Frequency shifts of the magnetic-resonance spectrum of mixtures of nuclear spin-polarized noble gases and vapors of spin-polarized alkali-metal atoms

We report the first quantitative theoretical and experimental studies of frequency shifts of nuclear-magnetic-resonance (NMR) lines of noble-gas atoms and the corresponding frequency shifts of electron-paramagnetic-resonance (EPR) lines of alkali-metal atoms in mixtures of nuclear spin-polarized noble gases and vapors of spin-polarized alkali-metal atoms. The shifts are primarily due to the Fermi-contact hyperfine interaction. For the heavier noble gases there can be relatively large (≊10%) contributions to the shifts from van der Waals molecules. The NMR frequencies of polarized ⁸³Kr and ¹²⁹Xe were measured in a vapor of spin-polarized alkali-metal atoms oriented parallel and antiparallel to the external magnetic field. The shift in the EPR frequency of the alkali-metal vapor due to the polarized noble-gas nuclei was measured simultaneously, thus providing a measurement of the absolute noble-gas nuclear polarization. The frequency shifts can be used as a convenient way to measure the absolute nuclear spin polarization of noble gases.