Xie Lu-You

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.

Relativistic Distorted-Wave Calculations of Electron Impact Excitation Cross Sections of Be-Like C2+ Ions

A fully relativistic distorted-wave program is developed based on the Grasp92 and Ratip packages to calculate electron impact excitation (EIE) cross sections. As a first application of the program, the EIE cross sections of Be-like C2+ ions from the metastable 1s22s2p 3P to 1s22p2 3P excitation and the inner-shell excitations are calculated systematically. Meanwhile, the correlation effects of target states are discussed. It is found that the correlation effects play an important role in the low energy EIE cross sections. An excellent agreement is found when the results are compared with previous calculations and recent measurements.

Polarization and Angular Distribution of Lℓ X-Ray Following Inner-Shell 2p3/2 Photoionization of Magnesium-Like Ions

The inner-shell 2p3/2 photoionization and the subsequent decay of Mg-like Fe14+, Cd36+, W62+ and U80+ ions are studied theoretically within the multiconfiguration Dirac—Fock method and the density matrix theory. Special attention is paid to exploring the influence of the non-dipole terms which arise from the multipole expansion of the electron-photon interaction in the photoionization process. The results show that the non-dipole contribution to the total cross section, the magnetic sublevels cross section of the photoionization process, the degree of linear polarization and angular distribution of the subsequent characteristic x-ray radiation become more important with the increase of photons energy and atomic nuclear Z. Especially for the cross section and the degree of linear polarization, the non-dipole contribution arrives at 50% for U80+ at four time energy threshold units. However, for the angular distribution, the maximum contribution does not exceed 4%, even for U80+ ions.

Electron Impact Excitations and Linear Polarization for 1s2 1S0—1s2p 3,1P1 Lines of Fe24+ Ions under Screened Coulomb Interactions

Electron impact excitation cross sections from the ground state to the individual magnetic sublevels of 1s2p3,1P1 states in high-temperature dense plasmas are calculated for highly charged He-like Fe24+ ions by using a fully relativistic distorted-wave method. The Debye—Huckel screening model is used to screen the projectile electron from the nucleus and target electrons. The linear polarization degrees for these lines are obtained. It is found that the cross sections at all incident energies decrease with the increase of the screening for these excitations. The influence of screening on linear polarization degrees of the 1P1 line is very small. The linear polarization degrees of 3P1 line decrease sharply at low incident energy with the increase of the screening.

Polarization Transfer in the 2p3/2 Photoionization of Magnesium-Like Ions

The inner-shell 2p3/2 ionization of Mg-like Fe14+, Cd36+, W62+ and U80+ ions by linear polarized light and the subsequent radiative decay are studied theoretically with the multiconfiguration Dirac—Fock (MCDF) method and the density matrix theory. Special attention is paid to exploring the influence of the polarization properties of the incident photon and the non-dipole term which arises from the multipole expansion of the electron-photon interaction on the properties of the subsequent x-ray radiation. The results show that there is a linear relationship between the degree of linear polarization of the radiative decay and ones of the incident light, which can be used for diagnosing the polarization of a light source. In addition, with the increasing photon energies, the non-dipole contribution to the alignment of the residual ions, the degree of linear polarization, as well as the angular distribution of the radiative decay following the inner-shell photoionization will also be increased.

Electron Impact Excitation of Xenon from the Ground State and the Metastable State to the 5p57p Levels

Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56s J = 2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon.

Energy-crossings and their effects on the spectra of the neon-like ions

Excitation energies, transition wavelengths and probabilities of the 2p6, 2p53l, 2s2p63l (l = 0,1,2) states along the Ne-like isoelectronic sequence from Z = 21–92 have been calculated by using the multi-configuration Dirac-Fock (MCDF) package GRASP92 and a newly developed radiative transition program REOS99. In the calculations, the correlation and relaxation effects are included systematically. Based on the calculations, all possible energy crossings among the level groups with the same parity and total angular momentum have been presented. It is found that there are strong configuration interactions in some particular Z regions with energy-crossings, which can cause a dramatic change of the related transition probabilities.

Influence of relaxation effects on probabilities of the 2s2p3 5S2-2s22p2 3P1,2 intercombination transitions in NII

Transition probabilities of the 2s2p3 5S2-2s22p2 3P1,2 intercombination transitions in NII have been calculated by using a large-scale multiconfiguration Dirac-Fock method. In the calculation the most important effects of relativity, correlation and relaxation are considered. From the calculated transition probabilities, the lifetime of the 2s2p3 5S2 metastable state is derived. The result is in excellent agreement with the latest experimental result. In the meantime the influence of anomalously strong relaxation effects on probabilities of the 2s2p3 5S2-2s22p2 3P1,2 lines in NII have been found.

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.