Measurement of atomic-hydrogen diffusion in helium

The diffusion constant of atomic hydrogen in helium gas, D/sub 0/(H-He), was measured with use of an optical-pumping--spin-exchange technique. Atomic hydrogen was produced by an inductive discharge in spherical Pyrex cells containing helium and small amounts of molecular hydrogen (<2%) and rubidium. The rubidium was optically pumped by a vapor lamp and the hydrogen was polarized by subsequent spin-exchange collisions. The decay rate of the hydrogen concentration was obtained from the observed time dependence of the hydrogen Zeeman signal and the diffusion constant was determined by measuring the decay rate in cells of different radius and helium pressure. D/sub 0/(H-He) was found to be 2.42(7) cm/sup 2/ sec/sup -1/ at 60 /sup 0/C, which may be extrapolated to 1.70(5) cm/sup 2/ sec/sup -1/ at 0 /sup 0/C. This result is significantly more accurate and more consistent with theoretical calculations than the results of previous experiments.