Differential cross sections for multiple ionization of Ne and Ar in collisions with fast protons.

Abstract

Differential cross sections for single and multiple ionization of Ne and Ar by protons have been measured at impact energies of 3 and 6 MeV, and at proton scattering angles between 0.1 and 0.9 mrad. The recoil ions formed in the collision processes were extracted from the collision region and detected in coincidence with the scattered protons. Their charge states were determined by their flight times. The experimental differential cross sections for single and multiple ionization are qualitatively explained by a simple model that takes into account the contributions of scattering from the electrons and from the target nucleus. The model indicates that ionization by hard proton-electron collisions remains the largest contributor to single and multiple ionization of both Ne and Ar for projectile scattering angles larger than 0.1 mrad. The ratio of double-to-single ionization cross sections for Ne and Ar increases with increasing proton scattering angle, suggesting an increasing importance of inner-shell ionization at small impact parameters.