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

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The isotopic activity ratios of ^<103>Ru to ^<106>Ru and ^<141>Ce to ^<144>Ce 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 Murayama, was applied to estimate the contributions of the ^<106>Ru and ^<144>Ce produced by a new explosion to the total depositions of these nuclides from the measured activity ratios of ^<103>Ru to ^<106>Ru and ^<141>Ce to ^<144>Ce. The contributions thus estimated ranged from zero to nearly 100 percent, depending on various factors. Informations on the time interval between the injection of nuclear debris into the atmosphere and their appearance on the earth surface would be useful for understanding the movement and mixing of the atmosphere. Moreover, informations of the contribution of fresh nuclear debris to the total deposition would be useful for the same purpose. In the present study it was attempted to obtain such informations by observing the variation with time of the activity ratios of ^<103>Ru to ^<106>Ru and ^<141>Ce to ^<144>Ce in rain water.
日本放射線影響学会の論文