Specific activity of nuclear debris from ground surface bursts as a function of particle size

Cloud samples from five coral surface bursts and one silicate surface burst were subjected to a size separation by means of a density gradient column. The fractions were analyzed for 90Sr, 147Pm, and uranium. One sample was also analyzed for 137Cs and 144Ce. Fraction weights were obtained by direct weighing or by matrix element analysis. Mean diameters of the particles in the size fractions were determined from size distribution measurements by optical and electron microscopy. The specific activities are varying functions of the radioactive species. No systematic differences between the behavior of 147Pm and 90Sr are apparent as a function of yield. Uranium behaves almost identically to 90Sr. There is evidence of a strong decrease in the specific activity at particle sizes above 60μ.