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

Recoil momentum spectroscopy has been used to distinguish experimentally between contributions to the ionization of hydrogenlike O and F projectiles from interactions with the electrons and with the nucleus of a target He atom. The electron-electron contribution is separated from the nuclear one in the final momentum space of the recoil He ion, and is found to produce much smaller recoil momenta, both transverse and longitudinal, than the nuclear process. The relative contributions of the two mechanisms are consistent with theoretical expectations.