The kinetics of the sorption and subsequent desorption of gaseous 3He in a C60 fullerite powder was studied at 2 to 292K. The temperature dependences of the diffusion coefficients of 3He and 4He impurities in fullerite were plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of 3He and 4He impurities in fullerite were qualitatively similar. A decrease in the temperature from 292 to 79K was accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8 to 10K led to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of 3He and 4He were independent of the temperature below 8K, indicating the tunnel character of the diffusion of helium in C60 fullerite. The isotope effect was manifested in the difference between the absolute values of the diffusion coefficients of 3He and 4He atoms at the same temperatures.

Kinetics of the Sorption of 3He by C60 Fullerite. the Quantum Diffusion of 3He and 4He in Fullerite. Dolbin, A.V., Eselson, V.B., Gavrilko, V.G., Manzhelii, V.G., Vinnikov, N.A., Popov, S.N.: JETP Letters, 2011, 93[10], 577-9