Decay mechanisms of oscillating quartz tuning fork immersed in He II

The dissipative processes due to viscous friction and acoustic emission from vibrating tuning fork prongs, in the hydrodynamic and ballistic regimes at the scattering of thermal excitations, are investigated by measuring current - voltage characteristics of a quartz tuning fork immersed in He II The vibrating tuning forks with resonant frequencies 32, 37, 77 and 97 kHz were used and measurements were carried out at saturated vapor pressure in temperature range 0.35 K–1.5 K It was found that at T > 1 K for the hydrodynamic flow regime in He II, the main dissipative process is the viscous friction and acoustic dissipation mechanism is essential only at frequencies above 70 kHz. At T < 0.5 K, for the ballistic regime, the scattering mechanism of the dissipation due to scattering of thermal excitations by vibrating tuning fork prongs predominates only for low frequency (32 kHz) and acoustic dissipation mechanism dominantes in almost the entire frequency range.