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

Abstract

Precise measurement of 234U/238U and 235U/238U isotope ratios was performed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in this study. The 234U ions were measured using a Daly detector, the 235U ions were measured using a Faraday cup with a 1012 Ω resistor, and the 238U ions were measured using a Faraday cup with the usual 1011 Ω 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 234U/238U and 0.05% for 235U/238U. The measured ratios were compared with the natural ratios, and the relative deviation obtained for uranium isotope ratios was less than 0.005% for 234U/238U and 235U/238U. Finally, the present method was applied to measure uranium isotope ratios in Fukushima microwave-digested soil samples.