The application of second order potentials to the scattering of charged particles from helium

This work is concerned with a theoretical description of the scattering of charged particles from a helium target, at non - relativistic velocities. Using a truncated atomic eigenfunction expansion it is necessary at high energies to make some allowance for all the channels not explicitly included in the expansion. This is done by constructing a second order potential matrix. The method is applied to the scattering by helium atoms of electrons between 50 ev. and 1000 ev., and results are presented for elastic scattering and the 2'S and 2'P excitations. It is found that the inclusion of the couplings between these channels and the inclusion of second order terms in the potential, leads to cross sections which are in significantly better agreement with the experimental data. By reversing the sign of the potential, a comparison is made between positron and electron scattering at the same energy.