Calibration of the MER alpha-particle x-ray spectrometer for detection of 'invisible' OH and H2O possibly present in Martian rocks and soils

摘要

An existing Monte Carlo code was modified and extended to predict the intensity ratio of elastically and inelastically scattered plutonium L alpha x-rays incident on rock samples in the Mars Exploration Rover's a-particle x-ray spectrometer (APXS) device. The systematics of the scatter ratio as a function of effective sample atomic number are explored. The simulated Rayleigh/Compton ratios (R/C)(sim) are compared with measured ratios (R/C)(meas) that are obtained by fitting APXS spectra of geochemical reference materials using an x-ray fluorescence version of GUPIX. The quantity K=(R/C)(meas) /(R/C)(sim) is then plotted against the mean atomic number of the sample to provide a calibration for known samples. Departures of K values of unknown samples from this calibration may then be attributed to the presence of light, 'invisible' elements in the sample. This work is part of an ongoing project aimed at developing methods to quantify bound water in Martian rocks analyzed by the present and the next generation APXS instruments. Copyright (c) 2006 John Wiley & Sons, Ltd.