Regulatory Guide 5.9: Difference between revisions

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{{Adams
{{Adams
| number = ML003740012
| number = ML13350A205
| issue date = 12/31/1983
| issue date = 06/30/1973
| title = (Task SG 042-2), Revision 2, Guidelines for Germanium Spectroscopy Systems for Measurement of Special Nuclear Material
| title = Specifications for Ge(Li) Spectroscopy Systems for Materials Protection Measurements
| author name =  
| author name =  
| author affiliation = NRC/RES
| author affiliation = US Atomic Energy Commission (AEC)
| addressee name =  
| addressee name =  
| addressee affiliation =  
| addressee affiliation =  
Line 10: Line 10:
| license number =  
| license number =  
| contact person =  
| contact person =  
| document report number = RG-5.9 Rev 2
| document report number = RG-5.009
| document type = Regulatory Guide
| document type = Regulatory Guide
| page count = 8
| page count = 10
}}
}}
{{#Wiki_filter:Revision 2*
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                                                                                                                                      December 1983 U.S. NUCLEAR REGULATORY COMMISSION
U.S.!-ATOMIC ENERGY: COMMISSION
                        REGULATORY GUIDE
REGULATORY
                        OFFICE OF NUCLEAR REGULATORY RESEARCH
DIRECTORATE OF REGULATORY STANDARDS
                                                            REGULATORY GUIDE 5.9 (Task SG 042-2)
June 1973 GtUUIDE
                              GUIDELINES FOR GERMANIUM SPECTROSCOPY SYSTEMS
REGULATORY GUIDE 5.9 SPECIFICATIONS FOR Ge(Li) SPECTROSCOPY SYSTEMS
                                FOR MEASUREMENT OF SPECIAL NUCLEAR MATERIAL
FOR MATERIAL PROTECTION MEASUREMENTS
                                                                              to boxes and cans of uncharacterized waste materia
PART I: DATA ACQUISITION SYSTEMS


====l. Meas ====
==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.


==A. INTRODUCTION==
Ge(Li); gamma ray spectroscopy systems. This guidance applies to the .selection of.a special nuclear material (SNM)
urement conditions also vary widely from controlled laboratory environments to the unpredictable plant environ Section 70.51, "Material Balance, Inventory, and Records              ment that can be hostile to the measurement equipment Requirements," of 10 CFR Part 70, "Domestic Licensing                      and can often contribute serious background interferences of Special Nuclear Material," requires, in part, that licensees            to the spectral data. As a result, there is no single gamma authorized to possess at any one time more than one                        ray assay system that can be effective in all cases. The effective kilogram of special nuclear material establish and                system chosen for a particular NDA task must therefore be maintain a system of control and accountability so that                      determined from careful consideration of all factors that the standard error (estimator) of any inventory difference,                  may affect the measurement and of the requirements for ascertained as a result of a measured material balance,                     the precision and accuracy of the assay.
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.


meets established minimum standards. The selection and proper application of an adequate measurement method for                        The scope of this guide is limited to the consideration of each of the material forms in the fuel cycle is essential for                high-resolution gamma ray spectroscopy with lithium-drifted the maintenance of these standards.                                          germanium, Ge(Li), or high-purity germanium, HPGe (also referred to as intrinsic germanium, IG), detectors. No Many types of nondestructive assay (NDA) measurements                    discussion of thallium-activated sodium iodide, NaI(Tl), or on special nuclear material (SNM) can involve, or even                      lithium-drifted silicon, Si(Li), gamma ray systems is
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
>  require, a high-resolution gamma ray spectroscopy system.                    presented. In addition, no discussion of specific NDA
. guide.
  This guide is intended both to provide some general guide                    applications of gamma ray spectroscopy is provided. The lines acceptable to the NRC staff for the selection of such                  measurement procedures (including calibration), analysis systems and to point out useful resources for more detailed                  methods, Inherent limitations, and overall precision and information on their assembly, optimization, and use in                      accuracy attainable are specific to each application and are material protection measurements.                                            therefore the subject of separate application guides. Guide lines for measurement control, calibration, and error Any guidance in this document related to information                    analysis of NDA measurements are dealt with in detail in collection activities has been cleared under OMB Clearance                  Regulatory Guide 5.53, "Qualification, Calibration, and No. 3150-0009.                                                               Error Estimation Methods for Nondestructive Assay,"
                                                                                which endorses ANSI N15.20-1975,                  "Guide to Calibrating
                                                                                                                            1


==B. DISCUSSION==
==B. DISCUSSION==
Nondestructive Assay Systems." ANSI N15.20-1975 was reaffirmed in 1980.
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.


