Designation: C1871 − 18Standard Test Method forDetermination of Uranium Isotopic Composition by theDouble Spike Method Using a Thermal Ionization MassSpectrometer1This standard is issued under the fixed designation C1871; the number immediately following the designation indicates the year oforiginal adoption or, in 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 describes the determination of theisotope amount ratios of uranium material as nitrate solutionsby the double spike (DS) method using a thermal ionizationmass spectrometer (TIMS) instrument.1.2 The analytical performance in the determination of the235U/238U major isotope amount ratio by the DS method is fiveto ten times better in terms of the internal and externalreproducibility compared to the (“classical”) total evaporation(TE) method as described in Test Method C1672 and the“modified total evaporation” (MTE) as described in TestMethod C1832. This is due to the use of an internal rather thanexternal mass fractionation correction by using a double spikematerial with a known or certified233U/236U isotope ratio,which is mixed with the sample prior to the measurement,either during the sample preparation or directly on the TIMSfilament.1.3 The DS method cannot be applied for the determinationof the236U/238U minor isotope amount ratio, and is also notrecommended for the determination of the234U/238U minorisotope amount ratio.1.4 In case the uranium amount concentration of the doublespike is known or certified, the uranium amount concentrationof the sample can be determined using the isotope dilutionmass spectrometry (IDMS) method as described in TestMethod C1672, by blending the sample gravimetrically withthe double spike and performing a DS measurement.1.5 An external mass fractionation correction by measure-ments of a certified reference material loaded on differentfilaments and measured in the same measurement sequence, asrecommended for TE and required for MTE measurements, isnot necessary for the DS method. However, for quality control(QC) purposes it is recommended to perform DS measure-ments of low enriched or natural uranium isotopic referencematerials on a regular basis.1.6 The DS method can only be applied to uranium sampleswith relative isotope abundances233U/U and236U/U below10–5, the DS method is therefore mainly used for low enrichedor close to natural uranium samples.1.7 Units—The values stated in SI units are to be regardedas the standard. When no SI units are provided, the values arefor information only.1.8 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, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.9 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C753 Specification for Nuclear-Grade, Sinterable UraniumDioxide PowderC776 Specification for Sintered Uranium Dioxide Pellets forLight Water ReactorsC787 Specification for Uranium Hexafluoride for Enrich-mentC833 Specification for Sintered (Uranium-Plutonium) Diox-ide Pellets for Light Water ReactorsC859 Terminology Relating to Nuclear MaterialsC967 Specification for Uranium Ore ConcentrateC996 Specification for Uranium Hexafluoride Enriched toLess Than 5 %235U1This 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 Feb. 1, 2018. Published February 2018. DOI: 10.1520/C1871-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1C1008 Specification for Sintered (Uranium-Plutonium)DioxidePellets—Fast Reactor Fuel (Withdrawn 2014)3C1068 Guide for Qualification of Measurement Methods bya Laboratory Within the Nuclear IndustryC1128 Guide for Preparation of Working Reference Materi-als for Use in Analysis of Nuclear Fuel Cycle MaterialsC1156 Guide for Establishing Calibration for a Measure-ment Method Used to Analyze Nuclear Fuel Cycle Mate-rialsC1347 Practice for Preparation and Dissolution of UraniumMaterials for AnalysisC1411 Practice for The Ion Exchange Separation of Ura-nium and Plutonium Prior to Isotopic AnalysisC1672 Test Method for Determination of Uranium or Pluto-nium Isotopic Composition or Concentration by the TotalEvaporation Method Using a Thermal Ionization MassSpectrometerC1832 Test Method for Determination of Uranium IsotopicComposition by the Modified Total Evaporation (MTE)Method Using a Thermal Ionization Mass SpectrometerD1193 Specification for Reagent WaterE2586 Practice for Calculating and Using Basic StatisticsE2655 Guide for Reporting Uncertainty of Test Results andUse of the Term Measurement Uncertainty in ASTM TestMethods3. Terminology3.1 Terminology C859 contains