1、Designation: C 1268 94 (Reapproved 2000)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:C 758 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Radiochemical Analysis ofNuclear-Grade Plutonium Metal2C 759 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Rad
6、iochemical Analysis ofNuclear-Grade Plutonium Nitrate Solutions2C 859 Terminology Relating to Nuclear Materials2C 982 Guide for Selecting Components for Energy Disper-sive X-ray Fluorescence (XRF) Systems2C 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemistry Laboratorie
7、s Within theNuclear Industry2C 1168 Practice for Preparation and Dissolution of Pluto-nium Materials for Analysis2E 181 Methods for Detector Calibration and Analysis ofRadionuclides32.2 ANSI Standards:ANSI N15.20 Guide to Calibrating Nondestructive AssaySystems4ANSI N15.35 Guide to Preparing Calibra
8、tion 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:Regulatory Guide 5.9, Rev. 2Guidelines for GermaniumSpectroscopy Systems f
9、or Measurement of SpecialNuclear Materials5Regulatory 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 samp
11、le, 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 c
12、ountrates.3.5 Acorrection is made for the contribution to the 59.5 keVintensity due to gamma rays produced in the decay of uranium237.1This test method is under the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Curren
13、t edition approved June 10, 2000. Published June 1994.2Annual Book of ASTM Standards, Vol 12.01.3Annual Book of ASTM Standards, Vol 12.02.4Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.5Available from U.S. Nuclear Regulatory Commission, 1717 H ST
14、., NW,Washington, DC 20555.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.6 The relationship between the measured gamma-rayintensity and the americium 241 content is determined by theuse of appropriate standards.4. Significance an
15、d Use4.1 This test 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 materi
16、als are dissolved (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
17、C 759).4.4 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.4.5 The minimal sample preparation reduces the amount
18、 ofsample handling 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
19、the detector used 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 Compt
20、on 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.5.2 The presence of uranium 237 will interfere if a correc-tion is not applied. This interference will lead to an overestimat
21、ion of the amount 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 sh
22、ielding is not 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.6. Apparatus6.1 High-Resolution Gamma Ray Counting SystemA
23、highresolution gamma-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 shouldinclud
24、e the following items 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 ha
25、lf maximum resolutionof 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 detecto
26、r selected is required. 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
27、MCA with a minimum 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 digitizing
28、the input voltage 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 so
29、urces, is required.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 t
30、he sample is viewed 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
31、 should be used for 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 a
32、ll the precautions 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.
33、 Appropriate sample 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 sourcesC 1268 94 (200
34、0)2which emit gamma rays with well known 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.8.2 Determine the relative detection efficiency (counts/emitted gamma ray) of the counting system in the 0 to 300 keVrange. S
35、pecifically, the efficiency 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
36、nuclear constants, 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 diluti
37、onrequired to provide 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 preci
38、sion. Samples which 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
39、 detector should see 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 sa
40、me methods as used 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!
41、1 2 BU/ BAm(1)where: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= 1.566
42、8, andBAm= 45385.6.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 thes
43、ample using the count 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 providesfurt
44、her guidance in this 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 roomback
45、ground. Ideally a measurement 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 o
46、f a standardor sample 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 ma
47、y be improved with 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
48、.12.4 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.12.5 The full energy peak efficiency at a given energydetermined from the calibration function may i
49、ntroduce 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 provided by thepulse pile-up rejection and dead time correction circuits in thecounting electronics. Generally count rates that cause signifi-cant problems can be easily avoided by sample dilution. Ingeneral the total count rate should be less than 20 000 countsper second to minimize biases.
