1、Designation: C1268 15Standard Test Method forQuantitative Determination of241Am in Plutonium byGamma-Ray Spectrometry1This standard is issued under the fixed designation C1268; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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 quantitative determinationof241Am by gamma-ray spectrometry in plutonium nitratesolu
3、tion samples that do not contain significant amounts ofradioactive fission products or other high specific activitygamma-ray emitters.1.2 This test method can be used to determine the241Am insamples of plutonium metal, oxide and other solid forms, whenthe solid is appropriately sampled and dissolved
4、.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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 establish app
5、ro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C758 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and RadiochemicalAnalysis ofNuclear-Grade Plutonium MetalC759 Test Met
6、hods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and RadiochemicalAnalysis ofNuclear-Grade Plutonium Nitrate SolutionsC859 Terminology Relating to Nuclear MaterialsC1009 Guide for Establishing and Maintaining a QualityAssurance Program forAnalytical Laboratories Within theNuclear Indu
7、stryC1168 Practice for Preparation and Dissolution of PlutoniumMaterials for AnalysisC1592/C1592M Guide for Making Quality NondestructiveAssay MeasurementsE181 Test Methods for Detector Calibration and Analysis ofRadionuclides2.2 U.S. Nuclear Regulatory Commission RegulatoryGuides:3Regulatory Guide
8、5.9, Rev. 2Guidelines for GermaniumSpectroscopy Systems for Measurement of SpecialNuclear MaterialsRegulatory Guide 5.53, Rev. 1Qualification, Calibration,and Error Estimation Methods for Nondestructive Assay33. Terminology3.1 Except as otherwise defined herein, definitions of termsare as given in T
9、erminology C859.4. Summary of Test Method4.1 An aliquot of the sample that contains about 10 to 100ng of241Am is analyzed by measuring the intensity of thecharacteristic 59.5 keV gamma ray emitted by241Am.4.2 Multiple sample geometries may be used if an appro-priate calibration for each geometry is
10、made.4.3 The sample geometry must be reproducible. This in-cludes the physical characteristics of the sample container, thepositioning of the sample, and the volume of sample viewed bythe gamma-ray detector.4.4 Electronic corrections are made, if required, for theeffects of pulse pile-up and dead ti
11、me losses due to the activityof the sample. The necessity of dead time and pulse pile-upcorrections can be reduced by sample dilution to control countrates.4.5 Acorrection is made for the contribution to the 59.5 keVintensity due to gamma rays produced in the decay of237U.4.6 The relationship betwee
12、n the measured gamma-rayintensity and the241Am content is determined by the use ofappropriate standards.1This test method is under the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved June 1, 201
13、5. Published July 2015. Originally approvedin 1994. Last previous edition approved in 2008 as C1268 94 (2008). DOI:10.1520/C1268-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inform
14、ation, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Nuclear Regulatory Commission, One White Flint North,11555 Rockville Pike, Rockville, MD 20852. Also through www.nrc.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
15、 19428-2959. United States15. Significance and Use5.1 This test method allows the determination of241Am in aplutonium solution without separation of the americium fromthe plutonium. It is generally applicable to any solutioncontaining241Am.5.2 The241Am in solid plutonium materials may be deter-mined
16、 when these materials are dissolved (see Practice C1168).5.3 When the plutonium solution contains unacceptablelevels of fission products or other materials, this method maybe used following a tri-n-octylphosphine oxide (TOPO)extraction, ion exchange or other similar separation techniques(see Test Me
17、thods C758 and C759).5.4 This test method is less subject to interferences fromplutonium than alpha counting since the energy of the gammaray used for the analysis is better resolved from other gammarays than the alpha particle energies used for alpha counting.5.5 The minimal sample preparation redu
18、ces the amount ofsample handling and exposure to the analyst.5.6 This test method is applicable only to homogeneoussolutions. This test method is not suitable for solutions con-taining solids.5.7 Solutions containing as little as 1 105g/L241Am maybe analyzed using this method. The lower limit depend
