Amorphous High Density Plutonium

Abstract

Metastable aluminum-alloyed $\hat{I}´$-plutonium shrinks rapidly and pure $\hat{I}\pm$-plutonium swells rapidly at 4 K. At ambient temperature alloyed $\hat{I}´$-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 $\hat{I}\pm$ and $\hat{I}´$. This phase, when formed from alloyed $\hat{I}´$-plutonium, rapidly but not instantaneously anneals to $\hat{I}´$-plutonium at temperatures $⪆100$K; when formed from pure $\hat{I}\pm$-plutonium it anneals to $\hat{I}\pm$ at similar temperatures. The room temperature discrepancy between growth of lattice parameter and length of $\hat{I}´$-plutonium is also explained by ingrowth of a denser amorphous phase that is continuously formed and annealed out.

16 pp., 2 figures