A positron is the antimatter counterpart of the electron with which it can form a short lived bound state called positronium (Ps). The interactions of both of these particles with matter is the concern of the present work. These are of relevance in a variety of fields, for example, galactic astronomy, condensed matter physics and positron emission tomography. In the present work, the progress toward the realisation of a positron reaction microscope is described which will hopefully lead to the measurement of fully differential cross sections for ionizing collisions. To achieve this, a crossed beam system has been developed, in which a positron beam is passed through a supersonic gas jet target. Ions produced in the resulting collisions are guided onto a position sensitive detector for imaging using a spectrometer. A complementary theoretical study of target ionization caused by positron collisions has also been carried out. This has involved the development of a 3-body classical trajectory Monte Carlo simulation which has been applied to the calculations of direct-ionization, Ps formation, and excited state Ps formation cross sections. The development of the code also included a study of numerical integrator techniques, as well as, by way of diagnostics, the calculation of cross sections for collision systems which have been previously studied (e.g. proton - hydrogen). Finally, the mono-energetic Ps beam line at UCL has been used to measure the Ps total scattering cross section (TCS) for collisions with CO2. This work has contributed towards the observation that the Ps TCS is remarkably similar to that of an equivelocity electron. An enhancement in the TCS has also been observed in the vicinity of the 2 \Pi u shape resonance in the electron - CO2 TCS.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:625626 |
| Date | January 2011 |
| Creators | Williams, A. I. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1318149/ |
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