Abstract
The monthly fall rate of 239+240Pu in Tokyo and Tsukuba Science City during January 1974 through December 1980 is given. The cumulative amount of plutonium fallout in Tokyo from the beginning of nuclear detonations to the end of 1980 is estimated to be about 1.2 mCi/km2. The ratio of 239+240Pu to 90Sr deposition during the same period was about 1.6%. Samples collected at Akita, the Japan Sea side of Honshu Island, Japan, during 1963 to 1964 indicate that the fall rate of plutonium isotopes is about 2 times higher than that in Tokyo. After the removal of our Institution to Tsukuba Science City, about 60 km north of Tokyo, the sampling and analysis of plutonium isotopes were continued and it was confirmed that the amount of plutonium deposition in both cities are in good agreement with each other.
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