Muonium (Mu) is the atom formed by an electron bound to a positive muon "nucleus" (charge:+l, spin:1/2, lifetime: 2.2 μs). Since muons are 207 times as massive as electrons, the reduced mass of Mu is 0.996 that of the hydrogen atom, and the Bohr radii and ionization potentials of Mu and H are essentially the same. Therefore, the chemical behaviour of the Mu atom is that of a light H isotope (m[sub Mu] = 1/9 m[sub H]) with a greatly enhanced sensitivity to H isotope effects. Mu reaction rates are measured by a method called "Muonium Spin Rotation" (MSR) which resembles conventional resonance techniques such as NMR or ESR in that it monitors the characteristic Larmor precession of the Mu atom. However, unlike NMR or ESR, the MSR method does not detect the Mu Larmor precession by resonant power absorption, but rather through the peculiar spin dependent radioactive decay of the muon itself. The theoretical basis for the application of the MSR technique to the measurement of muonium reaction rates is derived. An extensive discussion is given to the practical aspects of the experimental implementation of the MSR technique. Rate constants and activation energies are reported for the gas phase reactions: Mu + F₂  MuF + F and Mu + Cl₂ + MuCl + Cl between 300 and 400K, and room temperature rate constants are reported for the reactions: Mu + Br₂  MuBr + Br and Mu + HX  [sup MuH + X][sub MuX +H], X = Cl, Br, I. While in most of these systems Mu reacts considerably faster than the heavier H isotopes, attention is focussed on hydrogen isotope effects in the Mu + F₂ and Mu + Cl₂, reactions. This discussion is based on the extensive theoretical investigations of Connor et al., which show the Mu + F₂ reaction to be dominated by quantum mechanical tunnelling at room temperature. Experimentally, quantum tunnelling manifests itself in this reaction by producing two dramatic isotope effects at 30OK: (1) the bi-molecular rate constant for the Mu reaction (1.4 x 10¹⁰ 1/mole-s) is at least six times that for the analogous H atom reaction, and (2) the apparent Arrhenius activation energy of this Mu reaction (0.9 kcal/mole) is less than half of that for H + F₂ In contrast, the Mu + reaction does not show any such strong isotope effects at 300K: (1) the bimolecular rate constant for Mu + Cl₂ (5.1 x 10¹⁰/mole-s) is no more than four times that of the analogous H reaction, and (2) the apparent activation energies for both Mu and H reactions are the same (1.4 kcal/mole) Preliminary calculations of Connor et al. on Mu + Cl₂ suggest that classical "wall reflection" partially offsets any rate enhancement due to quantum tunnelling. Quantitative isotope effects cannot be defined for the Mu + Br₂ and Mu + HX reactions and their hydrogen isotopic analogues because of the absence of sufficient experimental and theoretical data; these reactions are discussed in terms of the general theory of isotope effects. / Science, Faculty of / Chemistry, Department of / Graduate

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1977.

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 125-127).

Thesis (Ph. D. in Physics)--University of California, Berkeley, Jan. 1961. / Includes bibliographical references (leaves 64-69).

Negative muons produced via the backward decay of pions in the M9b beam channel at TRIUMF were stopped in a ²⁸Si target. The energies of the muonic X-rays and nuclear γ-rays following the muon capture were measured in order to identify a Doppler broadened γ ray line in ²⁸A1 which is suitable for analysis in terms of a γ — ν angular correlation to determine a value for the induced-pseudoscalar coupling constant (gp ). The muon beam was also stopped in 6 other background targets ( polythene, A1, stainless steel, Cu, Pb and BGO ) and their X- and γ-ray energies have been studied so as to fully understand the backgrounds associated with such a transition. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

We have studied the quantum diffusion of positive muons in pure copper over the temperature range 20 mK ≤ T ≤ 200 K using the technique of muon spin relaxation (μSR). The rate of diffusion has been deduced from its effect upon the muon polarization function. The measurements were made in a weak longitudinal external magnetic field, where the spin relaxation has proved to be the most sensitive to the muon hop rate below 150 K. Our results for the behaviour of the muon hop rate are well explained by the recently developed theories of the quantum diffusion of light interstitials in metals by Kondo, Yamada and others. These theories stress the effects of the conduction electrons in the metal in providing a form of "friction", retarding the diffusion process. In addition we have utilized the technique of level-crossing resonance spectroscopy, in its first application to μSR measuring the electric quadrupole interaction strength of the copper nuclei. These results have enabled us to show that the muon occupies the same octahedral site at all the temperatures studied. This allows one to rule out the possibility of metastable muon sites contributing to any significant portion of the muon polarization. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An unbound muon at rest decays into two neutrinos and an electron. Momentum conservation forbids the electron to have energy greater than one half the muon mass. However, if the muon is bound to a nucleus, its orbital motion -and nuclear recoil make it possible for the decay electron energy to approach the muon mass. These high energy electrons are an important background effect in the search for muon to electron conversion. This thesis investigates recoil corrections to the electron spectrum and asymmetry from bound muon decay using an effective potential approach. This approach simplifies the equations describing a finitely massive nucleus and electron (or muon) interacting electromagnetically, to a one particle Dirac equation for a potential well. For large Z, calculation of the electron spectrum requires including the effects of finite nuclear size and electron wave function distortion. Such a calculation would involve numerically generated wave functions and numerical integrations, and is not done here, though the applicable methods and general formulas are presented. For small Z the calculation can proceed analytically and an expression has been derived for the spectrum and asymmetry including recoil. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An experiment resulting in the reduction of the upper limit for muonium (µ+e⁻) conversion to antimuonium (µ⁻e*) is described. The limit obtained for the effective four fermion coupling constant is G < 42GF (95% confidence level). The muon in a system initially formed as muonium and evolving under the most favorable conditions will thus be identifiable as a negative particle in less than 4% of the observed decays. The results improve by over one order of magnitude the best previous limit obtained from a search for e⁻e⁻ ->µ⁻µ⁻ interactions. Neither process is expected to exist if an additive conservation law is obeyed by muon number. The present status of the theory of electroweak interactions, as it pertains to muonium conversion, is reviewed. It is shown that muon number noncohservation can be accommodated in a variety of ways, some of which might allow a value for G of 0.1GF. The steps that were taken to make the present experiment as sensitive as possible are detailed. The major improvement over previous conversion experiments is the use of fine silica powder in carefully arranged layers to allow muonium to exist for a large fraction of its lifetime in vacuum, where conversion is not highly suppressed. Another important facet of the technique, which is described in detail, is the use of an intense beam of surface muons with a stopping density previously unattainable. A chapter on the analysis of the data contains a quantitative discussion of the processes which must occur for conversion to be detected. The numbers derived there are essential to the establishment of a realistic limit on the coupling of muonium to antimuonium. / Science, Faculty of / Physics and Astronomy, Department of / Graduate