Thermal Relaxation near the Critical Point

Abstract

We have measured thermal-relaxation times ($\ensuremath{\tau}$) near the critical point of ${\mathrm{He}}^{3}$. $\ensuremath{\tau}$ remains small in one-phase states throughout the critical region. In two-phase states, $\ensuremath{\tau}$ increases as the critical temperature (${T}_{c}$) is approached in proportion to ${({T}_{c}\ensuremath{-}T)}^{\ensuremath{-}1.0}$ at all densities. An extra increase in $\ensuremath{\tau}$ 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.