Regulatory Guide 5.9

Specifications for Ge(Li) Spectroscopy Systems for Materials Protection Measurements

ML13350A205
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Issue date:	06/30/1973
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June 1973 U.S.!-ATOMIC ENERGY: COMMISSION

0

REGULATORY GtUUIDE

DIRECTORATE OF REGULATORY STANDARDS

REGULATORY GUIDE 5.9 SPECIFICATIONS FOR Ge(Li) SPECTROSCOPY SYSTEMS

FOR MATERIAL PROTECTION MEASUREMENTS

PART I: DATA ACQUISITION SYSTEMS

A. INTRODUCTION

nuclear material forlims encounteled in the fulel cycle hoth for quantitative determintiont of the special Proposed revisions to section 70.51 ofl 0 CFR Part nuclear material cuntent, and for the determination of

70. "Material Balwncc. Inventory and Records radionuclide abundances. In addition to the NDA of Requirenricnts." woold require licensees authorized to hulk materials, ganim:i ray spectroscopy is used in the possess at any one time more than one effective analysis of specially prepared. homogeneous lahor:,lory kilogram n.it" special nuclear material to establish and samples.

maintain a system of control and accountability such that. the limit of error of any material unaccounted for There is no single gainnna-ray spectroscupy system (UL1F): ascertained asa result of a measured mnaterial available which is satisfactory to r all a pplic ition s nor is halance, meets established minimum .standards. The there I standard which defines and specilies the typv or selection and proper application of an. adequate types of Isstenls it) be used in cach of tihe above measurement method for each of the material forms in applications. T"his guide defines and details thle the fulccycle is essential for the maintenance of these specifications for ganmma ray spectroscopy dalta standards. aquisition systems appropriate for special nuclear mnalcrial assay.

This is lhe. first in a two-part series of guides which present specifications for Iithium-drifted germanium. The scope of this guide is limited to tht Ge(Li); gamma ray spectroscopy systems. This guidance consideration of Ge(Li) gamma ray spectroscopv applies to the .selection of.a special nuclear material systems; No discussion of thallitim-activa ted sodium (SNM) assay system which utilizes gamma ray iodide. NaI(TI), gamma ray systems is presented. In spectroscopy for the quantitative delermination of the. addition. no discussion of applications of ganmma ray

• SNM content and a qualitative detertuination of tile spectroscopy arc presnted. The nieasiremeit radionuclide abundances. Within each of the, guides in procedures (including calibration), analysis nelthods.

this series, Data Acquisition and Data Reduction. inherent limitations, and overall precision and accuracy I variations of a basic spectroscopy system are defired and are specific to each application and are therelbre the individual specifications provided. The procedures for subject of separate application guides.

applying these systems to specific materials and the analysis of the reduced data is tile subject of a later An elementary introduclion to the concepis

. guide. associated with the application of G;etLU spectroscopy to problems of nuclear material assay is available.'

B. DISCUSSION

Descriptions of the physical processes of gamma ray detection, discussiotIs of important instrumenlalion I. Background L. A. Kull, '.'An Introduction to (;C('Li) Uitsd Nal GammaIray spectroscopy systems have been used Garnma-Ray Derectorz ror Safeiiuard% Applicauiiomu."

for the nondestructive assay (NDA) of various special ANL.AECA-103 (1973).

USAEC REGULATORY GUIDES Copies of published quides may be obtained by request indicating the divisions deIlred 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 lot methods acceptable to the AEC. Regulatory staff of Imp*iamen5'ng specific parts Of Imptrovements in these guides are encouraged and should be sent to the Secretary the Commilsio"'$ regulations, to .de*tnea*s 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.

compliance applicents. Regutato*y Guides are not subtiltules fat regulations and with 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 to the issuance or continuance of a permit.ot license by thecCommisionI'. L Poesre R ReacTrtors

6. Products

2.'Resorch end Test neactots 7.. Teerssportetiors

3." Fuels and Materlels Facilities B OccuPational Health Published guides will be revispe periodically. as appropriate. to ea-ommodate 4. Environmental end Siting 9. Antitrust Review cosm entI* nd to reflect new inlermatlon or experience. 5. Materials and Plant Protection 1

0. General

characteristics, and a step-by.step description of~a simple assay. work. The system is designed to measure gamnnma assay problern.are. included in this document. Relevant rays with energies greater than 120 keV.

