Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure

The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am LIII in neptunium dioxide (NpO2) and americium dioxide (AmO2) with CaF2-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO2 than for NpO2 because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms.

► Np LIII XANES of NpO2 and Am LIII XANES of AmO2 are theoretically examined. ► The core-effect in the measuremernt of these spectra was evaluated in detail. ► Core-hole screening by O p is more remarkable in AmO2 than in NpO2. ► Charge density analysis clarifies the peak creation mechanism of these spectra.