Coupling and binding effects in L-shell ionization of heavy atoms by oxygen, silicon and sulphur ions

The coupling and binding effects in ionization of L-shell electrons by heavy ions have been studied by measuring the Lγ(L-N,O) X-ray transitions in gold excited by an impact of O, Si and S ions in the energy range 0.3-5 MeV/amu. The L-subshell ionization cross sections were extracted from measured X-ray spectra taking into account their substantial modifications due to the multiple ionization effects, which also change the fluorescence and Coster-Kronig yields. In order to interpret the data the L-subshell couplings were incorporated in the theoretical calculations based on the semiclassical approximation (SCA) within the “coupled subshell model” (CSM). Resulting SCA-CSM calculations, which describe the data for oxygen ions quite satisfactory, are further modified to include the saturation of the binding effect in order to describe the data for heavier Si and S ions. We find that the semiclassical SCA-CSM calculations of L-shell ionization by heavy ions (Z1 ≫ 1), which include corrections both for coupling and binding saturation effects, agree reasonably well with the measured data.