Uranium and Plutonium Isotope Ratio Measurement as a Tool for Environmental Monitoring - Experiences in Osaka, Gifu and Hiroshima, Japan

We measured U-234/U-238, U-235/U-238 and Pu-239/240 isotope ratios in soil samples from Osaka, Gifu, and Hiroshima, Japan by inductively coupled plasma – quadrupole mass spectrometry. Deviation in U-235/U-238 isotope ratio from natural ratio was not found in soil collected three days after A-bomb detonation in Hiroshima, where approximately 50 kg of U-235 should have been discharged. U-234/U-238 ratio variation in soil that was dependent on the soil particle size and soil digestion procedure was found. Variation in Pu-240/Pu-239 ratio due to incomplete dissolution of soil samples was found in soil from Osaka. The results indicated the necessity of further investigation on natural variation of U isotope ratios in Japanese environment, and selection of sample processing technique depending on sample characteristics in order to obtain accurate isotope ratio.