The size distribution of radioactive atmospheric aerosols

Abstract

Atmospheric air containing natural and fission product radioactivity was passed successively through a series of filters of increasing retentivity for small particles. The size distribution of the radioactive particles in the atmosphere has been deduced from the relative amounts of radioactivity collected on the various filters and a knowledge of the retention characteristics of the filters as a function of particle size. This method has demonstrated that the short-lived radon daughter products (Pb214 and Bi214) are associated primarily with particles less than 0.3 μ in diameter, whereas fission products from the stratospheric source of old bomb debris on arrival at ground level are associated with particles averaging between 0.5 and 1.0 μ diameter. Large, apparently random, changes in size distribution often occur from one collection to another. Radiochemical analyses indicate little fractionation of one isotope relative to another except during late October and early November 1964, when the shorter-lived radioisotopes from the Chinese atomic test were found to be associated with the largest particles.