1、Designation: C 1268 94 (Reapproved 2008)Standard Test Method forQuantitative Determination of Americium 241 in Plutoniumby Gamma-Ray Spectrometry1This standard is issued under the fixed designation C 1268; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 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 quantitative determinationof americium 241 by gamma-ra
3、y spectrometry in plutoniumnitrate solution samples that do not contain significant amountsof radioactive fission products or other high specific activitygamma-ray emitters.1.2 This test method can be used to determine the ameri-cium 241 in samples of plutonium metal, oxide and other solidforms, whe
4、n the solid is appropriately sampled and dissolved.1.3 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 appro-priate safety and health practices and determine the applica-bility of
5、regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 758 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Radiochemical Analysis ofNuclear-Grade Plutonium MetalC 759 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Rad
6、iochemical Analysis ofNuclear-Grade Plutonium Nitrate SolutionsC 859 Terminology Relating to Nuclear Materials3C 982 Guide for Selecting Components for Energy-Dispersive X-Ray Fluorescence (XRF) SystemsC 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemistry Laboratories W
7、ithin theNuclear IndustryC 1168 Practice for Preparation and Dissolution of Pluto-nium Materials for AnalysisE 181 Test Methods for Detector Calibration and Analysisof Radionuclides2.2 ANSI Standards:4ANSI N15.20 Guide to Calibrating Nondestructive AssaySystemsANSI N15.35 Guide to Preparing Calibrat
8、ion Material forNondestructiveAssay Systems that Count Passive GammaRays4ANSI N15.37 Guide to the Automation of NondestructiveAssay Systems for Nuclear Material Control42.3 U.S. Nuclear Regulatory Commission RegulatoryGuides:5Regulatory Guide 5.9, Rev. 2Guidelines for GermaniumSpectroscopy Systems f
9、or Measurement of SpecialNuclear MaterialsRegulatory Guide 5.53, Rev. 1Qualification, Calibration,and Error Estimation Methods for Nondestructive Assay53. Summary of Test Method3.1 An aliquot of the sample that contains about 10 to 100ng of americium 241 is analyzed by measuring the intensity ofthe
10、characteristic 59.5 keV gamma ray emitted by americium241.3.2 Multiple sample geometries may be used if an appro-priate calibration for each geometry is made.3.3 The sample geometry must be reproducible. This in-cludes the physical characteristics of the sample container, thepositioning of the sampl
11、e, and the volume of sample viewed bythe gamma-ray detector.3.4 Electronic corrections are made, if required, for theeffects of pulse pile-up and dead time losses due to the activityof the sample. The necessity of dead time and pulse pile-upcorrections can be reduced by sample dilution to control co
12、untrates.3.5 Acorrection is made for the contribution to the 59.5 keVintensity due to gamma rays produced in the decay of uranium237.3.6 The relationship between the measured gamma-rayintensity and the americium 241 content is determined by theuse of appropriate standards.1This test method is under
13、the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved Jan. 1, 2008. Published February 2008. Originallyapproved in 1994. Last previous edition approved in 2000 as C 1268 94 (2000).2For referenced
14、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 standards Document Summary page onthe ASTM website.3Withdrawn.4Available from American National Standards Institute (ANSI), 25 W
15、. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.5Available from U.S. Nuclear Regulatory Commission, 1717 H ST., NW,Washington, DC 20555.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 This test
16、 method allows the determination of americium241 in a plutonium solution without separation of the ameri-cium from the plutonium. It is generally applicable to anysolution containing americium 241.4.2 The americium 241 in solid plutonium materials may bedetermined when these materials are dissolved
17、(see PracticeC 1168).4.3 When the plutonium solution contains unacceptablelevels of fission products or other materials, this method maybe used following a tri-n-octylphosphine oxide (TOPO) extrac-tion, ion exchange or other similar separation techniques (seeTest Methods C 758 and C 759).4.4 This te
