Multiple electronic instabilities and the anomalous thermodynamics of plutonium*

Given plutonium's importance in energy production, an understanding of its anomalous electronic and thermodynamic properties is essential for its safe handling and long term storage. In common with rare earth and other actinide elements and compounds, plutonium's physical and chemical properties are determined by f-electrons, whose transformation from localized to itinerant behavior are known to drive a significant collapse in volume. However, the occurrence of a volume collapse on both reducing and increasing the temperature and its anomalously large magnitude, reaching as much as 25% at low temperatures, represent extreme departures from the behavior of other known metals. Here we discuss new magnetostriction measurements on δ Pu, made using an optical fiber Bragg grating technique adapted for use on encapsulated radiological materials, that plutonium's exceptional thermodynamic behavior with temperature derives from its f-electron shell having multiple electronic instabilities.