Linear polarization of the 2p⁵3s→2p⁶ lines following the inner-shell photoionization of sodiumlike ions

The inner-shell photoionization of highly charged, many-electron ions and their subsequent radiative decay are studied theoretically within the multiconfiguration Dirac-Fock approach. Special attention is paid to the linear polarization of the characteristic x-ray radiation. Detailed calculations have been carried out, in particular for the 2p⁵3s→2p⁶ radiative transitions following ionization of the 2p electron of the sodiumlike iron Fe¹⁵⁺ and uranium U⁸¹⁺ ions. For these elements, the inner-shell photoionization was found to induce the (relatively) low linear polarization of the subsequently emitted photons which is strongly affected, moreover, by the higher-order (nondipole) effects in the electron-photon interaction.