===1. BACKGROUND===
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.
                                                                                    ýX of the major commercial vendors of Ge(Li) and Gamma ray spectroscopy systems are used for NDA of                      HPGe detectors and the associated electronics maintain various special nuclear material forms encountered in the                   up-to-date documentation on the specifications of currently nuclear fuel cycle, both for quantitative determination                      available equipment, as well as a variety of useful and infor of the SNM content and for the determination of radio                        mative notes on applications. This literature is available nuclide abundances.                                                               The substantial number of channes in this revision has made it Impractical to Indicate the changes with lines in the margin.


the American Applications of high-resolution gamma ray spectroscopy                        Covpies of this standard may be obtained fromNew
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:
                                                                                    1 Standards Institute, Inc., 1430 Broadway,            York, New have multiplied greatly in recent years. The samples encoun                National York  10018.
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


tered range from fresh fuel rods and reprocessing solutions Comments should be sentCommissionto the Secretary      of the Commission.
===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.


USNRC REGULATORY GUIDES                                    U.S. Nuclear Regulatory                        Washington, D.C. 20555.
5. Materials and Plant Protection
1


make available to the        Attention: Docketing and Service Brancn.
===0. General===


Regulatory Guides are Issued to describe andstaff    of implementing public methods acceptable to the NRC                to delineate tech-       The guides are Issued In the following ten broad divisions:
characteristics, and a step-by.step description of~a simple assay problern.are. included in this documen
  specific parts of the Commission's    regulations, niques used by the staff in evaluating specific problems or postu            1. Power Reactors                      6. Products Regulatory iated  accidents or to provide guidance to applicants.              with    2. Research and Test Reactors            7. Transportation Guides are nof substitutes for regulations, and compliance from  those set    3. Fuels and Materials    Facilities    S. Occupational Health them Is not required. Methods  and  solutions different                                                              9. Antitrust and Financial Review
                                                                                4. Environmental and Siting out in the guides will be acceptable If they provide of a permit the a basis  for or    5. Materials  and  Plant Protection    10. General findings requisite to the issuance or continuance license by the Commission.                                                    Copies  of  issued  guides may  be  purchased  at the current Government Printing Office price. A subscription service for future      guides in spe This guide was Issued after consideration of comments received      from                                                    Government    Printing Office.


in these    cific divisions  is available through    the the public. Comments and suggestions for Improvements will  be revised,  as    Information on the subscription service and current        GPO  prices may guides are encouraged at all times, and guides                                be obtained by writing the U.S. Nuclear RegulatorySales        Commission, appropriate, to accommodate comments and to reflect new informa-              Washington, D.C. 20555, Attention: Publications                    Manager.
====t. Relevant====
*"information.presented :at a 'somewiat higher' technical level.


tion or experience.
including nomenclature and definitions.


from the manufacturers upon request, and the potential                an integral part of the detector package. The preamplifier customer may use this literature as a source of the most signal is further amplified and shaped and is then converted current information on the highest quality systems available.
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.


into digital information that can be stored, displayed, and otherwise processed by the data reduction and analytical Finally, the potential user ought to consult with those            components of the system.
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.


individuals currently active in the field of nondestructive assay of special nuclear material and seek their advice in the         
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.


===4. TYPES OF SYSTEMS===
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.
  particular assay problem being considered.


