Coupling And Binding-Saturation Effects In L-Subshell Ionization Of Heavy Atoms By 0.3-1.3-Mev/Amu Si Ions

The coupling and binding effects have been studied in L-subshell ionization of heavy Au, Bi, Th, and U atoms by an impact of Si-28(q+) ions in the energy range of 8.5-36.0 MeV. The measured L x-ray spectra were analyzed taking into account the multiple ionization effects in outer M and N shells. The L-subshell ionization cross sections have been obtained from measured x-ray production cross sections using the L-shell fluorescence and Coster-Kronig yields which were modified for a reduced number of electrons and closed Coster-Kronig transitions in the multiply ionized atoms. The results are compared with the available calculations, which are based on the semiclassical approximation (SCA) as well as the plane-wave Born approximation (PWBA). We demonstrate that for silicon ion impact these theoretical approaches have to be modified to include the L-subshell coupling effect using the "coupled subshell model" (CSM) as well as the saturation of the binding effect at the united atom limit. The calculations modified for both effects are in much better agreement with the data. In particular, an order-of-magnitude improvement of agreement between the data and the SCA-CSM calculations including the binding-saturation effect is reported for low-energy Si ions for the L-2-subshell. The results are also compared with the predictions of the PWBA based ECPSSR and ECUSAR theories accounting for the energy-loss (E), Coulomb-deflection (C), and relativistic (R) effects treating the binding effect within the perturbed stationary state (PSS) approximation with correction for the binding-saturation effect introduced to describe the united-atom and separated-atom (USA) limits.