Resonant Inelastic Soft X-Ray Scattering Spectroscopy of Light-Actinide Materials

Abstract

Resonant inelastic X-ray scattering (RIXS) measurements at the actinide 5d threshold provide an opportunity to study elementary excitations in actinide systems in detail. It has turned out that the technique is very sensitive to the valency and the chemical state of actinide in contrast to X-ray absorption spectroscopy, being hampered by the substantial smearing of spectral structures due to a large core-hole lifetime broadening. In this situation, the virtually unlimited resolution (defined by the response function of the instrument) of the RIXS technique and its ability to enhance transitions to low-lying excited states are especially useful. RIXS spectroscopy provides good signatures in terms of new distinct transitions, representing electronic excitations within the 5f shell and having a characteristic profile. This helps to distinguish between actinide species with different oxidation states, especially in the case when one of the species has a much lower concentration than another. Experimental data for systems of light actinides, such as U, Np, and Pu, are presented and discussed along with the results of model calculations.