K-shell ionization by 16O and 32S ions: Reduced-velocity dependence of the binding effect.

Abstract

K-shell ionization probabilities ${P}_{K}$ were measured for 2.2-MeV/u $^{16}\mathrm{O}$ ions with impact parameter b=16--51 fm on 24 targets ranging from Sc to Bi. For Bi, the distribution ${P}_{K}$(b) was also measured. Total K-shell ionization cross sections ${\ensuremath{\sigma}}_{K}$ for $^{16}\mathrm{O}$ and $^{32}\mathrm{S}$ projectiles are reported for the same target range. Semiclassical calculations using the velocity-dependent electron binding energies from the relativistic two-center approximation of Andersen, Laegsgaard, and Lund reproduce both ${P}_{K}$ and ${\ensuremath{\sigma}}_{K}$ very well, except where polarization effects become important.