Proton angular distributions and highly differential cross sections for ionization of helium by proton impact.

Abstract

The eikonal distorted-wave method is applied to single ionization in proton-helium collisions at laboratory energies of 300 keV, 500 keV, 1 MeV, and 3 MeV. The angular distributions of scattered protons agree well with recent experimental results, showing substantial improvement over the plane-wave Born approximation especially at large scattering angles \ensuremath{\Theta}. The momentum distributions of the ejected electrons at fixed values of \ensuremath{\Theta} are calculated. In particular, those of the electrons ejected mainly in binary proton-electron collisions are studied in detail. The momentum distributions of the recoil ${\mathrm{He}}^{+}$ ions at fixed values of \ensuremath{\Theta} are also discussed by comparing with the results of recent coincidence measurements. At such small \ensuremath{\Theta} at which the plane-wave Born and the eikonal distorted-wave approximations give nearly the same cross sections and are expected to be accurate, these approximations lead to average momenta of recoil ions significantly lower than the measured values.