Xenon and krypton isotopic abundances in African pitchblende

The xenon and krypton isotopic abundances in a sample of African pitchblende have been measured mass-spectrometrically in a temperature-release experiment. The patterns observed indicate that approximately 5 percent of the fission xenon is due to fast neutron-induced fission of 238U, while neutron-induced fission of 235U contributes about 25 percent. Some of the individual temperature fractions show as much as 15 percent contribution from 238U neutron fission. All of the rare gas data fit into this three-component model. The bulk xenon/krypton ratio is lower for this experiment than has previously been reported for African pitchblende. Possible reasons for this discrepancy are discussed, as are the retention patterns of the heavy rare gases