While the understanding of single ionization has proceeded considerably in the recent years, for particle impact double ionization comparatively few kinematically complete experiments and corresponding theoretical calculations have been performed.
Since the exact theoretical treatment of this four-body system (e.g. three electrons and one ion) with inclusion of all mutual interactions is not possible, existing theories restrict themselves to identify the most important interactions for a given kinematical situation and to consider only these in the calculation.
E.g. for fast collisions (E_{0} >2 keV) the projectile can be treated as a small pertubation neglecting its influence before and after the collision. Then the description of the two ejected target electrons in the continuum including their mutual interaction and the interaction with the ion can be performed with the methods developed for low energy (e,2e) collisions. Therefore the reaction can be treated as an effective three-body system. |