Optical Pumping System Design for Large Production of Hyperpolarized ${}^{129}\mathrm{Xe}$

We present a design for a spin-exchange optical pumping system to produce large quantities of highly polarized ${}^{129}\mathrm{Xe}$. Low xenon concentrations in the flowing gas mixture allow the laser to maintain high Rb polarization. The large spin-exchange rate between Rb and ${}^{129}\mathrm{Xe}$ 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. We report a maximum polarization of 64% achieved for a $0.3\mathrm{l}/\mathrm{h}$ Xe flow rate, and maximum magnetization output of $6\mathrm{l}/\mathrm{h}$ at 22% polarization. Our findings regarding the polarization dependence on temperature, nitrogen partial pressure, and gas mixture flow velocity are also reported.

Figure 1

Polarizer schematic: (1) gas mixture input coming from the mass flow controllers panel; (2) Rb saturator—spiral shaped containing Rb puddles; (3) SEOP region; (4) Rb condensation region; (5) cooling jacket; (6) down-tube; (7) NMR coils; (8) freezeout spiral inside the 0.3 T permanent magnet box; (9) gas output to pressure controller and exhaust vacuum pump; (10) heating oven; (11) laser and optics; (12) laser monitor spectrometer; (13) $B_0$ seven-coil tower. The solid arrows show the gas flow in the system, while the dotted arrows show the laser propagation in the column.

Figure 2

Simulated polarization buildup for Xe and Rb inside the polarizer for 10 sccm Xe, 350 sccm ${\mathrm{N}}_2$, 1000 sccm He flow rates, and 500 torr total pressure. The gas mixture flows from right to left, with the laser shining from left to right. The temperature is considered uniform at 160 °C inside the oven (85–180 cm on the graph) and drops exponentially to room temperature within 10 cm. Rb density is calculated from the empirical relation of Killian [27].

Figure 3

${}^{129}\mathrm{Xe}$ polarization values produced by the UNH polarizer at optimum experimental parameters. On the graph are also plotted the largest polarization numbers reported in the literature (University of Florida [20] and the Marburg group [19]).