Theoretical models for continuous-flow and stopped-flow spin-exchange optical pumping of 129Xe have long predicted much higher 129Xe polarization values than are measured experimentally, leading to a search for additional depolarization mechanisms. In this work, we show that a misapplication of the general theory of spin-exchange optical pumping along with the incorrect use of previously measured spin-exchange constants has been perpetuated in the past 20 years and is the main cause of the long-held discrepancy between theoretical and experimental 129Xe polarization values. Following the standard theory of spin-exchange optical pumping developed almost 40 years ago by Happer et al., we outline the common mistake made in the application of this theory in modern theoretical models and derive a simplified expression of the spin-exchange cross section that can be used to correctly predict 129Xe polarization values under any set of experimental conditions. We show that the complete expression of the spin-exchange cross section derived using the work of Happer et al. predicts spin-exchange rates tenfold higher than those previously assumed in theoretical models of continuous-flow and stopped-flow spin-exchange optical pumping and can fully rectify the long-standing discrepancy between theoretical and experimental polarization values
