Multiple scattering effects in X-ray fluorescence experiments

BRUSA, D.; TIRAO, G.; G. STUTZ

Campinas, Brasil

Congreso; IX Workshop Anual de Usuarios del LNLS; 1999

Elastic and inelastic x-ray scattering as well as multiple scattering processes are usually ignored in x-ray fluorescence experiments designed to perform quantitative chemical analysis using fundamental parameter algorithms[i] or to measure physical constants as photoelectric cross sections[ii]. In both cases simple theoretical expressions relating measured x-ray fluorescence intensities from a sample, its composition and fundamental parameters as photoelectric cross sections, fluorescence yields, transitions rates etc., are used to evaluate the experimental data. In that theoretical formalism the ionization of atomic inner-shells is considered as being produced only by photoelectric interactions of primary photons with core electrons, and scattering and multiple scattering of incoming and outgoing photons are neglected, which could conduce to an underestimation of the theoretically predicted fluorescence intensity. In this theoretical framework the intensity of fluorescence photons emitted by a pure sample, which is excited by a monochomatic incident photon beam, is calculated as:   ,          (1)   where normal incidence and an infinitely thick sample were assumed. m (m¢) is the attenuation coefficient for the incoming (fluorescence) photons, t the photoelectric cross section and w the fluorescence yield for the corresponding atomic orbital, ¦ the transition probability for the considered fluorescence line and q the take-off angle. DW is the solid angle of the detector and e its detection efficiency. I0 is relative to the intensity of the incident beam. The contribution of scattering and multiple scattering to characteristic x-ray intensities was experimentally studied by measuring fluorescence production from a pure aluminum sample at different x-ray take-off angles and by comparing it to the prediction of eq. (1).