Regulatory Guide 5.9
| ML13350A205 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/1973 |
| From: | US Atomic Energy Commission (AEC) |
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| References | |
| RG-5.009 | |
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0
U.S.!-ATOMIC ENERGY: COMMISSION
REGULATORY
DIRECTORATE OF REGULATORY STANDARDS
June 1973 GtUUIDE
REGULATORY GUIDE 5.9 SPECIFICATIONS FOR Ge(Li) SPECTROSCOPY SYSTEMS
FOR MATERIAL PROTECTION MEASUREMENTS
PART I: DATA ACQUISITION SYSTEMS
A. INTRODUCTION
Proposed revisions to section 70.51 ofl 0 CFR Part
70.
"Material Balwncc.
Inventory and Records Requirenricnts." woold require licensees authorized to possess at any one time more than one effective kilogram n.it" special nuclear material to establish and maintain a system of control and accountability such that. the limit of error of any material unaccounted for (UL1F):
ascertained asa result of a measured mnaterial halance, meets established minimum .standards. The selection and proper application of an. adequate measurement method for each of the material forms in the fulccycle is essential for the maintenance of these standards.
This is lhe. first in a two-part series of guides which present specifications for Iithium-drifted germanium.
Ge(Li); gamma ray spectroscopy systems. This guidance applies to the .selection of.a special nuclear material (SNM)
assay system which utilizes gamma ray spectroscopy for the quantitative delermination of the.
- SNM content and a qualitative detertuination of tile radionuclide abundances. Within each of the, guides in this series, Data Acquisition and Data Reduction.
I variations of a basic spectroscopy system are defired and individual specifications provided. The procedures for applying these systems to specific materials and the analysis of the reduced data is tile subject of a later
. guide.
B. DISCUSSION
I. Background Gamma Iray spectroscopy systems have been used for the nondestructive assay (NDA) of various special nuclear material forlims encounteled in the fulel cycle hoth for quantitative determintiont of the special nuclear material cuntent, and for the determination of radionuclide abundances. In addition to the NDA of hulk materials, ganim:i ray spectroscopy is used in the analysis of specially prepared. homogeneous lahor:,lory samples.
There is no single gainnna-ray spectroscupy system available which is satisfactory to r all a pplic ition s nor is there I standard which defines and specilies the typv or types of Isstenls it) be used in cach of tihe above applications.
T"his guide defines and details thle specifications for ganmma ray spectroscopy dalta aquisition systems appropriate for special nuclear mnalcrial assay.
The scope of this guide is limited to tht consideration of Ge(Li)
gamma ray spectroscopv systems; No discussion of thallitim-activa ted sodium iodide. NaI(TI), gamma ray systems is presented. In addition. no discussion of applications of ganmma ray spectroscopy arc presnted.
The nieasiremeit procedures (including calibration), analysis nelthods.
inherent limitations, and overall precision and accuracy are specific to each application and are therelbre the subject of separate application guides.
An elementary introduclion to the concepis associated with the application of G;etLU spectroscopy to problems of nuclear material assay is available.'
Descriptions of the physical processes of gamma ray detection, discussiotIs of important instrumenlalion L.
A. Kull,
'.'An Introduction to
(;C('Li)
Uitsd Nal Garnma-Ray Derectorz ror Safeiiuard% Applicauiiomu."
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.
applicents. Regutato*y Guides are not subtiltules fat regulations and compliance 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
R
Poesre 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 problern.are. included in this documen
t. Relevant
- "information.presented :at a 'somewiat higher' technical level.
including nomenclature and definitions.
is inmiained in two useful standards documentls.2 - These des. ribe .detailed techmiques for defining and..obtaining meaningful peirormance data for Ge(Li) detectors and amplifiers. 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 valuable backgroundmnaterial published by he. manufacturers of detectors'aid associated 'electronic hardware which is available. fro ithemnon request.
2. Functional Description A. block diagram of those components of the Ge Li)
spcctroscopy system which perform the data acquisition
- funlction in material protection measurements is shown S"
in Fig. I.
lhe function of these components is first to convert the charge produced by the interaction of an incident irmma ray with the Ge(Li)-delector into an amplified. analog electrical signal. The analog signal is then converted into digilal information which can be stored, displayed, and otherwise processed by appropriate data reduction and analytical modules.
