Amorphous High Density Plutonium

TL;DR

This study investigates the phase transformations and density changes in plutonium alloys at cryogenic and ambient temperatures, proposing the formation of an amorphous phase as a key factor.

Contribution

It introduces the concept of an amorphous phase influencing density and phase behavior in plutonium alloys, explaining discrepancies in experimental observations.

Findings

Alloyed δ-plutonium swells at 4 K and slowly decreases in density at room temperature.

An amorphous phase with intermediate density forms and anneals to crystalline phases.

Cryogenic and room temperature behaviors are explained by amorphous phase ingrowth and annealing.

Abstract

Metastable aluminum-alloyed $\delta$-plutonium shrinks rapidly and pure $\alpha$-plutonium swells rapidly at 4 K. At ambient temperature alloyed $\delta$-plutonium swells about $10^{-3}$ as fast as it shrinks at 4 K, but its bulk density decreases more slowly than would be inferred from the increase in its lattice parameter determined by X-ray diffraction. These results might be explained as the result of ingrowth of the opposite phases, but they have not been found in X-ray diffraction. The cryogenic results may be explained by ingrowth of an amorphous phase with density intermediate between those of $\alpha$ and $\delta$. This phase, when formed from alloyed $\delta$-plutonium, rapidly but not instantaneously anneals to $\delta$-plutonium at temperatures $\gtrapprox 100\,$K; when formed from pure $\alpha$-plutonium it anneals to $\alpha$ at similar temperatures. The room temperature discrepancy between growth of lattice parameter and length of $\delta$-plutonium is also explained by ingrowth of a denser amorphous phase that is continuously formed and annealed out.