Precise measurement of uranium isotope ratios in Fukushima soils using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

Precise measurement of U-234/U-238 and U-235/U-238 isotope ratios was performed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in this study. The U-234 ions were measured using a Daly detector, the U-235 ions were measured using a Faraday cup with a 10(12) Omega resistor, and the U-238 ions were measured using a Faraday cup with the usual 10(11) Omega resistor. Chemical separation of uranium was carried out by three different methods using either combinations of anion exchange and UTEVA resins or UTEVA resin three times. Chromatography combining three UTEVA resin columns provided the highest recovery (%) of uranium and biggest improvement in precise measurements of uranium isotope ratios. The certificate reference material (CRM) JLk-1 was used as an in-house standard for the uranium isotope ratio measurements. The long-term reproducibility of the in-house standard was 0.60% for U-234/U-238 and 0.05% for U-235/U-238. The measured ratios were compared with the natural ratios, and the relative deviation obtained for uranium isotope ratios was less than 0.005% for U-234/U-238 and U-235/U-238. Finally, the present method was applied to measure uranium isotope ratios in Fukushima microwave-digested soil samples. (C) 2021 Elsevier B.V. All rights reserved.