K-shell processes in heavy-ion collisions in solids and the local plasma approximation

We have investigated K-shell vacancy production due to ionization and electron transfer processes, in collisions of highly charged oxygen ions with various solid targets such as Cl, K, Ti, Fe, and Cu at energies between 1.5 and 6.0 MeV/u. The K-shell ionization cross sections were derived from the measured K x-ray cross sections. An ab initio theoretical model based on the local plasma approximation (LPA), which is an extension of the dielectric formalism to consider core electrons, provides an explanation of the measured data only qualitatively. In case of asymmetric collisions (Z_p/Z_t<0.35, Z_p, Z_t being the atomic numbers of the projectile and target, respectively) and at higher energies, the LPA model explains the data to some extent but deviates for more symmetric collision systems. On the other hand, a perturbed-stationary-state (PSS) calculation (ECPSSR), including the corrective terms due to energy (E) loss, Coulomb (C) deflection, and relativistic (R) wave functions designed for ion-atom collisions agree quite well with the data for different combinations of target and projectile elements. In addition, we have also measured the K(target)-K(projectile) electron transfer cross sections and compared them with a model based on perturbed-stationary-state approximation.