• "information.presented :at a 'somewiat higher' technical I!. A moderate to high efficiency system which level. including nomenclature and definitions. is can. satisfy all 'ihe requisites for System I and whirh. in inmiained in two useful standards documentls.2 - These addition, hasthe improved energy resolution necessary des. ribe .detailed techmiques for defining and..obtaining to.assay for the pltitonitmni isotopes 238 through 241.

meaningful peirormance data for Ge(Li) detectors and .This system is commonly used to determine tile relative amplifiers. The glossary of technicalmterns found in both radionuclide abundances and is designed to measure

[ohese standards documents will priwve valuable to those gamma rays with energies greater than 120 keV.

" *Unfamiliar.it I gamma-ray. spectrosc pic nomenclature. Ill..A. system. designeUl specifically for low-energy gamma ray..and X-ray 'spectroscopy (at gamma ray Finall,..there :is a coiisiderable :amouit Of valuable energies less than 200 kcV) having an energy resolution backgroundmnaterial published by he. manufacturers of adequate to perform quantitative and qualitative.assays detectors'aid associated 'electronic hardware which is of specially . prepared samples for the isotopes of available. fro ithemnon request. plutonium (238-241) and uranium (235 and 238).

2. Functional Description 4. Equipment Acceptance Practices A.block diagram of those components of the Ge Li) Standard practices regarding the final acceptance of spcctroscopy system which perform the data acquisition equipment arc ustially prescribed by individual

• funlction in material protection measurements is shown companies. laboratories, or departments. However. some S" in Fig. I. lhe function of these components is first to of the following procedures have. beens found to be convert the charge produced by the interaction of an useful in providing the user with the assurance that he incident irmma ray with the Ge(Li)-delector into an will acquire equipment which will perform as expected amplified. analog electrical signal. The analog signal is in nuclear materialassay applications.

then converted into digilal information which can be stored, displayed, and otherwise processed by Equipment descriptions .(including tile theory of appropriate data reduction and analytical modules. operation) and instructional material covering operation.

maintenamce. and servicing of all electronic components

3. Types of Systems should be supplied for individual components or complete systems. Such descriptions should include There are three variations of the basic data complete and accurate schematic diagrams for possible acquisition system presented in this guideline. This in-house equipment servicin

g. Carefully specified

• variance in the basic configuration is the result -of operational tests of system performance should be made attempts to optimize each system to obtain specific at the vendor's'facility and the original data supplied to assay information from certain types of material forms. the- user before equipment delivery is scheduled, with final acceptance based. on the user's own performance The. three ..variations -of the basic system are data taken at the user's facility.

' described below' and will be referred to by' Ronan numeral in the remain der of the document. (For It is necessary to have calibration sources on hand example. System II refers to paragraph II below.) to verify the operational capabilities of the system. The

1. A' moderate to high efficiency system having an following radioactive sources (with appropriate

• . energy resolution which is adequate for assays of activities) will provide sufficient counting rates to materials for the fissile isotopes 2 4 'Pu, 2 3 9 Pu, 235 U. perform the tests specified in the regulatory position:

• and 2 -13U. it can also be used to perform assays of "0 Co- 10.30 MCi

• materials for fertile isotopes such as 2"1 Th and 2"%BU ,',co-1-10o Ci and to determine tile "ag" of plutonium samples from

• measurements of their americium-241 conten

t. This

• system is used in those applications where Nal resolution

C. REGULATORY POSITION

is inadequate to accurately resolve the gamma ray lines of the isotopes of interest from those from an interfering Lithium-drifted germanium, Ge(Li), gamma ray

