The high-temperature delta phase (δ) of plutonium (Pu) can be retained at room temperature by the addition of small amounts of an alloying element such as gallium (Ga). Macroscopic and microscopic variations in gallium solute concentrations will, however, affect the long-term stability of the delta phase. In low-solute regions, the delta phase is metastable and will partially transform into the alpha (α) phase at ambient or low-temperature conditions. The amount of transformation as a function of time and temperature can be represented on a time-temperature transformation (TTT) curve; see Figures 1 and 2.
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