Experimental separation of electron-electron and electron-nuclear contributions to ionization of fast hydrogenlike ions colliding with He

Electron- and proton-impact excitation of hydrogenlike uranium in relativistic collisions

The K shell excitation of H-like uranium (U(91+)) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.

Simultaneous projectile-target ionization: a novel approach to (e, 2e) experiments on ions

A kinematically complete experiment for simultaneous ionization of a projectile and target has been performed for 3.6 MeV/u C2+ on He collisions measuring the final vector momenta of the He1+ recoil ion and of two electrons (projectile, target) in coincidence with the emerging C3+ projectile. The feasibility of an event-by-event separation of the various reaction channels, among them the ionization of C2+ by the interaction with a quasifree target electron, is demonstrated in agreement with six-body classical trajectory Monte Carlo calculations, paving the way to kinematically complete electron-ion scattering experiments.

Effective strength of the electron-electron interaction in simultaneous projectile and target ionization

The determination of the right balance between the strong-field interaction of the screened target nucleus and the two-center electron-electron interaction has been controversial since the early attempts to describe the stripping of light, swift ions, by heavy targets. In this work, we find a region of influence for the electron-electron contribution which clearly indicates that this interaction is an essential contribution to the stripping process for both light and heavy targets.