On the natural radioactivity in the air

Abstract

The concentrations of the various radioactive decay products of radium in the air have been determined by observing the beta activity (1) of pieces of filter paper through which air has been passed, and (2) of chemically separated isotopes obtained from such filter papers. The relative amounts of long-lived and short-lived products found indicate that, besides the radioactive decay of the substances, some other process which removes radioactive particles from the air is active. The mean life of the particles with respect to this removing process is found to be about 10 days. The hypothesis that this process is the capture of the radioactive particles by rain droplets (clouds) is consistent with measurements made of the radioactive content of rain-water. On the other hand, the removal of the ionized radioactive particles by the electric field of the earth leads to a much smaller effect.