Transport and fallout of stratospheric radioactive debris

Abstract

The average stratospheric residence half-time of particulate radioactive debris, as represented by strontium-90 and manganese-54, was approximately 10 months during the two years following the last atmospheric tests of high yield nuclear weapons. During this interval, the carbon-14 which was produced artificially by nuclear weapons tests showed a stratospheric residence half-time which increased with time, but averaged about 18 months. It is suggested that the stratospheric residence half-time of particulate debris did not increase significantly during 1963 until early 1965 because in the upper stratosphere, above 20 km, the rate of particle settling of the debris exceeded the rate of upward diffusion, and as a result, this debris remained highly concentrated in the lower stratosphere throughout this period. It is also suggested that the relatively more rapid meridional movement of particulate debris, compared to the movement of carbon-14, into the stratosphere of the Southern Hemisphere during the second half of 1963 resulted to some extent from the partial separation of the particulate debris from the carbon-14 in the equatorial stratosphere as a result of particle settling.DOI: 10.1111/j.2153-3490.1966.tb00243.x