Experimental studies of wall interactions of adsorbed spin-polarizedXe131nuclei

Abstract

We have made a quantitative study of nuclear spin relaxation of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ atoms adsorbed on the surface of glass cells. By using highly asymmetric glass cells we have increased the wall-induced quadrupole splitting of the nuclear-spin sublevels of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ atoms by almost two orders of magnitude over previously reported values. These large surface interactions were used to extract quantitative information about the electric-field gradients experienced by the nuclei of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ atoms adsorbed on the glass surface and about the activation energies for surface adsorption. The experimental results indicate that the electric-field gradients at any surface site are nearly isotropic. The residual nonzero mean value of the fluctuating field gradient has cylindrical symmetry about the normal direction to the surface. The mean-field gradient along the surface normal direction is only 2.3% as large as the rms value. We find that silicone wall coatings, which slow down the relaxation of ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$ nuclear spins, speed up the relaxation of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ nuclear spins. This may be due to the nuclear quadrupole interactions of ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ atoms dissolved in the relatively thick silicone wall coatings. Measurements of the temperature dependence of the coherent wall interaction show that the activation energy (≊0.03 eV) for the coherent wall interaction in well-cured, hydrogen-free cells is about three times smaller than the activation energy (≊0.10 eV) in hydrided cells.