The Beagle 2 x-ray spectrometer for Mars

This thesis is concerned with the Beagle 2 X-ray spectrometer (XRS) for Mars. The scientific goals of the XRS were to perform (i) geochemical analyses of Martian rocks and soils and (ii) in situ 40K >40Ar dating of rocks. The major aims of this study were the development of the XRS to achieve its scientific goals and to inform the design of future versions of the instrument. The XRS is described and compared with the previous X-ray Spectrometers that have been successfully deployed on Mars. A characterisation of the XRS investigated the fundamental behaviour of the instrument in terms of its spectral features (gain, resolution and artefacts), gain variation with temperature of its components, deadtime and quantum efficiency. The XRS was calibrated to convert elemental intensities from its analyses into concentrations. The concentrations of several major and trace elements of interest in reference materials were linearly correlated with the certified concentration. The analytical performance of the XRS was evaluated in comparison with a terrestrial portable X-ray spectrometer (PXRF) and a wavelength dispersive X-ray spectrometer (WD XRF). The performance was characterised in terms of accuracy, detection limit and fitting precision. This study showed the importance of energy resolution to the analytical performance of the XRS. The operational performance of the XRS was evaluated. The geochemical composition of several basalts analysed by the XRS agreed with complementary analyses by the PXRF and WD XRF. The 40K >40Ar radiometric ages for two basalts were determined using the K content in the basalts in conjunction with their 40Ar isotope content (analysed by a laboratory version of the Beagle 2 Gas Analysis Package). The 40K 40Ar ages were found to differ to the Ar-Ar ages because of various effects associated with inhomogeneity of the K content in the rock and radiogenic40Ar loss.