Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is 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 24,100 years.
Read more about Plutonium-239: Nuclear Properties, Manufacturing, Plutonium-239 in Nuclear Power Reactors