A Low‐Power Radioisotope <scp>XRF</scp> Spectrometer for Detection of Light Elements on Planetary Missions

ABSTRACT Current X‐ray spectrometers for in situ geochemical analysis on planetary missions typically rely either on X‐ray tubes, which demand electrical power and add mass and thermal complexity, or on alpha particle X‐ray spectrometers (APXS) that use rare sources, and come with severe concerns on radiation safety and isotope availability. In this work, we present a compact XRF spectrometer that avoids both limitations by combining commercially available silicon drift detectors with ultra‐thin silicon nitride windows and and radioisotope sources. This configuration overcomes the low‐energy transmission limits of traditional beryllium windows and enables direct detection of light elements down to oxygen. Simulations and laboratory measurements on a lunar‐analog anorthosite target demonstrate sensitivity to K α lines from oxygen to mid‐ Z elements, with clear oxygen peaks observed in vacuum for SiN‐window detectors, showing a viable, low‐power, alpha‐free alternative to ‐based APXS and tube‐driven systems for future planetary missions.