Determination of uranium isotopic composition and U-236 content of soil samples and hot particles using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (N-PP) the environment was contaminated with spent nuclear fuel. The U-236 isotope wa s used in this study to monitor the spent uranium from nuclear fallout in s oil samples collected in the vicinity of the Chernobyl NPP. Nuclear track r adiography was applied for the identification and extraction of hot radioac tive particles from soil samples. A rapid and sensitive analytical procedur e was developed for uranium isotopic ratio measurement in environmental sam ples based on double-focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) with a MicroMist nebulizer and a direct injection high-efficien cy nebulizer (DIHEN). The performance of the DF-ICP-MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4x 10(-4) and 10(-3) counts per atom were achieved for U-238 in DF-ICP-QMS wit h the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2x10(-4) and 1.4x10(-4), respectively. T he precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 mug L-1 NBS U-020 standard solution was 0.11% (U-238/U-235) and 1.4% ( U-236/U-238) using a MicroMist nebulizer and 0.25% (U-235/U-238) and 1.9% ( U-236/U-238) using a DIHEN. The isotopic composition of all investigated Ch ernobyl soil samples differed from those of natural uranium; i.e. in these samples the U-236/U-238 ratio ranged from 10(-5) to 10(-3). Results obtaine d with ICP-MS, alpha- and gamma -spectrometry showed differences in the mig ration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil sam ples.