Specific heat of δ-Pu stabilized by Am

Detailed specific heat C-p measurements of delta-Pu stabilized by Am (8%-20%) were performed in the temperature range 4.5-300 K. The coefficient of the electronic specific heat gamma, which reflects the quasiparticle density of states at the Fermi level E-F, is smaller than originally assumed and, depending on the estimate of phonon contributions, a value between 35 and 55 mJ/mol K-2 can be deduced for Pu-8%Am. For higher Am concentrations, which expand the lattice, gamma decreases slightly with the Am content. An applied magnetic field of 9 T had no effect on C-p. The results strongly suggest that itinerant 5f states at E-F are not appropriate for describing delta-Pu.