Equation of state and critical exponents ofHe3and aHe3-He4mixture near their liquid-vapor critical point

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Abstract
We report a determination of the effective critical exponents βeff and γeff in He3 as a function of the distance T−Tc from the liquid-vapor critical point. These exponents characterize respectively the singular behavior of the densities for the coexisting phases (T<Tc) and of the compressibility along the critical isochore for T>Tc. The density measurements use the dielectric-constant method and cover the range 2×10−1>|t|>3×10−5 where t=(T−Tc)Tc. Far away from Tc we find βeff=0.36, but as Tc is approached, βeff decreases progressively. Although the error becomes large for t≲5×10−4, βeff tends into the direction of the limiting value β=0.32 that is predicted by recent theories. For 2×10−2>t>5×10−4, we find γeff=1.19±0.01. Both the coexistence curve and the compressibility are fitted to power-law series that include correction-to-scaling terms. The amplitudes of these terms for the coexistence curve are compared with those for Xe and SF6. The slope of the rectilinear diameter is found to be dρρcdt=−0.022. For the 80%-He3—20%-He4 mixture above Tc, the singular density gradient in the earth's gravity field is found to diverge strongly as Tc is approached. The relevant exponent is again γ