NATURE OF SURFACE-INDUCED NUCLEAR-SPIN RELAXATION OF GASEOUS HE3

Surface-induced spin-lattice relaxation times are reported as a function of temperature for gaseous He3 in glass containers. The results are interpreted in terms of a phenomenological theory incorporating distinctly different relaxation processes at low and high temperatures, respectively. The low-temperature mechanism involves He3 adsorption on the glass surface, while the high-temperature mechanism (applicable to Pyrex and quartz surfaces) involves permeation of He3 into the container material. The latter mechanism can be eliminated by using relatively impermeable aluminosilicate glass containers, and the resulting He3 nuclear-spin relaxation times become quite long (>105 sec) at low gas densities and moderate temperatures. Preliminary experiments using aluminosilicate containers suggest that spin exchange with optically pumped rubidium vapor may lead to sizeable He3 nuclear polarization at relatively high densities; in these experiments a He3 nuclear-spin relaxation time approaching 106 sec was observed at 100° C in a 500-Torr He3 sample containing rubidium vapor. Phenomenological theory suggests that spin-lattice and spin-spin relaxation times are equal for adsorption-controlled relaxation. © 1969 The American Physical Society.