Development of High-Energy µ-X-ray Fluorescence and X-ray Absorption Fine Structure for the Distribution and Speciation of Rare Earth Elements in Natural Samples

Abstract

Micro-X-ray fluorescence and X-ray absorption fine structure (µ-XRF-XAFS) is one of the most powerful tools to identify the distribution and speciation of trace elements in natural samples with µm spatial resolution. However, conventional µ-XRF-XAFS studies applied to rare earth elements (REEs: lanthanide elements + Y in this study) are mainly limited to their L-edges and L lines (except for Y) that are subject to strong interferences from other elements (mainly transition metals). In this study, we extend µ-XRF-XAFS to the higher energy region (HE-µ-XRF-XAFS) by using an incident X-ray microbeam (size: ca. 1 × 1 µm2) between 38 and 54 keV to realize K-edge excitation lanthanide analysis without interferences from other elements at the BL37XU beamline, SPring-8 (Japan). This method enables us to simultaneously analyze (i) REE patterns (from La to Dy), (ii) XAFS spectra, and (iii) µm-scale distribution of each REE in the natural sample. The proposed method also realizes the simultaneous application of µ-XAFS at low (e.g., Fe K-edge) and high (lanthanide K-edges) energy at the same spot without changing the setup of the µ-XRF-XAFS system using the detuning technique.

Application of transition-edge sensors for micro-X-ray fluorescence measurements and micro-X-ray absorption near edge structure spectroscopy: a case study of uranium speciation in biotite obtained from a uranium mine

“…The optic of this beamline consisted of a double Si (111) crystal monochromator and a Kirkpatrick-Baez (KB) mirror to adjust the incident beam size on the sample to 1.0 × 1.0 μm 2 . 40,41 The sample position was observed using a microscope through the optical lens next to the KB mirror. After the X-ray focused by the KB mirror was irradiated on the sample, fluorescent X-rays from the sample were detected via the TES, and the SDD was placed on both sides of the sample.…”