Calibration method for confocal x-ray microanalysis simplified by Montecarlo simulation

C..A. SOSA; R.D. PÉREZ; H. J. SÁNCHEZ

Congreso; RAU XXIII; 2013

The confocal setup consists of x-ray lenses in the excitation as well as in the detec- tion channel. in this configuration, a probing volume defined by the overlap of the foci of both x-ray lenses is analyzed. Scanning the sample through this micro vol- ume, 1-3 dimensional studies can be performed. An elemental analysis is obtained by the detection of the x-ray fluorescence produced in the micro volume. The fundamental parameters method (FP) applied at the confocal configuration relies on a three- dimensional model for the probing volume which depends on the characteristics of both x-ray lenses. The model describes the sensitivity of the spectrometer which relates the theoretical and measured XRF intensities in every pixel of the sample. For the particular case of polychromatic excitation, the theory shows that the focalization properties of the excitation lens for all incident energies affect the x-ray fluorescence intensity. Therefore the traditional calibration method for FP based on the measurement of standard samples becomes unstable since the number of required fitting parameters is too high. To overcome this problem a previous characterization of the excitation lens is recommended. In this work Montecarlo radiation transport simulation was tested as a low cost solution for the characterization of the excitation lens. An own programming code was written in FORTRAN language considering the multiple Fresnel reflections and refractions of the incident beam in the walls of the excitation lens. The proposed calibration method simplified by Montecarlo simulation was ap- plied for a confocal spectrometer implemented in the Brazilian Synchrotron Ra- diation Source (LNLS) with white beam. The experimental parameters of the sensitivity were obtained by means of depth profile analysis of several thin films (MicromattersTM). The calibrated confocal setup was used to quantify reference standards in order to validate the calibration procedure. Our results for elemental concentrations had good match with the nominal values of light matrix reference standards with relative error less than 15.