200 5 620 18 977 20 460 19 688 6 296 2 991 3 332 91 Pa Protactinium 95 851 92 271 108 408 11 575 12 581 13 291 3 120 6 700 6 022 19 559 21 102 20 311 6 731 3 077 92U Uranium 98 428 94 648 111 289 14 549 15 591 13 613 3 438 7 218 6 425 20 163 21 753 20 941 7 163 3 165 3 552 93 Np Neptunium 101 005 97 023 114 181 17 533 18 619 13 945 3 758 7 740 6 837 20 774 22 417 21 596 7 614 94 Pu Plutonium 103 653 99 457 117 146 20 592 21 720 14 279 4 802 8 278 7 254 21 401 23 097 22 262 8 066 95Am Americium 106 351 101 932 120 163 23 706 24 876 14 618 4 411 8 829 7 677 22 042 23 793 22 944 8 525 96 Cm Curium 109 098 104 447 123 235 26 875 28 088 14 961 4 743 9 393 8 106 22 699 24 503 23 640 8 960 97 Bk Berkellium 111 906 107 023 126 362 30 101 31 357 15 309 5 079 9 971 8 540 23 370 25 230 24 352 9 461 98 Cf Californium 114 745 109 603 129 544 33 383 34 683 15 661 5 420 20 562 8 980 24 056 25 971 25 080 9 938 99 Es Einsteinium 117 646 112 244 132 781 36 724 38 067 16 018 5 764 21 165 9 426 24 758 26 729 25 824 20 422 100 Fm Fermium 120 598 114 926 136 075 40 122 41 51 16 379 6 113 21 785 9 879 25 475 27 503 26 584 20 912 Appendix 5 Glossary ACTIVE REGION The region of a detector crystal in which charge created by ionizin
66. A at 1332 5 keV plus the count As in the sum peak and the absolute in well efficiency is given by W A AjJ Ns The Compton continuum below the sum peak may also be a factor PGT reports for well detectors in accordance with ANSI IEEE 325 1996 for Co to give efficiency informa tion about the whole crystal volume and for 1291 to give low energy 40 keV absorption information Additionally PGT also reports the external relative effi ciency of the detector There are two designs for well detectors the blind hole and the through hole as illustrated in Figure 1 14 blind hole is the original configuration used by PGT to manufacture its first Ge Li well detectors around 1968 PGT now uses the through hole geometry because it results in better performance At first glance it would appear that the blind hole design is more efficient because it has closer 10 47 counting geome try This holds true only for point sources or very small samples The through hole well allows for a deeper sample hole as shown in the illustration The surface area of the additional well length T in Figure 1 14 is greater than the area lost B at the bottom of the well for all standard well diameters Thus a larger sample volume longer sample tube can be analyzed for a given crystal length and the position of the sample can be centered within the crystal The result is that more counts from a larger volume can be analyz
67. If you are ordering a new detector with no restrictions for example spatial constraints the following suggestions in lower energy spectroscopy If you must have a dipstick cryostat consider the following 1 Lead shield 2 Internal shield between the back of the cryostat and the preamp and dewar Copper clad lead is prefera order would result in increasingly low background counts 1 NPR cryostat preferably with an external preamp and 2 A lead shield 3 Replace the endcap and internal metal parts with OFHC copper or low background aluminum more 60 expensive ble but tungsten is more compact therefore the choice may depend on how much space is available Material Application Material Data Oxygen free high conductivity copper OFHC endcaps 4 and 8 mounting cup pedestal unit and nut cooling rod clamp and coldfinger 0 24 dpm kg 209 0 78 dpm kg 2 Bi 15 2 dpm kg Ultra low background Pechiney aluminum 1ppb Th endcap and crystal holder well insert 96 Al 4 Si lt 150 parts per trillion U Th 50 mm virgin lead internal shield 8 endcap copper clad 50 mm tungsten internal shield Ultra low background beryllium IF I and IF II 2 5 and 3 entrance window for n type detectors Vacuum tight optically dense foils 99 9 Be IF I with 2 ppm U 1 ppm Th 99 6 Be IF II with 2 ppm U 3 ppm Th Vespel
68. Il 2 5 and 3 entrance window for n type detectors Vacuum tight optically dense foils 99 9 Be 1 1 with 2 ppm U 1 ppm Th 99 6 Be 1 11 with lt 2 ppm U 3 ppm Th Vespel SP 22 entrance window well insert 4096 graphite f you are ordering a new detector with no restrictions for Table 1 1 Background Material Specifications disintegrations minute typical example spatial constraints the following suggestions 1 order will result increasingly low background counts 2 1 NPR cryostat preferably with an external preamp and 2 A lead shield 3 Replace the endcap and internal metal parts with OFHC copper or low background aluminum more expensive 4 Use low background beryllium or Vespel window for lower energy spectroscopy If you must have a dipstick cryostat consider the following Lead shield Internal shield between the back of the cryostat and the preamp and dewar Copper clad lead is preferable but tungsten is more compact The choice may depend on how much space is available 17 Series Crysial Geometry Energy Resolution Sizes Peak Shape Crysial Range NIGC n type high purity 59 keV Peak Compton x Mn germanium 17 665 1200 m 38 1 62 1 Contact thickness A HpGe 10 Mev 1 33 MeV FWTM FWHM 0 3um coaxial 1 8 2 3 keV 1 9 2 0 3 p type high pur
69. Lederer and V S Shirley Table of Isotopes 7th edition Wiley Interscience New York 1978 U Reus and W Westmeier Atomic Data and Nuclear Data Tables 29 1 1983 C F Williamson J P Boujot and J Picard Centre d Etude Nucl aires de Saclay Report No CEA R 3042 1966 User s Manual Gamma and X ray Detectors Princeton Gamma Tech Inc 1994 92 Standards Standard Reference Material 477 National Institute of Standards amp Technology Washington D C 1978 The following are available through the Institute of Electrical amp Electronics Engineers IEEE Standard Test Procedures for Semi Conductor Charged Par ticle Detectors ANSI IEEE Standard 300 1988 R1993 IEEE Standard Test Procedures for Amplifiers and Preamplifiers Used with Detectors of lonizing Radiation ANSI IEEE Standard 301 1988 R1993 withdrawn IEEE Standard Test Procedures for Germanium Gamma Ray Detectors ANSI IEEE Standard 325 1996 ANSI IEEE 645 1978 IEEE Standard Techniques for Determination of Germanium Semi conductor Detector Gamma Ray Efficiency Using Standard Marinelli Re entrant Beaker Geometry ANSI IEEE 680 1978 IEEE Standard Test Procedures for Semiconductor X ray Energy Spectrometers ANSI IEEE Standard 759 1984 IEEE Standard Cryostat End Cap Dimensions for Germanium Semiconductor Gamma Ray Spectrometers ANSI IEEE Stan dard 1131 1987 withdrawn IEEE Standard Test Procedures for High Purity German
70. M is 2 65 The MCA selection itself may impose a limit on resolution For example if each channel covers 0 5 keV energy range of 2 MeV with only 4000 channels available the difference between detectors with resolutions of 1 17 and 2 2 keV at FWHM is hardly perceptible but the difference in cost is significant 1 8 Peak to Compton Ratio Compton scattering is the most important interaction in a germanium detector crystal for gamma rays with energies between 150 keV and 7 MeV Scattered photons that escape the crystal are not detected but their recoil elec trons produce counts in the energy region below the full energy peak of the incident photon This continuous back ground which is in addition to the background from ambi ent sources increases the minimum detectable activity MDA of any photons with peaks in that region Thus in 14 samples with multiple sources such as low activity envi ronmental samples the additional background due to Compton scattering of the higher energy photons occurs over all the lower energy regions The peak to Compton ratio is reported as the ratio of the peak height for the 1 33 MeV gamma ray of 0 to the average height of the Compton continuum over the energy range 1 040 1 096 MeV In general a detector with a higher peak to Compton ratio will have higher line to background ratios and better count ing statistics for complex spectra The value depends on detector geometry mount and
71. Np Parallel noise 111111 2 N S ries noise Not s 1 f Noise SE 1111 2 Np 10 Pulse Processing Time usec Figure 1 22 Electronic noise contributions as a function of pulse processing time in a resis tive feedback preamplifier Decreasing the shaping time to 0 5 can double the count rate capability of a system Increasing the noise and therefore resolution can raise the count rate capability by only about 12 The optimum shaping time Topt for a given germanium detector system is typically around 4 usec Gaussian shaping time corresponding to approximately 20 usec pulse processing time Np is negligible in pulsed optical preamps and small with transistor reset preamps This reduces Nop and shifts the Topt to longer pulse processing time as shown in Figure 1 23 Therefore a longer time constant is often used with pulsed reset preamps without loss of resolution Also 23 10 M Quadratic sum of T parallel and series noise Np Parallel noise i Ng Series noise 1 2 2 N SN m es N 2 o 10 up b Pulse Processing Time usec Source Count Increase in FWHM with line Rate cps Shaping Time 4 2 01 0 5us us us us 60 1000 0 1 4 8 1332 keV 10 000 5 4 5 8 20 000 9 6 7 9 50 000 17 12 10 11 100 000 20 18 15
72. Nuclear Products Catalog FIPGIT PRINCETON GAMMA TECH Princeton Gamma Tech Inc C N 863 Princeton NJ 08542 0863 USA Tel 609 924 7310 Toll Free 800 980 9284 Fax 609 924 1729 e mail nuclearsales pgt com www pgt com 1995 1998 1999 2000 2002 Princeton Gamma Tech Inc formerly American Nuclear Systems Inc All rights reserved The following are trademarks or registered trademarks of Princeton Gamma Tech Inc Quantum Quantum MCA Quantum LIB Quantum X QuantumGold Printed in USA TRADEMARK ACKNOWLEDGMENTS The following are registered trademarks of the companies listed Excel Visual Basic Microsoft MS DOS and Windows Microsoft Corporation IBM International Business Machines Corporation Intel Intel Corporation GPIB National Instruments IMPORTANT PLEASE READ CAREFULLY NOTIFICATION OF COPYRIGHT THE FIRMWARE IN THIS DEVICE IS PROTECTED BY COPYRIGHT LAWS AND INTERNATIONAL TREATY YOU MUST TREAT THE FIRMWARE LIKE ANY OTHER COPYRIGHTED MATERIAL COPYRIGHT LAWS PROHIBIT MAKING ADDITIONAL COPIES OF THE FIRMWARE FOR ANY REASON OTHER THAN SPECIFICALLY DESCRIBED IN THE LICENSE BELOW YOU MAY NOT COPY THE WRIT TEN MATERIALS ACCOMPANYING THE PRODUCT LIMITED WARRANTY LIMITATION OF REMEDIES All hardware purchased from Princeton Gamma Tech Inc PGT is covered by a one 1 year return to factory warranty If your system was pur chased directly from PGT contact the factory directly If the system was
73. RS 232 interfaces to make connec tion to the PC or network easy High Performance for X Ray Applications The System 4000 gamma spectrometer has been engi neered to give optimum performance in a wide range of applications with HPGe and Si Li detectors The three computer selectable time constants offer choices for high throughput applications standard operation and highest possible resolution The shaping amplifier features 8th order triangular and Gaussian filters for minimum series noise and optimum resolution Automatic noise discriminators and a gated baseline restorer with rate adaptive restoration give the ultimate in stability even at the highest count rates To provide the best possible pile up rejection even at the lowest energies the fast channel has adaptive time constants which ensure maximum possible sensitivity This translates into the best possible performance from your detector system Com puter control of all hardware functions also complements the power and flexibility of the system The System 4000 has 15 dedicated TTL ROI outputs and one ROI byte with strobe The ROI outputs can be directed to counters or rate meters for monitoring individual regions or peaks Analytical Software For qualitative analysis the System 4000 includes QuantumMCA software at no additional charge This package features an intuitive user friendly interface The main screen is not cluttered with buttons and controls Tool tips all
74. This discussion will concentrate on the interactions of pho tons gamma rays and X rays in semiconductor detectors The energy of a gamma ray or an X ray is characteristic of its source Gamma rays originate within the nucleus as a result of nuclear transformations and disintegrations and have energies ranging from approximately 100 eV to 100 MeV X rays are the result of electron transitions from a higher energy to a lower energy electron shell of an atom and have energies ranging from a few eV to almost 150 keV The basic energy unit for this application is the electron volt eV equal to 1 6 x 10 Joule 1 2 Photon Matter Interactions The three primary processes in which photons interact with matter to give up all or part of their energy in single events are The photoelectric effect Section 1 2 1 Compton scattering Section 1 2 2 Pair production Section 1 2 3 For narrow beam of photons traversing an absorber material of thickness y the attenuation of the beam is given by the equation Noe HY where Ny the number of remaining photons and u the total attenuation coefficient for the three processes 1 2 1 The Photoelectric Effect In a photoelectric event the entire photon energy is absorbed by a bound atomic electron which is ejected with a kinetic energy equal to the photon energy minus the bind ing energy of the electron The cross section for the pro cess increases with atomic
75. ULD and lower level LLD dis criminators and the ADC zero offset are all computer con trolled Conversion gain can be set in the following increments MCA 4001 250 channels 500 and 1000 MCA 4002 250 channels 500 1000 and 2000 MCA 4004 250 channels 500 1000 2000 and 4000 A wide range of presets is available including live time real time integral of all ROIs integral of selected ROIs total SCA counts net ROI statistics and gross ROI statis tics The MCA4000 has many of the I O connections you need for configuring any measurement application Exter nal rear panel BNC connections are provided for GATE REJECT BUSY IN and ADC INPUT The polarity of REJECT and BUSY IN can be programmed from the MCA software MCA outputs include SCA OUT PEAK DETECT and ADC BUSY The polarity of the PEAK DETECT and ADC BUSY signals can also be programmed from the soft ware A 44 pin DSUB connector is also provided for ROI outputs and digital control signals Analytical Software For qualitative analysis the MCA4000 includes Quantum MCA software at no additional charge However for those applications that require quantitative gamma analysis PGT offers QuantumGold as an option This package features an intuitive user friendly interface The main screen is not cluttered with buttons and controls Tool tips allow fre quently used functions to be quickly and easily identified For the user who wants to control the analytical pro
76. a multiple port RS232 interface which allows daisy chaining of System 4000 units together can be used In any case a total of eight units can be con nected to one PC Available configurations System 4004 with 4000 channels of spectrum memory Pulse shaping constants 1245 and 2405 0 to 1KV bias supply cuo mmo 9 oU o R n o mm mm 69 70 System 4000 Specifications ADC 2 75 successive approximation ADC 12 bit resolution PC adjusted discriminators upper 0 to 105 of full scale and lower lt 1 to 105 of full scale in 0 41 increments Zero adjustment in increments of 0 41 PC adjusted Maximum throughput 180 000 cps Non linearity Differential non linearity lt 1 over top 99 of range Integral non linearity 0 05 over top 99 of range Spectrum memory both models 250 500 1000 2000 4000 channels Maximum counts per channel 231 1 i e 2 1E9 Digital stabilizer Internal ADC zero and gain stabilization PC controlled time constants Balanced channel and ROI centroid modes Gain 12 5 range Zero 1 25 range Counting presets Real time Live time Integral of all ROIs Integral of selected ROIs e Gross ROI statistics Net ROI statistics Total system counts Total SCA counts Battery backup for Spectrum Setup parameters Clock memory Computer control e RS 232
