1、Designation: C1221 10Standard Test Method forNondestructive Analysis of Special Nuclear Materials inHomogeneous Solutions by Gamma-Ray Spectrometry1This standard is issued under the fixed designation C1221; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the con-centration of gamma-ray emitt
3、ing special nuclear materialsdissolved in homogeneous solutions. The test method correctsfor gamma-ray attenuation by the solution and its container bymeasurement of the transmission of a beam of gamma raysfrom an external source (Refs. (1), (2), and (3).21.2 Two solution geometries, slab and cylind
4、er, are consid-ered. The solution container that determines the geometry maybe either a removable or a fixed geometry container. This testmethod is limited to solution containers having walls or a topand bottom of equal transmission through which the gammarays from the external transmission correcti
5、on 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 solution con
6、tainer, countingequipment considerations, assay gamma-ray energies, solutionmatrix, 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 establis
7、h 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:3C1133 Test Method for Nondestructive Assay of SpecialNuclear Material in Low-Density Scrap and Waste bySeg
8、mented Passive Gamma-Ray ScanningC1490 Guide for the Selection, Training and Qualificationof Nondestructive Assay (NDA) PersonnelC1592 Guide for Nondestructive Assay MeasurementsC1673 Terminology of C26.10 NondestructiveAssay Meth-odsC1168 Practice for Preparation and Dissolution of Pluto-nium Mater
9、ials for AnalysisE181 Test Methods for Detector Calibration andAnalysis ofRadionuclides2.2 ANSI Standards:4ANSI N15.20 Guide to Calibrating Nondestructive AssaySystemsANSI N15.35 Guide to Preparing Calibration Material forNondestructiveAssay Systems that Count Passive GammaRaysANSI N15.37 Guide to t
10、he Automation of NondestructiveAssay Systems for Nuclear Material ControlANSI N42.14 American National Standard for Calibrationand Use of Germanium Spectrometers for the Measure-ment of Gamma-Ray Emission Rates of RadionuclidesANSI/IEEE 645 Test Procedures for High-Purity Germa-nium Detectors for Io
11、nizing Radiation3. Terminology3.1 For definitions of terms used in this test method, refer toCommittee C26.10s Terminology standard, C1673.4. Summary of Test Method4.1 Many nuclear materials spontaneously emit gamma rayswith energies and intensities characteristic of the decayingnuclide. The analysi
12、s 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 resolution gamma-ray detec-tor.1This test method is under the
13、jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on NonDestructive Assay.Current edition approved March 1, 2010. Published April 2010. Originallyapproved in 1992. Last previous edition approved in 2004 as C1221 92 (2004).DOI: 10.1520/C122
14、1-92R10.2The 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 volume information, refer to the stand
15、ards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.2 Count-
16、rate-dependent losses are determined and cor-rections are made for these losses.4.1.3 A correction factor for gamma-ray attenuation in thesolution and its container is determined from the measurementof the transmitted intensity of an external gamma-ray source.The gamma rays from the external source
17、have energies closeto those of the assay gamma rays emitted from the solution.Figs. 1 and 2 illustrate typical transmission source, solution,and detector configurations. Gamma rays useful for assays of235U and239Pu are listed in Table 1.4.1.4 The relationship between the measured gamma-rayintensity
18、and the nuclide concentration (the calibration con-stant) is determined by use of appropriate standards(ANSI N15.20, ANSI N15.35, and Guide C1592.4.2 In the event that the total element concentration isdesired and only one isotope of an element is determined (forexample,239Pu), the isotopic ratios m
19、ust 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, nuclear safety, and process control.5.2 It is assumed that the nuclide to be analyzed is in ahomogeneous
20、solution (Practice C1168).5.3 The transmission correction makes the test methodindependent of matrix (solution elemental composition anddensity) and useful over several orders of magnitude of nuclideconcentrations. However, a typical configuration will normallyspan only two to three orders of magnit
21、ude because of detectordynamic range.5.4 The test method assumes that the solution-detectorgeometry 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 collimator. For the upward
22、-looking geometry, a fixedsolution fill height must be maintained and vials of identicalradii must be used unless the vial radius exceeds the field ofview defined by the collimator.5.5 Since gamma-ray systems can be automated, the testmethod can be rapid, reliable, and not labor intensive.5.6 This t
23、est method may be applicable to in-line or off-linesituations.6. Interferences6.1 Radionuclides may be present in the solution, whichproduce gamma rays with energies that are the same or verynearly the same as the gamma rays suggested for nuclidemeasurement, count rate correction, or transmission co
24、rrection.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 transmission or coun
25、t rate correctionsources may be used.6.1.1 Occasionally, a significant amount of237Np is found ina plutonium solution. The237Np daughter,233Pa, emits agamma ray at 415.8 keV as well as other gamma rays in the300 to 400 keV region. These233Pa gamma rays may interferewith the analysis of239Pu at 413.7