18、st 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.4.5 The minimal sample preparation reduces the amount ofsample handling
19、 and exposure to the analyst.4.6 This test method is applicable only to homogeneoussolutions. This test method is not suitable for solutions con-taining solids.4.7 Solutions containing as little as 1 3 105g/Lamericium241 may be analyzed using this method. The lower limitdepends on the detector used
20、and the counting geometry.Solutions containing high concentrations may be analyzedfollowing an appropriate dilution.5. Interferences5.1 The presence of other radioactive nuclides in the sampleor in the vicinity of the detector may produce interferences.These may be due to the Compton scattering of h
21、igh energygamma rays which contribute to the background in the regionof interest or from gamma rays with energies close to theenergies used for the analysis.5.2 The presence of uranium 237 will interfere if a correc-tion is not applied. This interference will lead to an overestimation of the amount
22、of americium 241 present. Thisinterference is especially pronounced in plutonium from whichthe americium has recently been separated.5.3 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 ade
23、quate. 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.6. Apparatus6.1 High-Resolution Gamma Ray Counting SystemAhighresolution gam
24、ma-ray counting system is required. Generalguidelines for the selection of detectors and signal processingelectronics are discussed in Guide C 982 and NRC RegulatoryGuide 5.9. Data acquisition systems are addressed in ANSI15.37 and NRC Regulatory Guide 5.9. This system shouldinclude the following it
25、ems as a minimum.6.1.1 Germanium 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 resolut
26、ionof 600 eV or less at 122 keV. Consideration should be given tothe use of a high efficiency detector to enhance the ability toanalyze low levels of americium.6.1.2 High Voltage Power SupplyA high voltage powersupply with voltage range and current output compatible withthe detector selected is requ
27、ired. It is desirable that the voltageoutput be continuously adjustable.6.1.3 Nuclear Spectroscopy Amplifier Select a nuclearspectroscopy amplifier with pulse shaping, baseline restoration,and pulse pile-up rejection circuitry.6.1.4 Multichannel Pulse Height Analyzer (MCA)Selectan MCA with a minimum
28、 of 2048 channels. It is desirable 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
29、range into a minimum of 2048 channels(other types of ADCs which provide equivalent capabilitiescan be used). The ADC should also have dead time and pulsepile-up correction capabilities.6.2 Sample Holder, incorporating shielding to limit theinterferences from background radiation sources, is required
30、.Collimation to restrict the 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 viewe
31、d bythe detector.6.3 Sample Vials of sufficient volume to contain the desiredsample as described in 9.2 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 fo
32、r samples andstandards.7. Hazards7.1 Plutonium and americium bearing materials are radio-active and toxic. Adequate laboratory facilities, gloved boxes,fume hoods, etc., along with safe techniques must be used inhandling samples containing these materials.Adetailed discus-sion of all the precautions
33、 necessary is beyond the scope of thistest method; however, personnel who handle these materialsshould be familiar with such safe handling practices.7.2 Solutions and solids containing radioactive materialsrepresent a potential for high radiation exposure to personnelhandling them.Appropriate sample
34、 shielding, sample handlingprocedures, and radiation monitoring should be employed toensure personnel protection.8. Calibration and Standardization8.1 Calibrate the counting system for energy (eV/channel)in the range 0 to 300 keV using a radioactive source or sourceswhich emit gamma rays with well k
35、nown energies. A pluto-nium source is an obvious choice. See Methods E 181,ANSI N15.20, and U.S. Regulatory Guide 5.53 for furtherguidance.C 1268 94 (2008)28.2 Determine the relative detection efficiency (counts/emitted gamma ray) of the counting system in the 0 to 300 keVrange. Specifically, the ef