19、s on thedetector used and the counting geometry. Solutions containinghigh concentrations may be analyzed following an appropriatedilution.6. Interferences6.1 The presence of other radioactive nuclides in the sampleor in the vicinity of the detector may produce interferences.These may be due to the C
20、ompton scattering of high energygamma rays which contribute to the background in the regionof interest or from gamma rays with energies close to theenergies used for the analysis.6.2 The presence of237U will interfere if a correction is notapplied. This interference will lead to an over estimation o
21、f theamount of241Am present. This interference is especiallypronounced in plutonium from which the americium hasrecently been separated.6.3 The presence of radioactive materials in the vicinity ofthe gamma-ray detector which are not in the sample may createinterferences if detector shielding is not
22、adequate. Theseinterferences may be due to the Compton scattering of highenergy gamma rays which contribute to the background in theregion of interest or from gamma rays with energies close tothe energies used for the analysis.7. Apparatus7.1 High-Resolution Gamma Ray Counting SystemA highresolution
23、 gamma-ray counting system is required. Generalguidelines for the selection of detectors and signal processingelectronics are discussed in NRC Regulatory Guide 5.9. Dataacquisition systems are addressed in NRC Regulatory Guide5.9. This system should include the following items as aminimum.7.1.1 Germ
24、anium Photon Detector with IntegralPreamplifierA coaxial type detector should typically have afull width at half maximum resolution of 850 eV or less at 122keV and 2.0 keV or less at 1332 keV. A planar type detectorshould typically have a full width at half maximum resolutionof 600 eV or less at 122
25、 keV. Consideration should be given tothe use of a high efficiency detector to enhance the ability toanalyze low levels of americium.7.1.2 High Voltage Power SupplyA high voltage powersupply with voltage range and current output compatible withthe detector selected is required. It is desirable that
26、the voltageoutput be continuously adjustable.7.1.3 Nuclear Spectroscopy AmplifierSelect a nuclearspectroscopy amplifier with pulse shaping, baseline restoration,and pulse pile-up rejection circuitry.7.1.4 Multichannel Pulse Height Analyzer (MCA)Selectan MCA with a minimum of 2048 channels. It is des
27、irable thatthe MCA be compatible with computerized operations so thatdata acquisition and analysis may be automated. The analog todigital converter (ADC) associated with the MCA should havea clock rate of at least 100 MHz and the capability of digitizingthe input voltage range into a minimum of 2048
28、 channels(other types of ADCs which provide equivalent capabilitiescan be used). The ADC should also have dead time and pulsepile-up correction capabilities.7.2 Sample Holder, incorporating shielding to limit theinterferences from background radiation sources, is required.Collimation to restrict the
29、 view of the detector to a portion ofthe sample may be required. The sample holder may incorpo-rate more than one sample position. The sample holder shallprovide reproducible positioning for each sample position sothat a consistent volume or portion of the sample is viewed bythe detector.7.3 Sample
30、Vials of sufficient volume to contain the desiredsample as described in 10.2 are required. The sample vialsshould be made of low density materials and have reproducibledimensions such as wall thickness and internal diameter. Vialswith identical dimensions should be used for samples andstandards.8. H
31、azards8.1 Plutonium and americium bearing materials are radio-active and toxic. Adequate laboratory facilities, gloveboxes,fume hoods, and so forth, along with safe techniques must beused in handling samples containing these materials.Adetaileddiscussion of all the precautions necessary is beyond th
32、e scopeof this test method; however, personnel who handle thesematerials should be familiar with such safe handling practices.8.2 Solutions and solids containing radioactive materialsrepresent a potential for high radiation exposure to personnelhandling them.Appropriate sample shielding, sample hand
33、lingprocedures, and radiation monitoring should be employed toensure personnel protection.9. Calibration and Standardization9.1 Calibrate the counting system for energy (eV/channel)in the range 0 to 300 keV using a radioactive source or sourcesC1268 152which emit gamma rays with well known energies.
