Effective-charge theory for the electronic stopping of heavy ions in solids: Stripping criteria and target-electron models.

Abstract

The calculation of the ionization fraction of the ion as a function of the ion atomic number, ion velocity and target Fermi velocity is the first step in effective-charge theory for heavy-ion stopping. We show results using the energy stripping criterion for the ionization fraction and give reasons for its superiority as against the velocity stripping criterion. The second computational step is the transformation of the ionization fraction into an effective-charge fraction assuming a linear dynamic dielectric response of the target material. On the basis of the Kaneko shell theory of solid targets we explain, to what extent the simple free-electron gas model still may work, if the heavy-ion stopping calculation makes use of the heavy-ion scaling rule and experimental proton stopping data.