Total ionization cross sections of He, H2 and Ar by positron impact

Total positron impact ionization cross sections, including contributions from positronium formation, have been measured for He, H2 and Ar from below the positronium formation threshold, Eps, up to 60 eV, 31 eV and 41 eV respectively. These cross sections have been subtracted from corresponding total cross section measurements and a small decrease in the elastic cross section between Eps and the threshold for excitation has been deduced for all three targets.

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