Isotopic Ratios of Radioruthenium and Radiocerium in Rain Water at Osaka in Relation to Nuclear Explosions during the Period of Late 1969 to 1972

The isotopic activity ratios of 103Ru to 106Ru and 141Ce to 144Ce in rain water were studied during the period from the end of 1969 to August, 1972. The ratios demonstrated many peaks during the observation period, each of which was likely to resulted from settlement of stratospheric or tropospheric nuclear debris produced by nuclear explosions during the same period. The method to distinguish fresh nuclear debris from old debris on the basis of measured radiostrontium activity ratios, developed by Telegadas and Murayama10), was applied to estimate the contributions of the 106Ru and 144Ce produced by a new explosion to the total depositions of these nuclides from the measured activity ratios of 103Ru to 106Ru and 141Ce to 144Ce. The contributions thus estimated ranged from zero to nearly 100 percent, depending on various factors.