Possible positronium formation in the collisions of positrons with calcium positive ions

The collisions of positrons with calcium positive ions (²⁰Ca⁺) are treated under the assumption that the elastic and positronium formation channels are open. A one-valence-electron model for the target, based on the Clementi-Roetti Slater-type basis functions, as well as a coupled-static approach allowing for the polarisation of the positroniums, are used for calculating the partial cross sections of eight partial waves (0 ≤ l ≤ 7, where l is the total angular momentum). The calculations are carried out for 28 values of the incident energy lying between the positronium formation threshold (at 4.52 eV) and extending to a wide region above the ionisation threshold of Ca⁺ (at 11.32 eV).