Symmetric ion-atom collisions at medium energies. Characteristic x rays

We report the characteristic $\mathrm{Ke}$-shell x-ray production cross sections for Al ions (500 keV to 40 MeV) incident on thin, solid Al targets and for Ni ions (10-63 MeV) incident on thin, solid Ni targets. In these energy regions the transition from predominately quasimolecular excitation to predominantly Coulomb excitation occurs. For incident Al-ion energies up to ∼ 10 MeV the experimental cross sections are predicted reasonably well by deuteron-deuteron cross sections, scaled according to a recipe provided in a model of Briggs and Macek. For higher incident Al-ion energies the reported cross sections fall below the predicted results given by the modified plane-wave Born approximation and probably reflect the dependence of the x-ray cross section on the charge of the incident ion.