PS BEAM PRODUCTION AND SCATTERING FROM GASEOUS TARGETS

We have investigated the conversion of a positron beam into an ortho-P a 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 th e 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 s cattering from H-2 and He have also been measured. A comparison with a vailable theories suggests that electron exchange at lower energies an d target inelastic collisions at higher energies are playing a major r ole in the collisions.