Low-Temperature Heat Capacities of Solid Argon and Krypton

The specific heats of high-purity argon and krypton have been measured between 0.4 and 12^∘{}K, permitting a reliable extrapolation to 0^∘{}K. The higher-temperature results are in agreement with those of Morrison et al., but for argon the extrapolation to 0^∘{}K is not. At the lowest temperatures the heat capacities are represented by C=(12/5)π⁴R(TΘ₀)³, with Θ₀=92.0 ^∘{}K for argon and 71.9^∘{}K for krypton. The apparatus and techniques are described, and the results are compared with theoretical estimates.