Fundamental Studies of Positron Scattering from Atoms and Molecules

Abstract

This thesis presents measurements of low-energy positron scattering from Argon and C60. Absolute elastic differential cross sections are presented for positron scattering from Argon in the energy range 2 to 50 eV, as well as absolute total elastic and inelastic cross sections up to 20 eV. These results are compared with theoretical calculations using the convergent close-coupling (CCC) and relativistic optical potential (ROP) methods and it was found that generally the measurements were in closer agreement with the CCC method than the ROP method across the energy range, although the ROP method was an excellent description of the total inelastic cross section in this energy range.

Argon was also the focus of the first results from the newly developed positron reaction microscope. Experimental techniques were developed to produce measurements of the kinematics of positron-induced single ionisation of Argon. Single ionisation events were detected in coincidence and their momenta reconstructed using data analysis methods detailed in this thesis. Although further work is required to provide total differential cross sections, the initial data presented in this thesis is in alignment with expectations based upon available theory and experiment and provides a promising starting point for future studies using the positron reaction microscope.

Finally, a search was conducted for resonant features in the total scattering and Positronium formation cross sections of C60. Motivated by the predictions of Gianturco and Lucchese (1999), which indicated experimentally-accessible resonances, the present data does not show any features. However, the current results in this thesis represent the first preliminary measurements of the total scattering and Positronium formation cross sections for C60 and follow the expected trend for positron-molecule scattering. Additional data to be collected in the future, would allow for confirmation of the presence, or lack thereof, of resonant features with a higher statistical confidence.