"Bulk" Hyperpolarized $^{131}$Xe with $P_{Xe}\sim 7\%$: a Potential Target for Neutron Optics Searches for Time-Reversal Invariance Violation*

The very large parity-odd asymmetry seen in the 3.2 eV p-wave resonance in $^{131}$Xe [1,2] makes it an interesting nucleus for NOPTREX. However this isotope is notoriously difficult to hyperpolarize owing to its strong nuclear quadrupole moment. We investigate the bulk preparation of hyperpolarized $^{131}$Xe via spin exchange optical pumping (SEOP). Isotopic enrichment and next-generation spectrally-narrowed laser diode arrays allow for real-time observation of polarization dynamics via in situ low-field NMR, and optimization as a function of temperature, alkali metal choice (Rb and Cs), resonance offset, and other parameters. $^{131}$Xe polarization values as high as 7.6$\%$$\pm$1.5$\%$ were achieved at 0.37 amagat in a ~0.1 L cell ($8.5\times10^{20}$ $^{131}$Xe spins), demonstrating feasibility for use in spin-polarized neutron-scattering targets. Ongoing efforts to scale up $^{131}$Xe SEOP to aluminosilicate cells with larger volumes for use in measurements of pseudomagnetic precession of polarized neutrons will also be described. [1] J. J. Szymanski, W. M. Snow et al., Phys. Rev. C 53, R2576 (1996). [2] V. Skoy et al., Phys. Rev. C 53, R2573 (1996).