UBC Theses and Dissertations
Production of positronium and muonium in oxide powders Kiefl, Robert Francis
A short review of positrons and muons, and their interactions with Batter is presented. The experimental techniques for studying these short lived particles are discussed. Attention is focussed on the formation, properties, and uses of the hydrogen-like atoms, positronium (e+e-) and muonium (μ+e-), in gases and insulators. Also, positrons have been injected into extremely fine evacuated powder samples of SiO₂, Al₂O₃,MgO, and ZnO. The fraction of positrons forming c-Ps within the powder grains and diffusing out into the vacuum region has been measured. The largest measurement of 26 ± 3,% was made for the 35Å radius SiO₂, powder. Using this powder as a moderator the O₂ quenching rate coefficient has been determined to be 1.43 ± .04 x 10⁻¹² cm³/sec. Doppler broadening measurements of the annihilation line verify that the guenching involves conversion of o-Ps to p-Ps. In addition polarized muons have been injected into SiO₂, Al₂O₃,MgO, CaO, SnO₂, GeO₂ and SiO powders. Using the techniques of μ+SB and MSB, upper and lower limits on the mucnium fraction have been determined. Non-zero muonium precession signals are reported for SiO₂, CaO, BgC, and Al₂O₃,. Evidence is presented that suggests that the muonium is diffusing into the intergranular regions for Al₂O₃ and MgO as reported earlier for SiO₂. Results from these two experiments indicate that the fornation and behaviour of muonium and positronium are correlated in insulators, at least in a qualitative sense. Future experiments using oxide powders to produce positronium and muonium are discussed.
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