Plutonium

Plutonium is a radioactive, silvery-gray metal that tarnishes in air. Only trace amounts occur naturally in uranium ores; most plutonium is produced in nuclear reactors when uranium captures neutrons. Its isotopes have different uses: plutonium-238 provides heat for radioisotope power systems on some spacecraft, while plutonium-239 and plutonium-241 can sustain fission and are used as nuclear fuel. Plutonium has also been used in nuclear weapons.