Calibration method for confocal x-ray microanalysis with polychromatic excitation

SOSA, C.; STOYTSCHEW V.; LEANI J.; SÁNCHEZ H.J.; PÉREZ C. A.; PEREZ, R.D

Journal of Spectroscopy

Hindawi

Año: 2015 vol. 2015 p. 1 - 7

2314-4920

In the confocal configuration, a probing volume defined by the overlap of the foci of two x-ray lenses is analyzed. Scanning the sample through this micro volume, depth profile studies of elemental concentrations can be performed by means of x-ray fluorescence detection. To apply the fundamental parameters method at the confocal setup the knowledge of the sensitivity of the spectrometer is required which depends on the characteristics of both x-ray lenses. 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 based on the measurement of standard samples becomes unstable since the number of required fitting parameters is too high. To overcome this problem a program in FORTRAN code was developed to simulate the radiation transport through the capillaries considering the multiple reflections on monocapillary walls. The characterization of the excitation lens by means of simulation reduces the number of fitting parameters required in the confocal setup calibration. The developed calibration method was applied for a confocal spectrometer implemented in the Brazilian Synchrotron Radiation Source (LNLS) with white beam. The experimental parameters of the sensitivity were obtained from depth profile analysis of several pure thin films. The calibrated confocal setup was used to quantify reference standards in order to validate the calibration procedure. Our results for elemental concentrations show relative errors less than 15% for the quantitative analysis of a light matrix reference standard.