PROTON ANGULAR-DISTRIBUTIONS AND HIGHLY DIFFERENTIAL CROSS-SECTIONS FOR IONIZATION OF HELIUM BY PROTON IMPACT

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 THETA. The momentum distributions of the ejected electrons at fixed values of 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 He+ ions at fixed values of THETA are also discussed by comparing with the results of recent coincidence measurements. At such small 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.