Ionization studies of channelled hydrogen-like F ions in a Si single crystal

Channelled ions in a Si single crystal see a very high density quasi-free e lectron gas and hence provide an opportunity to study e-impact ionization o f the projectile even though the e-e interaction responsible for this is mu ch weaker than the e-n interaction which usually dominates the process of p rojectile ionization. The e-e interaction has been experimentally identifie d through the observed fast increase in the impact energy dependence of the ionization of the hydrogen-like F ions, the calculated contribution from t he e-n interaction being impact energy independent at large impact paramete rs. The relative variation of the measured cross sections for well-channell ed ions is in good agreement with the convergent close-coupling theory of e -impact ionization and existing scaling laws. In addition to the M-shell el ectrons, participation of the Si L-shell in the ionization of the channelle d ion is suggested.