Scattering and annihilation experiments using a trap-based beam

The buffer gas trap technique for positron trapping and beam formation has made available a low energy, high resolution positron beam for the first time. This has opened the way for a range of new studies in positron-atom(molecule) scattering, including measurements of annihilation cross sections (Zeff) as a function of energy and processes such as excitation by low energy positron impact. New light is now being shed on the interactions of positrons with ordinary matter, including the first observation of positron-molecule resonances, and the latest progress in these studies is summarised here. The application of these techniques to the studies of larger systems, such as clusters, is also briefly discussed. (orig.)