Report on the use of ion mobilities to study phase transitions in liquid ⁴HE

We have measured positive and negative ion mobilities near the lambda transition, and positive ion mobilities and shear viscosities near the melting transition in liquid ⁴He. The results and their proposed interpretations are presented and discussed. In each of these cases, the ions studied are unshielded charges of sufficiently low density not to interact directly with each other (current densities are {reversed tilde equals} 10^-12 amps/cm²). Our basic description of conduction is hydrodynamic, governed by the shear viscosity. The hydrodynamic problem, however, is modified by the effects of electrostriction, and particularly by the fact that the ion tends to induce about itself the very phase transition under study. An apparent depression of the lambda transition observed in the mobility is explained by the presence of such an electrostively induced normal region surrounding the ion.