Universal scaling of the M- and N-shell ionization probabilities measured in collisions of O, Si and S ions with heavy atoms

Multiple ionization in outer M- and N-shells in Ta, Os, Au, Bi, Th and U targets was studied for O, Si and S ion impact at energies of 0.3-2.2 MeV amu-1. Excited Lγ(L-N, O) x-rays measured with a semiconductor Si(Li) detector were resolved by using a newly developed method accounting for simultaneous x-ray energy shift and line broadening due to the multiple ionization. The measured ionization probabilities, corrected for the effect of the vacancy rearrangement up to the moment of L x-ray emission, are interpreted as the ionization probabilities for M- and N-shells for the zero impact parameter. The ionization probabilities for the N-shell are found to be substantially increased by the super-Coster-Kronig transitions. Derived ionization probabilities for M- and N-shells are compared with the predictions of the geometrical model (GM) and the semiclassical (SCA) calculations in the united-atom limit. The universal scaling of the measured ionization probabilities for the M- and N-shells is discussed within the GM and SCA approaches.