26、 keV and at several othernormally useful239Pu gamma-ray energies. In this case,the239Pu gamma ray at 129.3 keV may be a reasonablealternative. In addition, the 398.7 keV gamma ray from233Pamay interfere with the transmission corrections based on the400.7 keV75Se gamma-ray measurements. Multiple fitt
27、ingtechniques can resolve these 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 source. The 63.1
28、 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 ConfigurationNOTE 1The sa
29、mple 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 413.775Se 400.1133B
30、a 356.3239Pu 129.357Co 122.1136.5109Cd 88.0C1221 1026.1.3 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 the peakarea calculation
31、 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 can be avoided entirely
32、by making two separate measure-ments on each item/solution; first, measure the peak area of thetransmission source with the solution in place and second,measure the peak area of the assay gamma ray while thedetector is shielded from the transmission source. An addi-tional benefit of the “dual scan”
33、is a better signal to noise ratioin the individual spectra.6.1.4 In239Pu solutions with 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
34、of the 208.0 keV gamma rays may interferewith the 413.7 keV gamma ray from239Pu. Use an absorber(for example, 0.5 to 0.8 mm of tungsten) between the detectorand solution to attenuate the 208.0 keV gamma rays. This willattenuate the intensity of the lower energy gamma rays and alsoreduce the sum peak
35、 interference. The resulting239Pu assaywill be based on the 413.7 keV gamma ray.6.1.5 X-rays 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
36、remove theinterference.6.2 Peaks may appear in the spectrum at gamma-ray ener-gies used for analysis when there is no solution 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 a
37、nd unacceptably highbackgrounds leading to poor measurement quality.6.2.1 Remove unnecessary 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 thee
38、xception of the collimator opening. Shielding opposite thedetector on the far side of the solution will also reduce theamount of ambient radiation incident on the detector.6.2.2 Use solution containers that are free of outer surfacecontamination. Remove any contamination from the instru-ment that ma
39、y interfere with analyses. It may not be possible tocompletely decontaminate in-line instrumentation. 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 proc
40、ess activities that often occur on regularschedules. These time-dependent backgrounds might not bedetected if the background is checked at the same time eachday.6.3 High-energy gamma rays from fission products in thesolution will increase the Compton background and decreasethe precision of gamma-ray
41、 intensity measurements in thelower energy (500 keV) region of the spectrum.6.4 Low energy X- and 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 interfe
42、rences. Anabsorber should be fixed between the source and detector toreduce the number of low energy X-rays detected.7. Apparatus7.1 Gamma-Ray Detector SystemGeneral guidelines forselection of detectors and signal-processing electronics arediscussed in Guide C1592, and ANSI N42.14. Refer to theRefer
43、ences section for a list of other recommended references.This system typically consists of a gamma-ray detector, spec-troscopy grade amplifier, high-voltage bias supply, multi-channel analyzer, and detector collimator. The system may alsoinclude an oscilloscope, a spectrum stabilizer, a computer, an
44、da printer. General guidelines for selection of detectors andsignal-processing electronics are discussed in Guide C1592.Data acquisition systems are considered in ANSI N15.37.Itisrecommended that the system be implemented by an NDAProfessional (C1490). The system should have the followingcomponents:
45、7.2 High Resolution, Germanium, Gamma-RayDetectorA coaxial-type detector with full width at halfmaximum (FWHM) resolution typically 1000 eV or better at122 keV may be used for the analysis. A planar-type detectorwith similar resolution may also be used.The stated resolutionsare for guidance only. Th
46、e selection of detector type, coaxial orplanar, should be based on the usual considerations of effi-ciency and resolution required for the specific application. Testprocedures for detectors are given in Test Methods E181 andANSI/IEEE 645.7.3 Detector CollimatorThe collimator defines the fieldof view
47、 of the detector to a reproducible solution geometry andshields the detector from ambient radiation. This test methodaddresses two potential solution/collimator geometries thatwill dictate the analytical expression used. Other designsrequire case-by-case assessment.7.3.1 The collimator in the slab g
48、eometry (both upwardlooking and sidelooking) is a cylindrical hole with its axisnormal to the slab. The diameter of the collimator should limitthe field of view of the detector to within the solution volume(see Figs. 1 and 2).7.3.2 The collimator in the cylindrical geometry should be aslit perpendic
49、ular to the axis of the solution. The field of viewin this case is within the solution volume in the axial direction(see Fig. 1) and includes the entire solution volume in theradial direction (Fig. 3).7.4 Absorber FoilsAbsorbers are used to reduce theoverall count rate due to low energy X-rays and gamma raysfrom the solution, transmission source, and count rate correc-tion source. The absorbers are usually cadmium, tin or copper,or combination. Any change of these absorbers requires reca-libration of the assay system.7.5 Count Rate Correction SourceTo minimize interfer-enc
