Dominance of the radiative cascades in the cross section and circular polarization of x-ray radiation

Abstract

The radiative cascade typically appears as a somewhat small correction to the direct impact process. We demonstrate here, however, that for the longitudinally-polarized electron impact excitation of highly charged ions, radiative cascades may play a significant role that can change the cross section and circular polarization of the emitted x-ray radiation qualitatively. This conclusion is verified by taking the 1s2 (J = 0) 1s2s1/2 (J = 1) excitation of He-like Fe Ge Mo Ag and ions as examples. For these ions, the dominant cascade channels from high-lying levels 1 snp (n = 2, 3, 4, 5, 6) will strongly dominate the direct excitation process and greatly modify the Mf = −1 magnetic sublevel cross sections, as well as leading to a considerable change in the expected circular polarizations of the x-ray emission pattern.