Laboratory experiments of particle size effect in X-ray fluorescence and implications to remote X-ray spectrometry of lunar regolith surface

We performed laboratory experiments to investigate the effect of particle size in X-ray fluorescence (XRF) with respect to interpreting remote X-ray spectrometry. To simulate microscopic roughness of the uppermost surface of lunar regolith, we used powdery specimens of crashed rocks ranging 25 to 500 mu m in size and flat rock plates for comparison. Our results show that XRF intensities from powdery specimens decrease relative to those from flat plates by up to 50%, especially for larger particle size and at increasing source-to-surface-to-detector angle (phase angle). Corrections should be required for elemental analysis by XRF spectrometry in the SELENE Kaguya and other planetary orbiter missions.