Annual fallout of ³²Si,²¹⁰Pb,²²Na,³⁵S and ⁷Be in rains in India

Abstract

The concentration of radioisotopes ⁷Be, ³⁵S were measured in Bombay since 1956 and ²²Na, ²¹⁰Pb, ³²Si since 1963. In Khandala and other stations such measurements have been made at irregular periods since 1961. In addition several measurements especially that of ³²Si were made in 1970. Data available todate from Indian stations is summarised and critically analysed. We conclude that appreciable amounts of ³⁵S, ²²Na and ³²Si, over and above their production by cosmic rays, were produced during the high yield Russian tests as evidenced by their fallout between 1962-66. Based on the bomb produced excess the half period for their removal from the stratosphere is deduced to be less than 1 year. The 'excess' contribution of ³²Si due to bombs is, however, small; about 1% of its inventory in the oceans. The present study shows that for stations where orogeny is the principal mechanism of precipitation, the annual fallout is independent of the annual rainfall.