ML20207H295

Rev 2 to Reg Guide 5.9, Guidelines for Germanium Spectroscopy Sys for Measurement of Snm

ML20207H295
Person / Time
Issue date:	12/31/1983
From:	NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:
References
TASK-RE, TASK-SG-042-2, TASK-SG-42-2 REGGD-05.009, REGGD-5.009, NUDOCS 8808250049
Download: ML20207H295 (8)

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e g flevision 28 U.S. NUCLEAR REGULATORY COMMISSION December 1983 nQ[g l

REGULATORY GU DE

,V OFFICE OF NUCLEAR REGULATORY RESEARCH f(

REGULATOhY GUIDE 5.9

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(Task SG 042 2)

F GUIDELINES FOR GERMANIUM SPECTROSCOPY SYSTEMS FOR MEASUREMENT OF SPECIAL NUCLEAR MATERIAL 1

A. INTRODUCTION to boxes and cans of uncharseterized waste material. Meas-urement conditions also vary widely from controlled

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Section 70.51,"MaterialBalance, inventory, and Records laboratory environments to the unpredictable plant envi on-l Requirements," of 10 CFR Part 70, "Domestic Licensing ment that can be hostile to the measurement equipment of Special Nuclear Material," requires,in part, that licensees and can often contribute serious background interferences authorized to possess at any one time more than one to the spectral data. As a result, there is no single gamma effective kilogra,n of special nuclear material establish and ray assay system that can be effective in all cases. The maintain a system of control and accountability so that system chosen for a particular NDA task must therefore be the standard error (estimator) of any inventory difference, determined from careful consideration of all factors that ascertained as a result of a measured material balance, may affect the measurement and of the requirements for meets established mmimum standards. The selection and the precision and accuracy of the assay, proper application of an adequate rneasurement method for each of the material forms in the fuel cycle is essential for The scope of this guide is limited to the consideration of the maintenance of these standards.

high resolution gamma ray spectroscopy with lithium drifted germanium, Ge(Li), or high purity germanium, llPGe (also

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Many types of nondestructive assay (NDA) measurements referred to as intrinsic germanium, IG), detectors. No j on special nuclear material (SNM) can involve, or even discussion of thallium-activated sodium iodide, Nal(TI), or k

j require, a high-resolution gamma ray spectroscopy system.

Lithium-drifted silicon, Si(L1), gamme ray systems is l

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This guide is intended both to provide some generalguide-presented. In addition, no discussion of specific NDA 1

Lines acceptable to the NRC staff for the selection of such applications of gamma ray spectroscopy is provided. The systems and to point out useful resources for more detailed measurement procedures (including calibration), analysis information on their assembly, optimization, and use in methods, inherent limitations, and overall precision.nd material protection measurements, accuracy attainable are specific to each application and are therefore the subject of separate application guides. Guide-Any guidance in this document related to information lines for measurement contro), calibration, and error collection activities has been cleared under OMB Clearance analysis of NDA measurements are dealt with in detailin No. 3150-0009.

Regulatory Guide 5.53, "Quahfication, Calibration, and Error Estimation Methods for Nondcstructive Assay,"

l B. DISCUSSION which endorses ANSI N15.201975, "Guide to Calibrating Nondestructive Assay Systems."3 ANSI N15.20-1975 was l

1. BACKGROUND reaffirmed in 1980.

1 Gamma ray spectroscopy systems are used for NDA of All of the major commercial vendors of Ge(LI) and various special nuclear material forms encountered in the llPGe detectors and the associated electronics maintain nuclear fuel cycle, both for quantitative determination up-to date documentation on the specifications of currently of the SNM content and nor the determination of radio-available equipment, as well 34 a variety of useful and infor-nuclide abundances, mative notes on applications. This literature is available

• The sutistantial numtser of changes in this revision has made it Applications of high-resolution gamma ray spectroscopy impractical to indicate the changes with lines in the marstn.

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/ rom the manufacturers upon request, and the potential an integral part of the detector package. The preamplifier f

customer may use this literature as a source of the most signal is further amplified and shaped and is then converted I

current information on the highest quality systems available.

