On the natural radioactivity of rainfall

Abstract

Measurements by the authors of the natural radioactivity of rain water are reported. The radioactivity varied from one to 60 millimicrocuries per liter of rain water and was due primarily to RaB+C, The activities due to ThB and RaD were less than 10−10 and 10−11 curie per liter each, respectively. RaA is present in rain water at the time it reaches the Earth's surface. The mechanism for the accumulation of decay products in rain water is discussed. The total activity (per unit area and time) increases toward the limiting value determined by the supply of RaA from Rn. An average atmospheric Rn concentration within the cloud system of approximately 0.2×10−13 curie per liter is sufficient to supply the rain water with the observed radioactivity. The natural radioactivity of the atmosphere can be used as a tracer to study meteorological phenomena.