TECHNIQUES FOR MEASURING SOUND PROPAGATION IN LIQUID 4HE AND 3HE-4HE SOLUTIONS

The description of an instrument for the accurate measurement of ultrasonic attenuation and velocity in liquid 4He and 3He-4He solutions, and the details of the cell in which they were made, are presented. Measurements were made by matching the amplitude of a signal traversing the helium to a reference pulse of equal amplitude but opposite phase (both signals being derived from the same oscillator). By observing the change with temperature in the amplitude and phase of the signal passing through the helium, both the change in the velocity and in the attenuation could be determined. The cell in which the measurements were made employed two matched x-cut quartz crystal transducers, separated by a fused quartz spacer. The crystals, which were clamped only at the rim, were loaded on both sides by liquid helium. © 1969.