Shi Ying-Long

Polarization of M2 Line Emitted Following Electron-Impact Excitation of Beryllium-Like Ions

Detailed calculations are carried out for the electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the 1s2s22p3/2J = 2 excited state of highly-charged beryllium-like ions by using a fully relativistic distorted-wave (RDW) method. The contributions of the Breit interaction to the linear polarization of the 1s2s22p3/2 J = 2 →1s22s2 J = 0 magnetic quadrupole (M2) line are investigated systematically for the beryllium isoelectronic sequence with 42 ≤ Z ≤ 92. It is found that the Breit interaction depolarizes significantly the linear polarization of the M2 fluorescence radiation and that these depolarization effects increase as the incident electron energy and/or the atomic number is enlarged.

Energy-Crossing and Its Effect on Lifetime of the 4s24p 2P3/2 Level for Highly Charged Ga-Like Ions

The multi-configuration Dirac—Fock method is employed to calculate the energy levels and transition probabilities for the electric dipole allowed (E1) and forbidden (M1, E2) lines for the 4s24p, 4s4p2 and 4s24d configurations of highly charged Ga-like ions from Z = 68–95. The lifetimes of the 4s24p 2P3/2 level of the ground configuration are also derived. Based on our calculations, it is found that the energy level of the 4s24p 2P3/2 is higher than that of the 4s4p2 4P1/2 for the high-Z Ga-like ions with Z ≥ 74, so as to generate an energy crossing at Z = 74. The effect of the energy crossing is important to the calculation of the 4s24p 2P3/2 level lifetime for Ga-like ions with Z ≥ 74.

Theory of X-Ray Anisotropy and Polarization Following the Dielectronic Recombination of Initially Hydrogen-Like Ions

The angular distribution and polarization of the x-ray photoemission of highly charged helium-like ions is studied following the K—LL dielectronic recombination of initially hydrogen-like ions. Calculation is carried out within the framework of the density matrix theory combined with the multiconfiguration Dirac—Fock approach. Attention is paid to magnetic sublevel alignment in the resonant intermediate state and to its nonuniform radiative decay processes. It is shown that the Breit interaction between the incident and target electrons plays a significant role for the alignment of the resonant state and thus causes a substantial change in the x-ray emission characteristic, when compared to the incorporation of only the (non-relativistic) Coulomb interaction. The most prominent difference in alignment parameter is found in the 2s2p1/2 J = 1 resonant state for a wide range of atomic numbers from 9 to 92. For this resonant state of helium-like ions, the Breit interaction becomes significant for ions with nuclear charge Z ~ 30 already.

The Radiative and Auger Decay Properties of K-Shell Ionized Np Ions

The radiative and Auger decay processes of K-shell ionized Np ions are studied theoretically using the flexible atomic code (FAC). Relativistic effects, Breit interaction, QED corrections and nuclear finite mass and volume effects are considered systematically. The resulting calculated K x-rays and Auger spectra of Np are compared with the measured spectra emitted after the electron-capture (EC)-decay of mass-separated 237Pu. The general consistency between theory and experiment is good; the relative intensities and relative positions of the peaks in the measured spectra are reproduced with good accuracy, in spite of the existence of different ways to produce the primary K-shell vacancy, enabling identification of the observed structure in the experimental spectra. We find that most of the radiative transition rates are greater than the Auger transition rates, and the latter decrease rapidly with the transfer of initial vacancies to the outer shell.