Thermal cycling as a novel method to experimentally derive the “equilibrium” Pu–Ga phase diagram

The feasibility of using thermal cycling to experimentally derive the “equilibrium” Pu–Ga phase diagram in the Pu-rich end is discussed, in particular the effect of thermal cycling on the decomposition of δ-stabilized Pu alloys at ambient pressure. This is an alternative to the Russian method and was originally proposed by the author on the basis of a thorough analysis of data from a systematic thermal cycling experiment performed on annealed and aged δ-stabilized Pu–Ga alloys. These were subject to repetitive thermal cycling in the temperature range 25–180 °C, which was found to drive and accelerate the Pu–Ga system towards its “equilibrium” state, as demonstrated by continuous α-phase in-growth with each thermal cycle. An experimental programme to confirm these initial observations is proposed, and the “constrained” equilibrium Pu–Ga phase diagram that might be expected from this method is outlined.