The dynamics of target ionization by fast highly charged projectiles

Abstract

We report on the first kinematically complete investigation of single target ionization by fast heavy ions, on the measurement of all low energy electrons down to zero emission velocities and on the determination of the projectile energy loss on the level of ΔEp/Ep≈ 10−7. This has been achieved by combining a high-resolution recoil-ion momentum spectrometer with a novel 4π electron analyser. The complete momentum balance between electron, recoil-ion and projectile for single ionization of helium by 3.6 MeV/u Ni24+ was explored. Low energy electrons are found to be ejected mainly into the forward direction with a most likely longitudinal energy of only 2 eV. The electron momentum is not balanced, as might be expected, by the projectile momentum but is nearly completely compensated by the recoil ion. Surprisingly, the momenta of the helium-atom “fragments”, the electron and the He1+ recoil ion, are considerably larger than the total momentum loss of the projectile: the target atom seems to dissociate in the strong, long ranging projectile potential. The collision has to be considered as a real three-body interaction.