POSSIBLE POSITRONIUM FORMATION IN THE COLLISIONS OF POSITRONS WITH CALCIUM AND STRONTIUM POSITIVE IONS.

The inelastic collisions of positrons with calcium and strontium positive ions are treated for the first time as a three-channel problem within the framework of the improved coupled-static and frozen-core approximations with the assumption that the elastic, ground positronium and excited-positronium formation channels are open. The calculations of the partial and total cross sections are carried out for eight values of the total angular momentum ℓ (0 ≤ ℓ ≤7), at 20 values of the incident energy lying above the excited positronium formation threshold and extending to a wide region above the ionization threshold of the target ion. The total collisional positronium formation cross sections of e+–Sr+ scattering show a peak around the ionization threshold of Sr+ but display a peak at 30 eV for e+–Ca+ scattering. In both scattering problems the total excited Ps formation cross sections have considerable values in the energy range $15\, {\rm eV}\le k_1^2 \le 100\, {\rm eV}$. [ABSTRACT FROM AUTHOR]