Ionization of helium, neon and xenon by positron impact

Single ionization of xenon and double ionization of helium, neon and xenon by positron impact have been studied at energies from threshold to similar to 1 keV. The total single ionization cross section of xenon is seen to beh ave as expected. In particular, single ionization with positronium formatio n is a strong channel at low energies. For double ionization we found that positronium formation is strongly suppressed and makes no contribution to t he total cross section in the light noble gases, while some evidence for th is channel is observed in xenon.