Laboratory studies into the effect of regolith on planetary X-ray fluorescence spectroscopy

Abstract

Laboratory studies into the effect of regolith on planetary X-ray fluorescence spectroscopy. Icarus, Elsevier, 2008, 198 (2) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTLaboratory studies into the effect of regolith on planetary X-ray fluorescence spectroscopy A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractIn the analysis of X-ray fluorescence spectra from planetary surfaces, it is traditionally assumed that the observed surface is a plane-parallel, smooth, and homogeneous medium. The spectral and spatial resolutions of the instruments that have been used to measure X-ray emission from planetary surfaces to date have been such that this has been a reasonable assumption, but a new generation of X-ray spectrometers will provide enhanced spectral and spatial resolutions when compared with previous instrumentation. In light of these improvements in performance, it is important to assess how the requirements on the methodology of analysis of spectra may change when the surface is considered as a regolith. At other wavelengths, varying physical properties of planetary regoliths, such as the packing density, are known to have an effect on the observed signal as a function of viewing geometry. In this paper, the results from laboratory X-ray fluorescence measurements of regolith analogue materials at different viewing geometries are presented. Characteristic properties of the regolith such as particle sizes and packing density are found to affect the measured elemental line ratios. A semiempirical function is introduced as a tool for fitting fluorescent line intensity dependences as a function of viewing geometry. The importance of the results is discussed and recommendations are made for the future analysis of planetary X-ray fluorescence data.

C1XS results—First measurement of enhanced sodium on the lunar surface

“…The observed XRF intensity get affected by the distribution of particle size, as the mean free path of soft X-rays is smaller than the mean particle size of lunar regolith. Laboratory experiments by (Maruyama et al, 2008;Näränen et al, 2008) shows that XRF intensity decreases with increasing phase angles (angle between source-surface-detector) and increases with decreasing size of particles. However, this effect is expected to be small on C1XS results where the ground pixel dimensions are large (hundreds of km) and considers a large distribution of particle sizes (Weider et al, 2012).…”

Western Oceanus Procellarum as seen by C1XS on Chandrayaan-1

“…All other elemental abundances are therefore assessed against the fixed Si (21 wt %; Prettyman et al, 2006) and are expressed as elemental ratios (i.e., Mg/Si and Al/Si). This normalisation largely cancels out inaccuracies in the results caused by calibration uncertainties and variations in XRF intensity that are related to physical and compositional heterogeneities in the regolith (Clark and Trombka, 1997;Maruyama et al, 2008;Näränen et al, 2008;Weider et al, 2011). Theoretical and experimental investigations of XRF geometry effects (e.g., Maruyama et al, 2008;Näränen et al, 2008;Parvianen et al, 2011;Weider et al, 2011) have shown that it can be problematic to express XRF-derived abundances as ratios of two elements that differ significantly in energy (e.g., Si and Fe).…”

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

“…X-ray fluorescence intensity depends on a variety of factors other than solar x-ray spectra such as particle size, geometry of observation and the mineral matrix (Maruyama et al, 2008;Naranen et al, 2008;. It is very difficult to deconvolve the absolute flux from lunar elements uniquely given the multi parameter dependencies.…”