Attenuation and Dispersion of First Sound Near the Lambda Line of He³ — He⁴ Mixtures

Abstract

We have measured the attenuation and velocity of sound near the superfluid transition of several liquid He³-He⁴ mixtures at saturated vapor pressure, ranging in concentration from X₃=0.9% He³ to 36%. For these measurements, two acoustic cells were used covering the range of 1–15 MHz and above 12 MHz respectively. The pairs of quartz transducers were spaced approximately 2 mm apart. Sound frequencies ranged from 1.0 to 36 MHz for the 36% mixture, but so far the other mixtures were studied only at 12 and 36 MHz. For the sound velocity experiments, we used a pulse time-of-flight phase-comparison technique. The attenuation was measured by monitoring the amplitude of the received sound pulse.

Supported by a grant from the National Science Foundation.