Results of measurements and analyses of nuclear fallout up to the beginning of 1965

Abstract

In consequence of the Moscow Agreement on the cessation of nuclear tests in the atmosphere there was a further decrease in the activity of dry fallout and rainout, as well as in ground level air, in 1964 (Table I). The daily activities decreased in order to tenths of mc/km².From April to August an increase in the activity was again seen, which was caused by the fall of radioactive dust from the stratosphere to the troposphere in consequence of meteorological factors. Seasonal variation was not so pronounced in 1964 as in the previous year, when the activity increased in May and June 6 to 7 times that of February and March. In 1964 the activity increased approximately 3 times. The conception of the existence of a stratospheric reservoir of artificial radioactivity, formed as a result of nuclear tests, was thus confirmed once again and so was the existence of a certain residence time of radioactive dust in the stratosphere because in 1963 nuclear explosions were no longer performed. The mean residence time was calculated from the decrease of strontium 90, separated by radiochemical analysis. The mean value of the residence time is 1.6 of a year, which indicates a reservoir in the higher stratosphere.