77. activity radiation because they surround the analyte Their through hole design allows for analysis of larger samples at high resolution NIGP n type HPGe Semiplanar Detectors offer lower noise and consequently better resolution at low to moderate energies than any other detector geometry They are used in lung monitor arrays IGP p type HPGe Planar Detectors are rugged in construction and can deliver clean spectra with high efficiency Their maximum efficiency in the lower energy ranges makes them ideal for spectroscopy of transuranic materials and mixed gamma and X ray samples Si Li Lithium drifted Silicon Planar Detectors are used mainly for X ray spectroscopy They are suitable for energies from 100 eV to 60 keV IGX p type HPGe Planar Detectors have a thin entrance window for X ray spectroscopy in an energy range of 180 eV to 100 keV They have energy resolutions as good as 120 eV FWHM at 5 9 keV It is important to choose the right detector type and size A detector that is too big not only wastes money but may also create problems due to high count rates An under sized detector may be cheaper in price but expensive in time Of course PGT will gladly work with you to meet any special requirements you have 1 15 Crystal Materials HPGe has an impurity level of 10 9 cm Impurities may be either p or n types and determine the parity of the crys tal To fabricate a detector a thin P layer is formed
78. al experts can help you assemble a new system select a new detector or repair and update an older detector purchased from another manufacturer This page intentionally blank Section 1 Principles of Gamma and X ray Radiation Detection Princeton Gamma Tech specializes in the manufacture of semiconductor detectors for detection and high resolution spectroscopy of gamma rays and X rays This section describes the basic principles of gamma ray and X ray radiation detection 1 1 Radioactivity Naturally occurring radioactivity the emission of penetrat ing energy from matter was first studied in depth in the late nineteenth and early part of the twentieth century Max Planck deduced in 1900 that radiation is transmitted as dis crete energy packets which he called photons Further work by scientists such as Rutherford Curie Einstein Bohr and others established the wave particle duality of radiation the interrelationship of matter and energy and the basic understanding of atomic structure Figure 1 1 is a simplified representation of the Bohr model of the atom with a tightly packed nucleus of positively charged protons and uncharged neutrons and with nega tively charged electrons in fixed orbits around the nucleus y ray e g from Co decay 1 K shell electron is ejected by collision with a high energy particle or photon 2 L shell electron drops into the K shell 3
79. alysis summary 8 System 4000 specifications 70 System 4000 X ray Spectrometer 69 System 8000 specifications 75 System 8000 Spectrometer 74 U unitary cryostats 48 well detectors design 13 efficiency 13 window materials 15 20 46 X ray detectors 42 95
80. alysis using portable or truck installed detectors Nuclear plants and other industrial sites where vibra tions from heavy machinery are a problem For mechanically cooled detectors such as JT Cool the QUIET ONE mount offers the unique advantage of provid ing the same high performance specifications as a liquid nitrogen cooled system No other detector manufacturer can offer this advantage For less severe requirements the user can reduce micro phonics due to external vibrations by mounting the dewar and detector on cushioning such as foam or felt 1 20 Pulse Processing Electronics and Software PGT can provide a variety of pulse processing electronics and analytical software to complete a sodium iodide or ger manium based gamma spectroscopy system or a Si Li or germanium based X ray spectroscopy system These solu tions include integrated electronics and component elec tronics PGT also offers software for HPGe and Na l gamma spectroscopy applications Please see the follow ing sections for additional information about these prod ucts MCA 4000 Multichannel Analyzer on page 67 System 4000 X Ray Spectrometer on page 69 MCA 8000 Multichannel Analyzer on page 72 System 8000 Gamma or X Ray Spectrometer on page 74 MCA 2100R Multichannel Pulse Height Analyzer on page 65 Quantum MCA Software for Windows on page 77 If the system requires various components for example special shieldin
81. analysis Results are available by isotope or by ROI The method allows the user or the system to set ROls This method can include multiple lines to be ana lyzed Each ROI explicitly specifies the isotope to be analyzed Detector Parameters x Detector Designation Detector Type PGT 5020 20 Nal C 5411 Detector Window Parameters C Hp amp GelN Material Thickness Window ti far e 508 0 Window 2 None s 0 0 Window 3 None 3 0 0 Window amp None 0 0 Flow PC Detector Size Cylindrical C Well Coaxial Diameter 5 08 cm Thickness cm Incidence Angle DU NEU en Eo Iz ime tow SS aga T All QuantumMCA software products share a rich feature set and support a wide range of hardware from PGT Enjoy the convenience of controlling multiple MCA types from a single unified user interface Features Software True 32 bit application Simplified user interface New COM interface commands and added func tions for QScript Ethernet support for PGT spectrometers and mul tichannel analyzers that have ethernet capability Calibrations Automatic setup of HV coarse and fine gains using 137Cs source if hardware allows control Automated individual isotopic calibrations from single or multi isotopic s
82. annel 2 1 i e 2 1E9 Digital stabilizer Internal ADC zero and gain stabilization PC controlled time constants Balanced channel and ROI centroid modes Gain 3 range Zero 1 25 range Multichannel scaling Input rate 2 Dwell time 10ms to 2 1E7 seconds Dead time 3us between passes and between channels Signal sources internal SCA any ROI external input Counting presets Real time Live time Integral of all ROIs Integral of selected ROIs e Gross ROI statistics Net ROI statistics Total system counts Peak counts Total SCA counts External events Amplifier Gaussian and triangular shaping of unipolar pulses PC selectable Acceptable input positive negative pulses step or tail with rise times of 10ns to 500ns and decay times from 50ps to Input single ended or differential BNC PC selectable Shaping constants PC selectable 2 5 4us 8us Gamma systems 12 45 or 24us X ray applications Pole zero provided for DCR type preamplifiers Pole zero adjustment assistant eliminates need for oscilloscope Gain from 4x to 1300 PC controlled Coarse gain 4X 8X 32X 64X 128X 256X 512 Fine gain 1 to 2 55x in increments of 0 0007 Common mode rejection ratio 2500 typically 21000 Temperature instability Gain guaranteed lt 50 ppm C typical 25 ppm C 0 to 50 C Offset guaranteed lt 10 N
83. ap Materials Window Material Applications Beryllium For energies down to 3 keV for large diameter endcaps lower for smaller diame ter endcaps with thinner windows Low background Be IF I and also available PRISM polymer X ray detectors for elements down to boron 185 eV Vespel polymer Inexpensive low background although somewhat lower transmission than Be especially useful as well detector insert 46 Table 2 10 Window Materials See page 15 of the introductory section for examples of 2 7 Cryostats In broad terms cryostat refers to the detector endcap cold finger and the liquid nitrogen LNo dewar by which the detector crystal and FET are maintained at cryogenic tem peratures 2 7 1 Dipstick Cryostats In dipstick cryostats the vacuum system of the endcap coldfinger is separate from that of the dewar These dew ars are available in two standard models as shown at the right The basic construction is shown in Figure 2 10n page 27 Features Rugged aluminum construction Single or double neck models with 32 liter or 30 liter capacity respectively Holding time of up to 12 days Options Liquid Nitrogen Auto fill System Endcap configurations are shown below fill tube A 32 liter capacity Y 48 476mm gt 18 75 Double Neck Offset Dewar Standard Dips
84. ate such an electron hole pair is 3 0 eV in germanium 3 76 eV in silicon at 77 3 6 eV in silicon at room temperature These values are independent of the type or energy of the incident radiation The relatively high atomic number the low values of compared with the energy necessary to create an electron ion pair in a gas and the fact that they are independent of the type and energy of incident radiation make semicon ductor detectors ideal for nuclear spectroscopy 1 3 2 Fano Factor Comparison of these values with the forbidden bandgap values of 1 115 eV for Si at room temperature and 0 73 eV for Ge at 80 K provides evidence that not all the energy of the ionizing radiation is used in breaking covalent bonds Some is converted to phonons in the lattice The number of electron hole pairs n produced at a given energy of incident radiation is not fixed as would be the case if all the energy were used in breaking covalent bonds Nor is there a Poisson distribution to indicate an uncorrelated partitioning of the energy between covalent bond breaking and lattice vibrations or phonon production Several competing mechanisms are involved in the energy loss The Fano Factor F has been introduced to account for the variance in the number of electron hole pairs pro duced If there were no variation in the number of electron hole pairs F would be 0 If there were a Poisson distribution of energy loss mechanisms F wo
85. axial germanium detectors at Yale University Measurements were made both with 99Co 1 17 MeV and 1 33 MeV cas cade and with 22 511 keV annihilation sources In this set of experiments the timing spectrum was first collected with a 60 nsec delay and then the run was repeated with an additional 16 nsec delay in the germanium detector cir cuit Figure 1 10 shows a typical plot Note the clear sepa ration deep valley between the two peaks obtained with and without the 16 nsec delay The detectors had both excellent energy 1 8 keV and timing resolution 2 4 nsec 350r 1 300 At 16 nsec 1 250 tres 24 nsec 200r 150 100 8 i ple 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Time nsec Figure 1 10 Timing resolution of a 20 IGC detector 1 7 Detector Selection Parameters The detector characteristics used to judge the suitability of a detector for a particular application include Efficiency Energy resolution Peak to Compton ratio Generally the larger the detector the better the efficiency and peak to Compton ratio with perhaps some loss in res olution With poorer resolution however peaks become somewhat broader and therefore not as tall as a result the peak to Compton ratio decreases Moreover very large crystals require a lower impurity concentration 109 cm at a significantly higher cost The following discussion of detector characteristics is bas
86. baud rates 2400 9600 19200 38400 57600 and 115200 Maximum number of units connected to PC 8 Amplifier Gaussian and triangular shaping of unipolar pulses PC selectable Acceptable input pos neg pulses step or tail with rise times of 10ns to 500ns and decay times from 505 to Input single ended BNC or differential BNC selectable Pole zero provided for DCR type preamplifiers Pole zero adjustment assistant eliminates need for oscilloscope Gain from 4x to 1300 PC control Coarse gain 4X 8X 32x 64x 128 256x 512 Fine gain 1 to 2 55x in increments of 0 0007X Common mode rejection ratio 2500 typically 21000 Temperature instability Gain guaranteed 550 ppm C typical 25ppm C 0 to 50 C Offset guaranteed lt 10 Noise lt 0 05 typical lt 0 025 Baseline restorer slow channel rate adaptive with automatic threshold fast channel with automatic threshold Live time correction modes simple busy Lowes Gedcke Hale external Bias Supply Oto t 1 2kV External shutdown capability positive true or negative true polarity Ripple X20mV peak to peak Temperature instability lt 0 01 C 0 to 50 Bias polarity internally jumper selected Front panel indicators LEDs for acquire event serial com AUX I O in use power shaping constant bias on polarity fault PUR Dead time meter 3 color LED array
87. cess QuantumGold will still be a pleasure to use The Tools Setup window allows the fine tuning of parameters associ ated with the analytical calculations Some of these con trols include peak search sensitivity line matching for library based identification of isotopes and ROI definitions The efficiency calibration process is as simple as selecting energy lines associated with the various calibration stan dards and then pressing one button The efficiency curve is generated along with a theoretical model for the response of the detector The gamma activity report includes all information associ ated with the analysis Likewise each spectrum data file contains all information associated with the calibration that was in effect at the time of acquisition Computer and Network Connectivity Quantum MCA has a single hardware setup and search utility that establishes communication with PGT multichan nel analyzers using RS232 or ethernet Both methods offer the advantage of connecting the 4000 directly to a PC The RS232 interface is a quick and simple way to connect the MCA 4000 directly to a PC in the field or other location An unused COM port is all that is needed Multiple MCA4000s can also use Ethernet connections 67 4000 Specifications 2 75 successive approximation ADC 12 bit resolution Discriminators PC adjusted upper 0 to 105 of full scale and lower lt 1 to 105 of full scale in
88. cryostat configuration detector efficiency and detector resolution It increases with detector active volume and decreases with increase in the FWHM For ultimate detection sensitivity the Compton continuum can be diminished by using a Compton sup pression device 1 9 System Noise and Micro phonics Noise refers to the signal distortion which can obscure important information in the signal It leads to poor resolu tion and higher background System electronic noise is due primarily to the FET and detector components See Noise Effects on page 23 for a discussion of electronic noise Microphonics refers to mechanically generated noise resulting from such sources as the bubbling of nitrogen in the dewar or heavy equipment in the vicinity of the detec tor PGT offers a low microphonics assembly the QUIET ONE described on page 25 1 10 Energy Range The energy range of interest is another factor in detector selection X rays and low energy gamma rays are not effi ciently detected by coaxial germanium crystals Planar Si Li detectors are the choice for X rays from 100 eV to 60 keV For X rays and low energy gamma rays over the range 3 keV 1 MeV planar p type germanium and semi planar n type germanium detectors are ideal Coaxial detectors available in a range of sizes and effi ciencies are used at energies up to 10 MeV See Table 1 1 for a tabulation of detector types and energy ranges 1 11 High Count Rates For high ac
