Low-temperature heat capacity of normal and superconducting thorium hydride and thorium deuteride

The low-temperature heat capacities of several bulk samples of Th₄{H}₁₅$ and ${Th}₄D₁₅ have been measured over the temperature range from 1.4 to 20 K in both the normal and superconducting states. Average values of the electronic-heat-capacity coefficient γ and Debye temperature ΘD are found to be 8.07 ±{} 0.14 mJ K^-2/mole Th and 211.5 ±{} 1.1 K, respectively, for Th₄{H}₁₅$. Corresponding values for ${Th}₄D₁₅ are 7.84 ±{} 0.25 mJ K^-2/mole Th and 216.5 ±{} 6.6 K. A relatively large density of states at the Fermi level suggests the possibility of occupied $5f$ electronic states. Anomalies in the heat capacities of several samples were observed at the melting temperatures of molecular hydrogen and deuterium.