• " background. and where the lower efficiency Ge(Li) spectroscopy data acquisition systems meeting the detector still provides sufficient sensitivity for practical operating specifications given below are considered adequate for use in special nuclear materials assay. The

`-Te-t Procedure for Amplifiers and Preamplificrs far selection of a system meeting these specifications is Semiconductor Radiation IDoectors.' IEET Std 3011-969. The considered necessary but not suflicient for accurate Institute of Electrical and Electronics Engineers. Inc. (1969). gamma ray spectroscopic assay requiring resolution better than obtainable with Nal, No guarantee of

'"Tesi Procedures for Germanium Gamma-Ray Detectors.'.

IE-EE Sid 325-1971. 'nt:e Institute cif 'leciricil and ElectronlcN measurement quality as a result of the application of Engineers. Inc, (1971). such. systems should be assumed.

I" .. .*",:5.9-2'

characteristics, and a stcp-by-step description of a.simple assay work. The system is designed to nmeasure gatnma assay problem are. included in this.document. Relevant rays with energies greater than 120 keV.

hi 'ormation

. presented at a somewhatt higher technical. II. A moderate to high efficiency system which level. including nomenclature and definitions, is. can satisfy all the requisites for Systen I and which. in contained. in two useful standards documents. 2 . These addition, has thc imiproved energy resolution necessary de,;cribedetailed techniques for defining and obtaining to assay. for tile plttoniuim isotopes 238 through 241.

" tmeaningful perfornmance data for Ge Li) detectors:and This system is commonly used to determine the relative aplifiers.

n* The. glossayv o0f.technical terms found in both radionuclide abundances and is designed to measure

, these..standards docuiments Will prove valuable to those gamma rays with energies greater than 120 keV.

"ounfamiliar with camnia-rtvy spectroscopic nomenclature. Ill. A system designed specilically for low-energy gamma ray and X-ray spectroscopy (at gamma ray Finally. there is a considerable amnount of valuable energies less than 200 keV) having an energy resolution

.background material published by tile inanufacturers of adequate to perform quantitative and qualitative assays detectors and associated electronic hardware which is of specially prepared samples for the isotopes of available from them on request. plutonium (238-241) and uranium (235 and 238).

2. Functional Description 4. Equipment Acceptance Practices A block diagram of those components of the Ge( Li) Standard practices regarding the final acceptance of

• spectroscopy system which perform the data acquisition equipment are usually prescribed by individual function in .material protection measuremenis is shown companies. laboratories, or departments. However. some in Fig. .I. The function of these components is first to of the following procedures have beet, found to be convert the charge produced by the interaction of an useful in providing the user with the assurance that lie incident aninma ray wvith the Ge(Li) detector into an will acquire equipment which will perform as expected amplified, analog electrical signal. The analog signal is in nuclear material assay.applications.

then 'convertcd into digital information which can be stored., displayed, and otherwise processed by Equipment .descriptions (including the theory of appropriate data reduction and analytical modules. operation) and instructional material covering operation.

maintenance, and servicing of all electronic components

3. Types of Systems should be supplied .for individual components or complete systems. Such descriptions :should include There are, three -variations of the basic data complete and accurate schematic diagrams for possible acquisition system presnted, in this guideline. :This in-house, equipment servicing.. Carefully specified variance in thc basic configuration is tile result of operational tests of system performance should be made attempts to optimize each system to obtain specific at the vendor's facility and the original data supplied to assay information from certain types of material forms. the user before equipment delivery is scheduled, with fimal, acceptance based on the user's own performance The three variations of the basic system arc data taken at the user's facility.

described below and will be referred to by Roman numeral in the remainder of tile document. (For It is necessary to have calibration sources on hand example, System 11refers to paragraph 11below.) to verify the operational capabilities of thie system. The

• I. A moderate to high efficiency system having an *following radioactive sources (with appropriate