89. d angle lost by this geometry is minimal for stan dard hole sizes and is more than compensated for by bet ter detector performance particularly at low energies which translates to lower Minimum Detectable Activity values The closed end well detectors manufactured by other ven dors are forced by that design to have a longer FET gate wire as much as 6 inches or more which significantly degrades resolution due to microphonics The boitom line is performance PGT well detectors offer a lower MDA faster counting rate and greater sensitivity PGT believes that the through hole design makes these well detectors the best you can buy A more rigorous analysis of the two well detector designs starts on page 13 The usual energy range is from 10 keV to 10 MeV but the lower limit can be extended to 5 keV with beryllium or low Z organic inserts These detectors are ideal for use with sam ple changers A representative efficiency curve is shown on the next page With larger diameter holes the efficiency may be somewhat less Features p type high purity germanium with vapor deposited gold center contact Vertical dipstick cryostat Standard 32 liter dewar Aluminum endcap and well insert Proprietary microphonic suppression system RG 11 B C resistive feedback preamplifier 12 ft bias signal and power cables Unlimited temperature cycling without loss of resolution Passivated surface Aluminum endcap N lit
90. dering information 2 2 Ordering Information PGT employees have extensive experience in designing and manufacturing customized spectroscopy systems We will be happy to work with you to meet your current and future needs Please direct your inquiries to the Nuclear Products Group To contact PGT Phone 609 924 7310 FAX 609 924 1729 Toll Free 800 980 9284 E mail sales pgt com www pgt com Nuclear index html Please mail inquiries to Princeton Gamma Tech Inc C N 863 Princeton NJ 08542 0863 2 2 1 Sample Order A sample standard order of a p type detector of 1596 rela tive efficiency with 1 80 keV resolution at 1 33 MeV in an NPR cryostat with a 30 liter dewar would be specified as IGC15180 NPR 30 2 3 Limited Liability Warranty PGT warranties that its germanium and silicon detectors are free from all defects in materials and workmanship and will not fail in normal service for a period of one year after delivery if they are properly cared for High purity germanium HPGe or IG detectors are expressly covered for any damage or deterioration that may caused by warm ups or by temperature cycling of the detector PGT warrants that any IG detector will not fail to meet published specifications due to repeated or pro longed warm ups to room temperature during the warranty period PGT is not responsible for damage resulting from exposure to fast neutrons It is the responsibility of the user to make
91. ds are available see the MBSS List Appendix 82 The MBSS must be calibrated as to the pho ton emission rate at specified energies The Marinelli beaker geometry is shown in Figure 1 13 The absolute full energy peak efficiency M of such a detec tor assembly is defined as M A Ng where A is the num ber of counts detected in the full energy peak during collection for live time 1 and Ng is the number of gamma rays originating in the MBSS during time t The 1332 5 keV line of Co is the most frequently used line although at low energies the 88 keV ray of Cd is preferred 11 100 70 20 50 Ge absorption edge 30 20 10 20 coaxial Beryllium window 20 thickness mils 0 7 0 5 30 Intrinsic Detector Efficiency percent 0 3 0 2 0 1 Detector Thickne mm SS 5710 15 13 3 5 7 10 20 30 50 70 100 200 300 5007001000 2000 3000 Photon Energy keV Figure 1 12 Intrinsic Detector Efficiency for various planar crystal thicknesses deter mined for a point source approximately 25 cm from the crystal face and for compari 12 son for typical coaxial detectors _ support 1
92. duced in the detector Where the dead layer is the P layer formed by ion implan tation or metallization its thickness is typically about 0 3 For germanium planar and Si Li planar detectors the dead layer is approximately 0 1 um The IGC coaxial detec tor has a lithium diffusion dead layer 0 5 mm thick For detector crystals mounted in series in a single endcap there may be both an entrance and an exit dead layer 19 1 15 3 Window Materials In addition to the crystal dead layer any endcap or window material between the source and the detector crystal has the potential to absorb radiation and thus reduce efficiency As noted earlier see page 15 this is especially true at lower energies The standard endcap for coaxial and well detectors is alu minum Beryllium and polymer entrance windows are avail able for low energy spectroscopy Beryllium and supported organic thin windows are used with the Si Li X ray detec tors which can also be operated in a windowless mode for light element analysis Note that a detector with a light ele ment window must be kept in the dark or the endcap cov ered to protect it from lower energy radiation IR visible UV 1 16 Preamplifiers The preamplifier is an important component in a semicon ductor detector PGT offers three types of preamplifiers Resistive feedback PGT RG 11 B C PGT RG 15 in line PGT 352 Low Power Pulsed optical reset PGT PO 14B Transis
93. e cooling period required before the kV supply is turned on It is usually more efficient to maintain the detector at the ready by replenishing the LN supply at regular intervals This information is also furnished with the detector If the detector has started to warm up because the has run dry or because of power loss to the mechanical cooler it is necessary to warm it up completely before cool ing it down again The reason is that the molecular sieve getter which helps to maintain the cryostat vacuum begins to outgas in the early stages of warm up Unless the System is brought to room temperature these contami nants will deposit on the detector crystal and cause the res olution to degrade 27 Section 2 PGT Products 2 1 Introduction This section provides product specifications and descrip tions for the following PGT nuclear products Standard detector crystals Dewars Cryostats and mechanical coolers Special low background materials Preamplifiers and other electronic components The appendixes include Examples of spectra obtained using different PGT detectors Information on standard radionuclide sources A table of gamma and X ray critical absorption and emission lines for all elements Follow the steps listed below to put together the nuclear spectroscopy system that meets your requirements PGT can provide complete gamma spectroscopy systems including analytical software
94. e systems A variety of cryostat configurations Low background materials such as OFHC copper endcaps Ultra low background IF 1 beryllium windows Transistor reset preamplifier for high count rates Energy count rate product limit gt 800 000 MeV sec Low power preamplifier JT Cool mechanical cooler Ultra low microphonic QUIET ONE crystal mounting Optional Neutron Radiation Damage Repair Kit 50 absorption edg ve 1 2 3 5 710 20305070100 200 500 1000 2000 Photon energy keV 35 36 Typical Applications Extended range nuclear spectroscopy down to 3 keV and where neutron flux may be a problem With Compton suppression systems in particle accelerator studies High count rate measurements Detector of choice for space applications resistant to damage by high neutron and proton flux Portable systems for field characterization of materi als of unknown energy Optional Neutron Radiation Damage Repair Kit An optional kit which includes a special vacuum valve temperature controller and heater may be purchased for in house repair of neutron damage It is available for any standard cryostat and the MPS multi purpose spectrome ter Specify 110V or 220V for the power supply Resolution FWHM Model Number Relative 5 9 keV 0133 2 V Peak Peak Shape Efficiency 5 9 e Compton FWTM FWHM eV keV NIGC10180
95. eV 2000 57 271 7 122 1 250 139Ce 137 5 days 165 8 200 2030 46 6 days 279 2 600 1135n 115 1 days 391 7 1000 137 5 30 2 661 6 500 88 106 6 days 898 0 3500 1836 1 4000 60 5 27 years 1173 2 1500 1332 5 1500 82 Appendix 3 Major and X ray Lines for Various Radionuclides Nuclide Type of Decay Half Life Photon Energy MeV Yield Americium 241 Am alpha 433 years 0 026 2 596 0 033 0 196 0 043 0 196 0 0595 35 996 0 012 0 022 Np L X rays 40 Antimony 12556 beta 2 77 years 0 035 4 5 0 176 6 8 0 321 0 5 0 381 1 5 0 428 29 8 0 463 10 4 0 601 17 8 0 607 4 9 0 636 11 4 0 671 1 7 0 027 0 031 Te K X rays 50 125m 58 days 0 035 796 Daughter Te 0 109 0 3 0 027 0 032 X rays 110 Barium 33Ba electron capture 10 8 years 0 053 2 2 0 080 2 6 0 081 33 9 0 161 0 7 0 223 0 4 0 276 7 1 0 303 18 4 0 356 62 2 0 384 8 9 0 030 0 036 Cs K X rays 120 Barium 14 Ba beta 12 8 days 0 014 1 3 0 030 14 0 163 6 2 0 305 4 5 0 424 3 2 0 438 2 1 0 537 23 8 0 602 0 6 0 661 0 7 Cadmium 199 electron capture 462 days 0 022 0 026 Ag K X rays 67 7 109 40 seconds 0 088 3 8 Daughter 0 022 0 026 Ag K X rays 34 5 Cerium 144 beta 284 3 days 0 034 0 1 0 040 0 4 0 053 0 1 0 080 15 0 134 10 8 144 beta 17 minutes 0 696 1 53 Daughter Pr 1 409 0 28 2 186 0 72 Cesium 37Cs beta 30 17 years 137m 2 6 minutes 0 662 8
96. ecting a low background system there are some general factors that should be considered An external preamplifier is generally better than an in line preamp because the naturally occurring residual radioactive materials found in the circuit board are not in direct line of sight with the detector The molecular sieve getter which may have a slightly higher residual radioactivity than activated charcoal is significantly more effective in adsorbing contaminants and maintaining the vacuum The NPR cryostat with or without a lead shield is a better way to keep the getter Low background internal metal parts such as the crystal holder coldfinger etc Low background stainless steel screws OFHC or stainless steel endcap with beryllium window or Low background Pechiney aluminum endcap e g for Marinelli beaker OFHC lined lead internal shield Cryostat not in line with detector e g elbow dipstick External preamp remote location from the detector crystal as in the NPR cryostat is preferable from shining on the detector 4 Use low background beryllium or Vespel window for PGT recommends using low background beryllium entrance window rather than magnesium because magne sium is more easily corroded A Vespel window is also available Vespel has a lower energy transmission at the same window thickness 10 at the 14 4 keV line of 570 but costs less
97. ector but are inelastically scattered and escape This type of interaction yields a low energy Compton background Finally some photons reach the detector only after having been scattered by some material surrounding the detector or by the dead layer in the detector itself These rays will also yield lower energy pulses The relative importance of the photoelectric effect Comp ton scattering and pair production in germanium and sili con with respect to energy of the incident photon is illustrated in Figure 1 5 10 PE photoelectric effect Compton scattering lt pair production 5 g E L D Lm m o 5 101 o e 2 s E c 810 Germanium E Silicon 1o03L 10 107 1 10 102 Energy MeV Figure 1 5 Linear absorption coefficients for Ge and Si as a function of gamma ray energy In all these absorption processes one or more energetic electrons result and these in turn lose their energy largely through Coulomb interactions along the path of the elec tron in the absorber material The principal effect of gamma ray interaction with semiconductors is thus ionization which is shown by the creation of a large number of elec tron hole pairs in direct proportion to the energy of the inci dent photon The average energy necessary to cre
98. ed in a given time Furthermore the manufacturing process also puts limits on the blind hole wells This design requires that the center hole be bored out which is difficult for large sample holes For this reason blind hole wells are usually offered with sample holes no more than 15 mm in diameter Through hole wells are cored out a procedure which can be used for much larger sample holes PGT has manufac tured custom well detectors with sample hole diameters of up to 1 3 in 33 mm The large sample hole can accom modate both larger samples to reduce counting time and a larger variety of sample sizes and shapes Aside from the issue of efficiency through hole well detec tors also score better in resolution Blind hole wells are inherently microphonic As can be seen in Figure 1 14 the contact to the center electrode must be made at the front of the detector crystal in the small space between the well insert and the center contact The gate lead must then run from this contact all the way to the FET at the back of the crystal Very small movements in this wire for example 13 from external vibrations cause capacitance changes at the FET input and result in a microphonic signal at its output This electronic noise impairs resolution and adversely affects the lower limit of detection The uncertainty in how quiet the detector environment will be means that counting time must be increased to insure the integrity of the data In
99. ed on the ANSI IEEE Standards 645 1977 and 325 1996 Please consult also ANSI Standard 42 14 1991 and the ANSI IEEE Standards 680 1978 300 1988 R1993 759 1984B 1131 1987 1160 1993 301 1988 and their updates as well as any other ANSI IEEE stan dards which may relate to your applications NIST Stan dard Reference Material SRM Standards and US Regulatory Guides for fluorescence applications also con tain valuable information 1 7 1 Detector Efficiency The number of photons actually counted out of the total number of photons emitted by the sample is defined as the detector efficiency How precisely the energy of each photon is determined is its resolution 1 7 1 1 Counting Efficiency The counting efficiency of a detector is a function of the active volume and shape geometry of the detector crystal the source detector geometry and interactions in the materials in the immediate vicinity of the detector The tests described in ANSI IEEE 325 1996 call for a spectral peak at least 6 channels wide at half maximum with the total number of counts within the FWHM of at least 50 000 1 7 1 2 Absolute Efficiency The absolute efficiency 2 is simply the ratio of counts detected to counts emitted by the source or more accu rately the ratio of net counts A in the full energy peak to counts Ng emitted by the source Because is very dependent on the source detector geometry both the geometry and the energies at wh
100. een challenging because the detector resolution is a strong function of energy At high energies peaks become very broad and the detector s efficiency drops dramatically These broad weak peaks are hard to find and difficult to analyze At low ener gies the number of peaks is usually quite large and the peaks are closely spaced with reasonable resolution 8192 channel Wilkinson ADC spectrum of Ba133 and Co60 256 channel Wilkinson ADC spectrum of 133 and 1 f E PRAF i E ca 256 channel spectrum of 133 Co60 Figure 2 14 Each of the spectra above contains exactly the same data The 8192 channel Wilkinson spectrum shows all of the spectral detail at low energies but appears to be empty over the high energy range The 256 channel Wilkinson spectrum shows the high energy peaks better but distorts the low energy region losing several peaks The QCC spectrum provides full peak detail at all ener gies In the past people have addressed these problems by using high resolution ADCs so that the energy per channel was small enough to give good peak resolution at the low est energies However at the higher energies the channels were much too fine resulting in peaks being spread out over hundreds of channels When dealing with very low levels of high energy radiation the peaks can be very hard to detect because of this wide dispersal The QCC system solves
