This dissertation, "The Focusing of the HKU Positron Beam, and an Extended Design for Incorporating Secondary Electron-positron Annihilation Lifetime Spectroscopy" by Pui-ying, Rebecca, Kwan, 關珮瑩, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled THE FOCUSING OF THE HKU POSITRON BEAM, AND AN EXTENDED DESIGN FOR INCORPORATING SECONDARY ELECTRON-POSITRON ANNIHILATION LIFETIME SPECTROSCOPY submitted by Kwan Pui Ying, Rebecca for the degree of Doctor of Philosophy at The University of Hong Kong in February 2006 Variable Energy Positron Annihilation Lifetime Spectroscopy (VE-PALS) is a powerful diagnostic tool for studying defects in thin films and at interface. By varying the energy of the monoenergetic positron beam, positrons can be implanted to varying depths so that a depth profile of void size and concentration can be obtained. It has been proposed to add a VE-PALS system to the present positron (e ) beam facility at The University of Hong Kong so as to increase its usefulness. The present work describes in detail design work on a possible VE-PALS apparatus that can achieve excellent time resolutions 250 psec using secondary electron emission from a thin carbon foil. The difficulty in constructing a VE-PALS system lies in the fact that a "start" signal is required to signal the entry of the positron into the target. Two methods have been used in the past to overcome this problem, the first being a bunching technique which employs RF cavities and choppers, the second being the use of secondary electrons emitted from the target. The latter technique is in terms of experimental complexity much simpler, but has in the past suffered from poor time resolution (typically 500 psec). The present study demonstrates an important finding, namely that successful secondary electron based VE-PALS requires the use of a positron beam with small diameter ( 1 mm). Simulations of the HKU positron beam have been carried out using the SIMION software. These simulations led to the discovery of a hybrid lens system that has made it possible to achieve 1 mm beam sizes using conventional magnetic guidance. The hybrid lens design allows positrons to begin their trajectories from a 8 mm primary moderator in a magnetic field-free region after which they are focused into a solenoidal magnetic field that transports the positrons to the target. The results of the successful focusing operation of the positron beam based on the simulated design are given. The present work includes a series of detailed computer simulations of different possible VE-PALS designs. Designs used at Brookhaven National Laboratory and Oak-Ridge National Laboratory that have met with partial success in the past have been studied. Modified designs based on these systems have been suggested and studied using the SIMION software. A design based on a localized non-adiabatic lateral magnetic field that allows high detection efficiency coupled with good timing capability has been studied, but has been ruled out on the basis of operational complexity. An alternative design based on a modification of the Oak-Ridge National Laboratory design, although having slightly inferior timing capability has been chosen as a more optimal design. Design details are presented. DOI: 10.5353/th_b3683719 Subjects: Electron spectroscopy Positron annihilation Positron beams