Helium transport along lattice channels in crystalline quartz

The problem of He atom movement through channels of the quartz crystalline lattice is investigated. Providing the diameters of the atom and of the channel are of similar size the atom interacts with neighbor constituents of the wall. The conservation of momentum law in local form applied to the 'helium-constituent' interaction allows reduction of the problem to a one-dimensional one, which is similar to the movement of a dislocation in the Frenkel-Kontorova (FK) model. Within the framework of this model the activation energy for 'helium + neighbor constituents' is expressed by the shear modulus for the channel-forming material and the He polarizability. A metastable helium atom in the triplet state (2 S-3(1)) is able to penetrate through the channel. In contrast, helium atoms in the singlet states, both ground state (1 S-1(0)) and metastable (2 S-1(0)), cannot penetrate. (C) 2003 Elsevier Ltd. All rights reserved.