• energy resolution which is adequate for assays of activities) will. provide sufficient counting rates to materials for the fissile isotopes 24,Pu, 239pu, 2.15U. perform the tests specified in the regulatory position:

and 2 13U. It can also be used to perform assays of 6 OCo- 10-30 /Ci materials for fertile isotopes such as 23 2Th and 2 3 1U I 7 Co-I-10upCi and to determine the -age" orplutoniunt samples from measurements of their americium-241 content. This system is used in those applications where Nal resolution

C. REGULATORY POSITION

is inadequate to accurately resolve the gamma ray lines of the isotopes of interest from those from an interfering Lithium-drifted germanium, Gc(Li), gamma ray background and where the lower efficiency Ge(Li) spectroscopy data acquisition systems meeting the detector still provides sufficient sensitivity for practical operating specifications given below are considered adequate for use in special nuclear materials assay. The

"*'"lest Procedure. for. Amplificr.ý and Preamplifiers for selection of a system meeting these specifications, is Serniconductor Radiatinn IDteetors'" IEE:. Std 301-1969. The considered. necessary but. not sufficient for accurate Institute of Eteetricat and -leCtronies Engineers. Inc. (19691." gamma ray spectroscopic. assay requiring resolitilion better than obtainable :with Nal. No. guarantee, of

• "Test Prncedurcs for Gernmniurn Ga"niaýRay De"tectors.-

IF-.' Std 325-1.971. Tlhe Institute nlr Electrical and Electrunics measurement quality as a result of the application of Engineers. Inc. (1971). such sys!ems should be assumed.

5.92

".Q'" i The .enipho %ishere ison the 1perating specifications the. spectrutm lpeaks of interest in a reasonahle period of related to the overall performance off tile entire .data time. Est intates should be corrected for.

• acquisition system. Component specilicat ions have~been sample-to-detector distance and tlie effects of absorbing included in Appendix A to provide guidance in the materials placed between tile sample and detector.

selectiol,; of original Or replacenten I co1Iponen S which Whenever possible. it. is advisable Ito make preliminary are essential if adequate system performance is to be measurements oin tile samples under consideralion with

• attained. The system operating performance s,,hould not an available detector, and the efficiency of t(ie optimal be deduced from the component performances: overall deleclor determined by extrapolating the meastred system performance should be checked independently results. A Ilumni:al estilalte of the detector.efficicncy (..Is and compared to tile operating specifications presented defined above) required for most applications, is here. approximately 8%1: however, detectors with elficiencies a ithe rang of 5 " o 20., _ are ill use For nuclear material

1. Energy Resolution and Peak Shape assays. (To assist in providing some perspective here. an

8%,`detector as speciflied above has an active volumnL of (Systems 1, 11, 111) The eniergy resolution of the about 40 cc while 5 to 207, detectors have voltmes of

.system should be measured according to the procedure about 25 cc to 110 cc. respectively. Art , detector has

4

• specified in IEEE Standard 325-197i,4 with the absolute detection efficiencies of about 15 x .1"T 185 following additional stipulations: (I) the peaking time" keV, 4.5 x 10-4 (a: 411 keV. and 0.96 x 10" . (a 1.33 for the shaping amplifier should be no. greater than 4 MeV at a source-detector sepai:itionrof 25 cm.)

.pseec (2) the total number of counts in tthe Ltnter channel of the peak should be no less than 104 counts; (Systemn i11) The method described above for

(3) the count rate during the measurement should be in determining the detection efficiency witlh a high energy the range 102 to 10-1 counts per second as measured gamma ray source is not relevant for detectors used in with a total count rate meter. The full width of the peak low-energy gamma ray spectroscopy. Instead. it is more at half maximum (FWHM) and full width at appropriate to specify. (I) the active volume of the tenth-maximum (FWTM) are as defined in IEEE detector and (2) the maximum effect of absorbing Standard 325-1971.6 The full width at 1/50 maximum materials (absorbing materials include detector surfacc (FW.02M) is defined in a similar manner. The energy "dead layers," gold surface plating, and the end cap resolution and peak shape specifications for each of the window of the cryostat). The following specifications systems (I i1, 111)are given in Table I and the measured are therefore given for the low-energy gamma ray

