Positron-impact ionization and positronium formation from helium

Abstract

Detailed measurements of the total ionization cross-section by positron impact on He from threshold up to 850 eV are reported. Both the present total ionization cross-section and the direct ionization cross-section of Moxom et al (1996) and Ashley et al (1996) have been normalized to the latest electron-impact ionization cross-sections. The positronium formation cross-section for this target is thus extracted and compared with the existing experimental and theoretical data.