Propagation of Ordinary Sound in Liquid Helium near the λ Point

Publisher Website
Google Scholar
Abstract
The velocity and attenuation of ordinary sound in liquid helium have been measured at a frequency of 1 Mc/sec in the neighborhood of the λ point. By using measuring techniques of high resolution, it was possible to observe the behavior in this region in considerable detail. The velocity passes through a minimum approximately 2 × 10−4 °K below the λ point; the maximum attenuation occurs about 8 × 10−5 °K below Tλ. Both velocity and attenuation behave in a manner characteristic of a relaxation process, with the relaxation time a rapid function of temperature near Tλ. The results below Tλ can be described with good quantitative accuracy if this relaxation time is given by τ = 8.8 × 10−12(Tλ − T)−1. Excess attenuation is also observed above the λ point; this cannot be explained by the above relaxation process. The experimental uncertainties are so large in helium I that no reliable conclusions can be reached, but there is some indication that the quantity α/ω2 is not independent of frequency in this region. The behavior of the velocity is considered with regard to the Ehrenfest relations, and it is shown that the discontinuity in isothermal compressibility which those relations predict must be almost entirely due to a discontinuity in γ. No contradiction of the Ehrenfest relations is implied, since present knowledge of γ suggests that a discontinuity of the required magnitude may indeed occur.

This publication has 9 references indexed in Scilit: