Beale, J.E.; (2007) Positron and positronium interactions with atoms and molecules. Doctoral thesis , University of London.

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Abstract

Positronium is the lightest known atom, consisting of an electron and its antiparticle the positron. Because of its light mass (comparable with that of the electron and positron, rather than conventional atoms), recoil effects are expected to play an important role in its scattering from atomic and molecular targets. Up until recently positronium beam experiments have been restricted to total cross-section measurements from simple target atoms and molecules i.e. molecular hydrogen, molecular nitrogen, helium and argon where trends have been noted. Therefore, the aim of the project has been to look at more complex targets to supplement existing data and to investigate further positronium total cross-section measurements for molecular oxygen and xenon started by Gamer et al (1998) and Leslie (PhD thesis, 2005), as well as to compare with corresponding data for other projectiles and theoretical determinations. This has been achieved by looking at neon, xenon, molecular oxygen and water. The total cross-section for positron-water has also been measured in order to investigate the general performance of the system in the presence of water vapour. Also, as an extension of the fragmentation study by Armitage et al (2002) and Leslie (2005), the yields of residual electrons and positrons from positronium-xenon impact at an energy of 30eV have been examined to ascertain contributions from target ionization. Both the integrated cross-section and longitudinal energy distributions have been measured. Finally, due to the lack of data for water interacting with positrons and positronium, and to complete the work of Arcidiacono (PhD thesis, 2006), both doubly differential ionization cross-sections of water molecules by 100 and 153eV positron impact and total cross-sections of water molecules for positronium impact have been measured.

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