Accession Number : AD0712729

Title :   HEAT CONDUCTIVITY OF SOLID HELIUM.

Descriptive Note : Final scientific rept. 1 Jul 67-30 Jun 70,

Corporate Author : OXFORD UNIV (ENGLAND) CLARENDON LAB

Personal Author(s) : Berman,Robert

Report Date : 20 AUG 1970

Pagination or Media Count : 8

Abstract : 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)

Descriptors :   (*SOLIDIFIED GASES, HELIUM), (*HELIUM, THERMAL CONDUCTIVITY), CRYSTAL GROWTH, HIGH PRESSURE, BIREFRINGENCE

Subject Categories : Physical Chemistry
      Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE