Angular distribution of photons for the simultaneous excitation and ionization of He-like uranium ions in relativistic ion-atom collisions

Abstract

Simultaneous ionization and excitation processes are studied for initially He-like uranium ions in collisions with xenon gaseous targets at relativistic energy, $220\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/u$. The virtue of investigating the process of simultaneous excitation and ionization is that one electron ends up in the continuum, while the other electron ends up in a hydrogen-like final state. Experimentally, this process can be identified by observing the radiative decay of the excited levels in coincidence with ions that lost one electron (U${}^{91+}$). In particular, owing to the large fine-structure splitting of H-like U, the angular distribution of photons for the simultaneous ionization and excitation into the different total angular momentum $j=1/2$ and $j=3/2$ states of the L shell is determined directly from the obser-ved yields of Ly${}_{\ensuremath{\alpha}1}$ and Ly${}_{\ensuremath{\alpha}2}$ radiation at various observation angles. The experimental data show a progress for the dependence of the alignment on the collision impact parameter. It is shown that the current results confirm the theoretical predictions based on the independent-particle approximation and first-order perturbation, for which the simultaneous ionization and excitation processes occur at small impact parameter.