Sound propagation inHe3-He4mixtures near the liquid-vapor critical point

Measurements of the acoustic attenuation and the dispersion are reported for two ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures, along the critical isochore near the liquid-vapor critical point. At the frequencies of 1, 3, and 5 MHz used in the experiments, these properties showed no difference from those of pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ or ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The results are discussed in terms of the two energy dissipation mechanisms, thermal diffusion and mass diffusion, and the approach suggested by the postulate of Griffiths and Wheeler for mixtures.