Additional mass from a quartz tuning fork vibrating in He II

The additional mass caused by vibrations of tuning forks in He II with resonant frequencies of 6.7, 8.5, 12.1, 25, and 33 kHz is studied experimentally. The additional mass coefficient, given by the ratio of the additional mass to the mass of the fluid displaced by the tuning fork, is determined from the measured temperature and pressure dependences of the resonance frequencies of the tuning forks. These studies were made at temperatures from 2.2 to 0.1 K and the pressure dependences of the tuning forks were found for pressures from 1 to 24.8 atm at a constant temperature of 0.365 K. It is shown that for temperatures below 0.7 K, where the viscosity of He II is negligible, the resonance frequency of the tuning fork oscillations is determined by the additional mass of the fluid. It is found that measurements of the resonance frequencies as a function of pressure can be used to determine the additional mass coefficient with an accuracy that is almost an order of magnitude higher than when the temperature dependences are used. The additional mass coefficient is observed to depend on frequency and decreases as the frequency is raised.