Thermal Relaxation near the Critical Point

Abstract

We have measured thermal-relaxation times ($\tau$) near the critical point of ${\mathrm{He}}^3$. $\tau$ remains small in one-phase states throughout the critical region. In two-phase states, $\tau$ increases as the critical temperature ($T_c$) is approached in proportion to ${(T_c-T)}^{-1.0\mathrm{}}$ at all densities. An extra increase in $\tau$ occurs in two-phase states very near the phase boundary. These observations suggest to us that the diffusion of matter across the liquid-vapor interface is a bottle-neck for equilibration. Our data are of value in interpreting puzzling features of several other experiments near critical points.