Swift cluster-atom collisions: experiment and model calculations

Single, double and triple ionization cross sections of 10 MeV projectiles colliding with He atoms have been measured. This was achieved thanks to a new experimental set-up allowing for a complete collection and unambiguous identification (in particular with respect to their charge) of all the fragments emitted by the dissociative species (Q = 2, 3, 4). As a first attempt to understand the mechanisms of ionization in the cluster we use these results, together with those we obtained in the identical velocity 2 MeV system, for testing the predictions of an {independent atoms} - atom collision calculation within the impact parameter formalism and using the independent-electron approximation. The model is found to be surprisingly good in predicting the cluster - atom results when appropriate (i.e. able to reproduce the atom - atom case) impact parameter dependent ionization probabilities are used.