SINGLE IONIZATION BY POSITRON-IMPACT

The single direct ionization cross sections for positron scattering (s igma(i)(+)) on He, Ar, Kr, and H-2 were measured and compared with exi sting data and the corresponding cross sections for electron impact (s igma(i)(-)). At most impact energies the present data for He and H-2 a re in reasonable accord with other measurements and, in the case of He , with some of the available calculations. At low energies sigma(i)(-) is found to increase more slowly than sigma(i)(-), probably due to th e importance of Ps formation in this energy range.