Surface Relaxation Mechanisms of Laser-Polarized129Xe

We have determined the dominant mechanism for nuclear spin relaxation of laser-polarized ${}^{129}\mathrm{Xe}$ in silicone coated cells. The ${}^{129}\mathrm{Xe}$ relaxation rate is found to be strongly dependent on magnetic field, which indicates that ${}^{129}\mathrm{Xe}$ becomes trapped in the coating for extraordinarily long times ( $\tau >10\mathrm{}\mu$s). Relaxation is caused by dipolar coupling between the trapped ${}^{129}\mathrm{Xe}$ and the protons in the coating, which we confirm with a novel double resonance scheme. This result should aid the development of improved coatings, and offers new possibilities for using laser-polarized ${}^{129}\mathrm{Xe}$ as a probe of other polymer and biological systems.