Thermal Conductivity and Isotopic Impurities in Single Crystals of Helium.
DUKE UNIV DURHAM N C DEPT OF PHYSICS
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The authors used the enhancement of thermal conductivity by Poiseuille flow of the phonon gas to obtain highly sensitive measurements of phonon scattering by isotopic impurities in single crystals of helium. Crystal orientation, size, and quality may be inferred from the thermal conductivity data themselves. The hcp 4He crystals were grown at a constant pressure of 85.1 atmospheres using an apparatus and techniques which made possible some control over crystal orientation. In the Poiseuille region a relaxation time limit has been achieved experimentally which allows the data to be fitted as a function of temperature and concentration with only one parameter. The observed scattering strength is a factor of 2.7 greater than can be explained in terms of mass defect scattering alone. A number of current theories are examined in the light of this result. Author
- Solid State Physics