HEAT CONDUCTIVITY OF SOLID HELIUM.
Final scientific rept. 1 Jul 67-30 Jun 70,
OXFORD UNIV (ENGLAND) CLARENDON LAB
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Thermal conductivity measurements have been made on poly-crystalline specimens of He4-rich and He3-rich mixtures of the two isotopes. Helium was solidified at constant density at pressures up to about 1700 and 1300 atm for the two pure isotopes and to slightly different pressures for mixtures, in order to yield crystals with the same values of Debye characteristic temperature. The results for He4-rich solids have been analysed and indicate that the lattice distortion around a He3 impurity decreases with increasing density. The results on He3-rich solids are at present being analysed. Analysis consists in choosing the form of relaxation rates for phonon scattering by N-processes, U-processes, isotopic impurities and boundaries, so that the measured temperature variation of conductivity of crystals with the same Debye temperature but of different impurity concentrations, can be fitted by varying only the magnitude of the relaxation rate being ascribed to impurities. An apparatus has been built to look for a suggested very great anisotropy in the thermal conductivity of single crystals of He in the hexagonal-close-packed phase. Crystals are grown at constant pressure and the orientation determined optically from the known birefringence. Arrangements have been made for measuring the conductivity of each crystal in two directions at right anges. Author
- Physical Chemistry
- Solid State Physics