3. Types of Systems There are three variations of the basic data acquisition system presented in this guidelin
e. This
variance in the basic configuration is the result -of attempts to optimize each system to obtain specific assay information from certain types of material forms.
The. three ..variations -of the basic system are
'
described below' and will be referred to by' Ronan numeral in the remain der of the document. (For example. System II refers to paragraph II below.)
1.
A' moderate to high efficiency system having an
- .
energy resolution which is adequate for assays of materials for the fissile isotopes 2 4 'Pu, 23 9Pu, 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"%BU
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 is inadequate to accurately resolve the gamma ray lines of 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 far Semiconductor Radiation IDoectors.' IEET Std 3011-969. The Institute 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 ElectronlcN
Engineers. Inc, (1971).
assay. work. The system is designed to measure gamnnma rays with energies greater than 120 keV.
I!. A moderate to high efficiency system which can. satisfy all 'ihe requisites for System I and whirh. in addition, hasth e improved energy resolution necessary to.assay for the pltitonitmni isotopes 238 through 241.
.This system is commonly used to determine tile relative radionuclide abundances and is designed to measure gamma rays with energies greater than 120 keV.
Ill..A. system. designeUl specifically for low-energy gamma ray..and X-ray 'spectroscopy (at gamma ray energies less than 200 kcV) having an energy resolution adequate to perform quantitative and qualitative.assays of specially . prepared samples for the isotopes of plutonium (238-241) and uranium (235 and 238).
4. Equipment Acceptance Practices Standard practices regarding the final acceptance of equipment arc ustially prescribed by individual companies. laboratories, or departments. However. some of the following procedures have. beens found to be useful in providing the user with the assurance that he will acquire equipment which will perform as expected in nuclear materialassay applications.
Equipment descriptions .(including tile theory of operation) and instructional material covering operation.
maintenamce. and servicing of all electronic components should be supplied for individual components or complete systems. Such descriptions should include complete and accurate schematic diagrams for possible in-house equipment servicing.
Carefully specified operational tests of system performance should be made at the vendor's'facility and the original data supplied to the- user before equipment delivery is scheduled, with final acceptance based. on the user's own performance data taken at the user's facility.
It is necessary to have calibration sources on hand to verify the operational capabilities of the system. The following radioactive sources (with appropriate activities) will provide sufficient counting rates to perform the tests specified in the regulatory position:
"0Co- 10.30 MCi
,',co-1-10o Ci
C. REGULATORY POSITION
Lithium-drifted germanium, Ge(Li), gamma ray spectroscopy data acquisition systems meeting the operating specifications given below are considered adequate for use in special nuclear materials assay. The selection of a system meeting these specifications is considered necessary but not suflicient for accurate gamma ray spectroscopic assay requiring resolution better than obtainable with Nal, No guarantee of measurement quality as a result of the application of such. systems should be assumed.
I"
.. .*" ,:5.9-2'
characteristics, and a stcp-by-step description of a.simple assay problem are. included in this.document. Relevant hi .'ormation presented at a somewhatt higher technical.
level.
including nomenclature and definitions, is.
contained. in two useful standards documents. 2 . These de,;cribedetailed techniques for defining and obtaining
" tmeaningful perfornmance data for Ge Li) detectors:and n *
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 of detectors and associated electronic hardware which is available from them on request.
2. Functional Description A block diagram of those components of the Ge( Li)
- spectroscopy system which perform the data acquisition function in .material protection measuremenis is shown in Fig. .I. The function of these components is first to convert the charge produced by the interaction of an incident aninma ray wvith the Ge(Li) detector into an amplified, analog electrical signal. The analog signal is then 'convertcd into digital information which can be stored., displayed, and otherwise processed by appropriate data reduction and analytical modules.
3. Types of Systems There are, three -variations of the basic data acquisition system presnted, in this guideline. :This variance in thc basic configuration is tile result of attempts to optimize each system to obtain specific assay information from certain types of material forms.
The three variations of the basic system arc described below and will be referred to by Roman numeral in the remainder of tile document. (For example, System 11 refers to paragraph 11 below.)
- I.
