Hsiao-Ling Sun

L x-ray production in lanthanide elements by 1 - 5 MeV helium ions

L x-ray production in and was measured for bombardment in the energy range 1 - 5 MeV. Very thin target foils were used, and x-ray yields were measured simultaneously with elastically scattered ions. The L-shell and individual and production cross sections and their ratios were extracted. These cross sections are compared to the results of the ECPSSR theory (energy-loss and Coulomb deflection effects, perturbed stationary state approximation with the relativistic correction), its united-atom (UA) extension UA-ECPSSR and the UA-ECPSSR-MI, which also accounts for multiple ionization (MI). With a few exceptions, the standard ECPSSR appears to be better than its modifications when and ratios are analysed. and and total L x-ray production cross sections, however, are in the best overall agreement with the UA-ECPSSR-MI theory.

Charge state dependence of copper L-shell x-ray production by 4 - 14 MeV oxygen ions

Charge state dependence of L-shell x-ray production cross sections in bombarded by 4 - 14 MeV ions with charge states from q = 3+ to 8+ was measured using a Si(Li) x-ray detector with a resolution of 96 eV at 1 keV. An ultra-thin copper foil was used to ensure single-collision conditions. The data for the total L x-ray production cross sections are compared to the predictions of the first Born and the ECPSSR calculations for L-shell ionization converted to x-ray production cross sections using a single-hole fluorescence yield. Except at the lowest projectile velocity, the ECPSSR theory gives satisfactory agreement with the data while the first Born theory overpredicts all the data in the investigated energy range by almost two orders of magnitude. Measurements of the charge state dependence of the target L-shell x-ray production cross sections allowed the separate contributions of the electron capture (EC) and the direct ionization (DI) to the inner-shell ionization to be determined. The EC contributions were extracted from the x-ray measurements with two, one, and no K-shell vacancies in the oxygen ions. These EC cross sections are compared with the results of an OBK approximation and the ECPSSR theory, and found to be significantly smaller than both EC calculations.

Angular and polarization correlations in double-excitation resonances of Mg

Angular distribution and spin polarization of photoelectrons from 3s valence subshell of neutral magnesium are investigated by using the multiconfiguration relativistic random-phase approximation. Photoionization parameters for all five Rydberg series of double-excitation resonances P1o, P1o, and 3D1o between the Mg+[3s] and Mg+[3p] thresholds are presented to clarify the high-energy portion of the Rydberg series, in which peaks corresponding to double excitations can be identified unambiguously.

Impact-Ionization Processes in Fusion Plasmas

Starting from the relativistic equation of motion governing quantum collision processes in many-particle systems, we shall formulate the relativistic quantum collision theory in an ab initio manner. Quantum electrodynamic effects are however in corporated perturbatively. Because heavy projectiles or ultra-high incident energies are considered, the recoil of the target is also treated. Electron-impactionization of uraniumion U91+ and proton-impactionization of hydrogen will be given as examples.

Photoionization Processes of the Single-Ionized Boron

The relativistic calculations of the cross-section , the angular-distribution parameter , and spin-polarization parameters of photoelectrons using the multiconfiguration relativistic random-phase approximation theory for the photoionization of the ion are presented. Precise energies and widths of all five Rydberg series of doublyexcited states , , , , and are determined. Our predictions are in very close agreement with experiments and are consistent with other calculations.

Photoionization of Be, B+, C2+, N3+, O4+, and F5+ in the MCRRPA theory

The multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization along the Be isoelectronic sequence. Photoionization cross sections between (1s22s)2S1/2 and (1s22p)2P°1/2 ionization thresholds are calculated. There are five Rydberg series of doubly excited states that manifest themselves as autoionization resonances in the photoionization cross section. A comparative study of Be, B+, C2+, N3+, O4+, and F5+ is presented.

Electron-impact ionization for U/sup 91+/ in the QED theory

Electron-impact ionization of highly charged ions is studied in the QED theory. Our calculation will include the transverse-photon interaction as well as the vacuum-polarization potential between charges. We apply the two-potential distorted wave approximation to compute the ionization cross sections. Both direct and exchange effects are considered. The calculated results are compared with those from other theories and with experiment.

Stopping powers of MeV-energy ions 7LI, 12C, 16O and 28Si in some common target materials

Stopping powers for 0.4–8.5 MeV 7Li-ions, 0.4–10 MeV 12C-ions, 0.3–14 MeV 16O-ions and 0.5–11.5 MeV 28Si ions in four commonly used materials (Al, Cu, Ag and Au) have been determined by using the backscattering method. Elastic backscattering spectra were measured at a laboratory detection angle 170° using a passivated implanted planar Si (PIPS) detector. Energy dependence of stopping powers were obtained and compared to the semiempirical model (TRIM-91 and SRIM-96) predictions. The SRIM-96 calculations generally reproduce the experimental data more closely and lead to a significant improvement of the agreement of the 7Li data when compared to TRIM-91.