Simultaneous capture and ionisation by fast ion impact on helium

The authors show that the effects of saturation on the ionisation probability at small impact parameters can be exhibited in ion-atom collisions where simultaneous electron capture and ionisation occur. Such effects show up for this process because capture probabilities are only appreciable at small impact parameters, whereas saturation effects hardly appear in a simple ionisation process where significant contributions come from large impact parameters. When such effects are accounted for accurately, good agreement with experiments can be obtained within an independent-electron model. (author)