Spin-exchange Polarization Research Articles

Hybrid Optical Pumping of Optically Dense Alkali-Metal Vapor without Quenching Gas

Optical pumping of an optically thick atomic vapor typically requires a quenching buffer gas, such as N2, to prevent radiation trapping of unpolarized photons which would depolarize the atoms. We show that optical pumping of a trace contamination of Rb present in K metal results in a 4.5 times higher polarization of K than direct optical pumping of K in the absence of N2. Such spin-exchange polarization transfer from optically thin species is useful in a variety of areas, including spin-polarized nuclear scattering targets and electron beams, quantum-nondemolition spin measurements, and ultrasensitive magnetometry.

Pressure shifts and broadening of the Cs D1 and D2 lines by He, N2, and Xe at densities used for optical pumping and spin exchange polarization

The production of hyperpolarized gases by spin-exchange optical pumping (SEOP) requires exact knowledge of the alkali metal’s D1 absorption profile and the degree to which it is broadened and shifted by varying buffer gas composition and pressure. We have measured these parameters for cesium (Cs) in the presence of Xe, N2, and H4e perturber gases at densities up to 10 amagats. The effects of these gases are important as Cs is attracting increasing interest for SEOP applications. Our measurements were made using simple white-light illumination of the Cs vapor while characterizing the D1 (6S1/2 to 6P1/2) and D2 (6S1/2 to 6P3/2) resonances using a high-resolution optical spectrometer. For the Cs D1 resonance at T=120 °C, we report shifts from the 894.59 nm vacuum wavelength caused by H3e, H4e, N2, and Xe of −0.017±0.003, −0.013±0.002, 0.026±0.002, and 0.029±0.002 nm/amagat. We also report the shifts for the D2 resonance as well as pressure broadening coefficients for both resonances.

Polarization and relaxation rates of radon

Polarization and relaxation of radon isotopes by spin exchange with laser optically pumped rubidium were studied in preparation for electric dipole moment measurements with octupole deformed $^{223}\mathrm{Rn}$. \ensuremath{\gamma}-ray anisotropies provided a measure of nuclear polarization produced by spin exchange with laser polarized rubidium vapor, and the temperature dependence over the range 130 to ${220}^{\ifmmode^\circ\else\textdegree\fi{}}$C was measured to parametrize the spin exchange polarization and the quadrupole-dominated wall relaxation rate. These results provide quantitative data for developing electric dipole moment measurements of octupole-deformed $^{223}\mathrm{Rn}$ and other radon isotopes.

Polarization of3Heby Spin Exchange with Optically Pumped Rb and K Vapors

We report on extensive experimental measurements of the key rates that determine the efficiency for polarizing the nuclei of ${}^{3}\mathrm{He}$ by spin exchange with optically pumped Rb vapor. In agreement with recent theoretical predictions, we find a strong temperature dependence of the electron-spin loss rates due to ${}^{3}\mathrm{HeRb}$ collisions. We also find that the maximum possible efficiency for spin-exchange polarization of ${}^{3}\mathrm{He}$ by K is 10 times greater than for Rb.

Neutron-diffraction reinvestigation of NiCO3

Detailed powder neutron-diffraction experiments performed on NiC${\mathrm{O}}_{3}$ show that at low temperature this carbonate is an antiferromagnet with an antiferromagnetic direction perpendicular to the trigonal axis and not at an angle 63\ifmmode^\circ\else\textdegree\fi{} to this axis as has been previously reported. The oxygen parameter is found to be $u=0.2813\ifmmode\pm\else\textpm\fi{}0.0005$, the largest found in the series of carbonates of the iron family. A careful examination of the magnetic reflection intensities indicates in NiC${\mathrm{O}}_{3}$ a form-factor expansion and a magnetic-moment reduction leading to the same covalency parameter as that previously reported in NiO and KNi${\mathrm{F}}_{3}$. Comparison with the isomorphous compounds MnC${\mathrm{O}}_{3}$ and CoC${\mathrm{O}}_{3}$ indicates in NiC${\mathrm{O}}_{3}$ an increase of the superexchange interactions, both isotropic and anisotropic, a decrease of the spin-exchange polarization through the ${(\mathrm{C}{\mathrm{O}}_{3})}^{2\ensuremath{-}}$ radicals, and a substantial reduction of the covalency parameter.

Spin exchange polarization and measurement of the hyperfine splitting of short-lived8Li

Free8Li (T1/2=0.84 sec) atoms were polarized by spin exchange with optically pumped rubidium vapour. The8Li nuclei were produced by the reaction7Li(d, p)8Li in a thin LiF target. They recoiled into helium which was used as a buffer gas for optical pumping as well. Nuclear polarization up to 2% was detected by β-decay asymmetry. Rf transitions between hfs levels of the atomic ground state yielded the hfs separation ΔW=382.543(7) MHz. The nuclear spin assignmentI=2 was confirmed.

Spin exchange polarization and hfs anomaly measurement of β-active37K

Rf-spectroscopic measurements in the atomic ground state of the 1.2 sec-isotope37K yielded independent values of magnetic moment μI(37K)=0.20320 (6) nm (diamagnetically corrected), hfs separation ΔW(37K)=240.2672 (7) MHz and the resulting hfs anomaly37Δ39=(0.249±0.035) · 10−2. The37K was polarized by spin exchange scattering with optically pumped87Rb; as a detector for rf transitions the asymmetry of the β-decay of the polarized37K nuclei was used. A detailed analysis of the spin exchange mechanism under the conditions of experiments of this type was performed. This led to an explanation for the observed strong enhancement of the resonance signal heights by the spin bath. Furthermore the dependence of the nuclear polarization and relaxation time constants on the strength of the hfs coupling could be demonstrated.