Stopping of high-Z ions at intermediate velocities

The stopping of heavy ions at intermediate velocities is influenced by projectile screening, shell corrections, Barkas–Andersen effect and charge exchange. These effects are accounted for in the binary theory of stopping and implemented in the PASS code. Previous applications of this scheme have focused on ions up to argon. The present work is a first attempt to apply the PASS code to very heavy projectiles. It is known that as the ion/target atomic-number ratio increases, the stopping force becomes increasingly sensitive to the ionic charge state. Therefore, care has been taken to incorporate realistic mean charges based on experimental data. Calculated stopping cross sections are found to agree well with experiment at energies above ∼2 MeV/u, while a systematic overestimate of up to 20% is found at lower projectile speeds. Possible causes are studied. Charge-state averaging is shown to have a significant effect at low speed.