Comparison of indirect methods for incident spectrum determination in micro-XRF analysis

SOSA, C.; LEANI J.; POLETTI, M.; SÁNCHEZ H.J.; PEREZ, R.D.

Bologna

Conferencia; European Conference on X-Ray Spectrometry; 2014

For the Microanalysis by XRF (micro-XRF), the high intensity and anisotropy of the photon flux at the output of the focalization lens difficult a direct determination of the emergent spectrum. Different techniques have been used in the past to estimate the excitation spectrum using indirect measurements, such as x-ray scattering and induced x-ray fluorescence in targets. Both of them are susceptible to be adapted for the calibration of micro-XRF technique. The methods for micro-XRF calibration using x-ray scattering determines the lens transmission through the scatter spectra in a light matrix assuming only first order interactions and neglecting Compton shift. In spite of this approximations the reported accuracy is better than 15% for homogeneous samples. The induced x-ray fluorescence in targets technique consists of the measurement of the x-ray fluorescence intensity from several targets covering the emission energy interval of the x-ray source. In this work an iterative calculation based on linear piecewise approximation for the incident spectrum was developed. The method has the advantage that it not requires any assumption about the physical characteristics of the x-ray source. Both methods were implemented in our micro-XRF spectrometer with x-ray tube excitation and capillary optics focalization. We observed differences in the results mainly in the low energy range probably cause by the loss of accuracy in the scattering method. After that a standardless calibration of the micro-XRF spectrometer by Fundamental Parameter was developed with the incident spectrum of both methods. The quantification of reference standards shows that the accuracy is sensibly improved by the XRF method.