Energy Evolution in Pd2H below 1°K

Abstract

Energy evolution below 1°K has been observed in β‐phase palladium hydride (formal composition Pd₂H). The rate of evolution was strongly temperature‐dependent below 0.1°K, but became temperature‐independent between 0.1° and 1.0°K. It depended upon previous specimen history and was greatly reduced by annealing of the specimen below 50°K. For specimens kept below 1°K, the rate of energy production at a given temperature diminished with a half‐life of about 8 h. The results are explained semiquantitatively as a (spectroscopically forbidden) nuclear‐spin conversion in quasi‐molecular PdH₄ units left behind in small concentrations when the lattice is cooled through the rotational transition (at 55°K) of β‐palladium hydride. The temperature‐dependence below 0.1°K appears to result from limitation in the rate at which the lattice can remove the change in librational energy associated with the conversion process.