101. er of high performance gamma and X ray spectroscopy products including state of the art custom ized germanium detectors and systems PGT merged with American Nuclear Systems ANS of Oak Ridge Tennes see in 2000 and expanded the product line to include labo ratory based and portable sodium iodide Nal detectors and systems High purity germanium also known as intrinsic germa nium became available in 1972 73 PGT produced the first commercial HPGe planar detectors that did not require lith ium drifting and could be stored at room temperature with out performance degradation PGT then produced the first HPGe coaxial detectors These semiconductor radiation detectors were sold primarily to nuclear physics research laboratories PGT continues to offer a wide selection of systems and components for many different types of measurements in environmental monitoring health and safety research educational and medical fields PGT detectors have been used in a variety of locations including the bottom of a mine for double beta decay stud ies of enriched germanium in the ocean for remote sens ing applications and in a satellite for studies of the solar system One high profile use was in the Mars Observer That detector included a cryostat with variable temperature control to permit in flight annealing for repair of high energy photon and neutron damage Its design requirements included the ability to withstand a stress of 50 G s du
102. es Gedcke Hale or external dead time methods Full Computer Control The MCA 8000 is fully computer controlled There are no pots to adjust Upper level ULD lower level LLD dis criminators and the ADC zero offset are all computer con trolled Conversion gain can be set to 250 500 1000 2000 4000 8000 and 16 000 channels 8016 only A wide range of presets is available including live time real time integral of all ROIs integral of selected ROIs total SCA counts net ROI statistics and gross ROI statis tics The MCA 8000 has many of the I O connections you need for configuring any measurement application Exter nal rear panel BNC connections are provided for GATE REJECT BUSY IN and ADC INPUT The polarity of REJECT and BUSY IN can be programmed from the MCA software MCA outputs include SCA OUT PEAK DETECT and ADC BUSY The polarity of the PEAK DETECT and ADC BUSY signals can also be programmed from the soft ware A 26 pin DSUB connector is also provided for ROI outputs and digital control signals 72 e Be Quantum 8000 Analytical Software For qualitative analysis the MCA 8000 includes Quantum MCA software at no additional charge However for those applications that require quantitative gamma analysis PGT also offers QuantumGold sold as an option This package features an intuitive user friendly interface The main screen is not cluttered with buttons and controls T
103. ewar Aluminum endcap and beryllium window RG 11 B C resistive feedback preamplifier or PO14 B pulsed optical feedback preamplifier 12 ft bias signal and power cables Unlimited temperature cycling without loss of resolu tion Options A variety of cryostat configurations available Portable systems JT Cool mechanically cooled system Transistor reset preamplifier Ultra low microphonic QUIET ONE crystal mounting Typical Applications Spectroscopy of transuranic materials and of mixed gamma and X ray samples Be window posue Evaporated contact p type crystal N lithium diffusion layer Figure 2 7 P type HPGe Planar Detectors 39 Depletion Beryllium Window Model Area Diameter 7 FWHM 5 9 keV FWHM 122 key P e Y 2 Depth Window Diameter Number mm mm eV eV PO 14B RG 11 14 RG 11 IGP25145 25 5 6 5 0 145 165 480 485 1 0 IGP25175 25 5 6 5 0 175 200 495 505 1 0 Lieto 050 55165 50 8 0 5 0 165 180 490 490 1 0 55190 50 8 0 5 0 190 210 540 550 1 0 Tino dU IGP105185 100 11 3 5 0 185 195 490 495 5 0 IGP107175 100 11 3 7 0 175 190 495 495 5 0 IGP110175 100 11 3 10 0 175 185 495 495 5 0 2 94 e100 IGP205200 200 16 0 5 0 200 210 495 500 5 0 IGP207195 200 16 0 7 0 195 215 495 500 5 0 IGP210190 200 16 0 10 0 190 200 490 49
104. f the State of New Jersey SERVICE AND SUPPORT You may contact PGT at any time for support issues We can be reached by phone at 609 924 7310 toll free at 800 980 9284 or by FAX at 609 924 1729 We will be happy to discuss both technical and application problems with you Contents About Princeton Gamma Tech 1 Principles of Gamma ray and X ray Radiation Detection 3 142 Badioaclivity Bek fa eRe n b ee dae e pe et 3 1 2 Photon Matter 1 3 1 2 1 The Photoelectric 4 1 2 2 Compton Scattering 4 1 2 3 Pair 1 4 1 3 Radiation Detection 5 1 3 1 Photon Semiconductor Interactions 5 1 3 2 Fano Factor s E e Ex Rete e EAR Eee Rin Red 6 1 3 3 Charge 6 1 3 4 Preamplifier Rise 7 1 4 Counting Systems 1 7 1 5 Spectrum Analysis sa facade da 8 LST Peak Localo e hehe tegis ies 8 1 5 2 Peak Measurement
105. fier 12 ft bias signal and power cables Unlimited temperature cycling without loss of resolu tion Endcap Beryllium window P ion implant n type crystal m m Passivated surface N lithium diffusion layer Figure 2 8 N type HPGe Semi Planar Detec tors Options Specialized low background cryostats Low background materials including IF 1 and 2 beryllium windows for low level gamma ray detec tion Existing detectors can be retrofitted with larger crys tals JT Cool cryocooler Transistor reset preamplifier Ultra low microphonic QUIET ONE crystal mounting Typical Applications In vivo lung monitoring of actinides PGT sup ply a complete lung counting room including hard ware chairs and PC based software Body burden assessment Measurements requiring a high P B ratio Active Diameter Depletion Model Number Area mm2 mm sies 9 5 9keV 122keV Window eV eV mil NIGP1510420 1500 43 8 10 0 420 650 20 0 NIGP1513400 1500 43 8 13 0 400 620 20 0 NIGP1516400 1500 43 8 16 0 400 620 20 0 NIGP20010470 2000 50 5 10 0 470 650 20 0 NIGP20013450 2000 50 5 13 0 450 650 20 0 NIGP20016470 2000 50 5 16 0 420 625 20 0 NIGP20020370 2000 50 5 20 0 370 625 20 0 NIGP27030425 2700 58 6 30 0 425 700 20 0 NIGP38303450 3800 69 6 30 0 450 950 30 0 Table 2 7 NIGP Series Detector
106. for Nal detectors only Quantum Nal includes all the features of Quantum NalD except deconvolution analysis File Edit View Setup Analysis Tools Help Spectrum Display showing a portion of the primary spectrum Energy 106 8 Channel 850 Counts 69 0 RO Net E 77 78 QuantumMCA is the standard MCA software package It can control up to eight MCAs at one time with memory management for up to 16 000 channels of real time display and storage for each spectrum It includes libraries for alpha beta and gamma analysis with separate gamma libraries optimized for HPGe and Nal spectroscopy It is an excellent choice for any non quantitative task Ease of use is a keyword in all Quantum products The main screen provides direct access to all functionality The spectrum display area can display up to eight spectra simultaneously in live static or a mix of modes Vertical scales include linear square root and log with unique full view auto ranging Single clicks on the toolbar provide overlapped or tiled display full screen spectrum line mark ers radiation popup window and memory control The information you need is always readily at hand The graphic below shows the radiation lines pop up window with data on Co60 Simply click on a line in the table to place a marker on the screen and bring that section of the spectrum into view A similar approach is used in all single line per
107. for non pressurized LN storage dewars Pressurized LN fill dewar for portable models Features for Gravity Feed Systems 30 liter mother dewar Sturdy aluminum stand Options Flexible fill line for special applications and spatial constraints 53 Designations Description Specifications Auto Fill System 326 AF Timer controlled 326 X without storage dewar 326 Dewar and valve assembly only Swagelok Overflow fitting Overhead view Vent valve Pressure build up regulator LN Storage Dewar Pressure build Pressure up valve gauge Solenoid Evacuation power line valve amp Transfer line Storage Dewar Capacity 50 liter self pressurized with sensor Solenoid LN withdrawal and fill valve Hose barl Pipe plug a Pipe Vent valv Optional Manual plug Withdrawal vaN atm Withdrawal Y Mother Dewar System H i Capacity 30 liters o pressure valve Clamp JU 30 psi valve Clamp knob 10 relief valve 10 psi valve Inserted into 30 liter dewar Mother Dewar and Stand for GF Portable Spectrometer 7 Valve handle Valve
108. from an equivalent Si Li crystal The low capaci tance permits the use of a very short shaping time constant 0 5 us in the main amplifier circuit which in turn reduces the effect of crystal leakage current on the total noise of the system The insensitivity to leakage current eliminates the need for LN2 cooling The crystal may be operated at room temperature but optimum resolution lt 145 eV FWHM at 5 9 keV is achieved when the crystal is cooled below 10 C using Peltier counts The crystal has an intrinsically thin entrance window to incident X rays the back contact shown in Fig ure 2 10 This window allows X ray detection of light elements including the carbon ka X ray at 270 eV Direct sure of the cold crystal to oil and other contaminants in the chamber is avoided by using an ultra thin Polyamide window with 6096 transmisssion at 270 eV across the front of the crystal housing The pres sure between the crystal and the microscope cham ber is equalized by a small hole in the crystal housing Figure 2 11 Heat sink to cold finger Crystal housing Ultra thin window Crystal with Integral Peltier cooler Hole for pressure equalization Figure 2 11 Schematic cross section of SDD crystal housing The SDD incorporates three Peltier cooler devices One cooler is fabricated into the silicon crystal chip The others are located at the base of the copper c
109. g from other manufacturers these items can be purchased and integrated into the primary system to create a complete customized system 1 21 Cryostats In a detector system the crystal is housed in a protective endcap Both the crystal and the first stage FET of the preamplifier are maintained at cryogenic temperature by a cold finger cooling rod This is necessary to reduce the 25 leakage current from thermally generated charge carriers which would otherwise degrade the energy resolution of the detector Cryogenic temperatures are established and maintained by a liquid nitrogen cryostat assembly The LN supply is housed in a dewar and is in contact with a copper tubing cold finger Cooling may also be accomplished mechani cally with the JT Cool cryocooler Figure 1 25 is an expanded cross section diagram of a detector with an external preamp a dip stick style cryostat and a standard dewar The high vacuum of both the cry ostat housing and the dewar are maintained with the help of a molecular sieve material In dipstick systems the cryostat and the dewar are sepa rate entities In unitary systems Figure 1 25 center and right the LN reservoir and the cryostat itself are a single inseparable unit with a single vacuum system Cryostats are manufactured in straight line configurations facing up down or horizontally or in an elbow 90 form with either a stationary or swivel head The various configurat
110. g and counting detected photons signal pulses are stored in memory as a function of their analog amplitude MASS NUMBER A sum of the protons and neu trons in the element nucleus i e atomic weight of an ele ment MICROPHONICS Electrical noise due to mechanical or audio vibration in the detector assembly MULTIMETER DIGITAL DMM measuring instrument used to measure voltage resistance or current during trou bleshooting or system setup NEUTRON Particle with no charge and a mass of 1 found in the nucleus NOISE ELECTRICAL Unwanted disturbance in an elec trical signal which obscures the desired information in the signal NUCLIDE See ISOTOPE PAIR PRODUCTION Interaction of ionizing radiation with matter which produces an electron positron pair PEAK SPECTRAL LINE Sharply peaked portion of a spectrum usually representing the full energy peak of a mo noenergetic X ray or gamma ray PEAK TO BACKGROUND RATIO Ratio of the counts in a peak to the counts in the adjacent background region PHOTOELECTRIC EFFECT Interaction of ionizing radia tion with matter in which the full energy of the photon is im parted to an atom which ejects an electron whose energy is equal to that of the incoming photon less the binding energy of the electron PHOTON discrete packet of energy a quantum P I N DIODE A detector with an intrinsic or nearly intrinsic region between a p and an n region POSITRON Antimatter equ
111. g radiation contributes significantly to the output signal ADC ANALOG TO DIGITAL CONVERTER Electronic in strument that changes the magnitude of an analog signal to a digital form ALPHA PARTICLE helium nucleus consisting of two protons and two neutrons ATOMIC NUMBER Z The number of protons in the nu cleus of an atom and therefore also the number of elec trons in a neutral atom It is specific for each element BACKGROUND RADIATION Ambient radiation from cos mic rays radioactive materials in the detector surroundings or any source other than the nuclide being measured BACKGROUND PEAK Photon counts in a peak which are not from the monoenergetic line of interest con sisting of background radiation Compton scattering and de graded photons from higher energy events BALLISTIC DEFICIT Peak broadening especially at high count rates when the charge collection time is long com pared with the differentiating time constant of the electron ics BANDGAP The energy difference between the bottom of the conduction band and the top of the valence band BETA PARTICLE B An electron emitted by a nucleus BIAS DETECTOR Voltage applied to a detector to create an electric field which sweeps out the charge created by the ionizing radiation CHARGE COLLECTION TIME Thetime interval after the passage of an ionizing particle for the integrated current flowing between the terminals of the detector to increase from 1
112. hium diffusion layer typically 0 5 mm p type crystal A Center core with Passivated vapor deposited gold surface ontact Figure 2 6 HPGe Well Detector Options Custom well diameters up to 1 3 Other crystal sizes active volumes of 170 cc or more Low background NPR cryostat Ultra low background materials such as low back ground aluminum well inserts and OFHC copper endcaps Beryllium or low Z organic well inserts Other cryostat configurations Can be mounted in a customized shield for low background measurements Low power or transistor reset preamplifiers Typical Applications Analysis of small samples for environmental moni toring and radiochemistry studies Coastal and deep water sediment research Water and food pollution analyses Geological and biological sample testing Neutron activation analysis 37 38 100 70 with the optional Z organic window N NJ Absolute Efficiency Representative well detec or efficiency curve 1 10 50 100 300 500 1000 2000 Energy keV Well Dimensions mm Resolution FWHM Model Number Active Volume E 0122 keV 9133 MeV Diameter Depth keV keV IGW5021 10 50 10 40 1 20 2 10 IGW5022 10 50 10 40 1 20 2 20 IGW5022 14
