Regolith effects in planetary X-ray fluorescence spectroscopy: Laboratory studies at 1.7–6.4 keV

Laboratory measurements are presented to study the effects of the physical properties of regolith on planetary soft X-ray fluorescence spectroscopy. Two laboratory setups are used to independently measure these regolith effects using lunar regolith analog samples with three different particle-size ranges. Discussion is given on the data analysis. Some of the data may be valid only for qualitative conclusions. Analytical modelling is used to separate the effects expected for a plane-parallel and homogeneous medium from those of measured regolith analogs. The surface roughness and porosity of the regolith are observed to induce an enhancement of the higher-energy part of the spectrum as a function of the incidence angle. The enhancement is larger for rougher surfaces. A brief discussion is given on the relevance of this study for future planetary missions carrying soft X-ray spectrometers.