POSITRON SCATTERING BY ATOMIC-HYDROGEN INCLUDING POSITRONIUM FORMATION

Positron scattering by atomic hydrogen including positronium formation has been formulated using the R matrix method and a general computer code written. Partial wave elastic and ground state positronium format ion cross sections have been calculated for L less than or equal to 6 using a six-state approximation which includes the ground state and th e <(2s)over bar> and <(2p)over bar> pseudostates of both hydrogen and positronium. The elastic scattering results obtained are in good agree ment with those derived from a highly accurate calculation based upon the intermediate energy R-matrix approach. As in a previous coupled-ch annel static calculation, resonance effects are observed at intermedia te energies in the S-wave positronium formation cross section. However , in the present results, the dominant resonance arises in the P-wave cross sections at an energy of 2.73 Ryd and with a width of 0.19 Ryd. The mechanism for the formation of this resonance and its possible exp erimental verification are briefly discussed. Finally, the summed elas tic and positronium formation cross sections are presented and the lat ter compared with experiment for energies ranging from near threshold to 4.0 Ryd.