Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics and Applied Physics

Department

Physics

First Advisor

Alexander H Weiss

Second Advisor

Ali R Koymen

Abstract

This dissertation describes the construction of a multi-functional positron beam and the methods employed for the analysis of digitized data produced by electron time-of-flight and gamma spectrometers. The positron beam and the attached electron time-of-flight spectrometer feature a high flux solid Ne moderator and a 3 m electron flight path, and the digitization of the data acquisition methods enabled the coincident measurement of the energies of the positron-induced electrons and the Doppler shifted annihilation gamma. Additionally, the digital methods have led to the development of a multi-stop time-of-flight spectrometer. The methods employed in the extraction of timing and energy information from the detector traces have resulted in (i) a digital time-of-flight spectrum of positron-induced electrons utilizing signals from a micro-channel plate (MCP) electron detector and a high-purity germanium gamma detector (HPGe); (ii) a two-dimensional spectrum representing the correlation between the energy of the annihilation gamma and the times-of-flight of positron-induced electrons; and (iii) the first positron-induced multiple electron time-of-flight spectra. The digital analysis methods, when applied to positron annihilation-induced Auger electron spectroscopy (PAES), will be capable of providing the energy and momentum of the electron with which the positron annihilates. This information will allow the determination of the contribution of individual atomic orbital levels to the total Doppler broadening spectrum and may contribute to the understanding of the interaction of positrons with novel two-dimensional materials. The digital multi-stop time-of-flight spectrometer is expected to aid in the quest to unravel the complex decay pathways associated with the Auger decay of annihilation-induced core holes.

Keywords

Positron annihilation, Multi-electron, Doppler broadening, HPGe detector, Artificial neural networks

Disciplines

Physical Sciences and Mathematics | Physics

Comments

Degree granted by The University of Texas at Arlington

Included in

Physics Commons

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