THE POSITRON-HYDROGEN SYSTEM AT LOW ENERGIES

Calculations of low-energy positron-hydrogen and positronium-proton sc attering using the dose coupling method are reported at energies below the ionization threshold. The channel space included six hydrogen (Is , 2s, 2p, ($$$) over bar 3s, ($$$) over bar 3p and ($$$) over bar 3d) and six positronium (Is, 2s, 2p, ($$$) over bar 3s, ($$$) over bar 4s and ($$$) over bar 3p) states. Comparisons with more accurate calculat ions demonstrate that this model should give integrated cross sections accurate to 10%. Cross sections are computed with a fine energy mesh and a total of II resonances associated with the H(n = 2) and Ps(n = 2 ) thresholds have been identified and the resonance positions and widt hs determined. Calculations of the total cross section and the positro nium formation cross section for positron-hydrogen scattering are cons istent with the available experimental data Cross sections for elastic scattering in the Ps(ls)-p entrance channel are dominated by a strong polarization potential and vary from 1000 pi a0(2) at threshold to 15 pi a(0)(2) at 1.0 Ryd. Cross sections for the Ps(ls) + p --> e(+) + H (nl) rearrangement collision are also reported since these provide bas eline data relevant to experiments aimed at making antihydrogen atoms. Differential cross sections for elastic Ps(ls)-p and e(+) -H(ls) scat tering and for electron transfer to the hydrogen atom ground state are also reported at selected energies.