Second sound in3He-4He mixtures near the lambda point

Abstract

The velocity of second sound in pure liquid 4He and 3He-4He mixtures of 0.55%, 1.65% and 3.55% have been measured, using a resonance method, within 100mK of the lambda point. The results may all be represented by the expression U20(1-T/Tlambda )m where m=0.382+or-0.004 for all mixtures. Using Dash and Taylor's (1957) modification of Pomeranchuk's (1949) theory of dilute mixtures, these results give a super-fluid density proportional to (Tlambda-T)2/3 for all concentrations of 3He, as previously found by workers in pure 4He.