Physical Review Letters

Efficiency of Spin Exchange between Rubidium Spins and Xe129 Nuclei in a Gas

Natarajan D. Bhaskar, W. Happer, T. McClelland

Published Jul 5, 1982• 133 citations

Abstract

By directly observing the nuclear polarization of $^{129}\mathrm{Xe}$, the efficiency $\ensuremath{\eta}$ of spin exchange between optically pumped Rb spins and $^{129}\mathrm{Xe}$ nuclei has been measured. It is found that $\frac{1}{\ensuremath{\eta}}=23\ifmmode\pm\else\textpm\fi{}4$ rubidium ${D}_{1}$ resonance-line photons are required to polarize a $^{129}\mathrm{Xe}$ nucleus when long-lived van der Waals molecules are unimportant. The binary spin-exchange cross section deduced from our measurements is ${\ensuremath{\sigma}}_{\mathrm{ex}}=(7.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ ${\mathrm{cm}}^{2}$.

DOI: 10.1103/physrevlett.49.25

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Determination of spin-exchange parameters between optically pumped rubidium and Kr83

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Physical Review Letters

Efficiency of Spin Exchange between Rubidium Spins and Xe129 Nuclei in a Gas

Natarajan D. Bhaskar, W. Happer, T. McClelland

Published Jul 5, 1982• 133 citations

Publisher

Abstract

By directly observing the nuclear polarization of

^{129}\mathrm{Xe}

, the efficiency

\ensuremath{\eta}

of spin exchange between optically pumped Rb spins and

^{129}\mathrm{Xe}

nuclei has been measured. It is found that

\frac{1}{\ensuremath{\eta}}=23\ifmmode\pm\else\textpm\fi{}4

rubidium

{D}_{1}

resonance-line photons are required to polarize a

^{129}\mathrm{Xe}

nucleus when long-lived van der Waals molecules are unimportant. The binary spin-exchange cross section deduced from our measurements is

{\ensuremath{\sigma}}_{\mathrm{ex}}=(7.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}

{\mathrm{cm}}^{2}

DOI: 10.1103/physrevlett.49.25

Related papers

Determination of spin-exchange parameters between optically pumped rubidium and Kr83

S. R. Schaefer, G. D. Cates, W. Happer

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Measurement of spin-exchange rate constants between Xe129 and alkali metals

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Physical Review AAug 17, 200525 citations

Comparative spin-exchange efficiency of Rb– 129 Xe and Cs– 129 Xe in the long-lived van der Waals regime: implications for high-throughput 129 Xe hyperpolarization

Tao shi, Ge Jin, Liu Bowen +4 more

Abstract Efficient production of hyperpolarized 129 Xe at clinically relevant output levels remains an important challenge for spin-exchange optical pumping (SEOP). In this work, we report a comparative experimental study of Cs– 129 Xe and Rb– 129 Xe SEOP. The spin-exchange and spin-relaxation rates are measured and separated into binary-collision and van der Waals (vdW) molecular contributions. The resulting parameter set shows that long-lived vdW interactions enhance the intrinsic spin-exchange efficiency within a narrow pressure window, with Cs exhibiting a modest advantage over Rb under comparable conditions. Using these experimentally constrained quantities in a device-level model, we predict that clinically relevant 129 Xe polarization levels and throughput could be achievable at pump powers near 5 W.Abstract Efficient production of hyperpolarized 129 Xe at clinically relevant output levels remains an important challenge for spin-exchange optical pumping (SEOP). In this work, we report a comparative experimental study of Cs– 129 Xe and Rb– 129 Xe SEOP. The spin-exchange and spin-relaxation rates are measured and separated into binary-collision and van der Waals (vdW) molecular contributions. The resulting parameter set shows that long-lived vdW interactions enhance the intrinsic spin-exchange efficiency within a narrow pressure window, with Cs exhibiting a modest advantage over Rb under comparable conditions. Using these experimentally constrained quantities in a device-level model, we predict that clinically relevant 129 Xe polarization levels and throughput could be achievable at pump powers near 5 W.

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Experimental determination of the rate constants for spin exchange between optically pumped K, Rb, and Cs atoms and Xe129 nuclei in alkali-metal–noble-gas van der Waals molecules