113. ibility with this system The coldhead is integrated into the detector assembly which has the overall appearance and size of a portable cryostat The detector head has all attitude operation and may be mounted remotely up to 50 feet from the compressor The detector endcap easily fits within all existing lead shields with an optional mounting stand to further enhance the flexibility of this system Standard Features for JT COOL Closed cycle cooler with air cooled compressor and proprietary CFC free refrigerant mixture Detector head can be operated in any position Power requirement 115 VAC standard Cooling range of 70 290K 203 20 Automatic shutoff of high voltage in case of power failure QUIET crystal mount for elimination of mechanical vibration Flexible hose permits use of detector in one room with compressor in another 5 year projected service life before any maintenance is required Options p or n type coaxial or planar germanium and Si Li X ray detectors Low background endcaps Beryllium and light element windows Stand for bench top operation or removable carrying handle for portable uses Can be mounted on an electron column for energy dispersive spectrometry 10 25 and 50 ft hose lengths 100 VAC Japan and 230 VAC Europe Copper gas lines Typical Applications Nuclear power plants site characterization and radi ation monitoring In vivo lung
114. ich it is measured must be specified when absolute efficiency is quoted 10 To determine Ns the source intensity must be corrected for the age of the source since calibration as well as the branching ratio of the particular line used if applicable le X live accumulation time S At T 1 14X0 55 S 0 where l Source intensity at calibration At Age time since calibration T Half life ANSI IEEE 325 1996 standard requires that Eabs be determined from the spectrum obtained with a calibrated 60Co source placed 25 0 cm from the center of the front of the endcap or 1 cm from the bottom of the sample hole in a well detector The net number of counts A in the full energy peak at 1332 5 keV is determined by integration and background subtraction Absolute efficiency is the usual standard for characterizing well detectors and Marinelli beakers While it is sometimes quoted for large coaxial or planar detectors this measure ment usually does not represent real conditions Relative and intrinsic efficiencies are better suited for such detec tors 1 7 1 3 Relative Efficiency Because of the multitude of source detector geometries in use a standard efficiency measurement which is indepen dent of geometry and which involves the whole crystal vol ume is necessary Helative efficiency satisfies this requirement The efficiency of a coaxial or large planar germanium crys tal is determined relative to that of a 3
115. imum energy rate product and its decay time or reset time The decay reset time describes how quickly the charge induced in the capacitor can be discharged In the resistive feedback preamplifiers this is determined by the decay time con stant of the RC feedback loop which is typically on the order of 1 msec As shown in Figure 1 20 recovery occurs after each event indicated by the dashed curved line at low count rates Energy rate limit at high count rates s 1 9 3 5 e 8 time gt 22212 decay time Figure 1 20 Decay pattern for a resistive feed back preamp showing long recovery after each event In a pulsed reset preamp the resetting may be either by pulsed light feedback to the FET structure by a light emitting diode or by a transistor switch and reset occurs only after many events Figure 1 21 Ee oO 6 22 2 gt gt e reset time Figure 1 21 Decay pattern for pulsed reset preamp showing reset only after many events With the pulsed optical PO reset the reset time is approx imately 15 usec while in the transistor TR reset the time is 6 10 usec In a detector system counts cannot be processed during system dead time when the preamp and main amplifier are busy The contribution of reset time to system dead
116. ional charge For appli cations that require quantitative gamma analysis PGT offers the optional QuantumGold software This package features an intuitive user friendly interface The main screen is not cluttered with buttons and controls Tool tips allow frequently used functions to be quickly and easily identified For gamma applications a fast hardware setup routine using Cs137 eliminates the hassles of manually adjusting the coarse and fine gains There are also default parame ters for the peak search routine and other steps of the analysis process 74 24 222 Becr 8000 For the user who wants control of the analytical process QuantumGold will still be a pleasure to use The Tools Setup window allows the fine tuning of parameters associ ated with the analytical calculations Some of these con trols include peak search sensitivity line matching for library based identification of isotopes and ROI definitions The efficiency calibration process is as simple as selecting energy lines associated with the various calibration stan dards and then pressing one button The efficiency curve is generated along with a theoretical model for the response of the detector The gamma activity report includes all information associ ated with the analysis Likewise each spectrum data file contains all information associated with the calibration that was in effect at the time of acquisition Computer and Network Connect
117. ions and sizes can be customized to fit specific needs 26 Window Vespel Insulation Ge crystal External Preamp Cold finger LN Fill collar Dewar Copper A UNN Mole ular N sieve and high vacuum Dipstick Cryostat with External Preamp Unitary Cryostat with External Preamp uum and ecular sieve LN Fill Pa mol Dewar tank K LN Endcap Vacuum 2 Cold finger Cold finger In line Endcap and FET Ge crystal Unitary Cryostat with Inline Preamp Figure 1 25 Schematics showing major components of a dipstick cryostat left and representative unitary cryostats center and right Ultra low background materials are available for low level counting systems These materials include OFHC oxygen free high conductivity copper cap Mounting cup and cold finger Ultra low background aluminum endcap Low background Be or Vespel plastic entrance win dows Activated charcoal sieve Tungsten internal shielding in the endcap Radiation shielded counting chambers are also available 1 22 Detector Cool Down Require ments It is very important that the detector be completely cooled before the high voltage bias is applied Performance speci fication sheets which come with PGT detector systems specify th
118. ip stick cryostat An amplifier and ADC module such as the System 8000 A PC with spectroscopy software The ADC and the main amplifier with pile up rejection can be incorporated within the multichannel analyzer so that the output signal from the preamplifier is fed directly to the PC for processing and analysis He Ge detector external preamp amp standard dewar 127674 E System 8000 PC with spectroscopy software Figure 1 7 Schematic representation of a nuclear spectroscopy system 1 5 Spectrum Analysis Detection of photons is only the first step of the analysis process The spectral peaks must be located see Section 1 5 1 their energies measured and identified with the cor rect nuclides or elements see Section 1 5 2 and their areas quantified see Section 1 5 3 These functions are done by computer analysis and require certain preliminary calibrations for channel number vs energy detector reso lution peak width and detector efficiency A detailed dis cussion of spectrum analysis can be found in the users manuals for specific spectroscopy software products A spectrum peak is a span of channels with photon counts that are statistically higher than those of the underlying continuum A peak has a centroid with the highest counts and a roughly Gaussian shape The more channels per spectrum the smaller the energy range per channel but
119. ith horizontal NPR cryostat 4 46 gt 58 2 9 1 Model 5 5 Radiation Shields Shields are available for the 5 liter Multi Use Portable Spectrometer Features Low carbon steel outer jacket 3 8 1 2 thick Cast virgin low background lead bulk shield 1 thick Graded liner of tin 0 02 and soft copper 0 064 Integral steel handle and baseplate with detector attachments and latch for rigidity Removable collimator plug with 1 4 aperture Weight 40 1 5 without detector Options Back plate for in line detector Tripod for in situ soil sampling Applications Low background field analyses such as in situ soil sampling Emergency response monitoring with an MPS spectrometer Collimator plug A Q U 8 3 p 4 5 E 18 12 gt Steel baseplate with detector latch with an MPS in line spectrometer Backplate Gollimator plug C 9 59 2 10 Low Background Materials PGT offers a variety of low background materials as shown in the table below When incorporated into the low background cryostat designs with or without a lead radiation chamber background radiation is significantly reduced In sel
120. ity 122 keV 50 170 cm germanium i HPGe 10 1200 1300eV Sample hole FWTM FWHM IGW Contact thickness coaxial well 10 MeV 1 33 MeV 1 9 2 0 2 10 2 3 keV 10 20 mm diam 0 5 mm external 1 10 2 3 ke 40 high purity 4 122 keV Peak Compton germanium EY 40 keV 800 1400 373 773 A PE 1 33 MeV 10 100 IGC Contact thickness coaxial 10 Mev 1 75 2 30 0 5 mm f f keV FWTM FWHM 1 9 2 0 4 5 9 keV 5 scan P HPGe 3keV 420 470 1500 3800 mm semi planar 1 MeV 122 keV FWTM FWHM Contact thickness A 650 950 10 30 mm thick lt 1 9 0 3 um p type high purity germanium HPGe 180eV 59keV 10 1000 mm P IGP Contact thickness planar 1 MeV 120 400 eV 122 5 13 mm thick 5153 500 eV mm thic 480 610 eV Lithium drifted silicon Pins 2 2 lithium drifted 109 5 9 keV 10 60 mm FWTM FWHM Si Li Contact thickness Ng licen 138 163 did Planar 3 5 5 mm thick 150A p type high purity 29 2 germanium P ax aiye 180eV 5 9 keV 10 50 mm FWTM FWHM IGX 100keV 1 N HPGe 120 135eV 1 9 Contactthickness planar 4 5 mm thick 150A gt Incident Radiation m P layer ion implantation or metallization thin ayer lithium diffusion thick p type crystal n type crystal 18 Table 1 2 PGT Gamma ray and X ray Detectors
121. ium Crys tals for Radiation Detectors ANSI ANSI IEEE Standard 1160 1993 American National Standard for Calibration and Use of Germa nium Spectrometers for the Measurement of Gamma Ray Emis sion Rates of Radionuclides N42 14 1991 93 Index A absolute efficiency 10 B Bohr model 3 C Compton scattering 4 peak to Compton ratio 14 count rate 14 determination of maximum 22 Systems with high see high count rate systems 22 counting efficiency 10 cryostats about 25 47 dipstick 47 portable 51 unitary 48 crystal dead layer 19 materials 19 shape 19 types and geometries summary of 19 D dead layer 19 detector efficiency 10 absolute 10 counting 10 intrinsic 10 Marinelli beaker 11 relative 10 well detector 13 endcap materials 15 46 resolution 14 selection parameters 10 29 count rates 14 efficiency 10 14 energy range 14 resolution and sensitivity 14 System noise and microphonics 14 sensitivity 14 window materials 15 46 detector specifications Duo Detector 30 HPGe Coaxial Detectors 33 HPGe Planar Detectors 39 HPGe Well Detectors 37 N type Coaxial HPGe Extended Range Detectors 94 35 N type HPGe Planar Detectors 41 X ray detectors 42 detectors basic principles of 5 main types 5 summary of PGT brand 18 19 dipstick cryostats 47 Duo Detector 30 E endcap materials 15 46 energy range 14 F Fano factor 6 H high count rate systems 22 noise effects 23 HPGe Coaxial Detectors
122. ivalent of an electron with 1 charge and nearly 0 mass it annihilates with an atomic electron to produce two 0 511 MeV photons PREAMPLIFIER A charge sensitive amplifier which pro vides the first step in the amplifier chain of a semiconductor detector to cut down on noise the input FET is located in the cryostat as close to the crystal as possible PREAMPLIFIER PULSED OPTICAL FEEDBACK A preamplifier in which the charge is induced on the feedback capacitor in a stepwise fashion the capacitor is periodically reset by a light pulse PREAMPLIFIER RESISTIVE FEEDBACK A preamplifier whose capacitor is reset after each pulse by an RC feed back loop PREAMPLIFIER TRANSISTOR RESET preamplifier essentially similar to a pulsed optical preamp in which the charge on the feedback capacitor is drained off by a transis tor PROTON Nuclear particle with charge 1 and mass 1 the atomic number Z is the number of protons in the nucle us PULSE PILE UP arrival of a second signal pulse be fore the transient response of the preceding pulse has de cayed to a negligible value thus preventing measurement of the second pulse RADIOACTIVITY Nuclear transformation by spontane ous decay with emission of gamma rays or alpha or beta particles to achieve a stable proton neutron ratio in the nu cleus RESET TIME In a preamplifier the time required to drain the charge from the feedback capacitor RESOLUTION Ability of a detector
123. ive feedback pulsed optical reset or transistor reset preamplifiers Air tight preamplifier housing to keep out damaging environment Internal temperature sensor for high voltage shut off High purity copper low background electronics and internal shielding Lung counting patient chairs and applications soft ware available Typical Applications Field use for environmental monitoring Space constrained applications Emergency response situations Whole counting and in vivo lung monitoring Nuclear high spin experimentation Multipurpose Portable Spectrometer Stainless steel cryostat with 1 5 5 or 7 liter capacity Easily decontaminated Flat cryostat back permits the unit to stand vertically in addition to resting horizontally on its cradle PGT Autofill system or manual fill Gravity Feed Spectrometer Light weight aluminum cryostat with 1 2 or 3 liter capacity Detachable handle Mother dewar and stand keep the spectrometer always at the ready 51 Model Designation Cryostat Configuration Crystal Type Dewar Vol Holding Time Mutipurpose Portable Spectrometer MPS flat back BE f c VS Coaxial Germanium Planar Germanium 500 mm 1000 mm 1500 2000 mm Stainless Steel 1 5 liter 16 hrs 5 0
124. ivity QuantumMCA has a single hardware setup and search util ity that establishes communication with PGT multichannel analyzers via Ethernet or RS 232 Ethernet capability allows users to enjoy the benefits of connecting to labora tory instruments from PCs on the local area network The RS 232 interface offers quick and simple connection of the System 8000 directly to a PC in the field or other location where Ethernet is not available For RS 232 an unused COM port is all that is needed Available configurations System 8016G 16 000 channels of spectrum memory Pulse shaping constants 2us 4us and 845 0 to 5kV bias supply System 8008G 8000 channels of spectrum memory Pulse shaping constants 2us 4us and 845 0 to 5kV bias supply System 8000 Specifications ADC 8 1205 successive approximation ADC 14 bit resolution Discriminators PC adjusted upper 0 to 105 of full scale and lower lt 1 to 105 of full scale in 0 03 increments Zero adjustment in increments of 0 0005 adjusted Maximum throughput 70 000 cps ADC Non Linearity Differential non linearity lt 1 over top 99 of range Integral non linearity 0 05 over top 99 of range Spectrum memory System 8004 250 500 1000 2000 4000 channels System 8008G 250 500 1000 2000 4000 8000 channels System 8016G 250 500 1000 2000 4000 8000 16 000 channels Maximum counts per ch
