Electron-impact ionization and energy loss of 27-MeV/u ${\mathrm{Xe}}^{35+}$ incident ions channeled in silicon

We have measured the emerging charge-state distribution of 27-MeV/u ${\mathrm{Xe}}^{35+}$ beams channeled through a thin Si single crystal, and deduced electron impact ionization cross sections for ${\mathrm{Xe}}^{35+}$ to ${\mathrm{Xe}}^{45+}$ by 14.7-keV electrons. They are ≊2 to 4 times higher than predicted by usually accepted empirical estimations. We have also measured the energy loss versus emerging charge state. For hyperchanneled ${\mathrm{Xe}}^{\mathrm{Q}+}$ ions, the stopping power depends only on the mean (and not on the actually sampled) density of valence electrons and compares well with the prediction of the electron gas model.