Isotopic composition of commercially available uranium chemicals and elemental analysis standards

Reference information on isotopic composition of various uranium materials, determined with high accuracy and precision, is of essential value for nuclear safeguards and nuclear forensics. In addition, an accurate knowledge of the isotopic composition is important when isotope-specific measurement techniques such as inductively-coupled plasma mass spectrometry (ICP-MS) are employed for elemental analysis. Isotopic composition of ten uranium chemicals and standards for elemental analysis, acquired from various commercial suppliers, was measured using thermal ionisation mass spectrometry in the modified total evaporation mode. Two of the chemicals analyzed are based on either natural uranium (NU) or ‘commercial NU’. The majority of the materials were found to contain uranium substantially depleted in 234U and 235U, with presence of 236U significantly above the range observed for NU. Model scenarios are suggested for a combination of uranium irradiation and enrichment processes which may have resulted in such compositions.