Measurement of uranium isotope ratios in Fukushima-accident contaminated soil samples using multi collector inductively coupled plasma mass spectrometry

In the present study, Cs-137 and U-238 activity concentrations, U-234/U-238 activity ratio, and U-235/U-238 isotope ratio were measured in fifteen soil samples collected from the exclusion zone around the Fukushima Daiichi Nuclear Power Station (FDNPS). The Cs-137 activity concentrations of Fukushima-accident contaminated soil samples ranged from 29.9 to 4780 kBq kg(-1) with a mean of 2007 kBq kg(-1). On the other hand, the U-238 activity concentrations of these soil samples ranged from 5.2 to 22.4 Bq kg(-1) with a mean of 13.2 Bq kg(-1). The activity ratios of U-234/U-238 ranged from 0.973 to 1.023. The U-235/U-238 isotope ratios of these exclusion zone soil samples varied from 0.007246 to 0.007260, and they were similar to the natural terrestrial ratio confirming the natural origin. Using isotope dilution technique, the U-235/Cs-137 activity ratio was theoretically estimated for highly Cs-137 contaminated soil samples from Fukushima exclusion zone ranged from 5.01 x 10(-8) - 6.16 x 10(-7) with a mean value of 2.51 x 10(-7).

Automated summary

The study revealed elevated Cs-137 activity concentrations and lower U-238 activity concentrations in Fukushima-contaminated soil. The activity ratios of U-234/U-238 and U-235/U-238 were found to be similar to natural terrestrial ratios, confirming their natural origin. The U-235/Cs-137 activity ratio was estimated using isotope dilution technique for highly Cs-137 contaminated soil samples from the Fukushima exclusion zone.