X. Zeng, Z. Wu, T. Call +3 more

By analyzing the measured spin-relaxation transients of $^{129}\mathrm{Xe}$ nuclear spins and alkali-metal-atomic spins in mixtures of alkali-metal-atom vapors, Xe gas, and larger amounts of ${\mathrm{N}}_{2}$ gas, we have determined the three-body formation rates and the spin-transfer probabilities for alkali- metal--noble-gas van der Waals molecules. Three parameters, in addition to the spin quantum numbers of the alkali-metal and noble-gas nuclei, are needed to predict the spin-transfer rates. These parameters, which we have determined from experimental measurements, are x=\ensuremath{\gamma}N/\ensuremath{\alpha}, the ratio of the spin-rotation interaction \ensuremath{\gamma}N to the spin-exchange interaction \ensuremath{\alpha}; ${p}_{0}$ , the third-body pressure for which the molecular breakup rate ${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}1}$ is equal to the spin-rotation frequency \ensuremath{\gamma}N/h; and Z, the three-body rate constant for forming van der Waals molecules.By analyzing the measured spin-relaxation transients of $^{129}\mathrm{Xe}$ nuclear spins and alkali-metal-atomic spins in mixtures of alkali-metal-atom vapors, Xe gas, and larger amounts of ${\mathrm{N}}_{2}$ gas, we have determined the three-body formation rates and the spin-transfer probabilities for alkali- metal--noble-gas van der Waals molecules. Three parameters, in addition to the spin quantum numbers of the alkali-metal and noble-gas nuclei, are needed to predict the spin-transfer rates. These parameters, which we have determined from experimental measurements, are x=\ensuremath{\gamma}N/\ensuremath{\alpha}, the ratio of the spin-rotation interaction \ensuremath{\gamma}N to the spin-exchange interaction \ensuremath{\alpha}; ${p}_{0}$, the third-body pressure for which the molecular breakup rate ${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}1}$ is equal to the spin-rotation frequency \ensuremath{\gamma}N/h; and Z, the three-body rate constant for forming van der Waals molecules.

Physical Review AJan 1, 1985173 citations

By directly observing the nuclear polarization of

^{129}\mathrm{Xe}

, the efficiency

\ensuremath{\eta}

of spin exchange between optically pumped Rb spins and

^{129}\mathrm{Xe}

nuclei has been measured. It is found that

\frac{1}{\ensuremath{\eta}}=23\ifmmode\pm\else\textpm\fi{}4

rubidium

{D}_{1}

resonance-line photons are required to polarize a

^{129}\mathrm{Xe}

nucleus when long-lived van der Waals molecules are unimportant. The binary spin-exchange cross section deduced from our measurements is

{\ensuremath{\sigma}}_{\mathrm{ex}}=(7.3\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}

{\mathrm{cm}}^{2}

The spin-exchange rates due to binary collisions and due to the formation of van der Waals molecules between

^{83}\mathrm{Kr}

nuclei and optically pumped rubidium-metal vapor have been determined using a technique that relies on the simultaneous observation of frequency shifts of nuclear magnetic resonance lines of noble-gas atoms and corresponding frequency shifts of electron paramagnetic resonance lines of alkali-metal atoms. In contrast, earlier studies have relied on the observation of the spin-relaxation rate of either the alkali-metal atoms or the noble-gas atoms.

The

^{87}\mathrm{Rb}

^{129}\mathrm{Xe}

spin-exchange cross section has been measured in

{\mathrm{N}}_{2}

buffered cells as a function of the

{\mathrm{N}}_{2}

density using an alkali vapor magnetometer technique. The strong dependence of the spin-exchange cross section on the

{\mathrm{N}}_{2}

density indicates a significant role for the Rb-Xe van der Waals molecule in the spin-exchange process. Our data have allowed us to estimate the Rb-Xe molecular formation rate, which is in reasonable agreement with previous measurements. The extrapolated binary spin-exchange cross-section term is found to be ${\ensuremath{\sigma}}_{\mathrm{ex}}{\overline{V}}^{2}=1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$

{\mathrm{cm}}^{4}

${\mathrm{sec}}^{\ensuremath{-}2}$.

T=300

p=2.4

bar), in agreement with earlier findings. Besides the lifetime of the collision complex, the average and minimum Rb-Xe interatomic distances characterize the efficiency of the polarization transfer events. We obtain insight into magnetization transfer in both individual binary collisions and van der Waals complexes and demonstrate a stepwise buildup of

^{129}\mathrm{Xe}

spin polarization upon bond-length oscillations in the latter.

By measuring the relaxation rates of the nuclear spin polarization of

^{129}\mathrm{Xe}

in the presence of alkali-metal vapor at different densities, we have extracted the spin-exchange rates between

^{129}\mathrm{Xe}

and the three alkali metals K, Rb, and Cs. By studying the alkali-metal--

^{129}\mathrm{Xe}

spin-exchange rates as functions of the cell number density from 0.2 to 0.7 amagat, the binary collision and van der Waals molecular terms are separated, and constants governing both mechanisms are determined. The results from our work can be used to optimize the parameter space for polarizing

^{129}\mathrm{Xe}

, a promising agent for magnetic resonance imaging and other applications.

By analyzing the measured spin-relaxation transients of

^{129}\mathrm{Xe}

nuclear spins and alkali-metal-atomic spins in mixtures of alkali-metal-atom vapors, Xe gas, and larger amounts of

{\mathrm{N}}_{2}

gas, we have determined the three-body formation rates and the spin-transfer probabilities for alkali- metal--noble-gas van der Waals molecules. Three parameters, in addition to the spin quantum numbers of the alkali-metal and noble-gas nuclei, are needed to predict the spin-transfer rates. These parameters, which we have determined from experimental measurements, are x=\ensuremath{\gamma}N/\ensuremath{\alpha}, the ratio of the spin-rotation interaction \ensuremath{\gamma}N to the spin-exchange interaction \ensuremath{\alpha};

{p}_{0}

, the third-body pressure for which the molecular breakup rate ${\ensuremath{\tau}}^{\mathrm{\ensuremath{-}}1}$ is equal to the spin-rotation frequency \ensuremath{\gamma}N/h; and Z, the three-body rate constant for forming van der Waals molecules.