Spatially-Resolved Analyses of Aerodynamic Fallout from a Uranium-Fueled Nuclear Test

Abstract Five silicate fallout glass spherules produced in a uranium-fueled, near-surface nuclear test were characterized by secondary ion mass spectrometry, electron probe microanalysis, autoradiography, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Several samples display compositional heterogeneity suggestive of incomplete mixing between major elements and natural U ( 238 U/ 235 U = 0.00725) and enriched U. Samples exhibit extreme spatial heterogeneity in U isotopic composition with 0.02  235 U/ 238 U  235 U/ 238 U  235 U/ 238 U ratio is correlated with changes in major element composition, suggesting the agglomeration of chemically and isotopically distinct molten precursors. Two samples are nearly homogenous with respect to major element and uranium isotopic composition, suggesting extensive mixing possibly due to experiencing higher temperatures or residing longer in the fireball. Linear correlations between 234 U/ 238 U, 235 U/ 238 U, and 236 U/ 238 U ratios are consistent with a two-component mixing model, which is used to illustrate the extent of mixing between natural and enriched U end members.