HEAT OF MIXING AND GROUND-STATE ENERGY OF LIQUID HE3-HE4 MIXTURES

The heat evolved when He3 is added to liquid He3-He4 mixtures at the saturated vapor pressure has been measured for temperatures in the region of 0.05°K. The starting concentrations varied between zero and six atomic percent of He3. Since the variation of the energy with temperature (the specific heat) is known, the experiments give the ground-state energy and the He3 and He4 chemical potentials at 0°K as a function of concentration. The measurements were made in a calorimeter connected by a wire of high thermal resistance to a dilution refrigerator operating at ∼0.02°K. The He3 was added through a long tube containing thermal anchors connected to the refrigerator. The results give the difference in binding energy for one He3 atom in He4 relative to pure He3 as (E3-L30)kB=(0.312±0.007) deg K, in excellent agreement with the theoretical value of Massey and Woo. The concentration dependence of the energy and chemical potentials agrees with predictions using the Bardeen, Baym, and Pines empirical interaction. The osmotic pressure in a saturated solution at 0°K is found to be (17.8 ± 0.9) mm Hg. © 1969 The American Physical Society.