Plutonium
Plutonium is a radioactive metallic element with atomic number 94. It occurs naturally in trace amounts and is produced mainly in nuclear reactors.
Plutonium-239: A fissile plutonium isotope with a half-life of about 24,100 years, produced chiefly by neutron capture in uranium-238. Reactor production creates this isotope, which sustains fission in some nuclear systems.
Mixed oxide fuel: Reactor fuel made from uranium oxide blended with plutonium oxide. Reprocessing spent fuel can recover plutonium for reuse in this reactor fuel.
Glenn T. Seaborg: An American chemist who helped discover plutonium and several other transuranium elements. Seaborg led the Berkeley team that identified plutonium in 1940–1941.
Uranium: A radioactive metallic element with atomic number 92, found naturally and used as nuclear fuel. Uranium is both plutonium’s main reactor precursor and its closest fuel-cycle comparison.
Plutonium-238: A plutonium isotope whose radioactive decay produces substantial heat, used in radioisotope power systems. Its heat output makes plutonium useful when sunlight or chemical batteries cannot provide dependable power.
Radioisotope thermoelectric generator: A device that converts heat from radioactive decay into electricity using thermoelectric materials. Plutonium-238 has powered these generators in spacecraft and other remote systems.
Edwin McMillan: An American physicist who co-discovered neptunium, the first transuranium element. His uranium-239 experiments established the pathway that led to plutonium’s discovery.
Neptunium: A radioactive actinide element with atomic number 93, formed in trace amounts naturally and in nuclear reactors. It precedes plutonium in the actinide series and can be its immediate nuclear precursor.
Nuclear fission: The splitting of an atomic nucleus into lighter nuclei, often releasing neutrons and energy. Fission of certain plutonium isotopes releases energy and can sustain a chain reaction.
Nuclear weapon: A weapon that releases destructive energy through nuclear fission, fusion, or both. Plutonium-239 has been used as fissile material in nuclear weapons.