Certification of uranium hexafluoride reference materials for isotopic composition

The IRMM-019 to IRMM-029 series of uranium hexafluoride materials is certified for the isotopic composition. After conversion into uranyl nitrate solution, certification and homogeneity measurements were performed by thermal ionization mass spectrometry. Analyses were performed by Modified Total Evaporation and for some materials the major isotope amount ratio n(235U)/n(238U) was measured using a n(233U)/n(236U) double spike. Measurements were confirmed by UF6 gas source mass spectrometry. Major isotope amount ratios were certified with relative expanded uncertainties (k = 2) of 0.015–0.030 % and the minor isotope amount ratios n(234U)/n(238U) and n(236U)/n(238U) were certified with relative expanded uncertainties of 0.02–3 %.