High-resolution gamma ray spectroscopy systems are
3. Types of Systems There are three variations of the basic data acquisition system presented in this guidelin
  2. BIBLIOGRAPHIC INFORMATION                                            distinguished primarily by the type (p-type or n-type) and the configuration (planar or coaxial) of detector used. For An annotated bibliography is included in this regulatory assay applications involving the measurement of low-energy guide to provide more detailed information on spectros gamma radiation (i.e., energies below approximately copy systems and their use.                                            200 keV), a thin planar HPGe or Ge(Li) crystal is most appropriate. A coaxial detector crystal with a larger volume Elementary introductions to the concepts associated                is much better suited for higher energy gamma ray measure with the application of high-resolution gamma ray spectros            ments (i.e., for energies above approximately 120 keV).
  copy to problems of nuclear material assay are available in            The distinction between these two types of detectors is not Augustson and Reilly and in Kull. These works discuss                  sharp. For instance, there maý be some applications above the physical processes of gamma ray detection and impor                120 keV in which a planar detector would be useful to tant instrumentation characteristics. More advanced dis                render the system less sensitive to interferences from cussion of gamma ray detectors and associated electronics ambient high-energy gamma radiation.


may be found in Knoll and in Adams and Dams. A thorough treatise on the associated electronics is available in Nicholson.
====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.


It should be noted that Ge(Li) detectors have no real In addition, extensive discussion of a variety of NDA tech advantage over HPGe detectors with comparable perform niques and the implementation of some of these techniques              ance specifications. In addition, Ge(Li) detectors require with high-resolution gamma ray spectroscopy may be                      constant liquid nitrogen (LN) cooling, even when not in found in Sher and Untermeyer, in Rogers, and in Reilly and              operation. HPGe detectors are, of course, also operated at Parker. Detailed descriptions of detector efficiency and               LN temperature, but they can be stored at room tempera energy calibration procedures are available in section D of           ture. This is an advantage to potential users who may have Knoll and also in Hajnal and Klusek; in Hansen, McGeorge,              extended plant shutdowns. It also prevents complete loss and Fink; in Hansen et aL; and in Roney and Seale.                     of a detector due to operator procedure error, which can happen with a Ge(Li) detector when Ll4 cooling is not Relevant technical information beyond the introductory level, including nomenclature and definitions, is contained continuously maintained. This added convenience and the greater ruggedness of the HPGe detectors make them K
The. three ..variations -of the basic system are
  in three useful standards of the Institute of Electrical and especially attractive for in-plant NDA applications.
'
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.


Electronics Engineers, ANSI/IEEE Std 301-1976, "Test Procedures for Amplifiers and Preamplifiers for Semi                  5. EQUIPMENT ACCEPTANCE PRACTICES
A' moderate to high efficiency system having an
  conductor Radiation Detectors for Ionizing Radiation," 2 ANSI/IEEE Std 325-1971, "Test Procedures for Germanium Equipment descriptions and instructional material Gamma-Ray Detectors" 2 (reaffirmed in 1977), and ANSI/
* .
                                                                        covering operation, maintenance, and: servicing of all IEEE Std 645-1977, "Test Procedures for Hifh-Purity                    electronic components are supplied by the manufacturer Germanium Detectors for Ionizing Radiation,"" which for all individual modules or complete systems. Such supplements ANSI/IEEE Std 325-1971. These describe                      descriptions should include complete and accurate sche detailed techniques for defining and obtaining meaningful matic diagrams for possible in-house equipment servicing.
energy resolution which is adequate for assays of materials for the fissile isotopes 2 4 'Pu, 23 9Pu, 235 U.


performance data for Ge(Li) and HPGe detectors and                     Complete operational tests of system performance are to be amplifiers.                                                            made at the vendor's facility, and the original data are
*
                                                              /
and 2 -13U. it can also be used to perform assays of
                                                                        supplied to the user upon delivery of the equipment.
*
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


3. FUNCTIONAL DESCRIPTION                                              Extensive performance testing of all systems by the user is generally not necessary. 3 However, qualitative verification A block diagram of a typical high-resolution gamma ray            of selected equipment performance specifications and spectroscopy system is shown in Figure 1. In such a system,            detector resolution is recommended.
====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.


the solid state Ge(Li) or HPGe detector converts some or all of the incident gamma ray energy into a proportional It is necessary to have calibration sources on hand to amount of electric charge, which can be analyzed by the                verify the operational capabilities of the system. The subsequent electronics. The detector output is converted following radioactive sources (with appropriate activities)
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.
into an analog voltage signal by the preamplifier, which is
                                                                            3 Although the quality control and presh.pment testing may be obtained from the Institute of Electrical and      dures of the commercial vendors of detectors and associatedproce.elec.


