The
online nuclear reaction analysis technique has been applied
to study the temperature dependence of deuterium diffusion coefficients
for deuterium in sodium at temperatures ranging between 110 and 240
K, and at cryogenic temperatures, below 160 K, tunneling of deuterium
atoms in the metal lattice has been observed. Above 160 K, diffusion
occurs by the classical mechanism of overbarrier atomic jumps. Results
of quantum diffusion of deuterium in a metal have been obtained for
the first time; they used to be known only for the lightest hydrogen
isotope, protium, in niobium and tantalum. The analysis has shown
that the necessary condition for carrying out the quantum mechanism
of deuterium migration is low Debye temperature of a metal, below
200 K. Experimental data on diffusion of hydrogen isotope in an alkali
metal have also been obtained for the first time in this paper.