DigiGREF: A Digital Analogue of the Mercury Imaging X-ray Spectrometer Ground-Reference Facility

This paper presents a new X-ray fluorescence simulation (DigiGREF), designed as a digital analogue to the Mercury Imaging X-ray Spectrometer (MIXS) ground-reference facility (GREF). MIXS is a novel instrument, onboard the BepiColombo spacecraft, and requires characterisation of the flight-qualification model (FQM) in a laboratory setting. DigiGREF is the first step towards simulating the emission and detection of X-ray fluorescence (XRF), which will eventually allow the elemental abundances of Mercury’s surface to be accurately determined. DigiGREF solves the standard fluorescence integral, using a Monte-Carlo integration technique. X-ray emission processes simulated include photoemission, and Compton and Rayleigh scattering. An electron random-walk simulation is also presented, used to simulate an X-ray tube (XRT) input spectrum. The detection process is simulated using response functions for the FQM detector. The simulated spectrum is tested against a well characterised geological standard (JB-3) and produces a spectrum with an R2 value of 0.9513. The XRT spectrum is also tested, using two different split-pixel processing modes, and generates spectra with R2 values of 0.9864 and 0.9900. DigiGREF is thus considered a good first-order approximation of XRF and forms a suitable basis for future development, eventually leading to analysis of data returned by MIXS during the orbital mission.