Electronics Engineers, Inc., 34S East 47th Street, New York, New          onuic, h~ave improved and are quite dependable, some user verifica.
.This system is commonly used to determine tile relative radionuclide abundances and is designed to measure gamma rays with energies greater than 120 keV.


York 10017.                                                             tion of the specifications claimed by the manufacturer Is strongly recommended.
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.


5.9-2
Equipment descriptions .(including tile theory of operation) and instructional material covering operation.


I                        I
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.
      I                \      I
      I                        I
          I    Uquld          I
              Nitrogen                              High Dewa                          Voltage I      (Cooling)                            Supply                                Spectrum f        .Stabilization I
                                                              Spectroscopy      I        Analog-to-Digital I          Detector            Preamplifier              Amplifier                  Conversion                II
      I
        I.                                              I                                          ,                    I
                                                        II
                                                                Count                                                  I
                                                                  Rate Scaler              Data storage, display, and data reduction and analysis      I
                                                                                            components               I
                                                                                      I                              I
                                                          FIGURE 1 A block diagram of a typical setup of a high-resolution gamma ray spectroscopy system. The dashed boxes indicate which sets of modules are usually packaged as one component in commercially available systems. Liquid nitrogen cooling of the detector is required for proper operation of the system, but the field-effect transistor (FET) in the preamplifier input stage may or may not be cooled, depending upon the type of detector used and the energy resolution desired. A scaler is shown connected to the main amplifier, a common method of monitoring the total system count rate. For long-term data acquisi tion, spectrum stabilization is recommended, and the method is indicated here by a stabilizer module in communication with the analog-to-digital converter (ADC).
                                                              5.9-3


will provide sufficient counting rates to verify the energy                will always have LN-cooled FET preamplifiers in order to resolution specifications of the manufacturer and to carry                  achieve the excellent resolution of these systems. The out any other performance tests desired by the user:                       preamplifier feedback loop may be either pulsed optical or resistive, 7 and the system will have fairly modest rate
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.
      60Co 10-30 pCi, Gamma ray energies: 1173,1332 keV
 
      57                                                                      capabilities in the range of 5000 MeV/sec. 6 It is important CO 1-10 j0i, Gamma ray energies: 14, 122, 136 keV
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:
                                                                              to decouple the detector from noisy mechanical environ ments to avoid microphonic pickup.
"0Co- 10.30 MCi
,',co-1-10o Ci


==C. REGULATORY POSITION==
==C. REGULATORY POSITION==
2. ELECTRONICS PERFORMANCE
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.
      Ge(Li) or HPGe gamma ray spectroscopy data acquisi tion systems meeting the general guidelines outlined briefly                  For ease of use, maintenance, and replacement of the below are considered more than adequate for use in SNM                      components in a high-resolution gamma ray spectroscopy assay requiring resolution better than that obtainable with                 system, the electronic components should be standard Na! detectors. The potential user should select the detector                nuclear instrument modules (NIM) (Ref. 1), with the and associated electronics that meet the needs of the partic                possible exception of the pulse-height analysis (Le., multi ular assay task required, with careful consideration of all                channel analyzer) components. Pulse signals should be factors that could affect the quality of the assay.                         transmitted from module to module in shielded coaxial cable to minimize the effects of possible electronic noise
 
