1、Designation: C 1221 92 (Reapproved 2004)Standard Test Method forNondestructive Analysis of Special Nuclear Materials inHomogeneous Solutions by Gamma-Ray Spectrometry1This standard is issued under the fixed designation C 1221; the number immediately following the designation indicates the year ofori
2、ginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the con-centrati
3、on of gamma-ray emitting special nuclear materialsdissolved in homogeneous solutions. The test method correctsfor gamma-ray attenuation by the sample and its container bymeasurement of the transmission of a beam of gamma raysfrom an external source (Refs. (1), (2), and (3).21.2 Two sample geometries
4、, slab and cylinder, are consid-ered. The sample container that determines the geometry maybe either a removable or a fixed geometry container. This testmethod is limited to sample containers having walls or a topand bottom of equal transmission through which the gammarays from the external transmis
5、sion correction source mustpass.1.3 This test method is typically applied to radionuclideconcentrations ranging from a few milligrams per litre toseveral hundred grams per litre. The assay range will be afunction of the specific activity of the nuclide of interest, thephysical characteristics of the
6、 sample container, countingequipment considerations, assay gamma-ray energies, samplematrix, gamma-ray branching ratios, and interferences.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to
7、 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specifichazards, see Section 9.2. Referenced Documents2.1 ASTM Standards:3C 859 Terminology Relating to Nuclear MaterialsC 982 Guide for Selecting Components for Energy-Di
8、spersive X-Ray Fluorescence (XRF) SystemsC 1133 Test Method for Nondestructive Assay of SpecialNuclear Material in Low Density Scrap and Waste bySegmented Passive Gamma-Ray ScanningC 1168 Practice for Preparation and Dissolution of Pluto-nium Materials for AnalysisE 181 Test Methods for Detector Cal
9、ibration and Analysisof Radionuclides2.2 ANSI Standards:4ANSI N15.20 Guide to Calibrating Nondestructive AssaySystemsANSI N15.35 Guide to Preparing Calibration Material forNondestructive Assay Systems that Count Passive GammaRaysANSI N15.37 Guide to the Automation of NondestructiveAssay Systems for
10、Nuclear Material ControlANSI/IEEE 645 Test Procedures for High-Purity Germa-nium Detectors for Ionizing Radiation2.3 U.S. Nuclear Regulatory Commission RegulatoryGuides:5Regulatory Guide 5.9, Rev. 2, Guidelines for GermaniumSpectroscopy Systems for Measurement of SpecialNuclear MaterialsRegulatory G
11、uide 5.53, Rev. 1, Qualification, Calibration,and Error Estimation Methods for Nondestructive Assay3. Terminology3.1 For definitions of terms used in this test method, refer toTerminology C 859.4. Summary of Test Method4.1 Many nuclear materials spontaneously emit gamma rayswith energies and intensi
12、ties characteristic of the decayingnuclide. The analysis for these nuclear materials is accom-plished by selecting appropriate gamma rays and measuringtheir intensity to identify and quantify the nuclide.4.1.1 The gamma-ray spectrum of a portion of solution isobtained with a collimated, high resolut
13、ion gamma-ray detec-tor.1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non-Destructive Assay.Current edition approved June 1, 2004. Published July 2004. Originally approvedin 1992. Last previous editio
14、n approved in 1998 as C 1221 - 92 (1998).2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volum
15、e information, refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.5Available from U.S. Nuclear Regulatory Commission, Washington, DC 20555.1Copyright ASTM International, 100 Barr H
16、arbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.2 Count-rate-dependent losses are determined and cor-rections are made for these losses.4.1.3 A correction factor for gamma-ray attenuation in thesample and its container is determined from the measurementof the transmitte
17、d intensity of an external gamma-ray source.The gamma rays from the external source have energies closeto those of the assay gamma rays emitted from the sample.Figs. 1 and 2 illustrate typical transmission source, sample, anddetector configurations. Gamma rays useful for assays of235Uand239Pu are li
18、sted in Table 1.4.1.4 The relationship between the measured gamma-rayintensity and the nuclide concentration (the calibration con-stant) is determined by use of appropriate standards (ANSIN15.20, ANSI N15.35, USNRC Regulatory Guide 5.53, Rev.1).4.2 In the event that the total element concentration i
