Theory of the Forward Peak in the Angular Distribution of Electrons Ejecteed by Fast Protons

The cross section for ejecting electrons by 300-keV protons is calculated using the first term in the Neuman expansion of Faddeev's equation for the final state of the electron-proton-residual ion system. This approximation predicts a peak at 0° in the angular distribution of electrons ejected with a velocity approximately equal to the velocity of outgoing protons. Numerical results for He and ${\mathrm{H}}_2$ target gases are given and compared with the experiments of Rudd and co-workers. The qualitative behavior of the forward peak in the experimental angular distributions is well accounted for.