Abstract
Calculations are reported for 1s to 1s elastic scattering and for 1s to 2s and 1s to 2p excitation of atomic hydrogen by positron impact in the energy range 54.4-300 eV. A close-coupled pseudostate approximation is used to represent transitions between s, p and d states of the target while couplings to target states of higher angular momentum are treated perturbatively through the second Born approximation. Comparison is made with similar calculations of van Wyngaarden and Walters (1986) for electron scattering. The cross section for elastic scattering is smaller than its electron counterpart, the difference being as much as a factor of three at 54.4 eV. The cross sections for 1s to 2s and 1s to 2p excitation are larger than for electron collisions. By contrast the total cross sections for the two projectiles remain almost equal down to the lowest energy. Comparison is also made with other sophisticated theoretical calculations. At 100 eV and above good agreement is found with the previous theoretical work on elastic scattering.

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