NMR Spectroscopy of Adsorbed 129Xe at Low Temperatures and High Magnetic Fields

In this paper we report measurements of the nuclear magnetic resonance (NMR) spectrum of ¹²⁹Xe adsorbed on silica gel and Grafoil^? substrates in a 15 tesla magnetic field and temperatures in the range 10 mK to 1 K. Liquid ³He is used to shorten the spin lattice relaxation time of the ¹²⁹Xe spins and obtain a high degree of spin polarization of over 40% in around a day. The ¹²⁹Xe NMR spectrum generally exhibits two lines. We show that one line corresponds to the monolayer of surface xenon atoms and the other line to the monolayers of bulk solid xenon between the substrate and the surface monolayer. By comparing the spectra and relaxation rates for xenon of different ¹²⁹Xe concentrations and by adding ⁴He we were able to investigate the ¹²⁹Xe interlayer coupling. The work has important implications in the study of porous materials using hyperpolarized gases, the study of surface atoms by NMR and the production of hyperpolarized species by the brute force technique.