DEPENDENCE OF THE BINARY-ENCOUNTER-PEAK ENERGY ON THE PROJECTILE CORE

The energy of the binary-encounter peak has been determined for 0.6 Me V/u O, F, Si, Ti, Cu, and Br ions colliding with H-2 targets. The proj ectiles all had the same charge q=7, while the atomic number Z of the projectiles ranged from 8 (almost totally ionized) to 35 (retaining 28 electrons). We observe that the binary-encounter-peak energy for fixe d q increases as Z increases. This trend is opposite to that observed when Z is fixed and the charge q is varied, and it demonstrates that t he binary-encounter-peak energy depends not only on the net projectile charge but on the projectile core as well. The experimental trend is qualitatively reproduced by an impulse approximation showing that this variation in the binary-encounter-peak energy may be attributed to th e effect that the projectile core potential has on the electron elasti c-scattering cross section.