A moderate to high efficiency system having an
energy resolution which is adequate for assays of materials for the fissile isotopes 24,Pu, 239pu, 2.15U.
and 2 13U. It can also be used to perform assays of materials for fertile isotopes such as 232Th and 2 3 1U
and to determine the -age" orplutoniunt samples from measurements of their americium-241 content. This system is used in those applications where Nal resolution is inadequate to accurately resolve the gamma ray lines of the isotopes of interest from those from an interfering background and where the lower efficiency Ge(Li)
detector still provides sufficient sensitivity for practical
"*'"lest Procedure. for. Amplificr.ý and Preamplifiers for Serniconductor Radiatinn IDteetors'" IEE:. Std 301-1969. The Institute of Eteetricat and -leCtronies Engineers. Inc. (19691."
- "Test Prncedurcs for Gernmniurn Ga"niaýRay De"tectors.-
IF-.'
Std 325-1.971. Tlhe Institute nlr Electrical and Electrunics Engineers. Inc. (1971).
assay work. The system is designed to nmeasure gatnma rays with energies greater than 120 keV.
II. A moderate to high efficiency system which can satisfy all the requisites for Systen I and which. in addition, has thc imiproved energy resolution necessary to assay. for tile plttoniuim isotopes 238 through 241.
This system is commonly used to determine the relative radionuclide abundances and is designed to measure gamma rays with energies greater than 120 keV.
Ill.
A system designed specilically for low-energy gamma ray and X-ray spectroscopy (at gamma ray energies less than 200 keV) having an energy resolution adequate to perform quantitative and qualitative assays of specially prepared samples for the isotopes of plutonium (238-241) and uranium (235 and 238).
4. Equipment Acceptance Practices Standard practices regarding the final acceptance of equipment are usually prescribed by individual companies. laboratories, or departments. However. some of the following procedures have beet, found to be useful in providing the user with the assurance that lie will acquire equipment which will perform as expected in nuclear material assay.applications.
Equipment .descriptions (including the theory of operation) and instructional material covering operation.
maintenance, and servicing of all electronic components should be supplied .for individual components or complete systems. Such descriptions : should include complete and accurate schematic diagrams for possible in-house, equipment servicing.. Carefully specified operational tests of system performance should be made at the vendor's facility and the original data supplied to the user before equipment delivery is scheduled, with fimal, acceptance based on the user's own performance data taken at the user's facility.
It is necessary to have calibration sources on hand to verify the operational capabilities of thie system. The
- following radioactive sources (with appropriate activities) will. provide sufficient counting rates to perform the tests specified in the regulatory position:
6OCo- 10-30 /Ci I 7Co-I-10upCi
C. REGULATORY POSITION
Lithium-drifted germanium, Gc(Li), gamma ray spectroscopy data acquisition systems meeting the operating specifications given below are considered adequate for use in special nuclear materials assay. The selection of a system meeting these specifications, is considered. necessary but. not sufficient for accurate gamma ray spectroscopic. assay requiring resolitilion better than obtainable :with Nal. No. guarantee, of measurement quality as a result of the application of such sys!ems should be assumed.
5.92
".Q'" i The .enipho %is here ison the 1perating specifications related to the overall performance off tile entire .data
- acquisition system. Component specilicat ions have~been included in Appendix A to provide guidance in the selectiol,; of original Or replacenten I co1Iponen S which are essential if adequate system performance is to be
- attained. The system operating performance s,,hould not be deduced from the component performances: overall system performance should be checked independently and compared to tile operating specifications presented here.
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 the following 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 Ltnter channel of the peak should be no less than 104 counts;
(3) the count rate during the measurement should be in the range 102 to 10-1 counts per second as measured with a total count rate meter. The full width of the peak at half maximum (FWHM)
and full width at tenth-maximum (FWTM)
are as defined in IEEE
Standard 325-1971.6 The full width at 1/50 maximum (FW.02M) is defined in a similar manner. The energy resolution and peak shape specifications for each of the systems (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 necessaryfor theapplications defined in B.3. above.
2. Detection Efficiency (Systems 1, 11) The full energy peak efficiency (in percent) is defined relative to the full energy 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 distance of 25.0 cm. The detailed procedures for determining the. efficiency in accordance with this definitionare presented in IEEE Standard 325.1971.L
Tile efficiency required for specific assay applications should be determined .by estimating the gamma ray intensity at the detector from a sample of known...strength and the counting rates required to collect a statistically significant number of counts under S'IEEE Sid 325-1971, op. cit.. Srction 4.
