Plutonium
Plutonium is the chemical element with the atomic number 94 and chemical symbol Pu.  It is a highly radioactive metal, and is the metal used in most nuclear weapons.  The chemical element plutonium has some different isotopes.  The most important isotope of plutonium is 239Pu (or plutonium-239). It takes 24,110 years for half of a sample of plutonium-239 to decay, which is called its half-life. It can be made from natural uranium.  It is fissile and a nuclear fuel.