Calorimetry below 1 K: The specific heat of copper

A technique is described which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat switch. As a test of this technique the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04–1 K. The presence of hydrogen increases the specific heat by ≈ 1% as has been reported previously at higher temperatures. Above 0.3 K the data for hydrogen-free copper are in good agreement with the copper reference equation. At lower temperatures there is an additional contribution to the heat capacity which may be associated with oxygen impurities.