Simultaneous excitation and ionization of He-like uranium ions in relativistic collisions with gaseous targets - art. no. 052706

The process of simultaneous excitation and ionization is investigated for H e-like uranium (U90+) ions colliding with Ar, Kr, and Xe targets at an inci dent energy of 223.2 MeV/u. The two-electron transitions, where one of the ground-state electrons is promoted into the continuum and the other into th e L-subshell states of the projectile, are identified by the coincident obs ervation of U Lyman-series radiation and U91+ ions. The experimental cross sections are compared to relativistic calculations based on the independent particle approximation and first-order perturbation theory. It is shown, t hat simultaneous excitation-ionization occurs preferably at small impact pa rameters, for which the excitation process is dominated by the monopole par t of the interaction potential and the perturbation potential is largest. G ood agreement is found between experimental data and calculations for the A r target. For heavier targets the experimental results are generally smalle r than predicted pointing to the invalidity of the first-order perturbation theory in this energy-target atomic number domain.