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

individuals currently active in the fleld of nondestructive assay of special nuclear material and seek their advice ir 'he

4. TYPES OF SYSTEhtS particular assay problem being considered, liigh resolution gamma ray spectroscopy systems are

2. BIBL10GRAPillC INFORhf AT10N 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 ilPGe 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 spectre,-

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 detectorsis not Augustson and ReiUy and in Kull. These works discuss sharp. For instance, there may 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 hlore 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 end Dams. A thorough treatise on the asso iated electrcnics is available in Ncholson.

It should be noted that Ge(Li) detectors have no real in addition, extensive discussion of a variety of NDA tech-advantage over llPGe detectors witt comparable perform-niques and the implementation of some of these techniques ance specifications. In addition, Ge(Li) det:ctors require with high-resolution gamma ray spectroscopy may be onstant liquid nitrogen (LN) cooling, even when not in found in Sher and Untermeyer, in Rogers, and in Reilly and operation, llPGe detectors are, of course, also operated at Parker. Detailed descriptions of detector efficiency and LN temperature, but they car. 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 llajnal and Klusek;in llansen, hicGeorge, extended plant shutdowns. It also prevents complete loss and Fink;in llansen et al.;and in Roney and Scale.

of a detector due to operator procedure error, which can happen with a Ge(Li) detector when LN cooling is not Relevant techrueal information beyond the introdu-tory continuously maintained. This add-d convenience and level, including nomenclature and definitions, is contained the greater ruggedness of the llPGe detectors make therr in three useful standards of the Institute of Electrical and especially attractive for in-plant NDA applications.

Electronics Engineers, ANSI /IEEE Std 301 1976, "Test Procedures for Amplifiers and Preamplifiers for Semi-

5. EQUIPhlENT ACCEPTANCE PRACTICES l

conductor Radiation Detectors.~or Ionizing Radiation,"2 ANSI /IEEE Std 3251971, "Test Procedures for Germanium Equipment descriptions and instructional material l

Gamma-Ray Detect' ors"2 (reaffirmed in 1977), and ANSI /

covering operation, maintenance, and servicing of all IHl~5'td 6451977,' "TesTProWdlifes' for liigh-Punty electronic components are supplied by the manufacturer

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Germanium Detectors for Ionizing Radiation,"2 w hich for all individual modules or complete systems. Such s6plementi ANSI /IEEE Std 3251971. Thise describe descriptions should include cornplete and accurate sche-detailed techniques for defining and obtaining meaningful matic diagrams for possible in-house equipment servicing.

performance data for Ge(Li) and ilPGe detectors and Complete operational tests of system performance are to be amplifiers.

made at the vendor's facility, and the original data are supplied to the user upon delivery of the equirrrent.

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

the solid state Ge(Li) or llPGe 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 electronier. The detector output is converted following radioactive sources (with appropriate activities) into an analog voltage signal by the preamplifier, which is Althoush the quality control and preshipment testing dures of the commercial veadors or detectors and associate [roce.

elec-2Copies may t$e obtained from the Institute of EJectrical and tronics have improved and are quite dependable, some unet verinca-tion of the s recommende[cifications claimed t>y the manufacturer is strongly l IJectronics Enstneers, Inc., 34s list 47th Street, New York, New York lool 7.

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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 scaleris shown connected to the main amplifier, a common method of monitoring the total system count rate Forlong term data acquisi-i tion, spectrum stabilization is recommended, and the method is indicated here by a stabiliter modale in communication with the analog to-d:gital converter ( ADC).

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wilI provide sufficient counting rates to verify the energy eill alcays have LN cooled FET preamplifiers in order to resolution specifications of the manufacturer cnd to carry achieve the excellent resolution of these systems. The out any other performance tests desired by the user:

preamplifie7 feedback loop may be either pulsed optical or resistive,7 and the system will have fairly modest rate Co 10-30 pCi, Gamma ray energies: 1173,1332 kev capabilities in the range of 5000 MeV/sec.6 It is important 60 57 Co 1 10 pCi, Gamma ray energies: 14,122,136 kev to decouple the detector from noisy mechanical environ-ments to avoid microphonic pickup.