.values should be no greater than those shown here. system:

These values have been determined to be necessaryfor a. detector volume- 1.0 to 1.5 cc theapplications defined in B.3. above. b. drift depletion depth--0.5 to 0;7 cm c. layers of absorbing material between the

2. Detection Efficiency radiation source and the active volume of the detector must be thin enough so that the 14.4 keV peak from a (Systems 1, 11) The full energy peak efficiency (in s 7Co source is at least 5 times the conlitiltuin percent) is defined relative to the full energy peak background under the peak."

efficiency of a 3 in. x 3 in. Nal(TI) scintillation detector for 1.33 MeV gamma rays ( 6 'Co) at a source.detector 3. Count Rate Capabilities distance of 25.0 cm. The detailed procedures for determining the. efficiency in accordance with this The following specifications are related to a definitionare presented in IEEE Standard 325.1971.L system's ability to maintain adequate energy resolution at high co.unt rates.

Tile efficiency required for specific assay applications should be determined .by estimating the (Systems I. 11) The system should be capable of gamma ray intensity at the detector from a sample of o0ratingvat a" total counting rate of: 104 cps from a known...strength and the counting rates required to Co source (as measuredwith a total count rate meter)

collect a statistically significant number of counts under with less than a 10% i,-,lative increase in.the 1.33 MeV

peak width at 1/10 the maximum peak height (,VTMý

S'IEEE Sid 325-1971, op. cit.. Srction 4. as compared to the FWTM value measured at 102 ito 10:

cps.

'Peaking time-the time required for a pulse to reach its maximum height. Peaking times can be easily measured with an (System Ill) The system should be capable of oscilloscope and are less susceptible to misinterpretation than arc operating at a total counting rate of 5 x 103 cps fiomi a RC time constants. The relationship between RC time constants s Co source (as measured with it total count rate ittler)

.and peaking time varies as their is no standard method for defining RC time constants in semi-Gaussian shaping networks.

"Care should he^taken to ensure that the "Co saiurc:

6 IEEE Sid 325-197 1, op. cit., Section 3. encapsulation is *.thin cenough. (<1 0( ng/cut 2 plsi ic or . tte equivalent) so that self absorption in the source itself is nor

7Ibid., Section 5.2. significant.

__ _" " '." 5.9-3

witlh less than a IT0 relathe increac in the FWHM and well-known pillma ray soutces and the proecdure

. W.M * ol'the 1 2 keV peak as" iCOipared to th6 values dscribed in the literature.'

• .. obtained at 1.O

c. .

The long.term stability requirement for the system's

4. Peak-to-Coinpton Ratio. zero channel and gaiti shOuld be defined as follows: the drift in die position of a spectrum peak front a s L(S The peak-lo-Comlpton. ratio for tie selI1,i) calibration source shotld be less thin 0.1"'l (compared to

.. .33MeV peak Irom a Co source. as detined in I-EE full. scale) in a 24-hour period at constant room Standard 325-197 1' should be greater than the values teln'perature. (For example, tie centroid of a calibration peak placed in approximately channel 4000 of specilied in. T'lhký 2 for 'corresponding detector a 4096

-e fficienc-ies. channel spectrum should not vary in position by more than .4 channels over a 24-hnur period.) Tiie temperature

• (System 1Il) Tlifis specification is not applicable. coefficient of the systenm's zero channel and gain should

0

be less thau 0.02% .,,C in the temperature range from O"

to 50"C.

• 5. Linearity and Stability

" R. C. Greenwood, R. G. Ilcimer. and R. G. Gehrke.

