| Summary: | Energetic positive muons stopping in insulators often form the hydrogen-like neutral
atom muonium by capturing an electron from the stopping medium. In this thesis it is
shown that some of this muonium is formed by free electrons, produced along the muon's
radiolysis track, diffusing to the muon, and subsequently forming muonium. Electron
transport properties of the lattice play a role in delayed muonium formation in these
solids. Application of an electric field along the initial muon momentum reveals a strong
anisotropy of the spatial distribution of electrons in the vicinity of the muon, implying
that the muon's direction of motion during thermalization is not completely lost by
multiple scattering. Estimates of the initial electron-muon separation and muonium
formation time are given.
Diffusion of muonium in cryocrystals has been studied with both transverse and longitudinal
field muon spin relaxation techniques. Experimental results are compared to the
theory of quantum tunnelling diffusion. In solid nitrogen at temperatures much smaller
than the Debye temperature of the lattice, the data and theory are in good agreement,
with a temperature dependence approaching the T⁷ law predicted by the theory of twophonon
quantum diffusion. At higher temperatures the agreement is qualitative only, but
does show a key feature of two-phonon quantum tunnelling diffusion - a rapid increase
in hop rate as temperature decreases due to the reduction of the phonon scattering rate.
Muonium in solid Xe is an extreme case of a light interstitial atom in a heavy lattice.
This system was chosen to provide an example of tunnelling diffusion at relatively high
temperatures where lattice dynamics could be expected to play a role in determining the
muonium hop rate. The hop rate of muonium atoms in solid Xe was measured over a === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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