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The Compton effect is a well-known scattering process. When the incoming photon energy is sufficiently high, it represents a possible ionization mechanism for the inner shells of atoms. The resulting vacancies can be filled through spontaneous atomic relaxation, a process analogous to photoabsorption.
A preliminary description based on the Waller–Hartree approximation [1] showed that, for K lines, this contribution is relevant at high excitation energies and for low-Z elements. A more detailed description of the XRF line enhancement due to Compton ionization was subsequently performed, for unpolarized excitation, within the framework of the Boltzmann photon transport equation. Compton scattering was described using the impulse approximation (IA) to account for the energy dependence [2]. The calculations in [2] were extended to the L and M shells, showing that the enhancement term becomes relevant also for medium-Z elements and that the number of electrons per shell is not constant but varies with energy.
For the first time, the extent of the XRF line modification due to Compton ionization is computed for linearly polarized excitation using the expressions reported in [3]. It is shown that Compton ionization is responsible for the polarization-dependent enhancement observed in some L and M characteristic lines.
[1] G.V. Pavlinski and Yu. Pornoy, X-ray Spectrometry 43 (2014), 118-121.
[2] J.E. Fernández, V. Scot, E. Di Giulio, Spectrochimica Acta Part B: Atomic Spectroscopy 124 (2016), 56-66.
[3] J.E. Fernandez, J.H. Hubbell, L.V. Spencer, A.L. Hanson. Radiation Physics and Chemistry 41 (1993) 579-630.