Regulatory Guide 5.9
| ML13350A205 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1973 |
| Revision: | 0 |
| From: | US Atomic Energy Commission (AEC) |
| To: | |
| References | |
| RG-5.009 | |
| Download: ML13350A205 (10) | |
0U.S.!-ATOMIC ENERGY: COMMISSIONREGULATORYDIRECTORATE OF REGULATORY STANDARDSJune 1973GtUUIDEREGULATORY GUIDE 5.9SPECIFICATIONS FOR Ge(Li) SPECTROSCOPY SYSTEMSFOR MATERIAL PROTECTION MEASUREMENTSPART I: DATA ACQUISITION SYSTEMSA. INTRODUCTIONProposed revisions to section 70.51 ofl 0 CFR Part70. "Material Balwncc. Inventory and RecordsRequirenricnts." woold require licensees authorized topossess at any one time more than one effectivekilogram n.it" special nuclear material to establish andmaintain a system of control and accountability suchthat. the limit of error of any material unaccounted for(UL1F): ascertained asa result of a measured mnaterialhalance, meets established minimum .standards. Theselection and proper application of an. adequatemeasurement method for each of the material forms inthe fulccycle is essential for the maintenance of thesestandards.This is lhe. first in a two-part series of guides whichpresent specifications for Iithium-drifted germanium.Ge(Li); gamma ray spectroscopy systems. This guidanceapplies to the .selection of.a special nuclear material(SNM) assay system which utilizes gamma rayspectroscopy for the quantitative delermination of the.* SNM content and a qualitative detertuination of tileradionuclide abundances. Within each of the, guides inthis series, Data Acquisition and Data Reduction.I variations of a basic spectroscopy system are defired andindividual specifications provided. The procedures forapplying these systems to specific materials and theanalysis of the reduced data is tile subject of a later.guide.B. DISCUSSIONI. BackgroundGamma Iray spectroscopy systems have been usedfor the nondestructive assay (NDA) of various specialnuclear material forlims encounteled in the fulel cyclehoth for quantitative determintiont of the specialnuclear material cuntent, and for the determination ofradionuclide abundances. In addition to the NDA ofhulk materials, ganim:i ray spectroscopy is used in theanalysis of specially prepared. homogeneous lahor:,lorysamples.There is no single gainnna-ray spectroscupy systemavailable which is satisfactory to r all a pplic ition s nor isthere I standard which defines and specilies the typv ortypes of Isstenls it) be used in cach of tihe aboveapplications. T"his guide defines and details thlespecifications for ganmma ray spectroscopy daltaaquisition systems appropriate for special nuclearmnalcrial assay.The scope of this guide is limited to thtconsideration of Ge(Li) gamma ray spectroscopvsystems; No discussion of thallitim-activa ted sodiumiodide. NaI(TI), gamma ray systems is presented. Inaddition. no discussion of applications of ganmma rayspectroscopy arc presnted. The nieasiremeitprocedures (including calibration), analysis nelthods.inherent limitations, and overall precision and accuracyare specific to each application and are therelbre thesubject of separate application guides.An elementary introduclion to the concepisassociated with the application of G;etLU spectroscopyto problems of nuclear material assay is available.'Descriptions of the physical processes of gamma raydetection, discussiotIs of important instrumenlalionL. A. Kull, '.'An Introduction to (;C('Li) Uitsd NalGarnma-Ray Derectorz ror Safeiiuard% Applicauiiomu."ANL.AECA-103 (1973).USAEC REGULATORY GUIDES Copies of published quides may be obtained by request indicating the divisionsdeIlred to the U.S. Atomic Energy Commission, Washington, D.C, 20545,Regulatory G ures.ae issued to describe and make avIiiablato the public Attention: DIrctot, of Regulatory Stendards. Comments and suggestions lotmethods acceptable to the AEC. Regulatory staff of specific parts Of Imptrovements in these guides are encouraged and should be sent to the Secretarythe Commilsio"'$ regulations, to techniques used by. the naff In of the Commission. 