CLOSE-COUPLING THEORY OF POSITRON SCATTERING FROM ALKALI ATOMS

The close coupling equations for positron-alkali atom scattering are w ritten as a set of coupled momentum-space Lippmann-Schwinger equations . The alkali atom is represented by a frozen-core model based upon the Hartree-Fock approximation. The interaction between the positronium a nd the residual ion is modified by the inclusion of a core potential. Similarly, a core term is present in the interaction describing the re arrangement process. Close coupling calculations of positron scatterin g from sodium are performed in a model containing multiple sodium (3s, 3p, 4s, 3d, 4p) and positronium (1s, 2s, 2p) states. Cross sections a re reported for an energy range from threshold to 50 eV; the total cro ss sections are in agreement with experimental data.