TOTAL IONIZATION CROSS-SECTIONS OF HE, H-2 AND AR BY POSITRON-IMPACT

Total positron impact ionization cross sections, including contributio ns from positronium formation, have been measured for He, H-2 and Ar f rom below the positronium formation threshold, E(Ps), up to 60 eV, 31 eV and 41 eV respectively. These cross sections have been subtracted f rom corresponding total cross section measurements and a small decreas e in the elastic cross section between E(Ps) and the threshold for exc itation has been deduced for all three targets.