1U. Atomic Energy Commission, Washington. D.C. 20545,evaluating specIssc.probIems or poetuiatad accidents, or toprovtide guidance.to Attention: Chlef.PubltcPtoceedingsStaff.applicents. Guides are not subtiltules fat regulations and compliancewith them is not requited. Methods andrsolutions dilferent from those set out in The guides areIssued in the following ten broad divis!ons:the ipides will be acceptable it they providea bels'fot the findings reqiuisita tothe issuance or continuance of a permit.ot license by thecCommisionI'. L R Poesre ReacTrtors 6. Products2.'Resorch end Test neactots 7.. Teerssportetiors3." Fuels and Materlels Facilities B OccuPational HealthPublished guides will be revispe periodically. as appropriate. to ea-ommodate 4. Environmental end Siting 9. Antitrust Reviewcosm nd to reflect new inlermatlon or experience. 5. Materials and Plant Protection 10. General characteristics, and a step-by.step description of~a simpleassay problern.are. included in this document. Relevant*"information.presented :at a 'somewiat higher' technicallevel. including nomenclature and definitions. isinmiained in two useful standards documentls.2 -Thesedes. ribe .detailed techmiques for defining and..obtainingmeaningful peirormance data for Ge(Li) detectors andamplifiers. The glossary of technicalmterns found in both[ohese standards documents will priwve valuable to those" *Unfamiliar.it I gamma-ray. spectrosc pic nomenclature.Finall,..there :is a coiisiderable :amouit Of valuablebackgroundmnaterial published by he. manufacturers ofdetectors'aid associated 'electronic hardware which isavailable. fro ithemnon request.2. Functional DescriptionA. block diagram of those components of the Ge Li)spcctroscopy system which perform the data acquisition* funlction in material protection measurements is shownS" in Fig. I. lhe function of these components is first toconvert the charge produced by the interaction of anincident irmma ray with the Ge(Li)-delector into anamplified. analog electrical signal. The analog signal isthen converted into digilal information which can bestored, displayed, and otherwise processed byappropriate data reduction and analytical modules.3. Types of SystemsThere are three variations of the basic dataacquisition system presented in this guideline. This* variance in the basic configuration is the result -ofattempts to optimize each system to obtain specificassay information from certain types of material forms.The. three ..variations -of the basic system are' described below' and will be referred to by' Ronannumeral in the remain der of the document. (Forexample. System II refers to paragraph II below.)1. A' moderate to high efficiency system having an* .energy resolution which is adequate for assays ofmaterials for the fissile isotopes 24'Pu, 239Pu, 235 U.* and 2-13U. it can also be used to perform assays of* materials for fertile isotopes such as 2"1 Th and 2"%BUand to determine tile "ag" of plutonium samples from* measurements of their americium-241 content. This* system is used in those applications where Nal resolutionis inadequate to accurately resolve the gamma ray linesof the isotopes of interest from those from an interfering* " background. and where the lower efficiency Ge(Li)detector still provides sufficient sensitivity for practical`-Te-t Procedure for Amplifiers and Preamplificrs farSemiconductor Radiation IDoectors.' IEET Std 3011-969. TheInstitute of Electrical and Electronics Engineers. Inc. (1969).'"Tesi Procedures for Germanium Gamma-Ray Detectors.'.IE-EE Sid 325-1971. 'nt:e Institute cif 'leciricil and ElectronlcNEngineers. Inc, (1971).assay. work. The system is designed to measure gamnnmarays with energies greater than 120 keV.I!. A moderate to high efficiency system whichcan. satisfy all 'ihe requisites for System I and whirh. inaddition, hasth e improved energy resolution necessaryto.assay for the pltitonitmni isotopes 238 through 241..This system is commonly used to determine tile relativeradionuclide abundances and is designed to measuregamma rays with energies greater than 120 keV.Ill..A. system. designeUl specifically for low-energygamma ray..and X-ray 'spectroscopy (at gamma rayenergies less than 200 kcV) having an energy resolutionadequate to perform quantitative and qualitative.assaysof specially .prepared samples for the isotopes ofplutonium (238-241) and uranium (235 and 238).4. Equipment Acceptance PracticesStandard practices regarding the final acceptance ofequipment arc ustially prescribed by individualcompanies. laboratories, or departments. However. someof the following procedures have. beens found to beuseful in providing the user with the assurance that hewill acquire equipment which will perform as expectedin nuclear materialassay applications.Equipment descriptions .