Nonperturbative theory of projectile-electron loss in fast collisions with heavy atomic targets

The electron loss of ${\mathrm{He}}^{+}$ projectiles in heavy targets is studied within the framework of the sudden approximation. The main focus of the present study is in the elastic (screening) contribution to the electron loss. The calculations presented here unitarize the final populations of the projectile and of the target, take into account the nonperturbative character of the collision, and include the possibility of multielectronic transitions in the target atom concomitantly with the loss process. An analytical estimate for the screening contribution is also obtained.