Absolute magnetization calibration of polarized $^{131}$Xe for measurement of the $^{131}$Xe nuclear pseudomagnetism using neutron spin echo

We plan to investigate T violation in neutron interactions with heavy nuclei at a compound nuclear p-wave resonance by searching for a P-odd and T-odd term in the neutron forward scattering amplitude. $^{131}$Xe is a good candidate because its P-odd effects have already been measured to be sufficiently large. However, the pseudomagnetic precession of polarized neutrons, caused by the previously unmeasured neutron incoherent scattering length of the polarized $^{131}$Xe target, would be a large systematic error. Measurement of this incoherent neutron scattering length requires absolute polarimetry of $^{131}$Xe. Here neutrons provide us a method for NMR calibration using hyperpolarized $^3$He as the standard instead of the more typical thermally polarized $^1$H sample. Since the $^3$He polarization dependent neutron absorption cross section is accurately known, measurement of neutron absorption of the polarized $^3$He gives an absolute NMR calibration. The absolute $^{131}$Xe polarimetry/magnetization used to determine the neutron incoherent scattering length of $^{131}$Xe as measured from its pseudomagnetic precession observed in measurements on the JNSE instrument at the FRMII is discussed [1]. \par \noindent [1] Heinz Maier-Leibnitz Zentrum et al. (2015). JLSRF, 1, A11.