A Novel Method of Measuring Spin Polarization of Noble-Gas Atoms in Nuclear Magnetic Resonance Gyroscopes

We propose a precise and efficient method for measuring the ¹²⁹Xe polarization that is applicable to weak magnetic field, low-pressure, and low-temperature scenarios where van der Waals forces are dominant in the spin-exchange collisions of noble-gas and alkali-metal atoms based on the magnetometer in a nuclear magnetic resonance (NMR) gyroscope system. We also developed an optimized method for measuring the ¹²⁹Xe relaxation over a wide temperature range, which reverses the direction of the main magnetic field to flip the quantization axis and fits the free induction decay (FID) signals for obtaining the transversal and longitudinal relaxation times T₂ and T₁ of ¹²⁹Xe simultaneously. Using this accurate and stable method, the dependence of the ¹²⁹Xe relaxation on the cell temperature and the optical pumping rate is studied efficiently, and the depolarization relaxation rate Γ_n is measured. Thus, the ¹²⁹Xe polarization P_n is derived from the measured T₁ and Γ_n , with an error of 6%. This method is meaningful in quick tests and diagnosis online, which helps improve the sensitivity of the NMR gyroscope system.