(including tile theory ofoperation) and instructional material covering operation.maintenamce. and servicing of all electronic componentsshould be supplied for individual components orcomplete systems. Such descriptions should includecomplete and accurate schematic diagrams for possiblein-house equipment servicing. Carefully specifiedoperational tests of system performance should be madeat the vendor's'facility and the original data supplied tothe- user before equipment delivery is scheduled, withfinal acceptance based. on the user's own performancedata taken at the user's facility.It is necessary to have calibration sources on handto verify the operational capabilities of the system. Thefollowing radioactive sources (with appropriateactivities) will provide sufficient counting rates toperform the tests specified in the regulatory position:"0Co- 10.30 MCi,',co-1-10o CiC. REGULATORY POSITIONLithium-drifted germanium, Ge(Li), gamma rayspectroscopy data acquisition systems meeting theoperating specifications given below are consideredadequate for use in special nuclear materials assay. Theselection of a system meeting these specifications isconsidered necessary but not suflicient for accurategamma ray spectroscopic assay requiring resolutionbetter than obtainable with Nal, No guarantee ofmeasurement quality as a result of the application ofsuch. systems should be assumed.I".. .*" ,:5.9-2'
characteristics, and a stcp-by-step description of a.simpleassay problem are. included in this.document. Relevanthi .'ormation presented at a somewhatt higher technical.level. including nomenclature and definitions, is.contained. in two useful standards documents.2 .Thesede,;cribedetailed techniques for defining and obtaining" tmeaningful perfornmance data for Ge Li) detectors:andn
- aplifiers. The. glossayv o0f.technical terms found in both, these..standards docuiments Will prove valuable to those"ounfamiliar with camnia-rtvy spectroscopic nomenclature.Finally. there is a considerable amnount of valuable.background material published by tile inanufacturers ofdetectors and associated electronic hardware which isavailable from them on request.2. Functional DescriptionA block diagram of those components of the Ge( Li)*spectroscopy system which perform the data acquisitionfunction in .material protection measuremenis is shownin Fig. .I. The function of these components is first toconvert the charge produced by the interaction of anincident aninma ray wvith the Ge(Li) detector into anamplified, analog electrical signal. The analog signal isthen 'convertcd into digital information which can bestored., displayed, and otherwise processed byappropriate data reduction and analytical modules.3. Types of SystemsThere are, three -variations of the basic dataacquisition system presnted, in this guideline. :Thisvariance in thc basic configuration is tile result ofattempts to optimize each system to obtain specificassay information from certain types of material forms.The three variations of the basic system arcdescribed below and will be referred to by Romannumeral in the remainder of tile document. (Forexample, System 11 refers to paragraph 11 below.)*I. A moderate to high efficiency system having an* energy resolution which is adequate for assays ofmaterials for the fissile isotopes 24,Pu, 239pu, 2.15U.and 213U. It can also be used to perform assays ofmaterials for fertile isotopes such as 232Th and 231Uand to determine the -age" orplutoniunt samples frommeasurements of their americium-241 content. Thissystem is used in those applications where Nal resolutionis inadequate to accurately resolve the gamma ray linesof the isotopes of interest from those from an interferingbackground and where the lower efficiency Ge(Li)detector still provides sufficient sensitivity for practicalProcedure. for. Amplificr.