Positron impact ionization of krypton and xenon

Several distorted-wave models for positron ionization of krypton andxenon a re investigated. Our previous CPE (Coulomb plus Plane waves - full Energy r ange) model produces reliable cross sections for krypton. For xenon, at hig h positron energies, the CPE results fall below experiment. We have propose d an alternate model DCPE4 that works well for both krypton and xenon. A co mmon feature of both of these models is that the free electron andpositron are treated differently.