Plutonium-239

Pu239 is an important Plutonium isotope as it is one of the best radioisotopes to be used in nuclear weapons.

Uses
Plutonium and MOX Fuel.

Practically all thermonuclear weapons and nukes utilizing a Plutonium core.

Mini-Nuke weapons (only use nuggets!).

Breeds into Pu240, which is a disappointing isotope.

It can be used in the Custom Nuke. It contributes an impressive 25 to its nuclear stage.