ý and Preamplifiers forSerniconductor Radiatinn IDteetors'" IEE:. Std 301-1969. TheInstitute of Eteetricat and -leCtronies Engineers. Inc. (19691."Prncedurcs for Gernmniurn Ga"niaýRay De"tectors.-IF-.' Std 325-1.971. Tlhe Institute nlr Electrical and ElectrunicsEngineers. Inc. (1971).assay work. The system is designed to nmeasure gatnmarays with energies greater than 120 keV.II. A moderate to high efficiency system whichcan satisfy all the requisites for Systen I and which. inaddition, has thc imiproved energy resolution necessaryto assay. for tile plttoniuim isotopes 238 through 241.This system is commonly used to determine the relativeradionuclide abundances and is designed to measuregamma rays with energies greater than 120 keV.Ill. A system designed specilically for low-energygamma ray and X-ray spectroscopy (at gamma rayenergies less than 200 keV) having an energy resolutionadequate to perform quantitative and qualitative assaysof specially prepared samples for the isotopes ofplutonium (238-241) and uranium (235 and 238).4. Equipment Acceptance PracticesStandard practices regarding the final acceptance ofequipment are usually prescribed by individualcompanies. laboratories, or departments. However. someof the following procedures have beet, found to beuseful in providing the user with the assurance that liewill acquire equipment which will perform as expectedin nuclear material assay.applications.Equipment .descriptions (including the theory ofoperation) and instructional material covering operation.maintenance, and servicing of all electronic componentsshould be supplied .for individual components orcomplete systems. Such descriptions : should includecomplete and accurate schematic diagrams for possiblein-house, equipment servicing.. Carefully specifiedoperational tests of system performance should be madeat the vendor's facility and the original data supplied tothe user before equipment delivery is scheduled, withfimal, acceptance based on the user's own performancedata taken at the user's facility.It is necessary to have calibration sources on handto verify the operational capabilities of thie system. The* following radioactive sources (with appropriateactivities) will. provide sufficient counting rates toperform the tests specified in the regulatory position:6OCo- 10-30 /CiI 7Co-I-10upCiC. REGULATORY POSITIONLithium-drifted germanium, Gc(Li), gamma rayspectroscopy data acquisition systems meeting theoperating specifications given below are consideredadequate for use in special nuclear materials assay. Theselection of a system meeting these specifications, isconsidered. necessary but. not sufficient for accurategamma ray spectroscopic. assay requiring resolitilionbetter than obtainable :with Nal. No. guarantee, ofmeasurement quality as a result of the application ofsuch sys!ems should be assumed.5.92
".Q'" iThe .enipho %is here ison the 1perating specificationsrelated to the overall performance off tile entire .data* acquisition system. Component specilicat ions have~beenincluded in Appendix A to provide guidance in theselectiol,; of original Or replacenten I co1Iponen S whichare essential if adequate system performance is to be* attained. The system operating performance s,,hould notbe deduced from the component performances: overallsystem performance should be checked independentlyand compared to tile operating specifications presentedhere.1. Energy Resolution and Peak Shape(Systems 1, 11, 111) The eniergy resolution of the.system should be measured according to the procedure* specified in IEEE Standard 325-197i,4 with thefollowing additional stipulations: (I) the peaking time"for the shaping amplifier should be no. greater than 4.pseec (2) the total number of counts in tthe Ltnterchannel of the peak should be no less than 104 counts;(3) the count rate during the measurement should be inthe range 102 to 10-1 counts per second as measuredwith a total count rate meter. The full width of the peakat half maximum (FWHM) and full width attenth-maximum (FWTM) are as defined in IEEEStandard 325-1971.6 The full width at 1/50 maximum(FW.02M) is defined in a