Simulation of the relationship between element concentrations and X-ray yields in the Mars Exploration Rover's X-ray spectrometer

A simulation code has been developed, combining analytical and Monte Carlo methods, to predict the X-ray yields from minerals exposed to the Alpha-Particle X-Ray Spectrometer that is used for rock and soil analysis during the 2004 NASA expedition to Mars. Agreement is found between these simulated X-ray yields and the yields obtained by measurement and spectrum fitting carried out at the Max-Planck-Institut fur Chemie in Mainz. For elements having Z ⩾ 15, the yield-concentration relationship is linear, while for 11 ⩽ Z ⩽ 14, it is quadratic, as was hinted at in the results from the earlier Pathfinder mission. A study of the angle-dependence of X-ray yields provides an optimal pair of values for the excitation and emission angles, so that the simple yield programs from the GUPIX package may be used to predict X-ray yields from targets of known concentration.