I Was Wondering About This

Scientists at the Lawrence Livermore National Laboratory have finally figured out why added gallium to plutonium causes the later to form more stable crystalline structures:

Researchers now, for the first time, have determined why gallium works. In pure plutonium, the bonds between atoms are very uneven, causing the metal's high propensity to adopt a low-symmetry structure. However, when a gallium atom is put into the plutonium lattice, it causes the bonds to become more uniform and thus leads to the high-symmetry cubic structure.

Now we can all sleep easier.