Low temperature lattice expansion of americium dioxide

Abstract

The variation of the lattice parameter, of the thermal linear expansion, and of the coefficient of thermal linear expansion was determined for AmO 2 in the range 38–300 K. On cooling, AmO 2 contracts more strongly than the dioxides of lower actinides, but similarly strong contraction occurs for CeO 2 and PrO 2− x ; this confirms the observed analogy between Am and the lanthanides. The α self-irradiation causes lattice expansion and reversibly broadens the diffraction lines at low temperatures in both 241AmO 2 and 243AmO 2. The former effect partly anneals at room temperature; the room temperature lattice parameter of previously cooled specimens decreases to a steady state value within some days. A much faster process of defect formation and annealing is responsible for the change in line width; the line width characteristic of a given temperature establishes within a few hours.