We analyze the transverse nuclear magnetizations of 129Xe and 131Xe in a vapor cell containing natural Xe, 87Rb, and buffer gases. The Xe atoms are polarized through spin-exchange optical pumping (SEOP) with Rb atoms under low-magnetic-field conditions. From the free-induction-decay (FID) signal, we measure the nuclear magnetization of the Xe atoms in the Xe-Rb vapor cell. Furthermore, we measure the dependence of the gyromagnetic ratio on the magnetization of 129Xe and 131Xe by examining the amplitude of the FID signal of each isotope, and we evaluate the relationship between the magnetic field gradient and transverse relaxation rate for both of the 129Xe and 131Xe isotopes.
Nuclear spin dynamics of the 129Xe and 131Xe isotopes in an external magnetic field B 0 is considered. Nuclear spin is pumped by the laser through 87Rb, which transfers the electron spin to the 129Xe and 131Xe nuclei in the spin-exchange interaction. The nuclear spin dynamics is controlled with a transverse magnetic field that causes nuclear magnetic resonance in both 129Xe and 131Xe isotopes. Numerical calculations are performed to find conditions at which the transverse component of the nuclear spin in the established motion is of maximum and the slope angle relative to the vector of the constant magnetic field B 0 is 45°. This regime is taken to be optimal for simulation of practical applications. It is also found that the pump of the nuclear spin of xenon is strongly attenuated when the rubidium polarization vector is turned to the plane perpendicular to the external magnetic field vector B 0.
We demonstrate the measurement of the transverse spin relaxation rate of Xe without the influence of the Rb polarization-induced magnetic field gradient. The optical pumping beam and probe beam turn on and off repeatedly during the measurement to reduce the relaxation originating from the Rb polarization-induced magnetic field gradient. During the absence of the optical pumping beam, the nuclear spin of the noble gas atom does not experience the alkali-polarization-induced magnetic field gradient so that the transverse spin relaxation rate ( 1 / T 2 ) decreases. When the duty cycle reaches zero, the measured transverse relaxation time T 2 approaches the longitudinal spin relaxation time T 1 . Our method helps in roughly estimating the longitudinal spin relaxation time with a single measurement of the free induction decay.
We present a design for a spin-exchange optical pumping system to produce large quantities of highly polarized 129Xe and 131Xe. Low xenon concentrations in the flowing gas mixture which allow the laser to maintain high Cs polarization. The large spin-exchange rate between Cs and Xe through the long-lived van der Waals molecules at low pressure, combined with a high flow rate, results in large production rates of hyperpolarized xenon. The fast rates make it possible to obtain large nuclear polarizations after several minutes of optical pumping with a laser.At high Xe pressures. According to the theory, the longitudinal spin-elaxation rate 1T1 of Xe in a high-pressure sample containing only Xe and Cs vapor has the simple form is the velocity averaged binary spin-exchange cross section, It is the relaxation rate due to wall collisions and perhaps magnetic field inhomogeneities. Our results complement earlier studies performed at 129Xe pressures of about 20 Torr and 131Xe pressures of about 20 Torr and N2 pressures of 600 Torr . This work is useful for predicting spin-exchange rates between polarized Cs atoms and Xe nuclei.
In the atomic cell of the spin exchange optical pumping system, the optical pumping inevitably introduces a magnetic field gradient, which affects the measurement result of the nuclear spin relaxation time a lot. To address this issue, our method achieves the measurement while excluding the influence of this magnetic field gradient. In this method, the pump laser is turned off after the spins of 87Rb and 129Xe have been effectively polarized, which results in the spin polarization of the 87Rb atoms being provided only by the spin exchange with 129Xe. Ultimately, the transverse and longitudinal components of the polarization of 129Xe are detected by the in situ87Rb atom magnetometer to obtain the T1 and T2 of 129Xe under different conditions. Using our method, since the influence of inhomogeneity caused by the pump laser is eliminated, the relaxation characteristic of atomic cells can be measured more quickly, essentially, and conveniently, which helps compare the performance of different atomic cells and find the best cell fabrication process further.
Spin-exchange optical pumping (SEOP) is a method for producing spin-hyperpolarized noble gas nuclei, such as 129Xe and 131Xe, which are used in various magnetic resonance applications from fundamental physics to quantum sensing and medical imaging. In SEOP, optically polarized alkali-metal atoms transfer their spin polarization to the noble gas nuclei in gas-phase collision events via the hyperfine coupling (HFC) between the alkali valence electron and the noble gas nucleus. While the polarization transfer physics of spin
I=1/2 nuclei, such as 129Xe, is relatively well understood, that of spin
I>1/2 nuclei, such as 131Xe (
I=3/2), has been far less studied, and no rigorous theoretical model has been presented to date. To this end, we derive a simple analytical model for the upper limit, neglecting relaxation, of the SEOP polarization transfer, applicable to noble gases with arbitrary nuclear spin. Analytical evaluation of the Baker-Campbell-Hausdorff expansion for the time evolution of the spin density operator
ρ^(t) reveals that only even-order terms in the HFC contribute to the polarization transfer, with the leading-order quadratic term being the most significant. We obtain a result similar to that derived for the spin-exchange cross section by Herman [Phys. Rev. 137, A 1062 (1965)], but in a more general framework for the time evolution of
ρ^(t) that is also more familiar to magnetic resonance researchers. The model is applied to understand the difference in the polarization transfer efficiency between 129Xe and 131Xe, yielding results in agreement with previous experiments. We also validate the model by comparison to detailed numerical multiscale simulations of the SEOP process, where full quantum-chemically computed spin Hamiltonians sampled from molecular dynamics simulations of the gas-phase collision events are used to propagate the spin dynamics.
Spin-exchange collisions between polarized 87 Rb atoms and unpolarized 129 Xe nuclei have been used to produce nuclear spin polarized 129 Xe. Measurements of the longitudinal relaxation rate of 129 Xe nuclear polarization have been carried out in a 5.7G magnetic field. The present results show that the nuclear spin relaxation rate of 129 Xe in 87 Rb vapor is proportional to the density of the 87 Rb atoms, and the nuclear spin relaxation rates of 129 Xe induced by the 87 Rb atoms depend on the pressure of the buffer gas N 2 .