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 $\mathrm{C}=\left(\frac{12}{5}\right){\pi }^{4}R{\left(\frac{T}{{\Theta }_0}\right)}^3$, with ${\Theta }_0=92.0\mathrm{}$ °K for argon and 71.9°K for krypton. The apparatus and techniques are described, and the results are compared with theoretical estimates.