Variation of half-life and internal-conversion electron energy spectrum between U235m oxide and fluoride

The nuclear half-life of U-235m has been reported to vary depending on the chemical environment. In this study, both the half-life and the internal-conversion (IC) electron energy spectrum were measured for U-235m with identical chemical environments for the first time. U-235m oxide and fluoride samples were subjected to these measurements, and clear differences in the half-life and the energy spectrum between these samples were observed. The peaks in the energy spectra were identified with a relativistic density functional theory calculation. The molecular orbital states of the U-235m oxide and fluoride, which were estimated from the energy spectra and the calculation, qualitatively explained the difference in the half-lives between the samples.