  1. DETECTOR PERFORMANCE                                                    from nearby machinery at the measurement site. The cables should have a characteristic impedance that matches the Excellent performance, routinely available in coaxial                  terminations used in the NIM modules (generally 93 ohms).
I"
germanium detectors, may be represented by energy resolutions (FWHM) 4 of approximately 1.7 keV at 1332 keV                      The system power supplies (detector high voltage,
.. .*" ,:5.9-2'
( 60 Co) and approximately 0.7 keV at 122 keV ( 5 Co) for                  preamplifier, and NIM bin) should be capable of operating detectors with efficiencies up to 20 percent. 5 The full width              the system within the operating specifications when supplied at 0.1 maximum (FWTM) for such detectors is typically up                    with 115 volts (+10 percent) at 50 to 65 hertz (at constant to 1.9 times the FWHM. For these higher efficiency detec                    room temperature). The power supplied for the detection tors, "peak-to-Compton ratios" are usually quoted in the                   system should be stabilized against voltage shifts in order to range of 25 to 40. These ratios are strong functions of                    maintain resolution. The output voltage of the detector bias resolution, efficiency, and exact detector crystal geometry,                supply is determined by the detector requirements; 5 kilo and no typical values can be given without knowledge of all                volts is sufficient for most applications.
 
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.


of these parameters. Coaxial detectors with this kind of resolution will usually have cooled field-effect transistor                    The main amplifier, commonly referred to as the spectros (FET) preamplifiers and an energy-rate capability of                       copy amplifier, should have variable gain and pulse-shaping approximately 50,000 MeV/sec. 6 Room temperature pre                      controls for maximum setup flexibility. Most high-quality amplifiers have somewhat worse resolution but have rate                    amplifiers are equipped with baseline restoration and capabilities on the order of 150,000 MeV/sec.                              pole-zero cancellation circuits (Ref. 2), which greatly improve the resolution that can be achieved on a routine The resolution of planar detectors is a stronger function              basis. Baseline restoration is essential for assay situations in of the crystal size and shape than that of coaxial detectors,              which count rates in excess of several kilohertz are antici so representative resolutions cannot be given over a range of              pated. Pulse pileup suppression is also a useful feature, if sizes. As an example from the middle of the range of sizes                available; it may be found in some spectroscopy amplifiers usually offered, an excellent 2 cm 3 planar detector (le.,                and even in separate NIM modules designed for that purpose.
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.


2 cm 2 front face area x 1 cm thick) would have a resolution of approximately 0.5 keV at 122 keV (5 7 Co) and 0.21 keV                      Electronic components should be obtained with state-of at 5.9 keV (Mn X-ray from SaFe decay). Planar detectors                    the-art linearity and temperature sensitivit
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.


====y. Maintenance====
and 2 13U. It can also be used to perform assays of materials for fertile isotopes such as 232Th and 2 3 1U
    4 The full width of the gamma ray photopeak at half of its              of long-term gain stability may require the use of a spec maximum height (FWHM) is defined in ANSI/IEEE Std 301-1976.                 trum stabilizer. Centroid variations of a stabilization peak SThe full-energy peak efficiency (in percent) is defined relative      of less than one channel in a 4096-channel spectrum are to the full-energy peak efficiency of a 3-in. J.n. NaI(TI) scintilla        achievable with commercially available stabilizer modules.
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.


tion detector for 1332-keV gamma rays v Co) at a source-to.                Stabilization peaks can be provided either by a pulser or by detector distance of 25 cm. The detailed procedures for determining the efficiency in accordance with this definition are presented in         a radioactive source. Generally, a radioactive source is Section 5.2 of ANSI/IEEE Std 301-1976.
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.


preferred because it contributes less distortion to the
This system is commonly used to determine the relative radionuclide abundances and is designed to measure gamma rays with energies greater than 120 keV.
    6 Counting rate capabilities, expressed In MSV/sec, denote the          gamma ray spectrum and has a stable (although decaying)
maximum charge-to-voltay. conversion rate of which the pre                  emission rate. Furthermore, stabilization peaks from amplifier Is capable. For " Co, a SO,000-MeV/sec rate capability corresponds to a pulse iunting rate limitation of approximately            natural sources may be obtained from existing peaks
80,000 counts/sec. For Co a 000-MeV/sec rate capability also                in the assay spectrum itself, which simplifies the assay corresponds to a pulse rate limitation of approximately 80,000
counts/sec. Of course, nuclear material assays should be performed at count rates well below these limiting values in order to minimize            7 Feedback methods for charge-sensithve preamplifiers are dis rate-related losses from pulse pileup and dead time.                        cussed thoroughly in Chapter 5 of Reference 2.


