Extraction of Branching Ratios from HERFD Data

Historically, Branching Ratio measurements with X-ray Absorption Spectroscopy (XAS) and related techniques have played a key role in the advancement of the understanding of 5f electronic structure. [1] Specifically, the transitions utilized were the N₄ and N₅of the actinide elements, with electrons being moved from the occupied 4d states into unoccupied 5f states. For soft x-rays, the peak separations are small, allowing the doublet peaks to be collected together, in a single spectrum. The intensity calibration is intrinsic, within some small variations such as those due to storage ring beam current decay and fluctuations and other higher order effects. For tender and hard x-rays, the peak separations tend to be larger, often requiring two separate spectra and some sort of new normalization, especially for High Energy Resolution Fluorescence Detection (HERFD) XAS spectra. It will be shown that the step heights in the EXAFS regime can be used as a cross calibration between the M₄ and M₅spectra, if two well characterized cases can be used as controls. (EXAFS is Extended X-ray Absorption Fine Structure, typically about 20 eV or more above the white-lines (sharp, intense peaks) at threshold, e.g. the 5f peaks.) Thus, a quantitative analysis method has been developed that allows the cross calibration of separate Uranium M₄ and M₅ X-ray absorption spectra (XAS), in particular those collected with the new High Energy Resolution Fluorescence Detection (HERFD) method. With this method, it is now possible to generate experimental Branching Ratio (BR) values from the U M_4,5XAS HERFD data.<br/><br/>1. J. G. Tobin, S. Nowak, S.-W. Yu, R. Alonso-Mori, T. Kroll, D. Nordlund, T.-C. Weng, D. Sokaras, "Extraction of Branching Ratios from HERFD Data," J. El. Sp. Rel. Ph. 262, 147285 (2023) https://www.sciencedirect.com/science/article/abs/pii/S0368204823000026