This means that in solutions, the contributions of acoustic radiation become significant at lower temperatures. It was found that in pure 4He, at temperatures above 0.8 K, the dissipative losses can be attributed to viscosity dissipation, whereas for solutions this is true only above 1.4 K. The ratio of the tuning fork energy loss due to the thermal diffusion wave versus the loss due to the radiation flux of the second-sound wave in superfluid solutions was calculated using literature data with an accuracy of 10 –3–10 –4. This contribution was found to vary non-monotonically with a maximum at temperatures of ≈ 0.6–0.8 K. The possible contribution of the second-sound to the dissipation of the tuning fork vibrations in solutions was estimated using experiments with the “closed” tuning fork. For the “open” tuning fork, the contribution of the first-sound is consistent with the calculation results only for 4He, whereas for the solutions, the calculated values are underestimated compared to the experiment. For the solutions, the viscosity contribution is consistent with the experiment only at high temperatures (above 1.4 K). It was shown that the existing analytical expression for the contribution of viscous friction provides a good description of the experimental data for 4He only in the hydrodynamic region. The resonance width, which is a measure of dissipation of tuning fork vibrations, was found to be higher in solutions than in pure 4He, and to increase with increasing 3He concentration. For separation and evaluation of the contributions of viscous damping and first and second-sound waves, “closed” (in a factory capsule) and “open” (without a capsule) tuning forks were used. The experimental results for the key dissipation mechanisms, that is, viscous friction and first and second-sound emission of a tuning fork, were analyzed. The tuning fork resonance frequency and the resonance width were measured as functions of temperature for 5% and 15% concentrations of 3He and, for comparison, for pure 4He. The amplitude–frequency characteristics of tuning forks immersed in superfluid 3He– 4He solutions were measured in the temperature range of 0.1–2.5 K.
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