POSITRON-IMPACT IONIZATION OF HE, NE, AND AR

An ionization model containing a realistic description of the final st ate of the system, but employing only plane and Coulomb waves, is appl ied in positron ionization of helium, neon, and argon. This model was shown to agree perfectly with the earlier helium experiment of Fromme et al, for positron impact energies between 30-150 eV. Cross sections calculated with this model for impact energies up to 500 eV compare we ll with recent helium, neon, and argon measurements. Our work also sho ws that by improving the representation of the outgoing positron and e lectron one achieves a better agreement with the high-energy experimen tal cross sections.