K\
Ill.
                                                                      5.9-4


on the sensitivity, precision, and accuracy of any assay. The setup. Dead-time and pileup corrections may also be              range of gamma ray energies of interest also determines the performed using a pulser or a separate radioactive source        type of gamma ray detector appropriate for optimum fixed to the detector. The latter method is preferred for the    efficiency.
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.


reasons stated above.
Equipment .descriptions (including the theory of operation) and instructional material covering operation.


b. Full-Energy Peak Area Determination: The proce
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.
3. SYSTEM SELECTION AND USE                                      dure for extracting this fundamental information from the spectral data will be determined by the complexity of the The detailed requirements and constraints of a particular    gamma ray spectra as well as the intensity and complexity measurement situation will cause wide variation in the           of the gamma ray background at energies near the peaks of optimum choice of systems, even within a fairly well-defined      interest.


application. For example, a requirement for high through put may dictate higher efficiency detectors and highly                c. Gamma Ray Attenuation by the Samples and Sur automated data acquisition electronics. Anticipated inter        rounding Materials: Corrections for this effect are essential ferences from uranium, thorium, or fission products may          for accurate assays. The importance of this correction will make the best possible system resolution the most impor          increase as the gamma ray energies of interest decrease and tant consideration. Severe operating environments may            the absorptive power of the sample and surrounding mate make the use of digital stabilization highly desirable. Con      rials increases.
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


straints of space and location could dictate an unusually small LN dewar with automatic filling capacity. The list of such considerations in a given situation can be long, and          All of this emphasizes that by far the most important each situation should be considered carefully and indi            factor in choosing an appropriate data acquisition system, vidually in order to achieve a system that can acquire the       in Implementing proper assay procedures, and in supervising required measurement data.                                       the assay operations is a highly competent person, prefera bly experienced in gamma ray spectroscopy and its appli Beyond the choice of data acquisition systems, many            cation to assay measurements of special nuclear materials.
==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.


other factors influence the successful use of gamma ray          Such a person, with the assistance of the existing literature spectroscopy in quantitative assay measurements. Some of          and of others in the gamma ray field, will be able to consid these are:                                                        er a particular application in detail and choose an appro priate detector and electronics to create a data acquisition a. Gamma Ray Signatures: The energies and intensities          system that is well suited to the required assay task.
5.92


of the relevant gamma rays place fundamental restrictions
".Q'" i The .enipho %is here ison the 1perating specifications related to the overall performance off tile entire .data
                                                              5.9-5
* 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.


REFERENCES
1. Energy Resolution and Peak Shape (Systems 1, 11,  
  1. L Costrell, "Standard Nuclear Instrument Modules,"
111) The eniergy resolution of the
                                                                  2. P. W. Nicholson, Nuclear Electronics, John Wiley and U.S. Atomic Energy Commission, TID.20893, Revi Sons, New York, 1974.
.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.


sion 3, 1969.
These values have been determined to be necessaryfor theapplications defined in B.3. above.


BIBLIOGRAPHY
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
  Adams, F., and R. Dams, Applied Gamma-Ray Spectros                  This is an extensive treatise on electronics systems copy, Pergamon Press, New York, 1970.
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.


associated with high-resolution detectors.        Detailed descriptions are given of detector preamplifiers, pulse This work provides a comprehensive coverage of back shaping, rate-related losses, pulse-height analysis, and ground material pertinent to the gamma ray spectros spectral resolution.
'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.


copist. Considerable information is provided on both Nal and Ge detectors.                                        Reilly, T. D., and J. L Parker, "Guide to Gamma-Ray Assay for Nuclear Material Accountability," Los Alamos Augustson, R. H., and T. D. Reilly, "Fundamentals of Scientific Laboratory, LA-5794-M, 1975.
6 IEEE Sid 325-197 1, op. cit., Section 3.