19、sdesired and only one isotope of an element is determined (forexample,239Pu), the isotopic ratios must be measured orestimated.5. Significance and Use5.1 This test method is a nondestructive means of determin-ing the nuclide concentration of a solution for special nuclearmaterial accountancy, nuclea
20、r safety, and process control.5.2 It is assumed that the nuclide to be analyzed is in ahomogeneous solution (Practice C 1168).5.3 The transmission correction makes the test methodindependent of matrix and useful over several orders ofmagnitude of nuclide concentrations. However, a typical con-figura
21、tion will normally span only two to three orders ofmagnitude.5.4 The test method assumes that the sample-detector ge-ometry is the same for all measured items. This can beaccomplished by requiring that the liquid height in the side-looking geometry exceeds the detector field of view defined bythe co
22、llimator. For the uplooking geometry, a fixed sample fillheight must be maintained and vials of identical radii must beused unless the vial radius exceeds the field of view defined bythe collimator.5.5 Since gamma-ray systems can be automated, the testmethod can be rapid, reliable, and not labor int
23、ensive.5.6 This test method may be applicable to in-line or off-linesituations.6. Interferences6.1 Radionuclides may be present in the sample, whichproduce gamma rays with energies that are the same or verynearly the same as the gamma rays suggested for nuclidemeasurement, count rate correction, or
24、transmission correction.Thus, the corresponding peaks in the gamma-ray spectrum maybe unresolved and their areas may not be easily determinedunless multiplet fitting techniques are used. In some cases, thenuclide of interest may emit other gamma rays that can be usedfor analysis or alternative trans
25、mission or count rate correctionsources may be used.6.1.1 Occasionally, a significant amount of237Np is found ina plutonium sample. The237Np daughter,233Pa, emits a gammaray at 415.8 keV as well as other gamma rays in the 300 to 400keV region. These233Pa gamma rays may interfere with theanalysis of2
26、39Pu at 413.7 keV and at several other normallyuseful239Pu gamma-ray energies. In this case, the239Pu gammaray at 129.3 keV may be a reasonable alternative. In addition,the 398.7 keV gamma ray from233Pa may interfere with thetransmission corrections based on the 400.7 keV75Se gamma-ray measurements.
27、 Multiplet fitting techniques can resolvethese problems.6.1.2169Yb, used as the transmission source for235U assays,emits a 63.1 keV gamma ray that may interfere with themeasurement of the area of the peak produced by the 59.5 keVgamma ray of241Am, which is commonly used as the countrate correction s
28、ource. The 63.1 keV169Yb gamma ray shouldbe attenuated by placing a cadmium absorber over the trans-mission source.109Cd may be a suitable alternative count ratecorrection source.NOTE 1The sample geometry may be either cylindrical or a slab. (Notto scale.)FIG. 1 Schematic of a Sidelooking Configurat
29、ionNOTE 1The sample geometry in this case is a slab. (Not to scale.)FIG. 2 Schematic of an Uplooking ConfigurationTABLE 1 Suggested Nuclide/Source CombinationsNuclidePeakEnergy(keV)TransmissionSourcePeakEnergy(keV)CountRateCorrectionSourcePeakEnergy(keV)235U 185.7169Yb 177.2198.0241Am 59.5239Pu 413.
30、775Se 400.1133Ba 356.3239Pu 129.357Co 122.1136.5109Cd 88.0C 1221 92 (2004)26.1.3 In the special case of239Pu assays using75Se as atransmission source, random coincident summing of the 136.0and 279.5 keV gamma-ray emissions from75Se produces a lowintensity sum peak at 415.5 keV that interferes with t
31、he peakarea calculation for the peak produced by the 413.7 keVgamma ray from239Pu. The effects of this sum peak interfer-ence can be reduced by using absorbers to attenuate theradiation from the75Se to the lowest intensity required fortransmission measurements of acceptable precision. The prob-lem c
32、an be avoided entirely by making two separate measure-ments on each sample; first, measure the peak area of thetransmission source with the sample in place and second,measure the peak area of the assay gamma ray while thedetector is shielded from the transmission source.6.1.4 In239Pu solutions with
33、high activities of241Amor237U, or both, the Compton continuum from intense 208.0keV gamma rays may make the 129.3 keV gamma ray from239Pu unusable for assays. Also, the 416.0 keV sum peak thatresults from pileup of the 208.0 keV gamma rays may interferewith the 413.7 keV gamma ray from239Pu. Use an
34、absorber(for example, 0.5 to 0.8 mm of tungsten) between the detectorand sample to attenuate the 208.0 keV gamma rays. This willattenuate the intensity of the lower energy gamma rays and alsoreduce the sum peak interference. The resulting239Pu assaywill be based on the 413.7 keV gamma ray.6.1.5 X-ra
