Projectile ionization in fast heavy-ion—atom collisions

Electron emission following the ionization of projectile ions has been investigated systematically in collisions with ${\mathrm{Ne}}^{q+}$ and ${\mathrm{Ar}}^{q+}$ ions at several hundred MeV incident on different target gases. The projectile electrons are concentrated within one maximum, the electron-loss peak (ELP). The variation of the shape and intensity of the ELP with the projectile energy, its charge state, the observation angle, and the target gas has been measured. Theoretical predictions which are based on the binary-encounter approximation show, in general, good agreement with the experimental data. The contributions of the different subshells to the ELP are deduced. It is shown that electronic screening of the target nucleus plays an important role in the ionization process of the projectile ions.