'Peaking time-the time required for a pulse to reach its maximum height. Peaking times can be easily measured with an oscilloscope and are less susceptible to misinterpretation than arc RC time constants. The relationship between RC time constants
.and peaking time varies as their is no standard method for defining 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 of time.
Est intates should be corrected for.
sample-to-detector distance and tlie effects of absorbing materials placed between tile sample and detector.
Whenever possible. it. is advisable Ito make preliminary measurements oin tile samples under consideralion with an available detector, and the efficiency of t(ie optimal deleclor determined by extrapolating the meastred results. A Ilumni:al estilalte of the detector.efficicncy (..Is defined above)
required for most applications, is approximately 8%1: however, detectors with elficiencies a ithe rang
"
of 5
_
o 20., are ill use For nuclear material assays. (To assist in providing some perspective here. an
8%,` detector as speciflied above has an active volumnL of about 40 cc while 5 to 207, detectors have voltmes of about 25 cc to 110 cc. respectivel
y. Art
, detector has absolute detection efficiencies of about 15 x .1"T4
185 keV, 4.5 x 10-4 (a: 411 keV. and 0.96 x 10" . (a 1.33 MeV at a source-detector sepai:itionrof 25 cm.)
(Systemn i11)
The method described above for determining the detection efficiency witlh a high energy gamma ray source is not relevant for detectors used in low-energy gamma ray spectroscopy. Instead. it is more appropriate to specify. (I) the active volume of the detector and (2)
the maximum effect of absorbing materials (absorbing materials include detector surfacc
"dead layers," gold surface plating, and the end cap window of the cryostat). The following specifications are therefore given for the low-energy gamma ray system:
a.
detector volume- 1.0 to 1.5 cc b.
drift depletion depth--0.5 to 0;7 cm c.
layers of absorbing material between the radiation source and the active volume of the detector must be thin enough so that the 14.4 keV peak from a s 7Co source is at least 5 times the conlitiltuin background under the peak."
3. Count Rate Capabilities The following specifications are related to a system's ability to maintain adequate energy resolution at high co.unt rates.
(Systems I. 11) The system should be capable of o0ratingvat a" total counting rate of: 104 cps from a Co source (as measuredwith a total count rate meter)
with less than a 10% i,-,lative increase in.the 1.33 MeV
peak width at 1/10 the maximum peak height (,VTMý
as compared to the FWTM value measured at 102 ito 10:
cps.
(System Ill) The system should be capable of operating at a total counting rate of 5 x 103 cps fiomi a s 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/cut 2 plsi ic or .tte equivalent) so that self absorption in the source itself is nor significant.
__
_"
"
'."
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-Comlpto
n. ratio for tie
.. .33 MeV peak Irom a Co source. as detined in I-EE
Standard 325-197 1' should be greater than the values specilied 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 the data acquisition system's ener,, calibration should be less than 0.2-." over the top 95%' of the ADC. range. The
ystcm n .nlitiarity should be measured uwing a set of
'I* -:l "Sid 325-1971 , p. cit.. Section 3.4.
well-known pillma ray soutces and the proecdure dscribed in the literature.'
The long.term stability requirement for the system's zero channel and g aiti shOuld be defined as follows: the drift in die position of a spectrum peak front a calibration source shotld be less thin 0.1"'l (compared to full. scale)
in a 24-hour period at constant room teln'perature. (For example, tie centroid of a calibration peak placed in approximately channel 4000 of a 4096 channel spectrum should not vary in position by more than .4 channels over a 24-hnur period.) Tiie temperature coefficient of the systenm's zero channel and gain should be 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 Energies with a GOtLi) Detector I. 50-420 kcV,," Nuct. Inst
r. and Methods
77. 141 (197W).
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 Methods 96. 173 (1971.)
5.9-4 m
APPENDIX A
COMPONENT SPECIFICATIONS
3. Preamplifiers
1. Detector Crystal Geometry (Systcms. I,.II)The dctector should be of' tie closed end.. coaxial drift. right :circular. cylinder t)yp: 0hi con figuraation has the Iit;ixinttitn fraction oftusable activc volume:fit r detecturslof noderate tolhigh cfliciency. The crystal diameter should be approximnailclv equal to ib length to minimizc any Unusual e'f'icienicy v
s. gcunteirv
effects. The active volume or the detector should comprise at least '0'i.- 61' t[lie total crystal volumne with the undrifled core diameter kept as sitall as economically possible. This maximizes [lie prob:tabilily!
that a ganima-ray- interactiui will appear ill tile fill]
energy pcak of the spectrum. (Note: The specification ott peak-to-Compton ratio given in Section ('.4 is directly related to the crystal's aclive/total volume atio.]