C. REGULATORY POSITION

2. ELECTRONICS PERFORMANCE Ge(Li) or lipGe gamma ray spectroscopy data acquisi-tion systems meeting the general guidelines outlined briefly For case 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 re.olution better than that obtainable with system, the electronic components should be standard Nat 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 partie-possible exception of the pulse height analysis (i.e., multi-ular assay task required, with careful consideration of all channel analyzer) components. Pulse signals should be factors that could affect the quahty of the assay.

transmitted from m Jule to module in shielded coaxial cable to minimize the effects of possiWe 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),

germanium detectors, may be represented by energy resolutions (FWilM)* of approximately 1.7 kev at 1332 kev The system power supplies (detector high voltage, (60Co) and approximately 0.7 kev at 122 kev (s7Co) for preamplifier, and NIM bin) should be capable of o<erating detectors with efficiencies up to 20 percent.8 The full width the system within the operating specifications w hen supplied at 0.1 maximum (F%TM) for such detectors is typically up with 115 volts (+10 percent) st 50 to 65 hertz (at constant to 1.9 times the FWHM. For these higher efficiency detec-room temperature). The power suppbed for the detection tors, "peak to-Compton ratios" are usuaUy 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-of these parameters. Laxial detectors with this kind of resolution will usually have cooled field effect transistor The main amplifier, commonly referred to as the spect.os-(FET) preamplifiers and an energy rate capability of copy amplifier, should have variable gain and pulse-shaping approxunately 50,000 MeV/sec.6 Room temperature pre-controls for maximum setup, flexibility. Most high-quality amplifiers have somewhat worse resolution but have rate arr.olifiers are equipped with baseline restoration and capabtlities 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 antic;-

so representative resolutions cannot be given over a range of pated. Pulse pileup suppression is also a useful feature,if l

sizes. As an example from the middle of the range of sizes available;it may be found in some spectroscopy amplifiers 3

usually offered, an excellent 2 cm planar detector (ie.,

and even in separate NIM modules designed for that purpose.

2 2cm front f.e area x 1 cm thick) would have a resolution of approumately 0.5 kev at 122 kev (57Co) and 0.21 lev Electronic components should be obtained with state-of-58 at 5.9 kev (Mn Lray from Fe decay). Planar detectors the-art linearity and temperature sensitivity Maintenance f long term gain stability may require the use of a spec-4The full width of the samma ray hote ik at half of its maximum height (twitM) is defined in [NSI/fl EE Std 301 1976.

trum st.bilizer. Centroid variations of a stabilization peak of less than one channel in a 4096-channel spectrum are g

tu s',

achievable with commercially available stabihzer modules.

n r y peak efff cy of a 34 at )s to the ful i

tion detector for 1332. kev gamma rays t Co) at a source.to*

Stabilization peaks can be provided either by a pulser or by I

a radioactive source. Generally, a radioactive source is j

detector dtstance of 2s em. The detailed rocedures for determining the efficiency in accordance with this fefinition are presented in Sution s.2 of ANSI /IEEE Std 301 1976-preferred because it contnbutes less distortion to the gamma ray spectrum and has a stable (although decaying) s

, denote the countinbarse to-voltar,erate cartsiuties. expressed in MeV'"t'ich conversion rate of w the e.

em15slon rate. Furt hermore, stabilization peaks from maxim um c Erfe fcounti!see,nN Uo"a ruls in's ratIIrritat6o of 'sp$r0xNatel natural sources may be obtained from existing peaks D

so,oo t ot co a sooo.Mev/sec rate /capabihty also in the assay spectrum itself, which simplifies the assay corresponda to a pulse rate, imitation of approximately 80,o00 s

counts /sec. Of course, nuclear material assays should t$e performed 7

at count rates well below these lirnitin values in order to minimize feedback methods for charge-sensithe p eamphfiers are dh-rate < elated losses from pulse pileup an dead time.

cussed thoroughly in Chapter s of Reference 2 5.9-4

e e e setup. Dead time and pileup corrections may also be on the sensitivity, precision, and accuracy of any assay. The performed u:'ng a pulser or a separate radioactive source range of gamma ray energies ofinterest also determines the fixtd to the detector. The latter method is preferred for the type of gamma ray detector appropriate for optimum reasons stated above, efficiency.

