Shear viscosity measurements of liquid 4He and 3He-4He mixtures near the tricritical point

Abstract

A torsional oscillator cell is described, by means of which simultaneous precision measurements of ({rho}{eta}) and of the molar volume can be made in liquid {sup 4}He-{sup 4}He mixtures over the temperature range between 0.5 and 3 K. Here {rho} is the mass density, {eta} the shear viscosity, and in the superfluid phase they become the contributions {rho}{sub n} and {eta}{sub n} of the normal component. The results of {eta} for {sup 4}He near the superfluid transition are compared with the predictions by Schloms, Pankert and Dohm, and by Ferrell. Measurements of ({rho}{eta}) are reported for mixtures with 0.64 {le} X {le} 0.74, where X is the {sup 3}He mole fraction. Those for X = 0.67 and 0.70 are compared with data by Lai and Kitchens. The viscosity experiments show no evidence of a weak singularity at the tricritical point.