Mechanism of excitation of two-electron—one-photonKx rays in heavy-ion collisions

The energy dependence of the cross sections for both the $K\alpha$ (one-electron, one-photon) and $K\alpha \alpha$ (two-electron, one-photon) x-ray emissions for Ni-Ni collisions have been measured in the energy range 17.6-91.5 MeV. To account for these observations, we have extended the electron promotion model to the quantitative, ab initio calculation of double $K$-shell vacancies. The results furnish, for the first time, an independent test of both the Briggs-Macek formulation of the electron promotion model and the concept of velocity-dependent exit channels suggested by Fastrup et al. We also present, for the first time, a theory of the vacancy-sharing mechanism for double $K$-shell excitation in symmetric systems. The theoretical results are in quantitative agreement with experiment.