Observed Fractionation in Ground Level Fallout from Three Nuclear Cratering Detonations

Abstract

Abstract : Data relating to radionuclide deposition (fallout) within a few miles of the Danny Boy, Sedan, and Palanquin nuclear cratering shots are examined for evidence of fractionation - i.e. , differences in relative proportions of fission products in debris samples as compared with the relative proportions originally formed. A fractionation index is computed for several fission-product mass chains produced in each event. This index is particularly useful because it is independent of the total yield and fission yield of the detonation and also of the total amount of radioactive material deposited in the early fallout pattern. By comparing these indices with one another, one can determine whether fractionation occurred and obtain a quantitative estimate of its degree. For the three events studied here, only Danny Boy showed unambiguous evidence of fractionation in the early fallout, and the degree of fractionation was small. In Danny Boy there was only a factor of four difference between most enriched and most depleted species, as compared with the factors of several hundred that have been observed in many late time samples of airborne debris. If this small amount of fractionation proves to be true in general for crate ring shots, then predictions of early-fallout gamma radiation patterns will be greatly simplified.