Recent deposition of Sr-90 and Cs-137 observed in Tsukuba

Recent observations of Sr-90 and Cs-137 deposition at the Meteorological Research Institute, Tsukuba, are presented. The annual deposition of Sr-90 and Cs-137 in the 1990s was around 0.15 and 0.3 Bq m(-2), respectively. Although a spring peak was found in the deposition, it is difficult to explain this seasonal pattern only by the stratospheric fallout. The annual deposition trend of Cs-137 was found to be well fitted by the stratospheric constant and an additional constant term. The variation in the ratios of the radio-activity and corresponding stable elements did not show the maxima in the deposition peak months in spring. It was concluded that most of Sr-90 and Cs-137 deposited recently are the resuspended soil origin. The activity ratio (Cs-137/Sr-90) suggested that plural soul ces are present for resuspended radioactivity in Japan.