Elastic positron-cadmium scattering at low energies

Abstract

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 $126\ifmmode\pm\else\textpm\fi{}42$ meV, with a scattering length of ${A}_{\mathrm{scat}}=(14.2\ifmmode\pm\else\textpm\fi{}2.1)$${a}_{0}$, while the threshold annihilation parameter, ${Z}_{\mathrm{eff}}$, was $93.9\ifmmode\pm\else\textpm\fi{}26.5$. The $p$-wave phase shift exhibits a weak shape resonance that results in a peak ${Z}_{\mathrm{eff}}$ of $91\ifmmode\pm\else\textpm\fi{}17$ at a collision energy of about $490\ifmmode\pm\else\textpm\fi{}50$ meV.