Results of atmospheric radioactivity observations in 1985

This report is aimed at showning observations of atmospheric and sea water radioactivities made by Japan Meteorological Agency in 1985. Samples are collected at various sampling sites all over Japan. Radioactivity measurements are made at each land station and Marine Observatory. Collected samples are sent regularly to Geological Laboratory of Meteorological Research Institute of JMA in Tsukuba for identification and measurement of specified species. Measurements made are as follows. 1) Precipitation collected every 24 hours are dried and subjected to gross beta radioactivity measurement by an end-window type Geiger-Muller tube counter. 2) Air-borne dust is collected once a week on a filter paper, which is reduced to ashes and subjected to gross beta radioactivity measurement. 3) All the samples used in 2) are analyzed to determine the monthly mean 90Sr concentration in air-born dust. 4) Sea water is collected twice a year, in winter and summer, by research ships, and subjected to gross beta radioactivity measurement. 5) Precipitation and dry fallout are collected once a month. Radiochemical analysis is carried out at Meteorological Research Institute to determine the deposition of 90Sr and 137Cs. 6) Natural background radioactivity in atmosphere, in terms of gamma radiation rating, is observed for each hour to determine the daily mean, daily maximum and daily minimum values. 7) Observations are made of vertical distribution of radioactivity in free atmosphere. (Nogami, K.)