Detailed calculation of inner-shell impact ionization to use in photon transport codes

Abstract

Secondary electrons can modify the intensity of the XRF characteristic lines by means of a mechanism known as inner-shell impact ionization (ISII). The ad-hoc code KERNEL (which calls the PENELOPE package) has been used to characterize the electron correction in terms of angular, spatial and energy distributions. It is demonstrated that the angular distribution of the characteristic photons due to ISII can be safely considered as isotropic, and that the source of photons from electron interactions is well represented as a point source. The energy dependence of the correction is described using an analytical model in the energy range 1–150keV, for all the emission lines (K, L and M) of the elements with atomic numbers Z=11–92. It is introduced a new photon kernel comprising the correction due to ISII, suitable to be adopted in photon transport codes (deterministic or Monte Carlo) with a minimal effort. The impact of the correction is discussed for the most intense K (Kα1,Kα2,Kβ1) and L (Lα1,Lα2) lines.