Plutonium-239's an isotope of plutonium. Plutonium-239's the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and's currently the secondary isotope. Plutonium-239's also one of the three main isotopes demonstrated usable as fuel in nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half life of 24,110 years. Nuclear properties The nuclear properties of plutonium-239, as well as the ability to produce large amo… (More on Plutonium-239)