EVIDENCE FOR RESONANCE AND ABSORPTION EFFECTS IN POSITRON-ATOM DIFFERENTIAL ELASTIC-SCATTERING

This review focuses on recent positron-atom elastic differential cross section (DCS) measurements which reveal evidence that interference ef fects may be occurring between the elastic and inelastic scattering ch annels. These effects appear as (1) absorption effects which are obser vable in relative elastic DCSs by the ''washing out'' of structure in the DCS versus angle as the positron energy is increased above the pos itronium formation threshold, and (2) a new type of resonance-like str uctures at intermediate energies (well above the normal inelastic thre sholds) that have been observed in absolute elastic DCS measurements w hen plotted at a fixed scattering angle versus energy. A discussion is provided of possibly relevant information on positron-atom scattering that also indicates that coupling is occurring between various scatte ring channels.