High-sensitive XANES analysis at Ce L₂-edge for Ce in bauxites using transition-edge sensors: Implications for...

Accurate determination of cerium (Ce) valence state is important for interpreting the Ce anomaly in geological archives for (paleo)redox reconstruction. However, the routine application of Ce L₃-edge X-ray absorption near-edge structure (XANES) spectroscopy for detecting trace Ce in geological samples can often be restricted by coexisting titanium (Ti) due to the proximity of their fluorescence emission lines. Therefore, the signal-to-noise ratio of Ce L₃-edge XANES spectra may not be sufficiently high for high-quality spectroscopic analysis. This study introduces a semi-quantitative approach appropriate for Ti-rich, Ce-dilute geological materials by synchrotron-based X-ray measurement at the Ce L₂-edge. First, the results confirm that Ce L₂-edge XANES spectra are able to avoid overlapping Ti K_β emissions and provide more reliable information on the Ce valence state in Ti-rich materials relative to L₃-edge XANES. Moreover, the application of transition-edge sensor (TES) could reach the higher sensitivity with better energy resolution than conventional silicon drift detector (SDD) to detect fluorescence X-ray (Ce L_β1). The investigation on bauxites developed from the Columbia River Basalts shows that combining Ce L₂-edge XANES and TES allows for resolving weak Ce fluorescence lines at the L₂-edge from Ti-rich, Ce-dilute samples (Ti/Ce mass ratio up to ∼6000, tens of ppm Ce). The outcome emphasizes the practical possibility of investigating Ce redox state in Ti-rich geological samples.