Circular polarization of the Lyman-α 1 line radiation emitted by longitudinally-polarized electron impact excitation: effects of Breit interaction and radiation multipoles

Abstract

Detailed calculations are carried out for the longitudinally-polarized electron impact excitation cross sections from the ground state 1s 1/2 to the individual magnetic sublevels of the excited state 2p 3/2 of highly charged H-like ions using a fully relativistic distorted-wave method. The influence of the Breit interaction and radiation multipoles on the circular polarization of X-ray radiation are investigated systematically. Our results show that the Breit interaction, as the dominant correction to the Coulomb interaction, may lead to a considerable change in the magnetic sublevels cross sections and circular polarizations of Lyman-α 1 (2p 3/2 → 1s 1/2) line radiation with a more pronounced effect at higher incident energies and/or atomic numbers. Moreover, the interference between the electric dipole (E1) decay and the magnetic quadrupole (M2) decay may significantly alter the circular polarizations of the emitted X-rays. The circular polarizations of the Lyman-α 1 line are exhibit a different behavior than the linear polarizations for the same transition line regarding the radiative electron capture [Weber et al., Phys. Rev. Lett. 105, 243002 (2010)], radiative recombination [Bettadj et al., J. Phys. B 47, 105205 (2014)], and electron-impact excitation processes [Chen et al., Phys. Rev. A. 90, 012703 (2014)].