Dynamic screening of fast ions moving in solids

The electron charge polarization induced by a fast ion moving on a solid medium is considered in a linear response model. An inhomogeneous electron gas model is introduced to describe the contribution to this dynamic screening by the bound target electrons. The action of the bound electrons is to increase the effective number of electrons of the uniform electron gas that reproduces features of the induced potential. We find that the value of the induced potential at the ion position is equivalent to that produced by a jellium of a given density, smaller than that required for the jellium to reproduce the value of the induced electric field at the ion. For the case of fast bare charges we find the precise value of jellium densities required to describe the experimental values of the stopping power in several solid targets. For the case of hydrogenic Kr projectiles in a Cu target, the mixing of its $n=3$ states by the induced potential is just that required to explain recent measurements of radiative decay.