Fizika Nizkikh Temperatur: Volume 45, Number 12 (December 2019), p. 1462-1466 ( to contents , go back )
Stimulated echo and diffusion processes in 3He adsorbed by nanostructured material MCM-41
A.P. Birchenko, N.P. Mikhin, E.Ya. Rudavsky, and Ya.Yu. Sopelnyk
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Nauki Ave., Kharkiv 61103, Ukraine
Received June 26, 2019, published online October 25, 2019
Using pulsed nuclear magnetic resonance, diffusion processes in 3He adsorbed by the nanostructured material MCM-41 with a channel diameter of 25 Å have been studied. The measurements were carried out by the method of stimulated spin echo using a three-pulse regime of excitation of the spin system. The measured dependences of the amplitude of the stimulated spin echo on the square of the magnetic field gradient showed the presence of two different slopes of this dependence, which means the presence of two different diffusion processes in the adsorbed helium. These processes correspond to two different layered phases formed during gas adsorption in a narrow channel due to the van der Waals interaction with the walls. The identification of these phases was carried out by the measured values of the diffusion coefficient. It turned out that one of the layered phases corresponds to gaseous helium, and the other phase is close to liquid helium. The technique which used did not allow to register a solid phase, which is usually formed narrow parietal layer.
Key words: adsorbed helium, NMR, nanostructured material, MCM-41, diffusion.