Андрей Кривицкий » Публикация

Аннотация Chemical shifts (ChSh) of nine emission lines of the uranium L-series in uranium oxides UO2+x (x=0-1) with respect to UO2 were studied by using a precise crystal-diffraction X-ray spectrometer. ChSh of Lα1,α2 uranium and thorium lines in solid solutions yUO2·(1-y )ThO2 (y=0:1) were measured with respect to UO2 and ThO2, respectively. The changes in energy of spin-orbital splitting (SOS) — Δδnl± of inner nl-orbitals of the uranium atom were calculated from the data of ChSh of spin-doublet lines. For UO2+x oxides, a linear decrease in Δδnl± values with increasing degree of uranium oxidation was found. Sign inversion of Δδnl± for uranium levels was found on passing to solid solutions. No change in the SOS energy of inner thorium levels was detected. The values of Δδnl± were found to correlate with the experimental values of the effective magnetic moment of uranium in oxides. On the basis of the comparison of experimental Δδnl± values with Dirac–Hartree–Fock atomic calculations, it was concluded that the observed variations in Δδnl± values are due to the redistribution of electron and spin density between the 5f7/2- and 5f5/2-levels of the fine structure of the uranium atom without changes in atomic charge state. On the basis of the hypothesis of intraatomic relativistic U5f7/2↔U5f5/2 transition, a model of paramagnetic moment formation on the uranium atom in uranium dioxide was proposed.