Plutonium-239

Plutonium-239 is a fissile radioactive isotope with 94 protons and 145 neutrons. It occurs naturally in trace amounts and is produced mainly when uranium-238 captures neutrons in nuclear reactors.

Uranium-238: Uranium-238 is the most abundant uranium isotope, with 92 protons and 146 neutrons. Neutron capture by uranium-238 initiates the reactor pathway that produces plutonium-239.
Isotope: An isotope is a form of an element whose atoms have the same proton count but different neutron counts. Plutonium-239 is one member of plutonium’s family of isotopes.
MOX fuel: MOX fuel is mixed-oxide nuclear fuel made from plutonium oxide and uranium oxide. Reactor-grade plutonium containing plutonium-239 can be recycled into this fuel.
Glenn T. Seaborg: Glenn T. Seaborg was an American chemist who helped discover plutonium and several other transuranium elements. Seaborg’s group identified plutonium-239 in 1941 through uranium irradiation experiments.
Plutonium: Plutonium is a radioactive chemical element with atomic number 94 and multiple isotopes. Plutonium-239 is a particularly significant isotope within this element’s radioactive and fissile forms.
Neutron capture: Neutron capture is a nuclear reaction in which an atomic nucleus absorbs a neutron. It is the first step in converting uranium-238 into plutonium-239.
Fissile material: Fissile material can sustain a nuclear fission chain reaction with neutrons of suitable energies. Plutonium-239 is fissile because neutron absorption can trigger fission and replenish the neutron supply.
Nuclear reactor: A nuclear reactor is a system that controls a sustained nuclear fission chain reaction. Reactors produce plutonium-239 through neutron irradiation of uranium-238.
Edwin McMillan: Edwin McMillan was an American physicist who co-discovered neptunium, the first transuranium element. His discovery of neptunium helped establish the decay sequence that leads to plutonium.
Nuclear proliferation: Nuclear proliferation is the spread of nuclear weapons, weapons materials, or relevant capabilities to additional states or actors. Plutonium-239 production and separation are central concerns in nuclear safeguards.

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