34、 A pluto-nium source is an obvious choice. See Methods E181, GuideC1592/C1592M, and U.S. Regulatory Guide 5.53 for furtherguidance.9.2 Determine the relative detection efficiency (counts/emitted gamma ray) of the counting system in the 0 to 300 keVrange. Specifically, the efficiency at 59.5 keV and
35、208 keVneeds to be determined. See Methods E181, Guide C1592/C1592M and U.S. Regulatory Guide 5.53 for further guidance.9.3 The relationship between the mass of241Am and thenumber of 59.5 keV gamma rays is established throughfundamental physics and basic nuclear constants, that is, thenumber of 59.5
36、 keV gamma rays/sec/gram241Am = 4.543 1010.10. Procedure10.1 If necessary, prepare a plutonium solution from a solidsample following the procedure in Practice C1168 or otherdissolution procedure.10.2 Determine the amount of solution and the dilutionrequired to provide 10 to 100 ng of241Am in the sel
37、ectedsample volume. The sample volume viewed by the detectorshould be consistent for the samples and standards used,regardless of the concentration.10.3 Determine the counting time necessary to achieve thedesired statistical counting precision. Samples which containmore americium will generally requ
38、ire less time to achieve thesame statistical precision.10.4 Quantitatively transfer the predetermined volume ofsolution from 9.2 into a sample vial and close.10.5 Place the vial in the counting system sample holder andacquire a spectrum. The detector should see a consistentportion of the sample volu
39、me. The same counting geometryand sample size as used for the standards must be used.10.6 Record the sample counting time, sample volume,dilution factor, and counting geometry used if more than one isavailable.11. Calculation11.1 Using the same methods as used for the calibration,determine the backg
40、round corrected net count rates for the 59.5keV gamma ray and the 208 keV gamma ray using the spectraldata acquired in 10.5.11.2 Calculate the 59.5 keV counting rate due to241Am inthe sample.RAm59! 5Robs59!/D59! 2 BURobs208!/D208!1 2 BU/BAm(1)where:RAm(59) = 59.5 keV rate (gamma rays/s) due to241Am,
41、Robs(59) = measured 59.5 keV rate (counts/s),D(59) = detection efficiency (counts/gamma ray) at 59.5keV,Robs(208) = measured 208 keV rate (counts/s),D(208) = detection efficiency (counts/gamma ray) at 208keV,BU= 1.5668, andBAm= 45385.6.NOTE 1BUand BAmare dimensionless constants derived from thehalf-
42、lives of237U and241Am and the branching ratios of the 59.5 and 208keV gamma rays. The factor (1 BU/BAm) may be neglected for mostapplications.11.3 Calculate the amount of241Am present in the sampleusing the count rate from 11.2 and the factor in 9.3.11.4 Using the dilution factor for the sample calc
43、ulate theamount of241Am in the original solution.12. Measurement Control12.1 Establish a measurement control program for theanalytical method. Section 12 of Guide C1009 provides furtherguidance in this area.12.2 As a minimum, the following periodic checks shouldbe made.12.2.1 Make a daily check of a
44、ll instrument settings and ofthe energy calibration of the counting system prior to anymeasurement or series of measurements.12.2.2 Make a daily measurement of the counting roombackground. Ideally a measurement of the room backgroundshould be made both before and after any series of americiumdetermi
45、nations.12.2.3 Make a daily measurement of an americium standardor sample with a known concentration to provide a measure-ment bias check.12.2.4 Make weekly replicate measurements of a standardor sample to determine the precision of the measurementmethod.12.3 It is recommended that control charts an
46、d other peri-odic statistical analysis of the precision and bias data be used.13. Precision and Bias13.1 Within the different stages of the nuclear fuel cycle,many challenges lead to the inability to perform interlaboratorystudies for precision and bias. These challenges may includevariability of ma
47、trices of material tested, lack of suitablereference of calibration materials, limited laboratories perform-ing testing, shipment of materials to be tested, and regulatoryconstraints. Because of these challenges, each laboratoryutilizing these test methods should develop its own precisionand bias as
48、 part of its quality assurance program.13.2 The precision of the assay is a function of countingstatistics. Precision may be improved with increased countingtime.13.3 Variations in sample vial geometry and positioning willaffect the precision of the measurement.13.4 Differences in the plutonium and
49、acid concentrationbetween the sample and the calibration standards may cause abias due to self attenuation in the sample.13.5 The calibration of standard sources, including errorsintroduced in using a standard radioactive solution or aliquotthereof, to prepare a working standard for bias correction mayresult in a bias.C1268 15313.6 The full energy peak efficiency at a given energydetermined from the calibration function may introduce a bias.13.7 Errors in preparation including sample dilution, sampletransfer by pipetting, and so forth, can result in a bias.13.
