Radioactive hot particles from the recent Chinese nuclear weapons tests

Abstract

Variations in the number of individual fallout particles in the ground-level air at Fayetteville (36°N, 94°W), Arkansas, were measured for a period of about seven months after the 13th (January 7, 1972) and the 14th (March 18, 1972) Chinese nuclear test explosions. The fallout from the 13th test was typical of a tropospheric injection of debris and the effect lasted only for about five weeks, but the fallout from the 14th test persisted for about five months until August 1972, indicating that the fresh debris entered the stratosphere. The diameters of the particles ranged from about 0.1 to 7 μm in diameter, but a single unusually large particle (34 μm in diameter) was found during the night of March 23, 1972. Radiochemical studies were made on this 34-μm particle, in which the fission products belonging to the ‘volatile’ mass chains 89, 90, 91, 140, and 141 were highly depleted. The formation interval Ξ of this particle was calculated from the extent to which the volatile fission decay chains were depleted. A value very close to Ξ = 0 (second) was obtained from the mass 91 chain, but no positive Ξ values could be calculated from mass 140 and 141 chains. This discrepancy was explained as being due to the difference in the melting points of the oxides, of the elements belonging to the fission product decay chains (e.g., Rb, Cs, Sr, and Ba).