Low energy positron scattering and annihilation studies using a high resolution trap-based beam

A high resolution positron beam, generated from a Penning-Malmberg trap, has been used for a range of low energy scattering and annihilation studies on atoms and molecules. We describe measurements of total scattering, differential elastic scattering and integral vibrational and electronic excitation cross sections for a number of atoms and molecules using this beam, and compare the absolute cross sections that are obtained with data from electron impact. The first study of annihilation on atoms and molecules as a function of positron energy is described. The results in molecules indicate large resonant enhancements of the annihilation rates at energies corresponding to those of the molecular vibrations. (C) 2002 Elsevier Science B.V. All rights reserved.