抄録
Determination of the concentration and isotope ratios of uranium is required in environmental monitoring of nuclear contamination in nuclear safeguards. 238U, 235U and 234U are naturally occurring alpha-emitting long- lived radionuclides which are taken up daily at low levels with food and drinking. Natural isotopic composition of 235U/238U =0.00725. Therefore, isotope ratio measurements are important because they can provide information on the origin of uranium. Uranium, the heaviest naturally occurring element on earth, plays an important role in daily life because of its use in nuclear power plants. The isotope ratios of uranium, 234U/238U, 235U/238U and 236U/238U were measured by using a VG Sector 54 thermal ionization mass spectrometer (TIMS). Uranium isotopic compositions have been determined in soil samples as well as in some ground water samples 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 – 2.1 in case of soil samples. Similar variation was also observed for ground water samples. Enrichment of 235U was also noticeable for soil as well as ground water samples.
