The Scattering of Positrons and Positronium by Atoms in the Close-Coupling Approximation

We present some recent results obtained within the close-coupling approximation for both positron and positronium scattering by atoms. We begin by discussing a generalization of the method of Vincent and Phatak to study the formation of Ps- in Ps collisions with H(1s) in a simplified model. The important result of this calculation is that the overall Coulomb interaction which is present in the rearrangement channel is treated exactly. We also present results for positronium formation and ionization for positron scattering by argon atoms. The present calculations are for transitions from the Αr(3s$\text{}^{2}$) subshell and show the importance of the coupling to the continuum.