Implementation, validation, and analytical performance of high-accuracy minor isotope determination using modified total evaporation multi-collector TIMS for safeguards applications

Thedeterminationoftheuraniumisotoperatiosn(U$234)/n(U$238),n(U$235)/n(U$ 238),andn(U$236)/n(U$238)withhighaccuracyinnuclearsamplesisoneofthechallenges innuclearsafeguardsanalysis.Itisofparticularvalueintheidentificationandattributionof naturaluraniumsamplesincludingoresandyellowcakes.Forthatpurpose,themodifiedtotal evaporation(MTE)methodwasimplementedandvalidatedfortheanalysisofhigh$accuracy uranium isotope ratios at the IAEA Nuclear Material Laboratory (former SAL) in collaborationwiththeInstituteforReferenceMaterialsandMeasurements(IRMM)usinga ThermoFisherScientificTritonmulti$collectorthermalionizationmassspectrometer(TIMS). Theanalyticalperformance–accuracy,reproducibility,measurementuncertaintiesaccording toGUMprinciples,U$236limitofdetection,andsample throughput–oftheMTEmethod under routine operation is presented. It is compared with the performance of standard total evaporation(TE)aswellaswiththelimitsdictatedbytheInternationalTargetValues(ITVs). The limits of the analytical performance of the MTE method were probed by employing largersampleloadswithextendedmeasurementtimesandincreasedsignal$to$noiseratioand comparedtoresultsobtainedatotherlaboratoriesemployingcomparablemethodsforsimilar tasks. Finally,the MTE method wasapplied to quantify the rangeofvariationintheratios n(U$234)/n(U$238)andn(U$235)/n(U$238)andU$236abundanceinasetofnaturaluranium samples.