terms, definitions, descrip-tions of terms, nomenclature, and explanations of acronymsand symbols specifically associated with standards under thejurisdiction of Committee C26 on Nuclear Fuel Cycle.3.2 Definitions:3.2.1 abundance sensitivity, n—in isotope amount ratiomeasurements, the ratio of the measured intensity of an ionbeam at a mass, m, to the measured intensity from the sameisotope measured at one mass unit difference (for example, m6 1).3.2.1.1 Discussion—Abundance sensitivity is a measure ofthe magnitude of the peak tailing correction. For measuringuranium on thermal ionization mass spectrometer (TIMS) andinductively coupled plasma mass spectrometry (ICP-MS)instruments, the abundance sensitivity is typically calculated asthe ratio of the measured signal intensities at masses 237 and238 using a suitable uranium sample.3.2.2 modified total evaporation, MTE, n—analyticalmethod for determination of isotope amount ratios of uranium,as described in Test Method C1832.3.2.3 total evaporation, TE, n—analytical method for deter-mination of isotope amount ratios of uranium or plutonium, asdescribed in Test Method C1672, also called “classical” totalevaporation in this test method.3.2.4 turret, n—holder for sample filaments.3.2.4.1 Discussion—Alternate names for turret are carousel,magazine, and wheel.3.3 Acronyms:3.3.1 CRM—certified reference material3.3.2 DS—double spike3.3.3 DU—depleted uranium3.3.4 EU—European Union3.3.5 FAR—Faraday Cup3.3.6 HEU—high enriched uranium3.3.7 IAEA—International Atomic Energy Agency3.3.8 ICPMS—inductively coupled mass spectrometry3.3.9 IRMM—Institute for Reference Materials and Mea-surements (since 1 July 2016 called JRC-Geel, the only unitworking with nuclear materials at JRC-Geel is JRC-G.2)3.3.10 ITU—Institute for Transuranium Elements (since 1July 2016 called JRC-Karlsruhe, the only unit involved withthermal ionization mass spectrometry measurements of nuclearmaterials at JRC-Karlsruhe is JRC-G.II.6)3.3.11 JRC—Joint Research Centre3.3.12 LEU—low enriched uranium3.3.13 MTE—modified total evaporation3.3.14 NBL—New Brunswick Laboratory (since 15 May2016 called NBL-Program Office)3.3.15 NML—Nuclear Material Laboratory (part of theIAEA)3.3.16 QC—quality control3.3.17 RSD—relative standard deviation—SD (see below)divided by the mean value of the observations in repeatedsampling.3.3.18 RSE—relative standard error—SE (see below) di-vided by the mean value of the observations in repeatedsampling.3.3.19 SD—standard deviation—according to PracticeE2586, 3.1.30: The square root of the sum of the squareddeviations of the observed values in the sample divided by thesample size minus 1.3.3.20 SE—standard error—according to Practice E2586,3.1.29: Standard deviation of the population of values of asample statistic (that is, the mean value) in repeatedmeasurements, or an estimate of it.3.3.20.1 Discussion—According to Practice E2586, 3.1.30:If the standard error (SE, see above) of a statistic is estimated,it will itself be a statistic with some variance that depends onthe sample size, that is, the number of observed values in thesample (Practice E2586, 3.1.26).3.3.20.2 Discussion—According to Practice E2655, 5.8.4.1:From statistical theory, a 95 % confidence interval for the meanof a normal distribution, given n independent observations x1,x2, ., xndrawn from the distribution, is x¯ 6 t×SD/√n, wherex¯ is the sample mean, SD is the standard deviation of theobservations (see above), and t is the 0.975 percentile of theStudent’s t distribution with n-1 degrees of freedom. BecauseStudent’s t distribution approaches the normal as n increases,the value of t approaches 1.96 as n increases. This is the basisfor using the (coverage) factor 2 for expanded uncertainty. The3The last approved version of this historical standard is referenced onwww.astm.org.C1871 − 182standard error (SE) of the mean value of a series of nindependent repeated measurements can be derived from thatby usingt=1,sothestandard error (SE) is given by SD / √n.3.3.21 TIMS—thermal ionization mass spectrometry3.3.22 WRM—working reference material4. Summary of Test Method4.1 The double spike method has been developed with theintention to improve the precision and decrease the uncertain-ties for235U/238U major isotope ratio measurements comparedto the known methods such as the “classical” total evaporationtechnique (1-4),4also described in Test Method C1672, and themodified total evaporation technique (5 and 6), also describedin Test Method C1832. For the double spike method the