Passive Nondestructive Assay of Fissionable Material," Los Alamos Scientific Laboratory, LA-565 I-M, 1974.
7 Ibid., Section 5.2.


This report briefly covers the principles involved in using gamma ray spectroscopy in the quantitative assay of This manual contains helpful introductory descriptions SNM and attempts to describe both capabilities and of NDA applications of gamma ray spectroscopy, as well limitations of gamma ray assay techniques. The report as some discussion of gamma ray detection systems.
the. spectrutm lpeaks of interest in a reasonahle period of time.


also includes a description of procedures for determining Hajnal, F., and C. Klusek, "Semi-Empirical Efficiency                plutonium isotopic ratios.
Est intates should be corrected for.


Equations for Ge(Li) Detectors," Nuclear Instruments and Methods, Vol. 122, p. 559, 1974.
sample-to-detector distance and tlie effects of absorbing materials placed between tile sample and detector.


Rogers, D. R., "Handbook of Nuclear Safeguards Measure ment Methods," Nuclear Regulatory Commission, NUREG/
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)
Hansen, J., J. McGeorge, and R. Fink, "Efficiency Calibra CR-2078, 1983.
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


tion of Semiconductor Detectors in the X-Ray Region,"
====y.  Art ====
Nuclear Instruments and Methods, Vol. 112, p. 239, 1973.
, 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.


Chapter 5, "Passive Nondestructive Assay Methods,"
detector volume- 1.0 to 1.5 cc b.
Hansen, J., et al., "Accurate Efficiency Calibration and contains descriptions of many applications of high          K
                                                                    resolution gamma ray spectroscopy, as well as many Properties of Semiconductor Detectors for Low-Energy references to original papers and reports.


Photons," Nuclear Instruments and Methods, Vol. 106, p. 365, 1973.
drift depletion depth--0.5 to 0;7 cm c.


Roney, W., and W. Seale, "Gamma-Ray Intensity Standards Knoll, G. F., Radiation Detection and Measurement, for Calibrating Ge(Li) Detectors for the Energy Range 200
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."
John Wiley and Sons, New York, 1979.
3. Count Rate Capabilities The following specifications are related to a system's ability to maintain adequate energy resolution at high co.unt rates.


1700 keV," Nuclear Instruments and Methods, Vol. 171, p. 389, 1980.
(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.


This book provides extensive discussion of all types of radiation detection systems, including high-resolution Sher, R., and S. Untermeyer, The Detection of Fissionable gamma ray spectroscopy systems. In particular, Sec Materials by Nondestructive Means, American Nuclear tion D deals exclusively with solid state detectors, and Society Monograph, 1980.
(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.


Section F is devoted to detector electronics and pulse processing.                                                    This relatively short book summarizes the principles of most nondestructive assay methods and briefly describes Kuil, L A., "An Introduction to Ge(Li) and NaI Gamma many typical applications, including those of high Ray Detectors for Safeguards Applications," Argonne resolution gamma ray spectroscopy. Chapters 3 and 5 National Laboratory, ANL-AECA-103, 1974.
__
_"  
"  
'."
5.9-3


are of particular interest since they deal, respectively, with nuclear detection methods and passive NDA
witlh less than a I T0 relathe increac in the FWHM and
P. W. Nicholson, Nuclear Electronics,John Wiley and Sons, techniques. The book also contains many references to New York, 1974.
. W * .M
ol'the 1 2 keV peak as" iCOipared to th6 values
* ..obtained at
.O
1 c.


original papers and reports.
.
4. Peak-to-Coinpton Ratio.


5.9-6
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'lhk&#xfd;
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.


VALUE/IMPACT STATEMENT
5.9.5 I..
                                                                          1.3.4 Public
L~.


===1. PROPOSED ACTION===
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.
                                                                          No adverse impact on the public can be foreseen.


