High-Energy X-Ray Microprobe System with Submicron Resolution for X-Ray Fluorescence Analysis of Uranium in Biological Specimens

Total-external-reflection Kirkpatrick-Baez mirror optics for high-energy X-rays have been applied to the X-ray microprobe at beamline 37XU of SPring-8. A focused beam size of 1.0 μm (V)×0.83 μm (H) has been achieved at an X-ray energy of 30 keV, and a total photon flux of the focused beam was about 5×109 photons/s. Micro-X-ray fluorescence (μ-XRF) analysis of the uranium distribution in rat kidneys has been performed with the mirror-focused beam. The sensitivity of uranium was evaluated from the XRF intensity of thin standard samples, and the minimum detection limit was estimated at 10 μg/g. The high-spatial-resolution analysis revealed that uranium was concentrated in the epithelium of the proximal tubules in the inner cortex. The maximum concentration of uranium in the tubule was estimated to be 503 μg/g using a semiquantitative evaluation.