The thermal conductivity between 2° and 100°K has been measured on synthetic sapphire single crystals and on sintered alumina, before and after reactor and γ-ray irradiations. Reactor irradiation appears to introduce two types of thermal resistivity-producing defects, one of which is dominant at low temperatures. The only effect of γ irradiation is an extra thermal resistivity at low temperatures which saturates for quite small doses. This saturation value seems to depend on the initial perfection of the crystal and is increased by reactor produced damage. At present, detailed information about the defects cannot be derived from thermal conductivity measurements alone.

The author would like to express his thanks and appreciation to Professor C. F. Mate for his guidance and support in the completion of this work. The advice and assistance of Professor J. R. Gaines are especially appreciated, for if he had not provided the hydrogen samples, this work would never have been done. The author is also grateful to Mr. William Baker and his staff for technical assistance; to Mr. Larry Wilkes for the line drawings; and to Mr. James Constable, whose measurement of the ortho-hydrogen content of the samples was invaluable.

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