Pu–Ga has many practical advantages:[1] Stabilized δ-phase Pu–Ga is ductile, and can be rolled into sheets and machined by conventional methods.
The transition between δ-phase and α-phase plutonium occurs at a low temperature of 115 °C and can be reached by accident.
Prevention of the phase transition and the associated mechanical deformations and consequent structural damage and/or loss of symmetry is of critical importance.
Plutonium in its α phase has a low internal symmetry, caused by uneven bonding between the atoms, more resembling (and behaving like) a ceramic than a metal.
During aging of the stabilized δ alloy, gallium segregates from the lattice, forming regions of Pu3Ga (ζ'-phase) within α phase, with the corresponding dimensional and density change and buildup of internal strains.
The decay of plutonium however produces energetic particles (alpha particles and uranium-235 nuclei) that cause local disruption of the ζ' phase, and establishing a dynamic equilibrium with only a modest amount of ζ' phase present, which explains the alloy's unexpectedly slow, graceful aging.
[9][10] The alpha particles are trapped as interstitial helium atoms in the lattice, coalescing into tiny (about 1 nm diameter) helium-filled bubbles in the metal and causing negligible levels of void swelling; the size of bubbles appears to be limited, though their number increases with time.
However, if the alloying metal is sufficiently reductive, plutonium can be added in the form of oxides or halides.
Further dilution of plutonium oxide during the MOX fuel manufacture brings gallium content to levels considered negligible.
[15] During the Manhattan Project (1942-1945), the maximum amount of diluent atoms for plutonium to not affect the explosion efficiency was calculated to be 5 mol.%.