similar manner. The energyresolution and peak shape specifications for each of thesystems (I i1, 111)are given in Table I and the measured.values should be no greater than those shown here.These values have been determined to be necessaryfortheapplications defined in B.3. above.2. Detection Efficiency(Systems 1, 11) The full energy peak efficiency (inpercent) is defined relative to the full energy peakefficiency of a 3 in. x 3 in. Nal(TI) scintillation detectorfor 1.33 MeV gamma rays (6'Co) at a source.detectordistance of 25.0 cm. The detailed procedures fordetermining the. efficiency in accordance with thisdefinitionare presented in IEEE Standard 325.1971.LTile efficiency required for specific assayapplications should be determined .by estimating thegamma ray intensity at the detector from a sample ofknown...strength and the counting rates required tocollect a statistically significant number of counts underS'IEEE Sid 325-1971, op. cit.. Srction 4.'Peaking time-the time required for a pulse to reach itsmaximum height. Peaking times can be easily measured with anoscilloscope and are less susceptible to misinterpretation than arcRC time constants. The relationship between RC time constants.and peaking time varies as their is no standard method fordefining RC time constants in semi-Gaussian shaping networks.6 IEEE Sid 325-197 1, op. cit., Section 3.7 Ibid., Section 5.2.the. spectrutm lpeaks of interest in a reasonahle period oftime. Est intates should be corrected for.sample-to-detector distance and tlie effects of absorbingmaterials placed between tile sample and detector.Whenever possible. it. is advisable Ito make preliminarymeasurements oin tile samples under consideralion withan available detector, and the efficiency of t(ie optimaldeleclor determined by extrapolating the meastredresults. A Ilumni:al estilalte of the detector.efficicncy (..Isdefined above) required for most applications, isapproximately 8%1: however, detectors with elficienciesa ithe rang " of 5 _ o 20., are ill use For nuclear materialassays. (To assist in providing some perspective here. an8%,` detector as speciflied above has an active volumnL ofabout 40 cc while 5 to 207, detectors have voltmes ofabout 25 cc to 110 cc. respectively. Art , detector hasabsolute detection efficiencies of about 15 x .1"T4 185keV, 4.5 x 10-4 (a: 411 keV. and 0.96 x 10" .(a 1.33MeV at a source-detector sepai:itionrof 25 cm.)(Systemn i11) The method described above fordetermining the detection efficiency witlh a high energygamma ray source is not relevant for detectors used inlow-energy gamma ray spectroscopy. Instead. it is moreappropriate to specify. (I) the active volume of thedetector and (2) the maximum effect of absorbingmaterials (absorbing materials include detector surfacc"dead layers," gold surface plating, and the end capwindow of the cryostat). The following specificationsare therefore given for the low-energy gamma raysystem:a. detector volume- 1.0 to 1.5 ccb. drift depletion depth--0.5 to 0;7 cmc. layers of absorbing material between theradiation source and the active volume of the detectormust be thin enough so that the 14.4 keV peak from as 7Co source is at least 5 times the conlitiltuinbackground under the peak."3. Count Rate CapabilitiesThe following specifications are related to asystem's ability to maintain adequate energy resolutionat high co.unt rates.(Systems I. 11) The system should be capable ofo0ratingvat a" total counting rate of: 104 cps from aCo source (as measuredwith a total count rate meter)with less than a 10% i,-,lative increase in.the 1.33 MeVpeak width at 1/10 the maximum peak height (,VTMýas compared to the FWTM value measured at 102 ito 10:cps.(System Ill) The system should be capable ofoperating at a total counting rate of 5 x 103 cps fiomi as Co source (as measured with it total count rate ittler)"Care should he^ taken to ensure that the "Co saiurc:encapsulation is *.thin cenough. (<1 0( ng/cut2 plsi ic or .tteequivalent) so that self absorption in the source itself is norsignificant.__ _" " '." 