(Systenis I, Ii, Ill) The integral non linearity of the "Precise Comparison and Measuiement of Gamma-Ray Energies data acquisition system's ener,, calibration should be with a GOtLi) Detector I. 50-420 kcV,," Nuct. Instr. and Methods less than 0.2-." over the top 95%' of the ADC. range. The 77. 141 (197W).

• ystcm n.nlitiarity should be measured uwing a set of R. G. Wnlmer, R. C. Greenwood and R. G. Gehrke,

"Precise Comparison and Measurcment of Gamma-Ray Energies with a Ge(Li) Detector It. 400-1300 ke,," Nuclear. Insir. and

'I* -:l "Sid 325-1971 , p. cit.. Section 3.4. Methods 96. 173 (1971.)

5.9-4 m

APPENDIX A

COMPONENT SPECIFICATIONS

3. Preamplifiers

1. Detector Crystal Geometry S(Systems 1, II) It tamy cases prcampliler.s Comp'it iible with nuclear material speclroscorpy (Systcms. I,.II)The dctector should be of' tie closed applications are purchased in combination with :aGe( Li)

end.. coaxial drift. right :circular. cylinder t)yp: 0hi crystal as a package. The detector specifications con figuraation has the Iit;ixinttitn fraction oftusable activc t here fore relate to the d e t Cc Itor-prCetupliflCr volume:fit r detecturslof noderate tolhigh cfliciency. The combi;ia lion: however. tile following additiUnal crystal diameter should be approximnailclv equal to ib specifications should he included in the selection of .ill length to minimizc any Unusual e'f'icienicy vs. gcunteirv optimal system. A charge sensitive preamtplihlie shtmild

• effects. The active volume or the detector should he nmottned on t lie cryostat near lite detector. The field comprise at least '0'i.- 61' t[lie total crystal volumne with effect transistor (WET) in ite first staye o1 tlie the undrifled core diameter kept as sitall as preanipli*', Ti..mld lw operated at room tellrirature economically possible. This maximizes [lie prob:tabilily! (_300"i'K ' Tile detector sihtuld he d.c. coripled (:Is that a ganima-ray- interactiui will appear ill tile fill]

opposcd .o c.,p:,.'itively coupled) to tile aic of tle itpul energy pcak of the spectrum. (Note: The specification * stage of' tire 1i c.1triplilher for better ctenergy resohulion.

ott peak-to-Compton ratio given in Section ('.4 is directly related to the crystal's aclive/total volume atio.] The tti lowing procedures arc iccniittended to minimize the probability of destroying thei F1 " dtie to (System Ill) The detector shotuld be of the planar detector warmup or high-voltage Irantsients. Posilivc high type. Small detectors of this configuration offer the best voltage should be used, and the: e should be at lcast one resolution available for low-energy, gamma rays. filter section placed in t(le higl*-voltage system interntal Operating specifications are given in Section C.2 that to the cryostat. At least one filter should also be placed define the allowable thickness of detector surface .dead external to the cryostat to reduce tile possibility of shorl layers" which absorb low-energy gamma rays before circuiting due to condensate formation on thie internal they interact in the detector's active volume. filter. The total RC time constant of the filter network S (Systems I, II, Ill) Methods for specifying the physical size for tlte: detector crystals are covered in should be at least 30 seconds.

(System I1l) Sanme as above for Systenms I and II

Section C.2. except that the FET in the preantiplifier's first stage should he located within the cyrostat and operated it

• 2. Detector Mounting and Cryostat Description liquid nitrogen (LN) temperature. Att LN cooled 17ET is required, to achieve the excellent eiergy resolution (Systems 1, III) There are four detector cryostat characteristics of this system.