125. kage Easy installation and setup via RS232 or Ethernet No slots or reserved memory required in the PC Includes 32 bit QuantumMCA software The 4000 is a high performance multichannel pulse height analyzer This MCA was designed to give outstand ing performance and value at an economical price Pack aged as a stand alone unit it features total computer control excellent performance and flexibility There are two ways to connect the MCA4000 to the computer RS232 and Ethernet The 4000 is also available in three con figurations 1000 2000 or 4000 channels of spectrum memory Each unit includes QuantumMCA software for Microsoft Windows and is compatible with QuantumGold the full quantitative gamma analysis software package The MCA4000 features 2 7us successive approximation ADC With hardware add one to memory and an on board 20 MHz processor there is processing power to spare Dif ferential non linearity is less than 1 percent over the top 99 percent of the range and integral non linearity is less than 0 05 percent over the same range Digital stabilizers are provided for both the gain and offset Data is stored as 31 bits per channel with an additional 8 bits for ROI infor mation Flexible live time correction is provided with a choice of simple busy Lowes Gedcke Hale or external dead time methods Full Computer Control The MCA4000 is fully computer controlled There are no pots to adjust Upper level
126. ld ENERGY COUNT RATE PRODUCT LIMIT The highest product of energy and count rate MeVscps in a preampli fier dc coupled to a detector which causes no more than a specified fraction 196 of the pulses to overload the pream plifier 89 FANO FACTOR modification to the Poisson relation ship to account for the variance in the number of electron hole pairs produced in a semiconductor detector FULL WIDTH HALF MAXIMUM FWHM Width of a peak at half its maximum height at the peak centroid used as a measure of resolution See page 8 FULL WIDTH TENTH MAX FWTM and FULLWIDTH FIF TIETH MAX FWFM or FW 02M The width of the peak at one tenth and one fiftieth respectively of its full height FWHM FWTM and FWHM FW 02M ratios are used as a measure of peak shape page 14 GAMMA RAY Electromagnetic radiation of nuclear origin with wavelengths of 109 107 cm energy range of keV 40 MeV GEOMETRY DETECTOR The physical configuration of the detector and sample size sample to detector distance angle which determines what fraction of photon events ac tually reach the crystal HALFLIFE The time required for half of a given number of radioactive atoms to decay HIGH PURITY GERMANIUM HPGe Germanium with a net electrically active uncompensated defect concentration impurity level on the order of 109 1019 parts cm INTRINSIC GERMANIUM IG Older designation for HPGe INTRINSIC REGION Region of a semiconductor cr
127. liter SNPR m 5 30 liter Cryoflex ST swivel joint TT le 146 5 3 4 h lt 305 mm 23 std or as specified SNPR similar to NPR with added swivel joint Stainless Steel 15 liter Table 2 12 Common Vacuum Unitary Cryostats 49 Model Designation Cryostat Configuration Crystal Type Dewar Volume X ray Detectors Fixed Geometry HT Variable Distance Slide DS gt gl lt Variable I U lt Variable COC Optional motorized conirol and high vacuum bellows Planar Germanium 10 mm 30 mm Planar Si Li 10 mm 30 mm 2 2 60 mm Aluminum 7 5 liter 15 liter 50 Table 2 12 Common Vacuum Unitary Cryostats Continued 2 7 3 Portable Cryostats Portable cryostat spectrometers are designed to work in all attitudes without risk of LN spillage They are suitable for use in the field or where space is constrained Features Light weight hand held or stable bench top operation Compatible with both portable and standard MCAs Either in line or conventional preamplifier mounting All attitude operation Custom designs for whole body monitoring Holding times of 12 100 hours Options Resist
128. liter 72 hrs 7 5 liter 100 hrs Portable Gravity Feed GF B x Cla Coaxial Germanium Aluminum 1 2 liter 12 hrs 3 0 liter 50 liter pressurized LN mother dewar Lung Monitor DTIL nono Semiplanar Germanium Stainless Steel D 3 3 5 4 L variable per specifications 52 Table 2 13 Portable Unitary Cryostats 2 7 4 Liquid Nitrogen Handling Devices While small bucket dewars can be refilled manually using just a metal funnel and a length of plastic tubing to keep the overflow away from the electronics large dewars are best refilled using a transfer device from a storage container Features for Autofill Systems Self pressurized 50 liter aluminum storage dewar on heavy duty casters with 8 ft insulated transfer hose Pressure and liquid level gauges Choice of manual or autofill operation Data acquisition may be halted during fill or fill may be delayed until counting is complete Remote shutdown and fill command capability Rugged vent flow thermistor sensors for use with portable cryostats Options Fill adaptor for 7 5 15 and 30 liter dewars and for the Multi use Portable Spectrometer Optional level sensor for standard dewars Timer or level controlled model Expansion module to accommodate 4 dewars Electrically heated dewar head
129. m is able to accept pulses The live time is needed to calculate the true pulse rate and to perform quantitative analysis For X ray fluorescence quantitation involves a complex fundamental parameters analysis 1 6 Timing and Coincidence Mea surements Timing spectroscopy involves determining the relationship between two coincident or time related as in cascade events Applications include Gamma gamma and gamma particle coincidence studies Positron lifetime measurements Decay scheme determinations Plastic scintillator NE102A amp Photomultiplier tube Source Y x IGC Detector preamp Y CFD Delay 4 CFD 16 ns Y Delay 60 ns TAC ti vds Timing filter amplifier CFD Constant fraction discriminator Time to Amplitude converter Figure 1 9 Setup for timing measurements Basically the measurements are made by irradiating two detectors simultaneously with the same source The signal from one detector is used as a start signal in a Time to Amplitude Converter TAC The signal from the other detector is delayed by a fixed amount and used as the stop signal Output from the TAC is sent to the MCA where it is displayed as a time spectrum or more precisely as a histo gram of the number of events detected for each time inter val The distribution
130. nd not readily deter mined by the user However because they are very small compared with D R D Also because R is large com pared to the crystal diameter d AB and the surface area 2 d 2 Therefore _ 4 2 4 2 For large planars intrinsic efficiency at the 60 keV line of the 24 source at 25 cm is used to qualify the detector For lung monitors the source endcap distance is 10 cm Because the intrinsic efficiency measurement is dependent on geometry the distance D must always be included in the efficiency statement Figure 1 12 shows some representative intrinsic photo peak efficiencies for planar germanium detectors of dif ferent crystal thicknesses and for a typical coaxial germanium detector The curves on the left illustrate the percent transmission for beryllium windows of different thicknesses 1 7 1 5 Efficiency of Marinelli Beakers Marinelli re entrant beaker and well detectors are special geometries for which absolute efficiencies are the norm A Marinelli re entrant beaker is used for large volume low activity samples this situation the analyte surrounds the detector element usually a large coaxial detector The Marinelli beaker standard source MBSS used to deter mine detector efficiency consists of a sealed standard bea ker filled with the specified volume of uniformly dispersed radioactive material in a liquid or preferably solid carrier Several standar
131. number 24 to 25 and decreases rapidly with increasing photon energy E The residual ion may return to its ground state by emitting one or more X rays or an Auger electron The low energy X ray is almost invariably absorbed in a second photoelec tric event before it can escape from the crystal As a result the total photon energy appears as electron kinetic energy Thus a monoenergetic photon gives rise to a monoener getic peak in the charge distribution corresponding to the incident photon energy 1 2 2 Compton Scattering In the Compton Scattering process shown in Figure 1 2 the photon is scattered by an electron with a partial energy loss which is dependent on the angle of scattering The kinetic energy imparted to the electron is between zero and a higher value related to the energy of the photon If the scattered photon escapes before further interaction the detector will record only a fraction of the incident photon energy These fractional photon energies appear in the spectrum at less than the full energy peak As a result the spectrum exhibits a continuous electron energy distribu tion the Compton continuum below the full energy peak of the incident photon The cross section for this process is proportional to the atomic number of the scattering material and is some what less energy dependent than the photoelectric effect The maximum energy in the Compton continuum is called the Compton Edge CE Events in which the
132. oise lt 0 05 typical lt 0 025 Baseline restorer Slow channel rate adaptive with automatic threshold Fast channel with automatic threshold Live time correction modes simple busy Lowes Gedcke Hale external Battery backup for Spectrum Setup parameters Clock memory Computer control Ethernet 10 100 base e RS 232 baud rates 2400 9600 19200 38400 57600 115200 Maximum number of units connected to PC 8 75 76 Bias supply 0 to 5kV in 5V increments gamma systems to 1kV in 1V increments X ray systems External shutdown capability positive true or nega tive true polarity Ripple lt 20mV peak to peak Temperature instability lt 0 01 C 0 to 50 C Bias polarity internally jumper selected Front panel indicators LEDs for Acquire Event Serial Com AUX I O In use Power Shaping constant Bias on Polarity Fault PUR Dead time meter 3 color LED array Rear panel controls and connectors Power switch SHV female connector for detector bias 2 5mm power jack Fuse housing 9 pin D female preamplifier power connector 9 pin D male RS232 connector 15 pin D female pulse reset preamplifier interface 25 pin DB female connector for ROI output 15 pin D auxiliary I O connector including external input for alarm and or auto shutdown Ethernet interface connector RJ 45 Pole zero adjustment on off Pole zero oscilloscope monitor switch One potentiometer for PZ adju
133. old finger that connects the crystal to the body of the detector housing Figure 2 12 illustrates the place ment of the Peltier coolers Peltier coolers cooler Silicon Drift Crystal with integral Peltier Aluminum housing Cold finger Stainless steel endcap Figure 2 12 Location of the Peltier coolers Temperature sensors are located integral to the silicon chip and close to the Peltier coolers at the base of the cold fin ger Signals from the sensors are fed back to the tempera ture controller to stabilize the crystal at the optimum operating temperature independent of room temperature The preamplifier supplies the various bias voltages for the integral FET and the crystal rings and amplifies the FET signal The dimensions of the detector housing and the micro scope interface are dependent on the microscope model However all detector models have a cold finger and end cap and a detector body The endcap length is dependent on the application The detector body houses the preampli fier and provides the heat sink for the Peltier coolers Heat is ultimately dissipated from the air cooled fins on the detector body Standard Features High count rate capabilities with data acquisition at 100 000 cps Extremely sensitive to light elements including the carbon ka X ray at 270 eV Outstanding resolution better than 143 eV at Mn for both 5 and
134. on scattered gammas Each detector has its own preamplifier either resistive feedback or transistor reset depending on the anticipated count rates The two spectra are generated in just half the counting time required by two separate detectors This arrangement results in low MDAs in the low energy region because of the high resolution of the planar the reduction in background due to Compton scattering and the narrowing of the region of interest defining the peak At high energies the MDAs also improve because the Pb absorber cuts off the low and medium energy photons before they reach the coaxial crystal These photons would otherwise contribute to background clutter As a result both spectra exhibit higher peak to background ratios This detector was built in collaboration with John Fleissner of the USDOE Rocky Flats Site Features p type planar IGP and n type coaxial NIGC detectors mounted on a common axis Aluminum endcap with beryllium window preamp 2 d Be window Internal lead shield preamp 1 Figure 2 1 Duo Detector Elbow dipstick cryostat Two RG 11 B C resistive feedback preamplifiers 12 ft bias signal and power cables Standard 32 liter dewar Options Planar and coaxial crystals designed for specific energy ranges or distributed sources TR 14 transistor reset preamplifiers for applicati
135. ons at count rates higher than 80 000 cps Other cryostat designs including portables JT Cool cryocooler Typical Applications Measurement of Pu and Am isotopes in fuel fabrication facilities Non destructive assay NDA of spent nuclear material product scrap or waste forms Personnel dose reduction measurements Measurements for dismantlement verifications NDA measurements for public safety Resolution FWHM Peak Shape Coaxial Planar Area Depth 20 000 cps Efficiency mm mm FWTM FWFM 122 keV 1332 keV FWHM FWHM 210 200 213 0 lt 600 eV lt 2 0 keV lt 1 9 lt 2 65 40 2000 15 0 lt 700 eV lt 2 1 keV lt 2 0 lt 2 70 IEEE 325 1996 For other sizes and energy ranges PGT Sales Table 2 2 Duo Detector 30 Log 121 812782 152 Eu 75 06 96 Preset L 4528 600 000 10 4 Stopped 7 607 676 Live Time 600 000 1 0k Dead 1 26 Gross Count 215686 Counts sec 359 477 AA Start Time Sep 12 1996 on 3 38 54PM Stop Time vane SP Sept 21996 cia 3 49 01 PM User ID CLG 100 10 1 0 2 363 keV 407 7 ROI 12 Centroid 121 82 Gross 27997 Activity 45 4589 1 2496 cps FWHM O 55Net 27275MDA 0 212831 cps err 1 24 1 02Bkgnd 722 Sfr Dieta 21 ED i dirae _ 1 Ici ___ M Role ba Celi ESE 23 Grass 210 achat 1
136. ool tips allow frequently used functions to be quickly and easily identified For the user who wants control of the analytical process QuantumGold will still be a pleasure to use The Tools Setup window allows the fine tuning of parameters associ ated with the analytical calculations Some of these con trols include peak search sensitivity line matching for library based identification of isotopes and ROI definitions The efficiency calibration process is as simple as selecting energy lines associated with the various calibration stan dards and then pressing one button The efficiency curve is generated along with a theoretical model for the response of the detector The gamma activity report includes all information associ ated with the analysis Likewise each spectrum data file contains all information associated with the calibration that was in effect at the time of acquisition Computer and Network Connectivity QuantumMCA has a single hardware setup and search util ity that establishes communication with PGT multichannel analyzers via Ethernet 10 100 base T or RS 232 Ethernet capability allows users to enjoy the benefits of connecting the MCA8000 directly to a PC or to the local area network The RS 232 interface provides a quick and simple method of connecting the MCA 8000 directly to a PC in the field or other location where Ethernet is not available For RS 232 an unused COM port is all that is needed Available Configu
