Use of indirectly measured spectra in fundamental parameters X-ray fluorescence analysis

Abstract

X-ray fluorescence spectrometry by recourse to computations with fundamental physical parameters, requires one to determine the irradiation spectra with precision and as frequently as possible, since changes with anode material, high voltage conditions, age, contaminants, etc. are known to alter its shape. Knowledge of a spectrum before an experimental run, allows one to carry out computations of fluorescet intensities with better accuracy In order to do this, we have implemented a procedure of indirect determination of spectral shape through a parametric fitting of a mathematical model, containing the X-ray excitation spectra and detector characteristics convoluted with the attenuation factor. As shown elsewhere, this is a Laplace transform and it is proportional to the absorbed dose as measured with an ionisation chamber. Direct measurements were also performed on the collimated beam with an intrinsic germanium detector, for test purpose, with good results. Elemental concentrations for a sample of interest, were finally calculated by means of the Lachance-Traill method as modified by Claisse and Quintin, but with binary and multicomponent standards calculated with theoretical equations instead of using measurements on real standards. The final test of this proposal is given by measurements on standards from the National Bureau of Standards.