NUCLEAR SPIN WAVES IN SPIN POLARIZED HYDROGEN (TRANSPORT)

• Main Author: JOHNSON, BURGESS RALPH
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1984
• Subjects: Atomic physics
• ISBN: 9798204308039

In a dilute nuclear spin polarized gas at low temperatures, identical particle exchange effects greatly alter the spin diffusion process. The spin diffusion equation acquires a reactive term in addition to the ordinary dissipative term. This causes spin wave oscillations which are damped by the ordinary diffusion process. Spin waves can be observed even when the interaction Hamiltonian is independent of spin and the gas is not quantum mechanically degenerate. The spin diffusion equation is in general non-linear, and has the same form as the Leggett-Rice equation used to describe spin diffusion in liquid ('3)He. This thesis describes experiments studying nuclear spin transport in spin polarized hydrogen (H(DARR)) gas at temperatures between 150 mK and 700 mK, and number densities between 1 x 10('15) cm('-3) and 9 x 10('16) cm('-3). Pulsed Fourier transform and CW NMR were used for this purpose. The surfaces were coated with ('4)He for all the experiments. The observed NMR spectrum showed sharp resonances superimposed on a broader background. The background was attributed to the 'NMR image' of the NMR sample volume. The sharp resonances were attributed to standing spin wave modes in this volume. As recombination of the sample induced a large nuclear polarization, the spin wave resonances became narrower, more numerous, and more intense, as predicted by theory. The magnetic field gradient confined the observed spin wave modes to one side of the sample volume. The ordinary diffusion coefficient D(,0) was measured by observing the recovery of the longitudinal polarization in the NMR sample volume after a large tipping angle pulse due to diffusion of spins from outside the sample volume. By calculating the theoretical spectrum and comparing it with the observed spectrum, the dimensionless parameter (mu) was measured. This parameter determines the quality factor Q of the spin wave modes. The measured values of D(,0) and (mu) were in good agreement with theory.