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Eingeladener Vortrag
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Modelling of X-Ray Scattering for improved X-Ray Fluoescence Analysis - Monochromatic Excitation
(2010)
Modelling of X-Ray Scattering for improved X-Ray Fluorescence Analysis - X-Ray Tube Excitation
(2010)
A systematic series of measurements has been carried out with monochromatic X-ray excitation with synchrotron radiation in order to check a physical model on X-ray scattering. The model has recently been successfully tested for the case of polychromatic, unpolarised excitation emitted by an X-ray tube. Our main purpose is the modelling of a physical background in X-ray fluorescence spectra, so that improved quantitative results can be achieved especially for strongly scattering specimens. The model includes single Rayleigh and Compton scattering in the specimen, the effect of bound electrons, the challenging Compton broadening and the polarisation degree. Representative specimens, measurement geometries and excitation energies have been selected with synchrotron monochromatic light at BAMline/BESSY II. Monte-Carlo simulations have been also carried out in order to evaluate the quality of the results achieved with the model.
X-ray scattering may contribute significantly to the spectral background of X-ray fluorescence (XRF) spectra. Based on metrological measurements carried out with a scanning electron microscope (SEM) having attached a well characterised X-ray source (polychromatic X-ray tube) and a calibrated energy dispersive X-ray spectrometer (EDS) the accuracy of a physical model for X-ray scattering is systematically evaluated for representative samples. The knowledge of the X-ray spectrometer efficiency, but also of the spectrometer response functions makes it possible to define a physical spectral background of XRF spectra. Background subtraction relying on purely mathematical procedures is state-of-the-art. The results produced by the analytical model are at least as reliable as those obtained by Monte-Carlo simulations, even without considering the very challenging contribution of multiple scattering. Special attention has been paid to Compton broadening. Relevant applications of the implementation of the analytical model presented in this paper are the prediction of the limits of detection for particular cases or the determination of the transmission of X-ray polycapillary lenses.