Antiproton and proton excitation of atomic K-shell electron

We have investigated the dependence of sign of projectile charge on antiproton and proton impact K-shell ionisation cross sections of atoms using the Binary Encounter Approximation. The effects of Coulomb attraction/repulsion and decrease/increase in binding of K-shell electron have been incorporated in respective cases. The Hartree-Fock velocity distribution for the atomic K-shell electrons has been used throughout the calculations. Antiproton cross sections are larger by a factor of about 2 than proton cross sections at 1 MeV and the factor increases with decrease in impact energy. (author). 21 refs., 5 figs