Positron-impact ionization of atoms: Experiments

This review covers the recent experimental results on positron-impact ionization as well as results which can be expected in the near future. Topics of other Workshop reviews such as Ps formation and inner-shell ionization are not included here. In single ionization, interesting new developments are the comparison of positron/electron impact with proton/antiproton impact, cross-section measurements for atomic hydrogen, and threshold studies with H2 and noble-gas atoms. In double and triple ionization, some level of completion has been reached; further work along this line is to be expected when improved energy resolution will permit studying multi-ionization threshold behavior. The above remarks concern total ionization cross sections, the only type measured so far. Two experiments on single-differential and one on double-differential cross sections are on the way. Triple-differential measurements would be very interesting, but are not yet feasible. (orig.)