(System Ill) The detector shotuld be of the planar type. Small detectors of this configuration offer the best resolution available for low-energy, gamma rays.
Operating specifications are given in Section C.2 that define the allowable thickness of detector surface .dead layers"
which absorb low-energy gamma rays before they interact in the detector's active volume.
S
(Systems I,
II, Ill) Methods for specifying the physical size for tlte: detector crystals are covered in Section C.2.
2. Detector Mounting and Cryostat Description (Systems 1, III)
There are four detector cryostat configurations Which are typically' available: (I)
right angle dip-stick, (2) upright dip.stick. (3) gravity feed.
and (4) side entry (portable). Of these, the right angle dip-stick is widely used for Systems I and I1 and the upright dip-stick for System III: the configuration selected should be that considered to be most useful for a specific application. For reliable operation. the vacuum in the detector housing should be maintained by a zeolite getter. It is recommended that the liquid nitrogen Dewar have a minimum capacity of about 30 liters and a holding time of at least 10 days. The Dewar should have a connection which allows replenishment of the liquid nitrogen supply without removing the cryostat. A
separate high-voltage input to the cryostat housing should be provided in the event it is necessary or desirable :to apply a detector bias which exceeds the rating of. the preamplifier's high-voltage input. It is recommended that the high-voltage input be clearly marked and located at least 2.0 cm from the preamplifier signal output. The distance between the S
detector's front surface. and the window in the housing should be less than or equal to 1.0 cm to allow one to achieve minimal detector-sample separations when necessary.
S(Systems
1, II) It tamy cases prcampliler.s Comp'it iible with nuclear material speclroscorpy applications are purchased in combination with :a Ge( Li)
crystal as a package.
The detector specifications t here fore relate to the d e t Cc Itor-prCetupliflCr combi;ia lion:
however.
tile following additiUnal s pecifications should he included in the selection of .ill optimal system. A charge sensitive preamtplihlie shtmild he nmottned on t lie cryostat near lite detector. The field effect transistor (WET) in ite first staye o1 tlie preanipli*',
Ti..mld lw operated at room tellrirature
(_300"i'K
' Tile detector sihtuld he d.c. coripled (:Is opposcd .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 to minimize the probability of destroying thei F1 " dtie to detector warmup or high-voltage Irantsients. Posilivc high voltage should be used, and the: e should be at lcast one filter section placed in t(le higl*-voltage system interntal to the cryostat. At least one filter should also be placed external to the cryostat to reduce tile possibility of shorl circuiting due to condensate formation on thie internal filter. The total RC time constant of the filter network should be at least 30 seconds.
(System I1l) Sanme as above for Systenms I and II
except that the FET in the preantiplifier's first stage should he located within the cyrostat and operated it liquid nitrogen (LN) temperature. Att LN cooled 17ET is required, to achieve the excellent eiergy resolution characteristics of this system.
4. Main Amplifier (Systems I, I1. i11)
A main amplifier with adjustable pgin should include unipolat.
senti-Gaussia,"
pulse shaping networks with adjustable titiCe constants corresponding to peaking times between I atnd S usec. ( I
to 4 psec peaking times are typically used for Systemts I
and II while peaking titnes as long as 8 ,isec could be used in System I1l.) This choice fl" antplifier provides minimum resolving time for a given energy resolution and sufficient flexibility to optimize the amplifier characteristics for most' counting conditions. Nominal specifications to aid in identifyiing this class of amplifiers. commonly referred to as spectroscopy amplifiers, include the following: linear range 0 to IOV.
integral nonlinearity
<0.05%. temperature stability
<100 ppm gain shiftrc. attd thermal noise <5.,V rats
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
replacement. it is recomntended Ihat a detectorl he electu-d which attains adequate energy resolturion with an unct'i*thd l.T.
5.9.5 I..
L~.
referred t0 the input for 4 u.sec peaking times (the.noise level varies inversely withthc peaking time). The main anipliier %should be a standard NIM' 3 module.
