ABSOLUTE YIELDS OF THE XENON AND KRYPTON ISOTOPES IN U238 SPONTANEOUS FISSION

Abstract

The absolute abundances of the isotopes of fission-product xenon and krypton in six uranium minerals have been determined mass spectrometrically using the isotope dilution technique. The fission products were resolved into a U238 spontaneous fission component, a U235 neutron-induced fission component, and a U238 neutron-induced fission component. Internal consistency in the analysis was achieved only when the Xe129 yield used for the U235 thermal neutron fission component was 20% lower than that reported by Purkayastha and Martin at I129. This discrepancy in the mass 129 chain yield measured at I129 and at Xe129 has not been resolved.Only one of the six minerals, Cinch Lake pitchblende, retained essentially all of its fission product inert gases throughout geological time. Inert gas losses from the remaining five minerals ranged from 20% to 75%. The absolute yields of the stable xenon and krypton fission products in U238 spontaneous fission were determined from an analysis of the inert gases from the Cinch Lake mineral. This analysis showed that 95.9% of the fission gas in this case resulted from the spontaneous fission and only 4.1% from neutron-induced fission.