35、ys of approximately 88 keV from lead in theshielding may interfere with the measurement of the 88.0 keVgamma-ray peak when109Cd is used as the count rate correc-tion source. Graded shielding (4) is required to remove theinterference.6.2 Peaks may appear in the spectrum at gamma-ray ener-gies used fo
36、r analysis when there is no sample present. Thismay be caused by excessive amounts of radioactive materialstored in the vicinity of the detector or by contamination of theinstrument. This can cause variable and unacceptably highbackgrounds leading to poor measurement quality.6.2.1 Remove unnecessary
37、 radioactive material from thevicinity and also restrain movement of radioactive materialaround the assay area during measurements. Shielding shouldbe provided that completely surrounds the detector with theexception of the collimator opening. Shielding opposite thedetector on the far side of the sa
38、mple will also reduce theamount of ambient radiation incident on the detector.6.2.2 Use sample containers that are free of outer surfacecontamination. Remove any contamination from the instru-ment that may interfere with analyses. It may not be possible tocompletely decontaminate in-line instrumenta
39、tion. In this case,the contamination should be minimized to the extent practical.6.2.3 The measurement of background should be made atvarious times during the day. Varying backgrounds can becaused by process activities that often occur on regularschedules. These time-dependent backgrounds might not
40、bedetected if the background is checked at the same time eachday.6.3 High-energy gamma rays from fission products in thesample will increase the Compton background and decrease theprecision of gamma-ray intensity measurements in the lowerenergy (500 keV) region of the spectrum.6.4 Low energy X- and
41、gamma rays from either the trans-mission or count rate correction source may contribute signifi-cantly to the total system electronic pulse rate causing in-creased count rate losses and sum peak interferences. Anabsorber should be fixed between the source and detector toreduce the number of low ener
42、gy X-rays detected.7. Apparatus7.1 General guidelines for selection of detectors and signal-processing electronics are discussed in Guide C 982 and NRCRegulatory Guide 5.9, Rev. 2. Data acquisition systems areconsidered in ANSI N15.37 and NRC Regulatory Guide 5.9,Rev. 2. It is recommended that the s
43、ystem have the followingcomponents:7.1.1 High Resolution, Germanium, Gamma-RayDetectorA coaxial-type detector with full width at halfmaximum (FWHM) resolution typically less than 850 keV at122 keV and less than 2.0 keV at 1333 keV may be used for theanalysis. A planar-type detector with resolution t
44、ypically lessthan 600 keV FWHM at 122 keV may also be used. The statedresolutions are for guidance only. The selection of detectortype, coaxial or planar, should be based on the usual consid-erations of efficiency and resolution required for the specificapplication. Test procedures for detectors are
45、 given in TestMethods E 181 and ANSI/IEEE 645.7.1.2 Nuclear Spectroscopy AmplifierThe amplifier capa-bilities should include selectable pulse shaping time constants,pole zero adjustment, active gated baseline restoration, andpulse pileup rejection. A discussion of these functions is foundin Guide C
46、982.7.1.3 Oscilloscope, required for proper adjustment of thevarious amplifier controls and troubleshooting the electronics.The oscilloscope should have selectable time bases rangingfrom 1 ms/cm to 0.5 s/cm (20 MHz) and selectable verticalsensitivities ranging from 5 V/cm to 10 mV/cm.7.1.4 High Volt
47、age Bias Supply, equipped with continuouslyadjustable voltage control with a voltage range compatible withthe requirements of the above detector.7.1.5 Count-Rate Meter, to monitor the total electronicpulse rate in the system for acceptable rate. It should becompatible with the output of the above am
48、plifier.7.1.6 Multichannel Analyzer (MCA)An MCA with aminimum of 4096 data channels is recommended. The analyzershould operate using a Wilkinson type analog-to-digital con-verter (ADC) with a minimum ADC clock rate of 100 MHz, ora fixed conversion time ADC with a maximum conversion timeof 10 s. Anti
49、-coincidence gating for pulse-pile-up rejection,compatible with the above amplifier, and signal level discrimi-nation may be required. Analyzer control, data transfer, anddata analysis by computer are recommended. Spectrum displaymay be provided by the analyzer or computer.7.1.7 Digital Spectrum StabilizerThe stabilizer monitorstwo separate gamma rays, one at low energy and one at highenergy, to control changes in both zero intercept and energygain. The stabilizer must be compatible with the ADC/MCAcombination described in 7.1.6. The peaks chosen for stabili-zation must be pre
