Abstract
This paper provides a complete set of data on the monthly fall rate of tritium (HTO) in precipitation at the Meteorological Research Institute (Tokyo and Tsukuba) from August 1963 to December 1980. The concentration of tritium ranged from 5500 pCi/dm3 in March 1964 to 5 pCi/dm3 in November 1979. The highest frequency of appearance of the maximum and the minimum is seen June and November, respectively.
The trend of gradual decrease from 1963 to 1967, which gives the apparent residence time of tritium (23 months), has been disturbed by the series of Chinese thermonuclear tests.
The amount of tritium produced by the 1961-1962 testing is estimated to be 1900 MCi based on the cumulative amount of tritium and 90Sr in Tokyo and the ratio of the deposition between the two nuclides in Tokyo and the Northern Hemisphere.
