High equilibrium spin polarizations in solid 129Xe

Hyperpolarized Xe-129 produced by optical pumping is of great-current interest as a contrast agent for magnetic resonance imaging. The spin 1/2 nucleus has slow spin relaxation rates, allowing appreciable polarization retention times in a frozen-spin mode far from thermal equilibrium, such as a room temperature gas. This weakness of spin interactions also makes achievement of high polarizations by equilibrium methods in the condensed state take very long. At 1 K and modest magnetic fields, the relaxation time of pure Xe-129 exceeds days, and at 17 T and 10 mK, where the equilibrium polarization is about 44%, it is too long to be measurable. By forcing high concentrations of oxygen into xenon, polarizations near 10% have been obtained in about 1 day at high B and low T, and this can be improved. With rapid removal of the oxygen, this method can provide an economical source of frozen-spin hyperpolarized xenon. (C) 2000 Elsevier Science B.V. All rights reserved.