We present a constructed setup for polarizing 129 Xe noble gas. Hyperpolarized 129 Xe has been obtained via spin exchange with an optically pumped rubidium vapor. Optical pumping is based on polarizing the valence electron of rubidium by the resonant absorption of a circularly polarized laser light. The magnetic field of 30 G was used for obtaining 129 Xe polarization. The apparatus for detecting polarization is a nuclear magnetic resonance spectrometer. The highest 129 Xe polarization of 54% has been obtained using 60 W circularly polarized laser light with wavelength of 794.7 nm. The measured longitudinal relaxation time of the hyperpolarized 129 Xe was 72.3 minutes.
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.
We present a design for a spin-exchange optical pumping system to produce large quantities of highly polarized 129Xe. Low xenon concentrations in the flowing gas mixture allow the laser to maintain high Rb polarization. The large spin-exchange rate between Rb and 129Xe 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. We report a maximum polarization of 64% achieved for a 0.3 l/h Xe flow rate, and maximum magnetization output of 6 l/h at 22% polarization. Our findings regarding the polarization dependence on temperature, nitrogen partial pressure, and gas mixture flow velocity are also reported.
Abstract The polarization of 129 Xe gas by spin exchange with optically pumped Rb vapor is examined in high magnetic field. Measurements of the Rb–Xe velocity averaged spin exchange cross section 〈 σ v 〉 and the 129 Xe relaxation time in the absence of Rb, T 1 Xe , are discussed. Comparison of these high field results to low field literature values for 〈 σ v 〉 show that this parameter is essentially field independent. T 1 Xe is also found to be significantly longer in high field. On the basis of these observations, it is shown that production of large amounts of spin polarized 129 Xe gas can be made more efficient by high field operation.
Here we present a $\mathrm{Rb}\text{\ensuremath{-}}^{129}\mathrm{Xe}$ spin-exchange optical pumping polarizer capable of rapid generation of large volumes of highly polarized
129Xe gas. Through modeling and measurements we maximize the
129Xe nuclear spin polarization output to enable the generation of polarized
129Xe gas imaging volumes (
300 cm3) every 5 min within a clinical setting. Our model is verified by experiment to correctly predict the optimum Rb vapor density for maximum
129Xe nuclear polarization for a flux
3.4 W/cm2 of circularly polarized Rb
D1 photons incident on an 80 cm long cylindrical optical cell. We measure a
129Xe magnetization production efficiency of ${\ensuremath{\eta}}_{\mathrm{pr}}=1.8%$, which approaches the photon efficiency limit ${\ensuremath{\eta}}_{\ensuremath{\gamma}}=3.3%$ of this system and enables the polarization of $2.72\ifmmode\times\else\texttimes\fi{}{10}^{22}$
129Xe spins per hour, corresponding to
1013 cm3 of 100% polarized
129Xe at STP. This magnetization production rate is threefold higher than the highest previously published
129Xe magnetization production rate and has enabled routine clinical lung magnetic resonance imaging (MRI) with hyperpolarized
129Xe doses available on demand at run time, as well as high-SNR
129Xe MRI of the human brain and kidneys.
Gas mixtures with high xenon densities are explored for continuous flow spin-exchange optical pumping. It is shown that the Xe-NMR129 signal increases significantly with increasing xenon partial pressures up to about 200 kPa, despite a decreasing spin-polarization. Comparison of the rubidium infrared D2 emission with the xenon polarization demonstrates that radiation quenching by molecular nitrogen is of no substantial benefit for the pumping process at xenon pressures above 100 kPa. This reflects a diminished importance of spin-depolarization by radiation trapping due to the increased significance of spin-relaxation by rubidium-xenon collisions at high xenon densities. A quantitative expression for this effect is provided.