5.9-3 witlh less than a I T0 relathe increac in the FWHM and.W * .M ol'the 1 2 keV peak as" iCOipared to th6 values* ..obtained at .O 1 c. .4. Peak-to-Coinpton Ratio.s L(S selI1,i) The peak-lo-Comlpton. ratio for tie.. .33 MeV peak Irom a Co source. as detined in I-EEStandard 325-197 1' should be greater than the valuesspecilied in. T'lhký 2 for 'corresponding detector-e fficienc-ies.* (System 1Il) Tlifis specification is not applicable.* 5. Linearity and Stability(Systenis I, Ii, Ill) The integral non linearity of thedata acquisition system's ener,, calibration should beless than 0.2-." over the top 95%' of the ADC. range. The* ystcm n .nlitiarity should be measured uwing a set of-:l "Sid 325-1971 , p. cit.. Section 3.4.well-known pillma ray soutces and the proecduredscribed in the literature.'The long.term stability requirement for the system'szero channel and g aiti shOuld be defined as follows: thedrift in die position of a spectrum peak front acalibration source shotld be less thin 0.1"'l (compared tofull. scale) in a 24-hour period at constant roomteln'perature. (For example, tie centroid of a calibrationpeak placed in approximately channel 4000 of a 4096channel spectrum should not vary in position by morethan .4 channels over a 24-hnur period.) Tiie temperaturecoefficient of the systenm's zero channel and gain shouldbe less thau 0.02%0.,,C in the temperature range from O"to 50"C." R. C. Greenwood, R. G. Ilcimer. and R. G. Gehrke."Precise Comparison and Measuiement of Gamma-Ray Energieswith a GOtLi) Detector I. 50-420 kcV,," Nuct. Instr. and Methods77. 141 (197W).R. G. Wnlmer, R. C. Greenwood and R. G. Gehrke,"Precise Comparison and Measurcment of Gamma-Ray Energieswith a Ge(Li) Detector It. 400-1300 ke,," Nuclear. Insir. andMethods 96. 173 (1971.)5.9-4m APPENDIX ACOMPONENT SPECIFICATIONS3. Preamplifiers1. Detector Crystal Geometry(Systcms. I,.II)The dctector should be of' tie closedend.. coaxial drift. right :circular. cylinder t)yp: 0hicon figuraation has the Iit;ixinttitn fraction oftusable activcvolume:fit r detecturslof noderate tolhigh cfliciency. Thecrystal diameter should be approximnailclv equal to iblength to minimizc any Unusual e'f'icienicy vs. gcunteirv* effects. The active volume or the detector shouldcomprise at least '0'i.- 61' t[lie total crystal volumne withthe undrifled core diameter kept as sitall aseconomically possible. This maximizes [lie prob:tabilily!that a ganima-ray- interactiui will appear ill tile fill]energy pcak of the spectrum. (Note: The specificationott peak-to-Compton ratio given in Section ('.4 isdirectly related to the crystal's aclive/total volume atio.](System Ill) The detector shotuld be of the planartype. Small detectors of this configuration offer the bestresolution available for low-energy, gamma rays.Operating specifications are given in Section C.2 thatdefine the allowable thickness of detector surface .deadlayers" which absorb low-energy gamma rays beforethey interact in the detector's active volume.S (Systems I, II, Ill) Methods for specifying thephysical size for tlte: detector crystals are covered inSection C.2.* 2. Detector Mounting and Cryostat Description(Systems 1, III) There are four detector cryostatconfigurations Which are typically' available: (I) rightangle dip-stick, (2) upright dip.stick. (3) gravity feed.and (4) side entry (portable). Of these, the right angledip-stick is widely used for Systems I and I1 and theupright dip-stick for System III: the configurationselected should be that considered to be most useful fora specific application. For reliable operation. the vacuumin the detector housing should be maintained by azeolite getter. It is recommended that the liquid nitrogenDewar have a minimum capacity of about 30 liters and aholding time of at least 10 days. The Dewar should havea connection which allows replenishment of the liquidnitrogen supply without removing the cryostat. Aseparate high-voltage input to the cryostat housingshould be provided in the event it is necessary ordesirable :to apply a detector bias which exceeds therating of. the preamplifier's high-voltage input. It isrecommended that the high-voltage input be clearlymarked and located at least 2.0 cm from thepreamplifier signal output. The distance between theS detector's front surface. and the window in the housingshould be less than or