ENHANCEMENT OF SURFACE NMR BY LASER-POLARIZED NOBLE-GASES

The transfer of spin polarization from laser-polarized helium and xeno n to spins such as H-1 and C-13 On the surface of high-surface-area so lids (Aerosil) is demonstrated over a temperature range from 4 to 200 K. The transfer mechanism is dipole-dipole cross relaxation between th e spins of the adsorbed mobile noble gas and the surface spins (spin-p olarization-induced nuclear Overhauser effect). The enhancement of sur face proton magnetization by laser-polarized helium at 4 K and 10 K is between one and twofold. Using laser-polarized xenon, enhancement fac tors of up to 20 were obtained when compared to the Boltzmann polariza tion in a field of 4.2 T and at a temperature of 130 K.