Hypersonic Attenuation in the Vicintiy of the Superfluid Transition of Liquid Helium
CALIFORNIA UNIV LOS ANGELES DEPT OF PHYSICS
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The relative ultrasonic attenuation in liquid helium at 1 GHz has been measured in critical region with a fixed path interferometer. The sample was isolated from the main bath by a vacuum and the amplitude of the transmitted sound wave was measured while the temperature of the sample was made to drift at rates as slow as 3 x 10 to the minus 6th power Ksec. The attenuation is found to have a very large non-singular peak of about 2500cm with its maximum at 3.26 plus or minus 0.20 mK below the lambda point. After the contribution of viscous and thermal losses to the attenuation has been subtracted, the temperature dependence of the critical attenuation is found to vary approximately as 1th square root of Tp-T on both sides of Tp, the temperature of the peak. The attenuation peak cannot be explained by the Landau-Khalatnikov theory, and processes other than the decay of first into second sound must be considered. These results are in substantial agreement with earlier results but locate the peak with much greater reliability.
- Physical Chemistry