The kinetics of helium gas sorption by C60 powder and subsequent desorption of the He4 impurity from the saturated powder was studied at 2 to 292K. Evidence was obtained supporting the existence of two stages in the temperature dependences of sorption and desorption. These stages originate in different times taken by helium to occupy octahedral and tetrahedral interstices in the C60 lattice. The characteristic times of sorption and desorption coincide. It was found that the temperature dependences of the characteristic times for occupying the octahedral and tetrahedral interstices were non-monotonic. When the temperature was lowered from 292 to 79.3K, the characteristic times increase, which indicates thermally activated diffusion of helium in C60. With a further reduction to T = 10K, the characteristic times decrease by more than an order of magnitude. Below 8K the characteristic times of sorption and desorption were temperature-independent. This suggested tunnel diffusion of He4 in C60.

Kinetics of He4 Gas Sorption by Fullerite C60. Quantum Effects. Dolbin, A.V., Eselson, V.B., Gavrilko, V.G., Manzhelii, V.G., Vinnikov, N.A., Popov, S.N.: Low Temperature Physics, 2010, 36[12], 1091-3