equal to 1.0 cm to allow one toachieve minimal detector-sample separations whennecessary.S(Systems 1, II) It tamy cases prcampliler.sComp'it iible with nuclear material speclroscorpyapplications are purchased in combination with :a Ge( Li)crystal as a package. The detector specificationst here fore relate to the d e t Cc Itor-prCetupliflCrcombi;ia lion: however. tile following additiUnals pecifications should he included in the selection of .illoptimal system. A charge sensitive preamtplihlie shtmildhe nmottned on t lie cryostat near lite detector. The fieldeffect transistor (WET) in ite first staye o1 tlieTi..mld lw operated at room tellrirature(_300"i'K ' Tile detector sihtuld he d.c. coripled (:Isopposcd .o c.,p:,.'itively coupled) to tile aic of tle itpul* stage of' tire 1i c.1triplilher for better ctenergy resohulion.The tti lowing procedures arc iccniittended tominimize the probability of destroying thei F1 " dtie todetector warmup or high-voltage Irantsients. Posilivc highvoltage should be used, and the: e should be at lcast onefilter section placed in t(le system interntalto the cryostat. At least one filter should also be placedexternal to the cryostat to reduce tile possibility of shorlcircuiting due to condensate formation on thie internalfilter. The total RC time constant of the filter networkshould be at least 30 seconds.(System I1l) Sanme as above for Systenms I and IIexcept that the FET in the preantiplifier's first stageshould he located within the cyrostat and operated itliquid nitrogen (LN) temperature. Att LN cooled 17ET isrequired, to achieve the excellent eiergy resolutioncharacteristics of this system.4. Main Amplifier(Systems I, I1. i11) A main amplifier with adjustablepgin should include unipolat. senti-Gaussia," pulseshaping networks with adjustable titiCe constantscorresponding to peaking times between I atnd S usec. ( Ito 4 psec peaking times are typically used for Systemts Iand II while peaking titnes as long as 8 ,isec could beused in System I1l.) This choice fl" antplifier providesminimum resolving time for a given energy resolutionand sufficient flexibility to optimize the amplifiercharacteristics for most' counting conditions. Nominalspecifications to aid in identifyiing this class ofamplifiers. commonly referred to as spectroscopyamplifiers, include the following: linear range 0 to IOV.integral nonlinearity <0.05%. temperature stability<100 ppm gain shiftrc. attd thermal noise <5.,V rats2 ISystern II only) Tle preamplifncr\ First stape F-lV maybe located within the keryo,;iai and operated at liquiid nitmtgentemnperatures, but in order to faeiliLaie poSible ITTreplacement. it is recomntended Ihat a detectorl he electu-dwhich attains adequate energy resolturion with an l.T.5.9.5I..L~.
referred t0 the input for 4 u.sec peaking times (the.noiselevel varies inversely withthc peaking time). The mainanipliier %should be a standard NIM'3 module... .......At tin atesgreater than. 0-1 cps, problemsU. " I es a'dtgtadation of the:energy resolution resulting in.loss of counts. in the. spectrurn peaks begin to occur."..Thes effects are due. to.the overlap of portions of tw'oor 0.orL pulses in.time and to bas.line fluctuations. The.t .nagniitude of. Ihese effects can be mininized by tlieinclision Ofatile. following Ifatures in the amplifier'sdesitl-. (I ) a. b.baseline.. restorer.:(BLR) circuit at. theamnphi ocvrvut.pu and. (21) pole-zero. cancelled couplingnetworks.7TheiBLR circuit shouldbe adjustable for bothlow ind high couhiting lte..conditions.. .5. Analog to Digital Converter (ADC)(Systems I, Ii, .ll) The ADC should be capable ofdigitizing pulse amplitudes from the amplifier in therange of 0 to 10 volts in at least 409)6 channels. Thefrquency of thle internal clock should be at least 50ne,,ah,'tz to handle high counting rates with nominal" AD)C dead time losses. The integral nonlinearity shouldbe less .than 0.15% over the top 95%, of full scale and thedifferential nonlinearity should be less.than 1.0% overthe. top 95% of full scale for semi-Gaussian pulses withpeakingtirnes of I.to psec. These linearity specificationsare. not .siringent. but:. are *adequate to enableidentification of unknown peaks. which may.. appear in aspectrum...The short-term zero channel arid gain drifts should* be < .01%/f(?C and 4 .02%0rC, respectively (thepercentage refers to full scale), in the temperature rangefront 00. to 500C. For long term stability, the peak from*3NtM-Nuclear Instrument Module. see USAEC -TechnicalInformation Document. Standard Nuclear Instrument Modules.Revision 3. TID-20893 (1969L..t' 4For more details on BLR circuits see V. Radeka, "Effectof 'Baseline Restoration' on Signal-to-Notre Ratio in PulseAmplitude Mteasurements," Rev. Sci. Instr. 