Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 107-108).

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 233-242). Available also in a digital version from Dissertation Abstracts.

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This thesis is primarily concerned with a description of a new apparatus for the measurement of the angular correlation of positron-electron pairs produced internally in high energy, electromagnetic transitions in light nuclei. The apparatus consists of two counter telescopes, operating in coincidence, enclosed in a steel vacuum vessel whose axis coincides with the direction of the beam of bombarding particles. Each telescope consists of a proportional counter and a plastic scintillator spectrometer operating in coincidence. Because of the light construction of the proportional counters, the telescopes have a low sensitivity to gamma rays. The scintillation counters permit the use of fast coincidence techniques and the analysis of complex spectra, the latter being the great advantage of this apparatus. One of the telescopes is fixed in position while the other can be rotated about the direction of the beam. The reliability of the apparatus was established from measurements of the angular correlation of the internal pairs from the well-known pair emitting state of 0¹⁶. Preliminary measurements of the angular correlation of the internal pairs from the 7.48 mev. level in B¹º indicate that this transition is a mixture of E1 and M1 type radiations, the El being the predominant one. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis consists of two independent parts, both of which are applications of the quantum mechanical methods developed recently by R. P. Feynman. Part I is concerned with the non-relativistic theory, and applies Feynman’s formalism to the simple problem of the scattering of a particle by a potential field. The method and results are compared with those of the familiar Born-approximation. The two procedures are shown to be equivalent and to be valid under the same conditions. Feynman’s formulae are used to calculate the first and second order terms of the scattered particle wave function, with an arbitrary scattering potential. Part II uses the relativistic Feynman theory, and treats the scattering of positrons by electrons, and of two electrons. The calculation checks the work of H.J.Bhabha and C. Møller, who have obtained the same results by other methods. The differential cross-sections for the two scattering processes are calculated to first order, and an estimate is made of the feasibility of an experiment to determine whether the exchange effect described by Bhabha actually occurs in positron-electron scattering. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The development of a high-resolution gamma ray spectrometer incorporating a germanium lithium-drift radiation detector is described. Sources of electrical noise in detectors and low-noise field-effect transistor preamplifiers are discussed. Modifications were made to available preamplifier circuits with a slight improvement in noise characteristics. A very-low-noise preamplifier using a 2N3823 field-effect transistor was tested, and an unconventional design inductive-load field-effect transistor preamplifier was built and tested. Refinements on germanium detector preparation techniques previously in use are described with particular reference to the starting material used. The design of a stainless steel cryostat to house germanium detectors is discussed. Performance characteristics of a 5 cc. detector are given. Preliminary measurements with it of the Doppler broadening of the annihilation peak in Ni and Zn are presented. A spectrum of annihilations of ortho-positronium formed in Freon 12 is given. The detector system is evaluated with reference to suitability in positron physics. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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