Lambda-Point Measurements of ηρn for Pure He4 and for Three He3-He4 Mixtures

Abstract

Torsional crystal measurements of $\eta {\rho }_n$ have been made for pure ${\mathrm{He}}^4$ and for three ${\mathrm{He}}^3$-${\mathrm{He}}^4$ mixtures ($x_3=0.005, 0.047, \mathrm{and} 0.100$) over temperature intervals which included their respective $\lambda$ points. The precision of the measurements for the mixtures was greater than that of any previous $\lambda$-point $\eta {\rho }_n$ measurements. Doubly reduced plots of $\eta {\rho }_n$ versus $T$ showed a slight but definite tendency for such curves to rotate clockwise about the (1, 1) point with increasing $x_3$ up to about 0.05. Values of $\eta$ were derived from the measurements by computing ${\rho }_n$ as a function of $T^{*}$. For each mixture, both $\eta$ and $\frac{d\eta }{\mathrm{dT}}$ were continuous across $T_{\lambda }\left(x_3\right)$. No tendency was manifest for such curves to develop discontinuities as $x_3$ decreased. It was, therefore, inferred that both $\eta$ and $\frac{d\eta }{\mathrm{dT}}$ of pure ${\mathrm{He}}^4$ are continuous across $T_{\lambda }\mathrm{}\left(0\right)\mathrm{}$. A further result obtained here is that, up to $x_3=0.100\mathrm{}$, the $\lambda$ viscosity of the mixture ${\eta }_{\lambda }\left(x_3\right)$ bears a linear relationship to the $\lambda$ temperature of $T_{\lambda }\left(x_3\right)$.