36、ficiency at 59.5 keV and 208 keVneeds to be determined. See Methods E 181,ANSI N15.20 andU.S. Regulatory Guide 5.53 for further guidance.8.3 The relationship between the mass of americium 241and the number of 59.5 keV gamma rays is established throughfundamental physics and basic nuclear constants,
37、that is, thenumber of 59.5 keV gamma rays/sec/gram americium241 = 4.543 3 1010.9. Procedure9.1 If necessary, prepare a plutonium solution from a solidsample following the procedure in Practice C 1168 or otherdissolution procedure.9.2 Determine the amount of solution and the dilutionrequired to provi
38、de 10 to 100 ng of americium 241 in theselected sample volume. The sample volume viewed by thedetector should be consistent for the samples and standardsused, regardless of the concentration.9.3 Determine the counting time necessary to achieve thedesired statistical counting precision. Samples which
39、 containmore americium will generally require less time to achieve thesame statistical precision.9.4 Quantitatively transfer the predetermined volume ofsolution from 9.2 into a sample vial and close.9.5 Place the vial in the counting system sample holder andacquire a spectrum. The detector should se
40、e a consistentportion of the sample volume. The same counting geometryand sample size as used for the standards must be used.9.6 Record the sample counting time, sample volume,dilution factor, and counting geometry used if more than one isavailable.10. Calculation10.1 Using the same methods as used
41、for the calibration,determine the background corrected net count rates for the 59.5keV gamma ray and the 208 keV gamma ray using the spectraldata acquired in 9.5.10.2 Calculate the 59.5 keV counting rate due to americium241 in the sample.RAm59! 5Robs59! / D59! 2 BURobs208! / D208!1 2 BU/ BAm(1)where
42、:RAm(59) = 59.5 keV rate (gamma rays/s) due to ameri-cium 241,Robs(59) = measured 59.5 keV rate (counts/s),D (59) = detection efficiency (counts/gamma ray) at59.5 keV,Robs(208) = measured 208 keV rate (counts/s),D (208) = detection efficiency (counts/gamma ray) at208 keV,BU= 1.5668, andBAm= 45385.6.
43、NOTE 1BUand BAmare dimensionless constants derived from thehalf-lives of uranium 237 and americium 241 and the branching ratios ofthe 59.5 and 208 keV gamma rays. The factor (1 BU/BAm) may beneglected for most applications.10.3 Calculate the amount of americium 241 present in thesample using the cou
44、nt rate from 10.2 and the factor in 8.3.10.4 Using the dilution factor for the sample calculate theamount of americium 241 in the original solution.11. Measurement Control11.1 Establish a measurement control program for theanalytical method. Section 12 of Guide C 1009 providesfurther guidance in thi
45、s area.11.2 As a minimum, the following periodic checks shouldbe made.11.2.1 Make a daily check of all instrument settings and ofthe energy calibration of the counting system prior to anymeasurement or series of measurements.11.2.2 Make a daily measurement of the counting roombackground. Ideally a m
46、easurement of the room backgroundshould be made both before and after any series of americiumdeterminations.11.2.3 Make a daily measurement of an americium standardor sample with a known concentration to provide a measure-ment bias check.11.2.4 Make weekly replicate measurements of a standardor samp
47、le to determine the precision of the measurementmethod.11.3 It is recommended that control charts and other peri-odic statistical analysis of the precision and bias data be used.12. Precision and Bias12.1 The precision of the assay is a function of countingstatistics. Precision may be improved with
48、increased countingtime.12.2 Variations in sample vial geometry and positioning willaffect the precision of the measurement.12.3 Differences in the plutonium and acid concentrationbetween the sample and the calibration standards may cause abias due to self attenuation in the sample.12.4 The calibrati
49、on 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.12.5 The full energy peak efficiency at a given energydetermined from the calibration function may introduce a bias.12.6 Errors in preparation including sample dilution, sampletransfer by pipetting, etc. can result in a bias.12.7 Samples producing high count rates may cause a biasdue to dead time losses and pulse pileup. This bias will bedependent on the adequacy of the corrections provid
