A circuit for determining a polarization of a gas. The circuit includes a polarimetry circuit having an NMR coil that is configured to excite a polarized gas and that is responsive to an electromagnetic signal generated by the excited, polarized gas. The polarimetry circuit has a reproducible polarization measurement variability of less than about 2% when the NMR coil is exposed to a temperature in a range of about 0.degree. C. to about 200.degree. C.