.. .......
At tin atesgreater than.
0-1 cps, problems U. " 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'o or
0.orL pulses in.time and to bas.line fluctuations. The
.t .
nagniitude of. Ihese effects can be mininized by tlie inclision Ofatile. following Ifatures in the amplifier's desitl-. (I ) a. b.baseline.. restorer.:(BLR) circuit at. the amnphi ocvrvut.pu and. (21) pole-zero. cancelled coupling networks.7TheiBLR circuit shouldbe adjustable for both low ind high couhiting lte..conditions..
.
5. Analog to Digital Converter (ADC)
(Systems I, Ii, .ll) The ADC should be capable of digitizing pulse amplitudes from the amplifier in the range of 0 to 10 volts in at least 409)6 channels. The frquency of thle internal clock should be at least 50
ne,,ah,'tz to handle high counting rates with nominal
" AD)C dead time losses. The integral nonlinearity should be less .than 0.15% over the top 95%, of full scale and the differential nonlinearity should be less.than 1.0% over the. top 95% of full scale for semi-Gaussian pulses with peakingtirnes of I.to psec. These linearity specifications are. not . siringent.
but:. are *adequate to enable identification of unknown peaks. which may.. appear in a spectrum...
The short-term zero channel arid gain drifts should
- be <
.01%/f(?C
and 4 .02%0rC,
respectively (the percentage refers to full scale), in the temperature range front 00. to 500C. For long term stability, the peak from
- 3 NtM-Nuclear Instrument Module. see USAEC -Technical Information Document. Standard Nuclear Instrument Modules.
Revision 3. TID-20893 (1969L.
.t'
4For more details on BLR circuits see V. Radeka, "Effect of 'Baseline Restoration' on Signal-to-Notre Ratio in Pulse Amplitude Mteasurements," Rev. Sci. Instr. 38. 1397 ( 1967).
a stable pulsershould not shift by more than one channel 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 are closely ..re!'ttcd :to the.. overall system stability and lirearity operating specifications described in Section C.5.)
"Fhc ADC should be capable of being DC coupled to the main aniplifier in order that BLR circuits can be used. A digital: offset capability in the ADC is recommended. (Note: In some systems the ADC is an integral -part of a multichannel analyzer, a unit which also performnsi.the, funct ions .of.data storage, display, and sometimes rudimentary analysis. These latter functions are taken. up :in Part 2 of this series. In multichannel analyzersystems, however, the ADC function is usually specified separately and can be compared with the above recommendations.)
(System
1) For certain applicatiuns where energy resolution is definitely not critical, all the ADC
specifications above are applicable with the exception that a 1024 channel capacity with a 1024 digital offset may be adequate to provide a sufficiently small energy interval per channel (keV/channel) to cover a limited energy range of.. interest. It should be emphasized, however, that this choice may restrict the effective use of 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 the operating specifications listed in Section C.i when supplied with 115 volts (+/- 10%) at 50 to 65 hertz (at constant room temperature). The detector bias power supply should have an adjustable output that is short circit protected.with automatic power restoration after removal of the short. The maximum outputvoltage .is determined by detector requirements; 5 kilovolts is sufficient for most applications.
0. ,:..
5.9-6
TABLE 1 ENERGY RESOLUTION AND PEAK SHAPESPECIFICATIONS
SYSTEM I
Calibration Source Gamma Ray Energy FWHM (keVI
'ic o- 133 Q key
ý"Co- 122 keV
6'0CO- 1332 key FW.02MtFWHM
less than 2.7 less than 2.8
1.6
25 SYSTEM II
1.0
1.9 SYSTEM III
less than 2..
less titan 2.8 less than 2.5 less than 2.5
'Co-5.9 keV (Fe X-ray)
S'7Co- 122 keV
0.32
0.55 TABLE 2.
PEAK-TO-COMPTON RATIO VS. DETECTOR EFFICIENCY
Miiu Detector Efficiency (As defined in Section C.2)
5%
1070
1o%
20%
Minimum Peak-to-Compton Ratio
20:1
3o:1
35:1
38:1
59.7
LIQUID
'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
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"
"Design Considerations for Minimizing Residual Holdup of Special Nuclear Material in Drying and Fluidized Bed Operations."
"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