Pu

Plutonium (Pu) is a radioactive chemical element with atomic number 94. It is a heavy metal in the actinide series. All of its isotopes are radioactive, and most plutonium is produced artificially in nuclear reactors. Plutonium can exist in multiple oxidation states and forms several oxides; the metal is reactive in air and tends to form a protective oxide layer.

Plutonium was first synthesized in 1940 by scientists at the University of California, Berkeley, during early transuranic research. It was produced by irradiating uranium with neutrons and subsequently chemically separated and identified as a new element. The name plutonium was chosen to continue the planetary naming scheme after uranium and neptunium, referencing the planet Pluto.

Most plutonium in use today is manufactured in nuclear reactors rather than found naturally. It is produced when uranium-238 captures neutrons and undergoes beta decay to plutonium-239, among other pathways. The element has several important isotopes, of which plutonium-239 is the most significant for its fissile properties. Plutonium-238 is a strong alpha emitter used as a heat source in radioisotope thermoelectric generators for space missions. Other isotopes, such as plutonium-240, are byproducts that influence weapons design due to spontaneous fission, while plutonium-241 decays to americium-241.

Applications and safety are central to plutonium’s profile. Pu-239 has been used in nuclear weapons and as a reactor fuel in some designs, while Pu-238 powers space missions. Handling plutonium requires stringent containment and radiological protections because it is highly radioactive and chemically toxic. Its production and use are tightly regulated under international nonproliferation regimes, and environmental controls address long-term radiological hazards. Plutonium remains a key element in discussions of nuclear energy, safety, and security.