configurations Which are typically' available: (I) right angle dip-stick, (2) upright dip.stick. (3) gravity feed. 4. Main Amplifier and (4) side entry (portable). Of these, the right angle dip-stick is widely used for Systems I and I1 and the (Systems I, I1. i11) A main amplifier with adjustable upright dip-stick for System III: the configuration pgin should include unipolat. senti-Gaussia," pulse selected should be that considered to be most useful for shaping networks with adjustable titiCe constants a specific application. For reliable operation. the vacuum corresponding to peaking times between I atnd S usec. ( I

in the detector housing should be maintained by a to 4 psec peaking times are typically used for Systemts I

zeolite getter. It is recommended that the liquid nitrogen and II while peaking titnes as long as 8 ,isec could be Dewar have a minimum capacity of about 30 liters and a used in System I1l.) This choice fl" antplifier provides holding time of at least 10 days. The Dewar should have minimum resolving time for a given energy resolution a connection which allows replenishment of the liquid and sufficient flexibility to optimize the amplifier nitrogen supply without removing the cryostat. A characteristics for most' counting conditions. Nominal separate high-voltage input to the cryostat housing specifications to aid in identifyiing this class of should be provided in the event it is necessary or amplifiers. commonly referred to as spectroscopy desirable :to apply a detector bias which exceeds the amplifiers, include the following: linear range 0 to IOV.

rating of. the preamplifier's high-voltage input. It is integral nonlinearity <0.05%. temperature stability recommended that the high-voltage input be clearly <100 ppm gain shiftrc. attd thermal noise <5.,V rats marked and located at least 2.0 cm from the S preamplifier signal output. The distance between the detector's front surface. and the window in the housing should be less than or equal to 1.0 cm to allow one to

2 ISystern II only) Tle preamplifncr\ First stape F-lV may be located within the keryo,;iai and operated at liquiid nitmtgen temnperatures, but in order to faeiliLaie poSible ITT

achieve minimal detector-sample separations when replacement. it is recomntended Ihat a detectorlhe electu-d I.. necessary. which attains adequate energy resolturion with an unct'i*thd l.T.

5.9.5 L~.

referred t0 the input for 4 u.sec peaking times (the.noise level varies inversely withthc peaking time). The main a stable pulsershould not shift by more than one channel over a 24,hour period.for a line voltage of 115V

0.,:..

anipliier %shouldbe a standard NIM' 3 module. - li,. 50-65 Hz,7and at constant room temperature.

(Note: The. ADC. drift and.linearit

y. specifications are

.. .......tin atesgreater than. 0-1 cps, problems At closely ..re!'ttcd :to the.. overall system stability and U."I a'dtgtadation es of the:energy resolution resulting in lirearity operating specifications described in Section

. loss of counts. in the. spectrurn peaks begin to occur. C.5.)

"..Thes effects are due. to.the overlap of portions of tw'o or

0.orL pulses in.time and to bas.line fluctuations. The "Fhc ADC should be capable of being DC coupled to

.t .

nagniitude of. Ihese effects can be mininized by tlie the main aniplifier in order that BLR circuits can be inclision Ofatile. following Ifatures in the amplifier's used. A digital: offset capability in the ADC is desitl-. (I ) a. b.baseline.. restorer.:(BLR) circuit at. the recommended. (Note: In some systems the ADC is an amnphi ocvrvut.pu and. (21) pole-zero. cancelled coupling integral -part of a multichannel analyzer, a unit which networks.7TheiBLR circuit shouldbe adjustable for both also performnsi.the, funct ions .of.data storage, display, and low ind high couhiting lte..conditions.. . sometimes rudimentary analysis. These latter functions are taken. up :in Part 2 of this serie

s. In multichannel

5. Analog to Digital Converter (ADC) analyzersystems, however, the ADC function is usually specified separately and can be compared with the above (Systems I, Ii,.ll) The ADC should be capable of recommendations.)

digitizing pulse amplitudes from the amplifier in the range of 0 to 10 volts in at least 409)6 channels. The (System 1) For certain applicatiuns where energy frquency of thle internal clock should be at least 50 resolution is definitely not critical, all the ADC

ne,,ah,'tz to handle high counting rates with nominal specifications above are applicable with the exception