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3. SYSTEM SELECTION AND USE b.

Full. Energy Peak Area Determination: The proce-i dure for extracting this fundamentalinformation from the

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The detailed requirements and constraints of a particular spectral data will be determined by the complexity of the measurement situation will cause wide variation in the gamma ray spectra as well as the intensity and complexity optimum choice of systems, even within a fairly well-defined of the gamma ray background at energies near the peaks of application. For example, a requirement for high through-interest.

put may dictate higher efficiency detectors and highly automated data acquisition electronics. Anticipated inter-c.

Gamma Ray Attenuation by the Samples and Sur.

ferences from uranium, thorium, or fission products may rounding Materials: Corrections for this effect are essential make the best possible system resolution the most impor-for accurate assays. The importance of this correction will tant consideration. Severe operating environments may increase as the samma ray energies ofinterest decrease and make the use of digital stabilization highly desirable. Con-the absorptive power of the sample and surrounding mate-straints of space and location could dictate an unusually rials increases, smalt LN dewar with automatic filling capacity. The list of,uch considerations in a given situation can be long, and each situation should be considered carefully and indi-All of this emphasizes that by far the most important vidually in order to achieve a system that can acquire the factor in choosing an apprapriate data acquisition system, required measurement data.

in implementing proper assay procedures, and in supervising the assay operations is a highly competent person, prefera-Beyond the choice of data acquisit;on systems, many bly experienced in gamma ray spectroscopy and its appli-other factors influence the successful use of gamma ray cation to assay measurements of special nuclear materials, spectroscopy in quantitative assay measurements. Some of Such a person, with the assistance of the existintliterature these are:

and of othersin the gamma ray field, will be able to consid-er a particular application in detail and choose an appro-

a. Gamma Ray Signatures: The energies and intensities priate detector and electronics to create a data acquisition of the relevant gamma rays place fundamental restrictions system that is well suited to the required assay task.

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l 5.9 5

p REFERENCES

1. L. Ccottell, "Staadard Nuclear Instrument Modules,"

2. P. W. Nicholson, Nuclear Electronics, John Wiley and U.S. Atornic Energy Commission, TID-20893, Revi-Sons, New York,1974 sion 3,1969.

O BIBLIOGRAPHY Adams, F., and R. Dams, ApplicJ Camma Ray Spectrcs-This is an extensive treatise on electronics systems copy, Pergamon Press, New York,1970.

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, puhe height analysts, and ground material pertinent to the gamma say spectros-spectral resolution, copist. Considerable information is provided on both Na! and Ge detectors.

Reilly, T. D., and J. L Parker, "Guide to Gamma Ray Assay for Nuclear Material AccountaMlity," Los Alamos Augustson, R.11., and T. D.

Reilly, "Fundamentals of Scientific Laboratory, LA 5794-M,1975.

Passive Nondestructive Assay of Fissionable Material," Los Alamos Scientific Laboratory, LA 5651 M,1974.

T his report bnefly covers the principles involved in using gamma ray spectro copy in the quantitative assay of This manual contains helpful introductory descriptions SNM and atternpts to describe both capabilities and of N!'A applications of garama ray spectroscopy, as well limitations of gamma ray assay techniques. The report as some discussion of gamma ray detectic,n systems.

also includes a description of procedures for deterrnining plutoniam isotopic ratios.

Ilajnal, F.,

and C. Klusek, "Semi-Empirical Efficiency Equations for Ge(L1) Detectors," Nuclear Instruments and Methods, Vol.122, p. 5 59,1974 Rogers, D. R., "llandbc,ok of Nuclear Safeguards Measure-rnen' Methods," Nuclear Regulatory Commission, NUREG/

Ilansen, J., J. McGeorge, and R. Fink, "Efficiency Calibra-CR 2078,1983, tion of Semiconductor Detectors in the X Ray Region,"

Nuclear Instruments and Methods, Vol 112, p. 239,1973.