1.1 Description
.. .......
                                                                      1.4 Decision on Proposed Action
At tin atesgreater than.
-"    Licensees authorized to possess at any one time more than one effective kilogram of special nuclear material The guide should be revised to reflect improvements in (SNM) are required in &sect; 70.51 of 10 CFR Part 70 to techniques, to bring the guide into conformity with current establish and maintain a system of control and account practice, and to provide a list of pertinent information ability so that the standard error of any inventory difference      currently available.


ascertained as a result of a measured material balance meets established minimum standards. The selection and proper           
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.


===2. TECHNICAL APPROACH===
"..Thes effects are due. to.the overlap of portions of tw'o or
  application of an adequate measurement method for each of the material forms in the fuel cycle are essential for the          Not applicable.
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.


maintenance of these standards.
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.


Many types of nondestructive assay (NDA) measurements         
Revision 3. TID-20893 (1969L.


===3. PROCEDURAL APPROACH===
.t'
  on SNM can involve, or even require, a high-resolution gamma ray spectroscopy system. The proposed action is to                Of the alternative procedures considered, revision of the provide some general guidelines in the selection of such existing regulatory guide was selected as the most advan systems and to point out useful resources for more detailed        tageous and cost effective.
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.


information on their assembly, optimization, and use in material protection measurements.
(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.


4. STATUTORY CONSIDERATIONS
6. Power Supplies (Systems I,. II, .111)
    1.2 Need for Proposed Action                                        4.1 NRC Authority Regulatory Guide 5.9, which provides guidance in this Authority for the proposed action is derived from the area, has not been updated since 1974 and does not contain Atomic Energy Act of 1954, as amended, and the Energy a list of pertinent information currently available in the Reorganization Act of 1974, as amended, and implemented literature.
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.


through the Commission's regulations.
0. ,:..
5.9-6


1.3 Value/Impact of Proposed Action                                4.2 Need for NEPA Assessment
TABLE 1 ENERGY RESOLUTION AND PEAK SHAPESPECIFICATIONS
        1.3.1 NRC Operations The proposed action is not a major action that may significantly affect the quality of the human environment The experience and improvements in detector technology and does not require an environmental impact statement.
SYSTEM I
Calibration Source Gamma Ray Energy FWHM (keVI
'ic o- 133 Q key
&#xfd;"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.


that have occurred since the guide was issued will be made available for the regulatory proces
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


====s. Using these updated====
LIQUID
                                                                        5. RELATIONSHIP TO OTHER EXISTING OR
NITROGEN
    techniques should have no adverse impact.                              PROPOSED REGULATIONS OR POLICIES
'DEWAR
        1.3.2 Other Government Agencies                                    The proposed action is one of a series of revisions of existing regulatory guides on nondestructive assay tech Not applicable.                                                  niques.
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


1.3.3 Industry                                                  6. SUMMARY AND CONCLUSIONS
..,UNITED STATES
        Since industry is already applying the more recent Regulatory Guide 5.9 should be revised to bring it up to detector technology discussed in the guide, updating these          date.
ATOMIC =ENERGY COMMISSION
WASHINGTON.


techniques should have no adverse impact.
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.


5.9-7
Enclosed are a table of contents of issued Division 5 guides and a list of additional guides in this division currently being developed.


UNITED STATES
Sincerely, es~erog~e~rst Director of Regulatory Standards Enclosures:
NUCLEAR REGULATORY COMMISSION      emPST CLASS MAIL
As stated}}
                                  POSTAGE FEEISPAID
    WASHINGTON, D.C. 20585              USNRC
                                      WASH 0 C
                                    PERMIT MeoSL
        OFFICIAL BUSINESS
    PENALTY FOR PRIVATE USE, $300
                                                    K}}


{{RG-Nav}}
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Revision as of 00:18, 11 January 2025

Specifications for Ge(Li) Spectroscopy Systems for Materials Protection Measurements
ML13350A205
Person / Time
Issue date: 06/30/1973
From:
US Atomic Energy Commission (AEC)
To:
References
RG-5.009
Download: ML13350A205 (10)
v • d • e


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

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


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