The Thermodynamic properties of solid and fluid helium-3 and helium-4 above 3 °K at high densities

Measurements have been made of the specific heat at constant volume of solid 3He from 3 K up to the melting point at a number of different densities corresponding to pressures up to 2000 atm. The measurements have been extended through the melting region at constant volume up to 29 °K in the fluid phase. For comparison similar measurements have been made on 4He at four different densities. By combining these data with the p- V- T data of Mills & Grilly (1955) and Grilly & Mills (1959) the complete thermodynamic properties of the solids have been derived in the relevant pressureand temperature range. The results can be understood semi-quantitatively in terms of the zeropointenergy of the solids and a quasi-harmonic model of the lattice vibrations. A brief discussion of the specific heat of the fluid phase is also given.