Positronium collisions with rare-gas atoms: Free-electron gas plus orthogonalizing pseudopotential model

Abstract

Positronium collisions with rare-gas atoms are treated using the free-electron-gas approximation for exchange and correlation potential. The results confirm the absence of the Ramsauer-Townsend minimum in elastic scattering cross sections, but show lower cross sections in the lower-energy region when compared to previous pseudopotential calculations. This is explained by a more attractive ab initio correlation potential as compared to the previously used empirical potential. The results in the thermal-energy region agree very well with most swarm measurements for all rare-gas atoms. At higher energies, the results are compared with beam experiments and agreement for heavier rare-gas atoms Ar, Kr, and Xe is found to be very good. For He and Ne, some discrepancies with beam measurements are observed. This is explained by a poorer performance of the free-electron-gas potentials, based on the statistical Thomas-Fermi model, for systems with fewer electrons.