Proton and antiproton impact ionization of atomic hydrogen and helium.

Single ionization of helium and atomic hydrogen by the impact of protons and antiprotons is considered. Using a multiple scattering model, first proposed by Garibotti and Miraglia [1], angular and energy distributions of the ejected electrons are calculated. Structures arising in the cross section, especially the Coulomb density of states effect (CDS), are analysed. The contributions of various scattering amplitudes to the cross section are studied. It is concluded that multiple scattering together with the CDS-effect play an important role in determining the transition amplitude. Differences between particle and antiparticle impact are examined. In addition to the different behaviour of the CDS-effect, the interference of two scattering amplitudes turns out to be decisive in ionization by particle and antiparticle impact. [ABSTRACT FROM AUTHOR]