Single- and double-ionization cross sections for angular scattering of fast protons by helium

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Abstract
The angular scattering of H+ by He has been investigated for single ionization at energies of 0.5, 1.0, and 3.0 MeV; and for double ionization at 1.0 MeV. The classical-trajectory Monte Carlo method has been used within one- and two-electron models to illustrate the collision dynamics. The angular differential single-ionization cross sections are in good agreement with experiment, and display the combined effects of proton scattering from the He nucleus and its electrons. The relative fraction of double ionization, as a function of scattering angle, shows a maximum at ∼0.9 mrad that is in agreement with the experiments of Giese and Horsdal [Phys. Rev. Lett. 60, 2018 (1988)]. This maximum is found to be due to two uncorrelated scattering events between the H+ and the He atom’s two electrons in the double-ionization reaction from impact parameters different than that for the single-ionization reaction.