PROBLEMS CONCERNING THE EFFECTIVE CHARGE OF SWIFT HEAVY-IONS TRAVERSING GASEOUS AND SOLID TARGETS

The passage of heavy ions through solid targets is a topic which continues to puzzle investigators in various aspects. Although it is treated for several decades, and despite much progress in the understanding of both slow and fast ion-atom collisions, one of the difficulties remained unsolved: the high spatial density of foil target atoms causes a high rate of electronic collisions which, due to the formation of copious excited (and continuum) states, cannot be described independently. A basic lack of understanding is illustrated by the so-called density effect which arises from a comparison of ion passage through solid versus gaseous targets.