" AD)C dead time losses. The integral nonlinearity should that a 1024 channel capacity with a 1024 digital offset be less .than 0.15% over the top 95%, of full scale and the may be adequate to provide a sufficiently small energy differential nonlinearity should be less.than 1.0% over interval per channel (keV/channel) to cover a limited the. top 95% of full scale for semi-Gaussian pulses with energy range of.. interest. It should be emphasized, peakingtirnes of I.to psec. These linearity specifications however, that this choice may restrict the effective use are. not . siringent. but:. are *adequate to enable of the system for other applications.

identification of unknown peaks. which may.. appear in a spectrum... 6. Power Supplies The short-term zero channel arid gain drifts should (Systems I,. II, .111) The system power supplies

• be < .01%/f(?C and 4 .02%0rC, respectively (the (detector high- voltage, preamplifier, and NIM bin)

percentage refers to full scale), in the temperature range should be capable of operating the system within the front 00. to 500C. For long term stability, the peak from operating specifications listed in Section C.i when supplied with 115 volts (+/- 10%) at 50 to 65 hertz (at

• 3 NtM-Nuclear Instrument Module. see USAEC -Technical constant room temperature). The detector bias power Information Document. Standard Nuclear Instrument Modules. supply should have an adjustable output that is short Revision 3. TID-20893 (1969L. circit protected.with automatic power restoration after

.t'4For more details on BLR circuits see V. Radeka, "Effect removal of the short. The maximum outputvoltage .is of 'Baseline Restoration' on Signal-to-Notre Ratio in Pulse determined by detector requirements; 5 kilovolts is Amplitude Mteasurements," Rev. Sci. Instr. 38. 1397 ( 1967). sufficient for most applications.

5.9-6

TABLE 1 ENERGY RESOLUTION AND PEAK SHAPESPECIFICATIONS

SYSTEM I

Calibration Source Gamma Ray Energy FWHM (keVI FW.02MtFWHM

1.6 less than 2.7

'ic o- 133Q key 25 less than 2.8 SYSTEM II

ý"Co- 122 keV 1.0 less than 2..

0

6' CO- 1332 key 1.9 less titan 2.8 SYSTEM III

'Co-5.9 keV (Fe X-ray) 0.32 less than 2.5 S'7Co- 122 keV 0.55 less than 2.5 TABLE 2.

PEAK-TO-COMPTON RATIO VS. DETECTOR EFFICIENCY Miiu Detector Efficiency Minimum (As defined in Section C.2) Peak-to-Compton Ratio

5% 20:1

1070 3o:1

1o% 35:1

20% 38:1

59.7

LIQUID

NITROGEN

'DEWAR

DIGITAL OUTPUT

ANALOG TO DATA STORAGE

PREAMPLIFIER AMPLIFIER TO DIGITAL DISPLAYS, DATA

CONVERTER REDUCTION AND

ANALYTICAL MODULES

Figure 1.-BLOCK DIAGRAM OF A Ge(Li) DATA ACQUISITION SYSTEM

5.9-8

..,UNITED STATES

ATOMIC =ENERGY COMMISSION

WASHINGTON. C._ 20545 June 29, 1973 TO 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 Protected Areas, Vital Areas, and Material Access Areas"

Regulatory Guide 5.8 - "Design Considerations for Minimizing Residual Holdup of Special Nuclear Material in Drying and Fluidized Bed Operations."

Regulatory Guide 5.9 - "Specifications for Ge(Li) Spectroscopy Systems for Material Protection Measurements - Part I:

Data Acquisition."

The Division 5 Regulatory Guides are being developed to provide guidance on the acceptability of specific materials and plant protection related features of nuclear facilities licensed to possess special nuclear

• umaterial. Enclosed are a table of contents of issued Division 5 guides and a list of additional guides in this division currently being developed.

Sincerely, es~erog~e~rst Director of Regulatory Standards Enclosures:

As stated