137. opy system featuring rapid efficient Peltier cooling with no moving parts water or LN required The Sahara is ideal for applications requiring excellent resolution high count rate capa bility and high sensitivity to light elements The SDD consists of the following four components Silicon Drift crystal Peltier cooling components Preamplifier Detector housing The Silicon Drift crystal Figure 2 10 differs from a traditional Si Li crystal in that the charge generated by the interaction of incident X rays is channeled in a potential well towards a small central anode of very low capacitance The Field Effect Transistor FET that provides the first stage of signal amplification is incorporated into the silicon chip next to the anode eliminating stray capacitance and microphonic pick up normally observed in a Si Li detector The poten tial well is established by a series of bias rings each set to a different voltage Rings Anode FET NI A Back Charge path Incident X rays Figure 2 10 Schematic cross section of the SDD crysial The entire detector volume is sensitive to incoming radiation as the silicon is completely deleted The integrated FET is shown on the front side of the detector A typical crystal thickness is 0 3 mm The total capacitance and therefore Johnson noise from a 10 mm SDD crystal is a small fraction of that
138. ow frequently used functions to be quickly and easily identified There are also default parameters for the peak search routine and other steps of the analysis pro cess So getting reliable answers quickly is not a problem System 4000 For the user who wants to control the analytical process eXcalibur will still be a pleasure to use The Tools Setup window allows the fine tuning of parameters associated with the analytical calculations Some of these controls include peak search sensitivity line matching for library based identification of isotopes and ROI definitions The efficiency calibration process is as simple as selecting energy lines associated with the various calibration stan dards and then pressing one button The efficiency curve is generated along with a theoretical model for the response of the detector The activity report includes all information associated with the analysis Likewise each spectrum data file contains all information associated with the calibration that was in effect at the time of acquisition Computer and Network Connectivity QuantumMCA has a single hardware setup and search util ity that establishes communication with PGT multichannel analyzers via RS232 The RS232 interface allows for a quick and simple method of connecting the System 4000 directly to the PC All that is needed is an unused COM port on the PC For applications where multiple units need to be connected to the PC
139. rations MCA 8008 with 8000 channels of spectrum memory MCA 8016 with 16 000 channels of spectrum memory MCA 8000 Specifications ADC 8 125 successive approximation ADC 14 bit reso lution Discriminators PC adjusted upper 0 to 105 of full scale and lower lt 1 to 105 of full scale in 0 03 increments Zero 2 adjustment in increments of 0 0005 adjusted Maximum throughput 70 000 cps Spectrum memory MCA 8008 250 500 1000 2000 4000 8000 channels MCA 8016 250 500 1000 2000 4000 8000 16000 channels Maximum counts per channel 2 1 i e 2 1E9 Digital stabilizer Internal ADC zero and gain stabilization PC controlled time constants Balanced channel and ROI centroid modes Gain 3 of range Zero 1 25 of range Multichannel scaling Input Rate 5 MHz Dwell Time 10ms to 2 1E7 seconds Dead time 3us between passes and 3us between channels Signal sources internal SCA any ROI external input Counting presets Real time Live time Integral of all ROIs Integral of selected ROIs e Gross ROI statistics Net ROI statistics Total system counts Peak counts Total SCA counts ADC Non linearity Differential lt t1 over top 99 of range External events Integral lt t0 05 over top 99 of range Battery backup for Spectrum Setup parameters Clock memory Computer control Ethernet 10 100 base T RS
140. ring launch Even though the mission was ultimately aborted due to satellite failure the detector functioned according to specification and returned valuable data on solar flare induced gamma ray emissions PGT also developed the QUIET ONE cryostat design technology which allows the manufacture of mechanically cooled germanium detectors that still meet the stringent requirement for low microphonics No other manufacturer offers this option If your applications require mechanically cooled detectors with low microphonics design ask for the JT Cool option For gamma spectroscopy applications that require sodium iodide Nal technology PGT has a complete line of sys tems and components to meet your needs These include general purpose multichannel analyzers with conversion gains from 1000 channels to 8000 channels and instru ments specifically tailored to Nal detectors This handbook is divided into several sections Section 1 Principles of Gamma ray and X ray Radiation Detection starting on page 3 provides detailed technical information about the basic princi ples of gamma and X ray spectroscopy Section 2 PGT Products starting on page 28 pro vides descriptions of and technical specifications for specific products appendixes starting on page 81 include useful reference materials and a glossary If you require additional information or assistance please contact the Nuclear Products Department Our technic
141. s 41 2 5 8 X ray Detectors PGT manufactures both Si Li and HPGe detectors for X ray analysis Si Li detectors with a standard beryllium win dow have a useful energy range of 1 60 keV while HPGe detectors are suitable up to an energy of 100 keV Optional light element capability extends the lower limit to below 200 eV Both HpGe and Si Li detectors are fully temperature cyclable and may be stored indefinitely at room tempera ture with no degradation in resolution The X ray source can range from nuclear accelerators to secondary X rays generated by fluorescence X ray detec tors are used extensively for research quality control and failure analysis These detectors are also interfaced with scanning electron microscopes for simultaneous qualitative and quantitative microanalysis Standard Features High purity germanium 10 30 or 50 mm Lithium drifted silicon 10 30 or 60 mm Stainless steel endcap with beryllium window of 0 3 or 0 5 mil thickness for Si Li Horizontal unitary cryostat with fixed geometry and conflat flange 7 5 liter dewar TR 1 transistor reset preamplifier Appropriate bias signal and power cables Unlimited temperature cycling without loss of resolu tion HV cut off circuitry Options Variable position DS cryostat with manual or motor ized slide Bellows vacuum seal High angle entry configurations custom configura tions for unique applications 15li
142. se of the noise from the resistor and detector leakage current 1 18 1 5 System electronic noise is primarily due to the electronics associated with the FET and the detector itself There are three noise components Parallel noise from detector leakage current and all resistors which are electrically in parallel with the detector including the bias resistor and the preamp feedback resistor Series noise from total input capacitance gain and resistors between the detector and preamp 1 f noise The value of the parallel and series noise contributions is a function of the pulse processing time which is the time needed by the main amplifier to completely process a pulse from the preamp 5x the Gaussian shaping time Parallel noise Np is proportional to Ji e Series noise is proportional to 1 Jt 1 f noise is independent of Figure 1 22 shows how the parallel and series noise contri butions and the total noise in a resistive feedback pream plifier vary with the pulse processing time Minimum electronic noise occurs at when these two com ponents are equal The 1 f contribution indicated by the dashed line does not change the shape or position of the minimum on the time axis but only its height noise value The variation of detector resolution with pulse processing time essentially coincides with the curve for 2 Nro Total electronic noise
143. sintegration of an unstable radioactive nucleus by spontaneous emission of particles and or gam ma rays DEPLETION REGION Region in which the mobile charge carrier density is less than that needed to neutralize the net fixed donor acceptor density The active region of a semiconductor detector DMM See MULTIMETER EFFICIENCY ABSOLUTE Ratio of the counts measured by the detector to the total counts emitted by the source dur ing the same live time EFFICIENCY INTRINSIC Ratio of the counts measured by the detector to the counts emitted by the source and ac tually falling on the detector window during the same live time EFFICIENCY RELATIVE Ratio of the counts measured by the detector to the counts measured by a Nal TI scintil lation counter for the same source geometry and live time ELECTRON Asubatomic particle with 1 charge and neg ligible mass which revolves around the nucleus in discrete energy levels In a neutral atom the number of electrons is equal to the number of protons in the nucleus ELECTRON VOLT eV Basic unit for measuring the en ergy of interactions in semiconductor detectors It is the en ergy gained by an electron passing through a potential difference of 1 volt ELECTRON HOLE PAIR The product of the interaction of a photon within a semiconductor crystal An electron is freed and a positively charged hole remains The electron and the hole migrate toward opposite terminals in an elec tric fie
144. stment of each shaping time 3 total Input from detector preamplifier BNC Differential input from detector preamplifier BNC Amplifier output BNC 0 8V positive unipolar ADC input BNC 0 10V unipolar or bipolar positive lobe leading pulse ADC gate input BNC coincidence anti coincidence off CMOS TTL Pile up reject input BNC CMOS TTL Amp busy input for ext amp live time corr BNC CMOS TTL SCA output CMOS TTL Peak detect output BNC CMOS TTL ADC busy out BNC CMOS TTL Dimensions 10 5 26 7 cm wide 12 5 31 8 cm deep 4 5 in 11 5 cm tall Weight 7 25 lb 3 30kg Power requirements 10 18V DC 18 watts external 12V universal AC power converter provided Software 32 bit QuantumMCA compatible with Windows 95 98 NT 2000 XP Optional QuantumGold software for quantita tive analysis 2 13 6 Quantum MCA Software for Windows PGT produces the following Microsoft Windows based applications for MCA control and spectral analysis QuantumMCA is the basic MCA software for qualitative analysis QuantumGold adds quantitative analysis capabilities to the features of QuantumMCA Quantum includes both qualitative and quanti tative analysis capabilities for germanium detectors only Quantum Ge includes all the features of Quantum GeD except deconvolution analysis Quantum NalD includes both qualitative and quanti tative analysis capabilities
145. system to discriminate between peaks spectral lines close to one another in en ergy the narrower the peaks the better the resolution FWHM is used as a measure of resolution RISE TIME For the output pulse of a preamplifier this is the time interval between 10 and 90 of the pulse height for a sufficiently fast preamp it is approximately equal to the charge collection time SCINTILLATION DETECTOR Detector in which radiation impinging on a phosphor produces a pulse of light which is converted to an electrical signal by a photomultiplier tube SEMICONDUCTOR DETECTOR A detector with a p i n diode structure in which radiation produces excess free car riers that are used to detect and measure the incident radi ation SPECTRAL LINE Sharply peaked portion of the spectrum which is characteristic of the incident radiation usually the full energy peak for that photon WELL DETECTOR A coaxial detector in which the end cap has a well extending into the inner electrode and into which sample is placed the crystal nearly surrounds the sample which may be very small X RAYS Photons in the energy range between visible light and gamma rays 91 Bibliography R D Evans The Atomic Nucleus Krieger New York 1982 J J Friel X ray and Image Analysis in Electron Microscopy Princ eton Gamma Tech Princeton NJ 1995 C F Knoll Radiation Detection and Measurement 2nd edition John Wiley amp Sons New York 1989 C M
146. tandards Multi point quadratic energy calibrations from standards or manually Sophisticated detector modeling for efficiency calibration curve Sophisticated model based efficiency curve enhanced by fitting to multiple measured standards Analytical Tools Real time ROI analysis Ability to print all reports or send them to file Spectral output as bitmap metafile or text ROI detail report includes calculations of 20 parameters for each ROI Automated ambient background subtraction Automated or user directed continuum correction User controllable peak finder Cross correlation peak identification against library Multiple quantitative analysis routines available for fully automated or user directed analysis Gaussian peak deconvolution Display Capabilities Complete color control for all aspects of the spec trum display Tile or overlaid modes with dots lines or bars display options Linear log and square root scaling Unique full view auto scaling of each spectrum independently to permit optimum viewing Fully configurable line markers with labels which can include isotope and energy Popup X ray line data window with energy type and intensity Arbitrary screen annotations which track location relative to peaks ROI Capabilities Up to 256 user defined overlapping ROIs Detailed continuously updated ROI information User defined names for each ROI independent of isotopic assignment User definable
147. ter dewar Thin windows for light element detection Low microphonic crystal mounting JT Cool Cryocooler with convenient stand for all attitude LNo free operation 42 Thin window Very thin metallized contacts p type HPGe crystal Lithium diffusion layer IGP for X ray detection Beryllium window Ver thin metallized contacts lt p type Si Li crystal Lithium diffusion layer Si Li for X ray detection Figure 2 9 P type HPGe and Si Li Planar Detectors Typical Applications X ray fluorescence for simultaneous analysis of ele ments from boron through uranium for research and quality control Diagnostics in beam systems and other nuclear reactor applications Interfaced with beam systems scattering chambers and X ray fluorescence systems n EDS systems for spectra down to 185 eV 2 FWHM Window Model Number Crystal Type Area mm 95 9 KeV mils LS10133 Si Li 10 133 0 33 LS10138 Si Li 10 138 0 33 LS30138 Si Li 30 138 0 33 LS30148 Si Li 30 143 0 33 LS60155 Si Li 60 155 1 00 LS60160 Si Li 60 160 1 00 IGX10120 HPGe 10 120 0 33 IGX10125 HPGe 10 125 0 33 IGX30125 HPGe 30 125 0 33 IGX30130 HPGe 30 130 0 33 IGX50130 HPGe 50 130 1 00 IGX50135 HPGe 50 135 1 00 Table 2 8 X ray Detectors 43 44 2 5 9 Sahara Silicon Drift Detector The Sahara Silicon Drift Detector SDD is a state of the art X ray spectrosc
