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Viscosity of concentrated superfluid mixtures 3He−4He when vibrating a quartz tuning fork

The possibility has been investigated for measuring the viscosity of concentrated superfluid mixtures of 3He in 4He in the temperature range 0.4−2.2 K using commercial quartz tuning forks with a resonance frequency of ≈ 32 kHz. It was found that the temperature dependence of the viscosity coefficient in a mixture with a concentration of 5% of 3He in 4He is in good qualitative agreement with the data obtained using other experimental techniques in the entire temperature range of the research. The same dependence of a mixture with 3He concentration of 15% agrees with the previously obtained data only at temperature T > 1.4 K, and at lower temperatures a difference appears that grows with decreasing temperature. The experimental temperature dependences of the viscosity coefficient obtained by different methods are compared with those calculated within the framework of the kinetic theory for the quasiparticles in superfluid 3He−4He solutions, developed by Landau, Khalatnikov, and Zharkov for the temperature range T > 0.6 K and by Baym, Saam, and Ebner for lower temperature.