massfractionation correction for the235U/238U ratio is performedinternally throughout the measurement rather than externally,by using the mass fractionation observed for a double spikematerial with a known or certified233U/236U isotope ratio (alsospanning three mass units), which is mixed with the sampleprior to the measurement, either during the sample preparationor directly on the TIMS filament. If necessary, uranium isseparated from plutonium and other elements (to eliminateisobaric interferences) by selective extraction, anion exchange(see Practice C1411), or extraction chromatography. The puri-fied uranium fraction as nitrate solution is loaded onto anevaporation filament (made of metals such as rhenium, zone-refined rhenium, or tungsten with high evaporationtemperature), and blended with an appropriate amount ofdouble spike solution, and converted to an oxide by controlledheating of the filament under atmospheric conditions. In caseonly the235U/238U ratio of the sample has to be determined, itis recommended to mix the sample with the double spikeduring the loading process on the filament. In case the uraniumamount concentration of the sample has to be determined, thesample solution has to be blended gravimetrically with thedouble spike solution prior to filament loading, for whichweighable amounts have to be used.4.2 The sample amount to be loaded for DS analyses iswithin a range of about 4 to 6 µg to achieve ion beam signalsof about 20 to 30 V for the major isotope238U for DU, NU, andLEU samples.4.3 The235U/238U isotope amount ratios are corrected formass fractionation for each integration step individually. Thisis accomplished in an internal manner, the magnitude of themass fractionation is calculated from the measured massfractionation of the233U/236U ratio. The peak tailing contribu-tions are determined at two mass positions, 0.5 mass unitsbelow and 0.5 mass units above the isotope masses of interest.4.4 For the correction of isobaric interferences, a separatemeasurement of the isotopic composition of the (unspiked)sample is required, unless this information is already available.This measurement can be performed using the TE or MTEmethods (Test Methods C1672 and C1832, respectively).5. Significance and Use5.1 Uranium material is used as a fuel in certain types ofnuclear reactors. To be suitable for use as nuclear fuel, thestarting material shall meet certain specifications such as thosedescribed in Specifications C753, C776, C787, C833, C967,C996, and C1008, or as specified by the purchaser. The235U/238U isotope amount ratios and the amount content ofuranium material can be measured by mass spectrometryfollowing this test method to ensure that they meet thespecification.5.2 The double spike method has been used for studies ofuranium fractionation effects in isotope geochemistry andcosmochemistry, for uranium source attribution in nuclearforensics and for investigation of conversion or samplingprocesses in nuclear industry and nuclear safeguards (7-11).Most recently, the double spike method has been used for thevalidation of the Cristallini sampling method of UF6(12 and13). The double spike method can be used for a wide range ofsample sizes even in samples containing as low as 50 µg ofuranium. The concentration of the loading solution for the DSmethod has to be in the range of 1 to 6 mg/g to allow a sampleloading of 4 to 6 µg of uranium. A minimum loading of 4 µguranium per filament is recommended.5.3 The measurement of236U/238U ratios using this methodis not possible due to the large isobaric interference from the236U ion beam of the double spike onto the236U ion beam fromthe sample (50.000 times for close to natural material, forexample, like IRMM-184).5.4 The application of the double spike method for mea-surements of235U/238U ratio is limited by the isobaric inter-ference between the236U from the double spike material andthe236U contained in the sample. As a consequence, themethod is not suitable for samples which contain significantamounts of236U due to prior neutron capture from235Uinthepredecessor materials. For samples with236U/238U ratioshigher than about 10–6, the double spike method should beapplied with care for the isobaric correction.5.5 The measurement of234U/238U ratios using this methodis very limited in the analytical performance due to the isobaricinterference of the234U from the double spike with the234Ufrom the sample (range from 5 to 15 %). The correctionalgorithms are presented in 14.3, but statements for prec