Invisible structures in the X-ray absorption spectra of actinides

Abstract

The X-ray absorption spectra of actinides are discussed with an emphasis on the fundamental effects that influence their spectral shape, including atomic multiplet theory, charge transfer theory and crystal field theory. Many actinide spectra consist of a single peak and it is shown that the use of resonant inelastic X-ray emission spectra (RIXS) has the potential to reveal many new features in the X-ray absorption spectra of actinides. The new range of RIXS beamlines will allow the determination of new structures in the X-ray absorption spectra that have been hitherto invisible. This has the potential to become an important tool in the determination of the electronic structure of actinides.

Uranium speciation in weathered granitic waste rock piles: an XAFS investigation

“…However, it was noted that this technique is complimentary and must be coupled with ab initio quantum chemical calculations. [53][54][55] In the present work, the observed wide distribution of axial and equatorial U-O distance in all the samples indicates the presence of disorder in the heterogeneous soil mixture. Even in the samples displaying similar Uspeciation a wide range of U-O distances occurs.…”

High temperature singlet-based magnetism from Hund’s rule correlations

“…Density functional theory suggests that the charge and spin density on uranium are significantly modified by itinerancy effects [14,15] (see also Supplementary Note 1), as we will discuss in the analysis below, making it difficult to address this question from secondary characteristics such as the local or ordered moment. However, analyses in 2014-2016 have shown that resonant fine structure at the O-edge (5dà5f transition) provides a distinctive fingerprint for identifying the nominal valence state and electronic multiplet symmetry on uranium [16][17][18][19]. X-ray absorption spectra (XAS) of UBi 2 and USb 2 were measured by the total electron yield (TEY) method, revealing curves that are superficially similar but quantitatively quite different ( Fig.…”

“…The order parameter in USb 2 has a sharper onset that cannot be fitted sufficiently close to the transition point due to disorder, but can be overlaid with an exponent of β~0. 19, and may resemble high-fluctuation scenarios such as tricriticality (β=0.25 [28,29]). This sharp onset cannot be explained from the AM+MF model (blue curve in Fig.…”

Prospects of high-resolution resonant X-ray inelastic scattering studies on solid materials, liquids and gases at diffraction-limited storage rings

“…6 shows the difference between a normal 4d XAS spectrum of U 4+ and a RIXS detected 4d XAS spectrum. The RIXS detected spectrum is, as discussed in x5.1, much sharper and new spectral details become visible (Kvashnina & de Groot, 2014).…”