UBC Theses and Dissertations
Magnetic resonance on atomic hydrogen confined by liquid helium walls Morrow, Michael Robert
A gas of atomic hydrogen confined at and below 1K in a sealed cell has been studied by magnetic resonance at the zero-field hyperfine transition frequency of 1420 MHz. A review is presented of magnetic resonance theory for a two level system, with emphasis on determination of the absolute magnetization by two methods: calibration of the spectrometer sensitivity and by use of the radiation damping time constant. Measurements at 1K on a gas at low density, 10¹¹<n[sub=H]<5x10¹² cm⁻³, in the saturated ⁴He vapour density have yielded the rate for the reaction H+H+He￫H₂+He, the diffusion constant and pressure shift of the hyperfine transition for H interacting with the He gas, and the cross-section for spin exchange relaxation. At temperatures below 1K, measurements of the frequency shift and effective recombination rate for H adsorbed on the He film have yielded values of the binding energies for H on ³He and for H on ³He as well as the hyperfine transition frequency shift and surface recombination rate for H adsorbed on each of these surfaces. The binding energies are found to be 1.15(5) K for H on ³He and 0.42(5) K for H on ³He. Measurements have been carried out at temperatures as low as 162 mK for H on ³He and 65 mK for H on ³He. lineshape for H atoms undergoing occasional sticking events on the helium surface. This model has been applied to frequency shift and transverse relaxation data at low temperatures to yield sticking probabilities of 0.046(5) for H on ³He and 0.016(5) for H on ³He.
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