148. tick Dewar 644 mm 25 3 8 30 liter capacity 2 t 432 mm 17 Model Designation Endcap Configuration Crystal Type Vertical Dipstick SD Coaxial Germanium Planar Germanium Planar Si Li Elbow Dipstick ED Coaxial Germanium Planar Germanium Planar Si Li Inline SDIL Coaxial Germanium Planar Germanium 90 Inline EDIL Coaxial Germanium Planar Germanium Table 2 11 Configurations for Dipstick Cryostats 616 24 25 47 2 7 2 Unitary Cryostats In unitary cryostats there is a common vacuum system for the endcap coldfinger and the dewar This provides effi cient cooling in a variety of configurations The endcaps may be in a fixed horizontal or down looking vertical design The horizontal cryostats are also available with an extended coldfinger arm for insertion into a low back ground counting chamber The cryoflex option is a swivel arm which allows the endcap to be aimed for maximum efficiency Cryostats for X ray detectors may be ordered in a fixed horizontal geometry or with a slide mechanism for adjust ing the endcap sample distance A variable z control is also offered for detectors mounted on an electron column These
149. tion as a Function of Count Rate and Shaping Time 1 18 2 Gated Integrator with TR 14 Preamplifier A further source of peak broadening also related to the amplifier shaping time is called ballistic deficit It arises primarily at high count rates When a large volume coax ial crystal is used for its higher efficiency at higher ener gies some charges are produced in weaker less uniform field regions These charges are not collected as rapidly that is they have slow rise times If the charge collection time in the detector is long compared with the shaking time of the electronics these pulses will fall short of full energy value The result is a broadening and low energy tailing of the spectrum lines The effects of ballistic deficit can be compensated for by the use of a gated integrator amplifier GIA system This amplifier has variable shaping times controlled by the rise time of the pulses from the detector and it operates at a basic short time constant of 0 25 usec Ballistic Deficit h 0 25 us shaping Gaussian amplifier 0 25 us shaping Energy p gt Figure 1 24 Comparison of Co spectra obtained with a Gaussian shaping amplifier and with a Gated Integrator amplifier Figure 1 24 shows the dramatic improvement obtained with a PGT TR 14 transistor reset preamplifier and gated inte grator amplifier system for an n type coaxial germanium detector at 5000
150. tivity materials the ability of the preamplifier to process the detector input becomes a controlling factor The commonly used resistive feedback preamplifier has a standard energy rate product of 50 000 MeV second but can be modified to operate at 200 000 MeV second The pulsed optical feedback or transistor reset preamp is used for very low noise applications soft gamma or X rays with planar detectors Energy resolution remains optimal up to the performance limit of most main amplifiers Its energy rate product is 200 000 MeV second For highest count rates a transistor reset preamplifier is recommended It can operate at 800 00 Mev second or higher The upper count rate limit and resolution of the sys tem are thus determined by the gated integrator amplifier and ADC units A more detailed description of the PGT preamplifiers starts on page 20 ae T gg PRISM polymer 80 70 2 60 50 40 5 30 Transmission 20 10 Aluminum Thickness in mils 4 2 5 Energy keV 20 50 100 200 Figure 1 15 Energy transmission curves for window materials of various thicknesses in mils Some representative light element data are also reported for a polymer window 1 12 Window and Endcap Materials Standard aluminum endcaps absorb significant radiation below 10 20 keV The use of beryllium or polymer windows can extend the usability range to lower energies Figure
151. tor head is about the size of a portable cryostat and functions in any position Acoustically quiet operation and low mechanical vibration Detector performance guaranteed to match that of 1 2 cooled cryostats f Options p or n type coaxial germaniun planar germanium or Si Li crystals Model 483 Controller for continuous temperature monitoring automatic high voltage shutoff and heater assisted temperature cycling 10 25 and 50 foot gas lines Stand for bench top operation or a detachable han dle for portable use Retrofit available for existing detectors including those of other manufacturers Typical Applications Nuclear power plants site characterization and radi ation monitoring In vivo lung monitor installations Figure 2 3 Germanium Detector with JT Cool option 32 2 5 3 High Purity Germanium Coaxial Detectors PGT p type germanium coaxial detectors feature standard relative efficiencies up to 100 and excellent resolution and peak symmetry Their energy range is from 40 keV to 10 MeV Efficiencies of 10 100 are available These detectors have a long service life and can be stored warm for extended periods of time Features p type high purity germanium Vertical dipstick cryostat Standard 32 liter dewar Aluminum endcap RG 11 B C resistive feedback preamplifier 12 ft bias signal and power cables Unlimited temperature cycling without loss of resolution
152. tor reset PGT TR 14 p and n type PGT TR 1 The appropriate choice depends on your application The PGT RG 11 B C or RG 15 in line Resistive Feedback Preamplifier Figure 1 17 is the type most commonly used for gamma ray counting between 5 keV and 10 MeV It maintains a closed loop first stage amplification by means of negative feedback through a high value resistor and a selected low noise FET These components are mounted close to the crystal in the cryostat and maintained at liquid nitrogen temperature to minimize the noise and micro phonics contribution to system performance 20 Crystal FET 352 RG 11 output output HV stag o stage o 77777 Q 100 kQ 9 Test point Figure 1 17 Resistive feedback preamplifier The PGT 352 Low Power Preamplifier is a resistive feed back model designed for portable detector applications Its power requirement of lt 250 mW and operating voltage of 12 VDC minimize drain from the battery pack on the MCA The PGT 14 Pulsed Optical Feedback Preamplifier Figure 1 18 replaces the feedback resistor with light pulses to reset the preamp output Performance is close to that of an idealized charge sensitive preamplifier This preamplifier is ideal for very low noise applications such as the measurement of soft gamma and X rays using small to medium high purity germanium planar detectors
153. ts 102 8 lt 90 from Va gt 90 from Va gt 90 from Vi lt 90 from Vi 0 soo M 0 Compton scattering angle FEP full energy peak SEP single escape peak FEP 511 keV DEP double escape peak FEP 1022 keV Va active volume Vj inactive volume Figure 1 3 Spectral distribution of a monoener getic 1 4 Mev gamma ray incident on coaxial ger manium 1 3 Radiation Detection Radiation detectors measure the effects of incident parti cles or photons on matter There are three main types of detectors Gas filled detectors lonization chambers Proportional counters Geiger M ller counters Scintillation detectors and CsI TI crystals Various plastics Semiconductor detectors High purity germanium HPGe Lithium drifted silicon Si Li Lithium drifted germanium Ge Li PGT specializes in the manufacture of high purity germa nium HPGe and Si Li detectors for gamma and X ray detection HPGe crystals contain a non zero level of impu rities The type of impurity determines whether the crystal is a p or n type semiconductor For Si Li detectors silicon crystals with p type impurities are counter doped with n type lithium ions Ge Li detectors are no longer manufac tured but some are still in use These crystals are fabricated into p i n diodes capable of withstanding high reverse bias voltage with low current 0
154. uivalent equations for different detector geometries yield the contribution to I t of every charge carrier The total induced charge 4 is obtained by integration over all the charge carriers created 1 3 4 Preamplifier Rise Time The rise time of the generated pulse can be measured at the preamplifier output For gamma and X ray detectors if the preamp is sufficiently fast T is equal to the charge collection time An estimate of be made from the following equations 2 7 1077s 8 1078s for Si at room temperature for Ge at LN temperature 1 4 Counting Systems Nuclear spectroscopy requires determination of The energy of each voltage pulse induced in the semiconductor detector The number of pulses occuring at each energy This is the function of the main amplifier ADC MCA sys tem In its simplest form the process occurs as follows The voltage pulse from the charge sensitive preamplifier goes to the main amplifier where it is shaped and further amplified The shaping time is the time required by the amplifier to completely process each pulse Several inte grations are performed to smooth away most of the noise while retaining the information in the pulse The height of the pulse from the main amplifier is then con verted by the analog to digital converter ADC to a num ber proportional to its energy When this digital value arrives at the multi channel analyzer
155. uld be 1 The actual value is closer to 0 than to 1 In most cases a value of 0 11 for both silicon and germanium gives satisfactory agreement with laboratory results 1 3 3 Charge Detection When a semiconductor detector is used in a spectrometer the current signal from the detector is converted by a charge sensitive preamplifier to a voltage signal which is then processed in the main amplifier and multichannel analyzer MCA ea S D o I t current generator in the detector crystal Cp capacitance in the depletion region Rp resistance of the depletion region Z series impedance Figure 1 6 Detector equivalent circuit Determination of the current induced in the detector as shown in the equivalent circuit in Figure 1 6 requires first calculating the motions of the charge carriers in the electric field E see Figure 1 4 E is readily calculated from the applied bias voltage detector geometry and bulk resistivity of the crystal Once E is known the following differential equation can be solved dr _ r position of the charge carrier dt drift velocity in the electric field E For the example shown in Figure 1 4 of a detector with plane parallel contacts and a field E across a distance W the carrier 4 moving a distance x in the direction of the field induces a charge given by the following equation Ax Aq These two equations or eq
156. ustrial sites Any detector can be ordered with PGT s proprietary QUIET ONE anti microphonics mountings Space exploration NIGC in custom cryostat with shock and vibration insu lated mountings X ray fluorescence analysis of elements from B through U Planar HPGe and Si Li X ray detectors Emergency response monitoring Portable MPS or GF spectrometers with either coaxial or planar HPGe Non destructive assay of spent nuclear materials DUO detector for simultaneous measurements in two energy regimes Table 2 1 Applications and Suggested Detectors 29 2 5 Detector Specifications 2 5 1 Duo Detector The PGT Duo Detector for high level radioactive waste detection and analysis is an array of two germanium crys tals on a single axis in a common cryostat vacuum It per mits simultaneous detection in two energy ranges 100 450 keV and 600 1000 keV The combined spectral informa tion improves the precision in the measured isotopic ratios The front crystal is a planar IGP detector with inherently high resolution for low energy photons It is sized to reduce the amount of Compton scattering of high energy photons Most of these photons pass cleanly through the planar and are absorbed by the n type coaxial crystal NIGC mounted behind it A lead disk positioned between the two crystals attenuates any low energy photons that might otherwise reach the coaxial detector including remnants of Compt
157. with radiopure materials in an electronic scintil lator anticosmic shield above ground 1438 m underground inside a modern lead shield 7 3 cm thick copper inner shield added Copper shield replaced with 10 cm thick shield of 448 year old lead from a sunken Spanish galleon Q Indium electrical contact removed Electroformed copper hardware compo nents 99Ge removed Solder electrical connection removed From PNA SA 15497 Recent Progress in Ultralow Background Ge Detector Searches for the BB Decay of Ge Dark Matter Candidates and Solar Axions F T Avignone R L Brodzin Ski H S Miley and J H Reeves 1987 with Figure 1 16 Reducing background radiation PGT offers the following very low background materials Oxygen free high conductivity copper for the cold finger and detector mounts Ultra low background aluminum endcap 1 ppb Th Low background beryllium or Vespel entrance win dows Vespel plastic well insert Activated charcoal getter in place of the molecular sieve Tungsten internal shielding in the endcap Typical specifications are shown in Table 1 1 In addition the NPR cryostat configuration separates the endcap from a direct line of sight with the preamp whose circuit boards and components contain natural residual radiation The endcap itself may be enclosed in a lead shield In selecting a low background system there are some gen
158. x3 in Nal TI scintil lation crystal at a 25 0 cm source to endcap distance for the 1332 5 keV line from a 0 point source Ere where 1 2 x 107 Again the source intensity must be corrected for the age of the source since calibration 1 7 1 4 Intrinsic Efficiency For most planar detectors the relative efficiency as deter mined above does not apply since the 1332 5 keV line is out of range For these detectors the active surface area and entrance window absorption are more useful specifica tions at the lower energies where the gamma range is well within the thickness of the germanium crystal Intrinsic effi ciency can be used to specify these detectors The intrinsic counting efficiency takes into consideration just those photon events actually reaching the detector window Thus while is the total number of photons emit ted in all directions by a point source intrinsic efficiency relates to just the number of photons the conic section corresponding to the active area of the detector as shown in Figure 1 11 Endcap w 5 5 D distance R D A d 2 A Endcap crystal distance d Crystal diameter _ 2mRH W Solid angle Depth into crystal R D A H co A N in full Se RAT Net counts in full energy ntr Ns AM peak Figure 1 11 Intrinsic efficiency determination The values of A and H are very small a
159. ystal having equal numbers of free holes and electrons ION IMPLANTATION Process of embedding ions into the surface of a solid by irradiation with a beam of energetic ions often used to create one of the contacts for a semicon ductor detector IONIZING RADIATION Gamma rays or alpha or beta par ticles which interact with matter to produce ions either di rectly or indirectly ISOTOPES RADIOISOTOPES Atoms with the same atomic number but different atomic weight i e a different number of neutrons in the nucleus if the proton neutron ra tio is unstable it is a radioisotope which undergoes some kind of spontaneous decay to a more stable configuration JUNCTION Transition boundary between regions of dif ferent electrical properties in a semiconductor or between a semiconductor and a metal LEAKAGE CURRENT Total current flowing through or across the surface of a detector crystal with operating bias applied and no external ionizing radiation LITHIUM DRIFTED SILICON Si Li Silicon crystals which have been counter doped with Li ions by the process called lithium drifting to achieve the required impurity level for use as a semiconductor detector 90 MARINELLI RE ENTRANT BEAKER specially de signed beaker that fits over a coaxial detector endcap so that the sample essentially surrounds the detector see page 12 useful for the analysis of low activity samples MCA Multichannel analyzer an electronic device for sort in

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