Polarization and relaxation in hyperpolarized helium-3 and xenon-129

Large nonequilibrium polarizations on the order of 10% are achievable in the spin-1/2 isotopes 3He and 129Xe through a process called spin-exchange optical pumping (SEOP). Experiments utilizing hyperpolarized (HP) gases benefit from maximizing polarization and storage time. Interactions with other gas atoms and with the walls of the storage vessel limit the ultimate polarization and the longitudinal relaxation time. It is critical to understand the mechanisms governing the creation of HP gases and the interactions that cause relaxation. This thesis addresses the creation of HP 3He through a technique called hybrid SEOP and longitudinal relaxation in 129Xe due to the formation and breakup of 129Xe-Xe molecules.;At gas densities typical for SEOP of 129Xe, fluctuations in the spin-rotation and chemical shift anisotropy interactions mediated by the formation and breakup of loosely bound 129Xe-Xe molecules have been identified as the primary intrinsic spin-relaxation mechanism, with T1 limits of 4.6 hours for samples of pure Xe. We have shown that this relaxation mechanism can be suppressed at high magnetic fields, leading to longitudinal relaxation times of ≈ 100 h at 14.1 T. Further results showed a near doubling of relaxation times with temperature increases from 293 K to 393 K, implying a maximum intrinsic relaxation time of ≈ 9 h at 393 K. At fields practical for SEOP (2.8 mT), we observed 129 Xe relaxation times of nearly 5 hours in a 1 amagat Xe sample at 393 K suggesting a practical, low-field, noncryogenic storage system that will provide Xe hold times much longer than those currently available with standard techniques.;The creation of HP 3He via SEOP is traditionally done using rubidium as the alkali metal intermediary. One drawback to this method is the time required to polarize the 3He, typically requiring 10--20 hours to achieve 40--50% polarization in enough gas (≈1 L) for a single experiment. Two advances in SEOP have led to dramatic enhancements in efficiency: the use of spectrally narrowed diode laser arrays and hybrid SEOP, which employs both potassium and rubidium. We have combined these techniques to construct a dedicated 3He polarizing system capable of producing >60% 3He polarization in 0.5 bar·L of gas in valved and refillable glass cells in under 4 hours.