Atomic Charge Exchange Between Fast Singly- and Doubly-Ionized Helium Ions in Targets from Carbon to Bismuth at β = 0.36

Atomic charge exchange between singlyand doubly-ionized helium atoms in atomic collisions depends on the speed of the helium atoms and the atomic charge of the target foils. Atomic stripping (ionization) and capture cross sections contribute to this phenomenon, and both of these cross sections can in principle be determined individually. However, in targets of thickness greater than typically 50 pg/cm2 an equilibrium chargestate distribution is established. Only equilibrium charge-state distributions were determined in this work. While neutral atoms must in principle be included in the equilibrium charge-state distribution, their contributions can be neglected at the ion speeds considered in the present experiment. Therefore, in equilibrium we have