Isotopic composition of Uranium in soil and ground water samples collected around 30 km Chernobyl Exclusion Zone

¹ National Institute of Radiological Sciences, Research Centre for Radiation Protection, 4-9-1 Anagawa, Inage-ku, 263-8555 Chiba, Japan
² Research Centre for Radiation Medicine, 53 Melnikova, 252050 Kiev, Ukraine

Corresponding author: sahoo@nirs.go.jp

Abstract

Precise and accurate measurement of uranium isotope ratio is essential in environmental monitoring of any contamination in nuclear safeguards. ²³⁴U, ²³⁵U and ²³⁸U are naturally occurring alpha-emitting long-lived radionuclides, which are taken up daily at low levels with food and drinking. IUPAC has established natural isotopic composition of ²³⁵U/²³⁸U to be 0.00725. Therefore, isotope ratio measurements are important to provide information on the origin of uranium. The isotope ratios of uranium, ²³⁴U/²³⁸U, ²³⁵U/²³⁸U and ²³⁶U/²³⁸U were measured using a VG Sector 54 thermal ionization mass spectrometer (TIMS) as well as high resolution inductively coupled plasma mass spectrometry (ICP-MS) in soil samples as well as in some water samples collected in the exclusion zone of Chernobyl nuclear power plant. The isotopic composition of Chernobyl soil samples showed significant deviation from the natural uranium and presence of ²³⁶U is quite noticeable. The ²³⁴U/²³⁸U activity ratio varies in the range 1.06 to 2.1 and 1.42 to 5.75 for soil and water samples, respectively. Enrichment of ²³⁵U was also noticeable for soil as well as ground water samples.