Laboratory XRF measurements using Alpha Particle X-ray Spectrometer of Chandrayaan-2 rover: Comparison with Geant4 simulation results

India´s second mission to the Moon - Chandrayaan-2, will have a rover for in-situ exploration of lunar surface around the landing site. Alpha Particle X-ray Spectrometer (APXS) is one of the instruments on board Chandrayaan-2 rover, for measuring elemental composition of the lunar surface using state - of - the - art X-ray detector (Silicon Drift Detector - SDD) with higher energy resolution. The objective of the APXS instrument is to analyze several soil / rock samples along the rover traverse for the major elements with the characteristics X-rays in the 1 to 25 keV energy range. We have carried out XRF measurements in the laboratory using Alpha Particle X-ray Spectrometer which provides energy resolution of ~150 eV at 5.9 keV, when the detector is cooled to -35°C. These measurements are carried out using six ⁵⁵Fe X-ray sources for various target materials at different detector to target heights. We have also carried out detailed Monte-Carlo simulation based on GEANT4 for the APXS for various compositions of the lunar surface. Here we are comparing the GEANT4 simulation results with the experimentally acquired XRF data.