Radionuclide Distribution in the Particle Population Produced by the Schooner Cratering Detonation

The radionuclide distribution in the Schooner event can be understood in terms of a three-stage condensation process which produces two distinct particle classes, each having a uniform isotopic composition. One class of particles results from the breakup of the molten cavity liner and carries that fraction of each radionuclide that was condensed in the molten liner at vent time. The other class of particles is produced by the crushing action of the shock wave on the overburden material. This class of particles carries as a surface deposit that fraction of each radionuclide that was in the vapor state at vent time. The vapor/condensed state partitioning may be interpreted as a two-phase equilibrium in which the equilibrium constant is given by Henry’s Law. The distributions with particle size of the individual radionuclides in the whole particle population are expressed as linear combinations of two log-normal distribution functions which correspond to the two particle classes. For a given radionuclide and a particular particle size, the fraction that appears in the main cloud (and base surge) decreases exponentially as the square of particle diameter increases. Transport and deposition of airborne radioactive particulates for many hours after detonation is described in terms of Stokesian fall rates and horizontal diffusion.