On the production of radioisotopes in the atmosphere by cosmic radiation and their application to meteorology

Abstract

Cosmic radiation produces, in the atmosphere, various radioisotopes which are efficiently collected during the condensation of moisture and can be detected in rain-water. The production rates of various radioisotopes, mainly those whose half-lives make them suitable for studying meteorological phenomena, have been calculated for all parts of the atmosphere, and are presented in graphical form. For the isotope, ¹⁰Be, whose half-life is long compared to the characteristic time of mixing between the stratosphere and the troposphere, the fall-out rate agrees with the calculated production rate. For the isotopes, ⁷Be, ³³P, and ³²P, whose half-lives are short compared to the characteristic time of mixing between the stratosphere and the troposphere, the measured fall-out rates agree with the calculations, provided one assumes that, 1. (a) only the activity produced in the troposphere appears in rain-water and contributions from air irradiated in the stratosphere are comparatively rare, 2. (b) the mean period, between successive removals of radioisotopes from air masses, is about 1 month. Tentative measurements on the fall-out of ³⁵S activity indicate an appreciably higher rate than calculated. It is shown that the relative concentrations of any two radioisotopes with appreciably different half-lives, in a particular rain, do not depend on the local meteorological conditions, but only on the latitude and altitude at which the air mass was irradiated and can therefore be used as labels to trace the history of air-masses. The study of such isotope ratios in individual precipitations can, therefore, lead to useful meteorological information.