Ps beam production and scattering from gaseous targets

We have investigated the conversion of a positron beam into an ortho-Pa beam via charge exchange in gaseous H-2, He and Ar at energies up to 120 eV and gas pressures up to 14 mu mHg. H-2 has been found to be the most efficient converter at energies up to 90 eV. At higher energies, Ar has been found to be the best. Total cross sections of ortho-Ps scattering from H-2 and He have also been measured. A comparison with available theories suggests that electron exchange at lower energies and target inelastic collisions at higher energies are playing a major role in the collisions.