Elastic positron-cadmium scattering at low energies

The elastic and annihilation cross sections for positron-cadmium scattering are reported up to the positronium-formation threshold (at 2.2 eV). The low-energy phase shifts for the elastic scattering of positrons from cadmium were derived from the bound and pseudostate energies of a very large basis configuration-interaction calculation of the e(+) -Cd system. The s-wave binding energy is estimated to be 126 +/- 42 meV, with a scattering length of A(scat) = (14.2 +/- 2.1)a(0), while the threshold annihilation parameter, Z(eff), was 93.9 +/- 26.5. The p-wave phase shift exhibits a weak shape resonance that results in a peak Z(eff) of 91 +/- 17 at a collision energy of about 490 +/- 50 meV.