38. 1397 ( 1967).a stable pulsershould not shift by more than onechannel over a 24,hour period.for a line voltage of 115V-li,. 50-65 Hz,7and at constant room temperature.(Note: The. ADC. drift and.linearity. specifications areclosely ..re!'ttcd :to the.. overall system stability andlirearity operating specifications described in SectionC.5.)"Fhc ADC should be capable of being DC coupled tothe main aniplifier in order that BLR circuits can beused. A digital: offset capability in the ADC isrecommended. (Note: In some systems the ADC is anintegral -part of a multichannel analyzer, a unit whichalso performnsi.the, funct ions .of.data storage, display, andsometimes rudimentary analysis. These latter functionsare taken. up :in Part 2 of this series. In multichannelanalyzersystems, however, the ADC function is usuallyspecified separately and can be compared with the aboverecommendations.)(System 1) For certain applicatiuns where energyresolution is definitely not critical, all the ADCspecifications above are applicable with the exceptionthat a 1024 channel capacity with a 1024 digital offsetmay be adequate to provide a sufficiently small energyinterval per channel (keV/channel) to cover a limitedenergy range of.. interest. It should be emphasized,however, that this choice may restrict the effective useof the system for other applications.6. Power Supplies(Systems I,. II, .111) The system power supplies(detector high- voltage, preamplifier, and NIM bin)should be capable of operating the system within theoperating specifications listed in Section C.i whensupplied with 115 volts (+/- 10%) at 50 to 65 hertz (atconstant room temperature). The detector bias powersupply should have an adjustable output that is shortcircit protected.with automatic power restoration afterremoval of the short. The maximum outputvoltage .isdetermined by detector requirements; 5 kilovolts issufficient for most applications.0. ,:..5.9-6 TABLE 1ENERGY RESOLUTION AND PEAK SHAPESPECIFICATIONSSYSTEM ICalibration SourceGamma Ray EnergyFWHM (keVI'ic o- 133 Q keyý"Co- 122 keV6'0CO- 1332 keyFW.02MtFWHMless than 2.7less than 2.81.625SYSTEM II1.01.9SYSTEM IIIless than 2..less titan 2.8less than 2.5less than 2.5'Co-5.9 keV (Fe X-ray)S'7Co- 122 keV0.320.55TABLE 2.PEAK-TO-COMPTON RATIO VS. DETECTOR EFFICIENCYMiiuDetector Efficiency(As defined in Section C.2)5%10701o%20%MinimumPeak-to-Compton Ratio20:13o:135:138:15 LIQUIDNITROGEN'DEWARDIGITAL OUTPUTANALOG TO DATA STORAGEPREAMPLIFIER AMPLIFIER TO DIGITAL DISPLAYS, DATACONVERTER REDUCTION ANDANALYTICAL MODULESFigure 1.-BLOCK DIAGRAM OF A Ge(Li) DATA ACQUISITION SYSTEM5.9-8
..,UNITED STATESATOMIC =ENERGY COMMISSIONWASHINGTON. C._ 20545June 29, 1973TO REGULATORY GUIDE DISTRIBUTION LIST (DIVISION 5)Enclosed for your information and use are copies (which may be reproduced)of the following regulatory guides:Regulatory Guide 5.7 -"Control of Personnel Access to ProtectedAreas, Vital Areas, and Material Access Areas"Regulatory Guide 5.8 -"Design Considerations for Minimizing ResidualHoldup of Special Nuclear Material in Dryingand Fluidized Bed Operations."Regulatory Guide 5.9 -"Specifications for Ge(Li) Spectroscopy Systemsfor Material Protection Measurements -Part I:Data Acquisition."The Division 5 Regulatory Guides are being developed to provide guidanceon the acceptability of specific materials and plant protection relatedfeatures of nuclear facilities licensed to possess special nuclear* umaterial. Enclosed are a table of contents of issued Division 5 guidesand a list of additional guides in this division currently beingdeveloped.
Sincerely,es~erog~e~rstDirector of Regulatory Standards
Enclosures:
As stated