Abstract
The monthly fall rates of p lutonium 239 and 238 in Tokyo during the period from Jan.1967 to the end of 1973 are given. The cumulative amounts of plutonium fallout in Tokyo from the beginning of nuclear explosion to the end of 1973 are estimated to be 1.2 mCi/km2 and 55 ACi/km2 respectively for 239 and 238. Owing to the accidental release of 238 due to a satellite failure, ratio of 238 to 239 increased abruptly in 1967 from 1.8% in 1966 to 16% in 1967. The maximum value of the ratio,31%, was observed in 1970, and then the value decreased gradually to 6.3% in 1973. The ratio of 239 to Sr-90during the period of 1968 to 1973, in which the Chinese bomb tests prevailed, was about 1%, which was lower than the former value of 1,6% in the tests conducted by the USA and the USSR. The total amounts of deposition in the northern hemisphere of 239 and 238were calculated to be about 200 kCi and 9 kCi respectively. In 9 kCi of 238,2 kCi was of satellite origin.
