Relaxation of solid hyperpolarized xenon-129

An examination of two aspects of the nuclear spin relaxation of solid 129Xe is presented. The first is a study of the longitudinal relaxation of 129Xe to its thermal equilibrium value along an applied magnetic field. The thermal equilibrium polarization is determined by the Boltzmann distribution. The second is the transverse relaxation or the relaxation of the transverse components of magnetization to equilibrium when the magnetization is tipped into the transverse plane.; At large magnetic fields of ≈ 1 kG or more, the longitudinal relaxation is extremely slow. Thus hyperpolarized (HP) 129Xe is often stored at high fields while frozen. In this dissertation the longitudinal relaxation behavior of 129Xe at low magnetic fields of less than 50 G, and at temperatures of 4.2 and 77 K is examined. At the smaller magnetic fields, relaxation is much more rapid and depends strongly upon the ratio of 129Xe to 131Xe atoms in the sample. This dependence on isotopic ratios appears because cross relaxation with the rapidly relaxing quadrupolar 131Xe nuclei becomes the dominant relaxation mechanism for 129Xe at low magnetic fields and at 77 or 4.2 K.; The second part of this research examines the transverse relaxation of HP 129Xe. Understanding the free induction decay (FID) and spin echoes in solids has been a notoriously difficult many-body problem. Recently it has been proposed that the late-time part of the FID and echo decays may be dominated by chaotic features of the inherent spin dynamics. This late-time behavior is observed after only a few times the characteristic timescale for the decay. Because of the large nuclear magnetic resonance (NMR) signal, HP 129Xe is a good candidate for the examination of these late-time asymptotics. Here we show for the first time that the late-time behavior of the solid echo and FID signals is the same. In addition, using the theoretical model mentioned above, this work provides experimental evidence for the existence of eigenmodes of the quantum time-evolution operator in a system of spins-1/2. This behavior is reminiscent of Pollicott-Ruelle resonances in classical chaotic systems.