Detailed measurements of the total ionization cross-sections for
Ne, Ar, Kr and Xe by positron impact are presented in the
energy range from threshold up to ~1 keV. From these
and other available data, the cross-sections for positronium
formation are extracted. Comparison is made with other results
where available. Structure in the positronium formation
cross-section has been found which appears to be associated with
positronium formation in excited states. Upper and lower limits
on the contribution from these are estimated.
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.
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