LOW-ENERGY S-WAVE POSITRON LITHIUM SCATTERING

A detailed investigation has been made of low energy s-wave positron-lithium scattering using the Kohn variational method in the energy range in which only elastic scattering and positronium formation are possible (0-1.84 eV). The positronium formation cross section is infinite at zero energy, but then falls to be several orders of magnitude smaller than the elastic scattering cross section, which has a peak value of approximately 100 pia(0)2. The elastic scattering cross sections are almost unaffected by the uncoupling of the positronium channel, but the resulting phaseshifts are significantly more positive, and therefore probably more accurate, than those obtained in the most sophisticated previous study using the uncoupled approximation.