Quantum Diffusion of Deuterium in Sodium

Abstract

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.

Debye Temperature and Quantum Diffusion of Hydrogen in Body-Centered Cubic Metals

“…It is just simultaneous operations that provide the principal possibility for NRAOL to measure the diffusion coefficients at any temperatures, including cryogenic temperatures. As for the range of D values measured with an appropriate accuracy, it is controlled by the section of nuclear reaction 2 H(d,p) 3 H and the constants characterizing the interaction of accelerated deuterium with substances. Experiments were performed on a 2 MV Van de Graaff accelerator.…”

“…Devices for assembling samples and their annealing are described in the Supporting Information section and in works. 3,21,22 Examinations using methods of nuclear reactions (NRAs) showed that the samples were of purity sufficient for diffusion experiments, the oxygen content did not exceed 0.2 at. % and no nitrogen or carbon impurities were detected.…”

“…Data on the quantum diffusion of deuterium in Na were gained with an accelerator technique, nuclear reaction analysis online (NRAOL). 3 It employs Fick's diffusion equations and measurements of deuterium concentration using the nuclear reaction 2 H(d,p) 3 H. For NRAOL, the measured D values were several orders lower compared to the competing methods, from 10 −17 to 10 −12 m 2 s −1 , 19 which made it possible to expand the experimental database. At the same time, NRAOL has a disadvantageit can be applied to the investigation of only one hydrogen isotope, deuterium.…”

“…1 For the objective of our work, the NRAOL technique is the best fit; using it, particular data on D(T) for deuterium in another alkaline metal Na have already been obtained. 3 Methods of sample preparation, processing of initial data, and other procedures for Na and K were identical.…”

“…The issues of tunneling are mainly studied theoretically, and the main problem of this research trend is the quite scarce experimental database. The situation is somehow paradoxical because tunneling and overbarrier atomic jumps are the only existing mechanisms of atomic migration in solids; yet, experimental data on quantum diffusion of hydrogen have been obtained only for three metals: in Nb and Ta for protium , and in Na for deuterium . Tunneling was also observed when hydrogen diffusion occurred on the metal surface, not in the bulk, and in this case, experimental data were gained for many metals. − In all cases, observation of quantum diffusion was based on the registration of bends on the temperature dependences of diffusion coefficients D ( T ) in the coordinates log D – 1/ T .…”