Relaxation rates of low-field gas-phase $^{129}$Xe storage cells

A study of longitudinal nuclear relaxation rates T$_{1}$ of $^{129}$Xe and Xe-N$_{2}$ mixtures in a magnetic field of ~3.8 mT is presented. In this regime, intrinsic spin relaxation is dominated by the intramolecular spin-rotation interaction due to persistent xenon dimers, a mechanism that can be quelled by introducing large amounts of N$_{2}$ into the storage cell. Extrinsic spin relaxation is dominated by the wall-relaxation rate, which is the primary quantity of interest for the various low-field storage cells and coatings that we have tested. Previous group work has shown that extremely long gas-phase relaxation times T$_{1}$ can be obtained, but only at large magnetic fields and low xenon densities. The current work is motivated by the practical benefits of retaining hyperpolarized $^{129}$Xe for extended periods of time in a small magnetic field.