Thermal Diffusion Factors for the 4He–3He System

The thermal diffusion factor for the ${}^4\mathrm{He}{–}^3\mathrm{He}$ system has been measured from 200 to 900°K and as a function of composition at 215, 273, 373, and 473°K. These measurements were made in a 20‐tube trennschaukel which allowed the use of a rather small temperature difference relative to the absolute temperature. The other experimental parameters were adjusted to minimize the corrections for trennschaukel operation. The data demonstrate a marked decrease in α_T with increasing temperature and a composition dependence of approximately 10%. The experimental values were compared to theoretical calculations using six different intermolecular potentials. The Lennard‐Jones (12–6) and modified Buckingham (exp‐6) potentials were inadequate but two recently proposed multiparameter functions represent the data quite well.