Polarization of the nuclear spins of noble-gas atoms by spin exchange with optically pumped alkali-metal atoms

Abstract

The theory of spin exchange between optically pumped alkali-Inetal atoms and noble-gas nuclei is presented. Spin exchange with heavy noble gases is dominated by interactions in long-lived van der Waals molecules. The main spin interactions are assumed to be the spin-rotation interactions yN S between the rotational angular momentum N of the alkali-metalnoble-gas pair and the electron spin S of the alkali-metal atom, and the contact hyperfine interaction aK S between the nuclear spin K of the noble-gas atom and the electron spin S. Arbitrary values for EC and for the nuclear spin I of the alkali-metal atom are assumed. Precise formal expressions for spin transfer coefficients are given along with convenient approximations based on a perturbation expansion in powers of (o. '/yX), a quantity which has been shown to be small by experiment.

Functional lung imaging using hyperpolarized gas MRI

“…The valence electron subsequently exchanges polarization with the gas nucleus. This process is known as spin-exchange optical pumping (32)(33)(34), and typically takes 14 -20 hours to provide ϳ1.3 liter of 40% polarized He-3 at atmospheric pressure. Another polarization process for He-3 nuclei is known as metastability exchange (35).…”

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“…The use of optical pumping techniques for the production of hyperpolarized (HP) xenon can increase sensitivity of several orders of magnitude (Â10 4 ) [35,36] and laser-hyperpolarized (HP) 129 Xe NMR is proved to be powerful technique in studying the porosity of porous materials [31,37], or even reaction processes and kinetics [32,38]. The observed 129 Xe chemical shift could reflect mainly interactions between xenon atoms and the surface.…”

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“…14 Another frequently used transfer process includes optical pumping of alkali atoms, in particular Rb and Cs, and the transfer of their spin polarization to noble gas atoms like Xe. This method was pioneered by Happer et al 15 and applied to the study of surfaces in systems with high surface to volume ratios like graphitized carbon 16 or to the construction of NMR gyroscopes. 17, 18 The transfer from alkali to noble gas atoms is relatively efficient because they form van der Waals complexes.…”