Preparation and certification of the uranium nitrate solution reference materials series IRMM-2019 to IRMM-2029 for the isotopic composition

The IRMM-2019-2029 series of uranium nitrate solutions was certified for the isotopic composition. The solutions were originally prepared for the certification of the IRMM-019-029 series of uranium hexafluoride (UF 6 ) materials in 2014, for which certification measurements were performed by thermal ionization mass spectrometry after conversion of UF 6 into uranyl nitrate solutions. Analyses were performed using the modified total evaporation method and for some materials with low 236 U abundances, the n ( 235 U)/ n ( 238 U) ratio was measured using a n ( 233 U)/ n ( 236 U) double spike. The integrity of the certified values after dilution and ampouling of the original solutions was checked through process control measurements.