Studies of kinetic processes in a concentrated ³He-⁴He solution using an oscillating tuning fork

The dissipative processes causing the damping of quartz tuning fork vibrations in a solution of 15% ³He in ⁴He, are studied in a temperature range of 0.5–2.3 K. The resonance curves of the tuning forks are measured in the laminar flow region of the liquid, and their width is determined by the width of the dissipative processes. We examined tuning forks with a resonance frequency of 32 kHz, located inside a flask (“enclosed”) and tuning forks without a flask (“unenclosed”). The results of the experiment are compared to existing theories. It was found that a significant contribution to the damping of tuning fork oscillations for a solution, as opposed to pure ⁴He, is from the second sound radiation, the contribution of which exceeds the input of viscous dissipation at low temperatures. The radiation of the first sound does not contribute to the damping of the oscillations of the “enclosed” fork due to the small size of the cell versus the wavelength. In the case of the “unenclosed” fork, the damping is determined by three processes: viscous dissipation and radiation of the first and second sounds.