A fundamental parameters approach to calibration of the Mars Exploration Rover Alpha Particle X‐ray Spectrometer: 2. Analysis of unknown samples | CU Experts

Our fundamental parameters method was recently applied to results from geochemical reference materials to provide a new calibration of the laboratory Alpha Particle X‐ray Spectrometer (APXS) instrument from the Mars Exploration Rovers mission. The method is now extended to provide an iterative approach for the treatment of unknown samples, based upon that initial calibration. It is tested by regarding small subsets of the reference materials and other materials as unknown samples; agreement of derived element concentrations with suppliers' recommended values is good with the exception of certain igneous rock types. In these exceptions, the deviations can be explained via the location of the elements concerned in minority or accessory mineral phases, and different calibration schemes can be developed empirically for specific rock types which are defined via a TAS diagram. The necessary reliance upon an iterative approach in normalizing the sum of oxide concentrations to 100% is investigated. It turns out that this can cause significant errors in derived element concentrations when a significant amount of mineralogically bound water (H2O+) is present, but our method has been extended to enable determination of this H2O+ concentration under known geometry. Various implications for calibration of the new APXS selected for the Mars Science Laboratory are discussed.

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