Chapter 5, "Pessive Nondestructive Assay Methods,"

contains descriptions of many applications of high-

/ llansen, J., et at, "Accurate Efficiency Cahbration and\\

resolution gamma ray spectroscopy, as well as many Properties of Semiconductor Detectors for Low Energy )

references to original papers and reports, i Photons," Nuc! car Instruments and Methods, VoL 106, \\

p.365,1973.

J Roney, W., and W. Scale,"Gamma-Ray Intensity Standards

Knoll, G. F.,

Radiation Dctcction and Measuremen t, for Calibrating Ge(L1) Detectors for the Energy Ranee 200-John Wiley and Sons, New York,1979.

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

This book provides extensive discussion of al' types of radiation detection s>st ms, including high-resolution Sher, R., and S. Untermeyer, The Detection of fissionable gamma ray spectroscopy systems. In particular, Sec-Marcrwls by Non testructive Means, American Nuclear tion D deals exclusively with solid state detectors, and Society Monograph,1980.

Section F is devo&d to detector electronics and pulse processing.

This relatively short book summarizes the principles of most nondestructive assay methods and briefly describes Kull, L A., "An Introduction to Ge(Li) and Nat Gamma-many typical applications, including those of high-Ray Detectors for Safeguards Applications," Argonne resolution gamma ray spectroscopy Chapters 3 and 5 Nationa'. Laboratory, ANL-AECA 103,1974.

are of particular interest since they oeal, respectively, with nuclear detection methods and passive NDA P. W. Nicholson, Nuclear ficctronics, John Wiley and Sons, techniques. The book also contains many references to New York,1974.

original papers and reports.

5.9-6

VALUE/ IMPACT STATEMENT f

1. PROPOSED ACTION 1.3.4 Public 4

1.1 Description No adverse irnpact on the public can be foreseen.

Licensees authorized to possess at any one time r: ore 1.4 Decision on Proposed Action than one effective kilogram 'of special nuclear material (SNM) are required in 5 70.51 of 10 CFR Part 70 te The guide should be revised to refleet improvements in establish and maintain a system of control and account.

techniques, to brias the guide into conformity with current ability so that the standard error of anyinventory difference practice, and to provide a list of pertinent information ascertained as a result of a measured material balance meets currer.tly available.

established minimum standards. The selectica and proper application of an adequate measurement method for each

2. TECilNICAL APPROACil of the material forms in the fuel cycle are essential for the maintenance of these standards.

Not applicable.

Many types of nondestructive assay (NDA) measurements on SNM can involve, or even require, a high resolution

3. PROCEDURAL APPROACll gamma ray spectroscopy system. The proposed action is to provide sorne general guidelines in the selection of such Of the alte native procedures considered, revision of the systems and to point out usefui resources for more detailed existing regulatory guide was selected as the most advan-information on their assembly, optimization, and use in tageous and cost effective, material protection measurements.

4. STATUTORY CONSIDERATIONS 1.2 Need for Proposed Action 4.1 NRC Authority Reguatory Guide 5.9, which provides guidance in tnis area, has not been updated since 1974 and does not contam Authority for the proposed action is derived from the a list cf pertinent information currently available in the Atomic Energy Act of 1954, as amended, and the Energy hterature.

Reorganization Act of 1974, as amended, and implemented through the Commission's regulations.

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1.3 Value/ Impact of Proposed Action 4.2 Need for NEPA Assessment 1.3.1 NRC Operations The proposed action is not a major action that may The experience and improvements in detector technology significantly affect the quality of the human environment that have occurred since the guide was issued will be made and does not require an environmental impact statement, available for the regulatory process. Using these updated techniques should have no adverse impact.

5. RELATIONSillP TO OTilER EXISTING OR PROPOSED REGULATIONS OR POLICIES 13.2 Other Government Agencies s

The proposed tetion it one of a series of revisions of Not applicable.

existing regulatory guides on nondestructive assay tech-niques.

1.3.3 Industry

6.

SUMMARY

AND CONCLUSIONS Since industry is already applying the more recent detector technology discussed in the guide, updating these Regulatory Guide 5.9 should be revised to bring it up to techniques should have no adverse impact.

date.

5.9-7

UNITED STATES

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