- Allotropes of plutonium
Even at ambient pressure, plutonium occurs in a variety of
allotropes. These allotropes differ widely in crystal structure and density; the α and δ allotropes differ in density by more than 25% at constant pressure.
The presence of these many allotropes makes machining plutonium very difficult, as it changes state very readily. The reasons for the complicated phase diagram are not entirely understood; recent research has focused on constructing accurate computer models of the
phase transitions.inote|Ambient pressure phase diagram of plutonium
In weapons applications, plutonium is often
alloyed with another metal (e.g., delta phase with a small percentage of gallium) to increase phase stability and thereby enhance workability and ease of handling. Interestingly, in fission weapons, the explosive shock waves used to compress a plutonium core will also cause a transition from the usual delta phase plutonium to the denser alpha phase, significantly helping to achieve supercriticality.
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