plutonium

plutonium is a radioactive, actinide metal with significant applications in nuclear weapons and nuclear reactors. It was first synthesized in 1940 by a team led by Glenn T. Seaborg at the University of California, Berkeley during investigations prompted by the emerging Manhattan Project. This element is primarily produced artificially in nuclear reactors and is known for its complex chemistry and radiological hazards.

Properties

Plutonium exhibits an unusually large number of allotropic phases, with six distinct solid forms between room temperature and its melting point, a characteristic that complicates its metallurgy. Its most stable isotope, Pu-244, has a very long half-life, but the isotope Pu-239 is far more significant due to its fissile nature, readily undergoing nuclear fission when bombarded with thermal neutrons. The metal is chemically reactive, forming compounds such as plutonium dioxide (PuO₂) and plutonium tetrafluoride (PuF₄), and it readily alloys with metals like gallium to stabilize its delta phase for engineering use. Its intense radioactivity necessitates careful handling, as it emits alpha particles and generates significant decay heat.

History

The discovery was made in December 1940 when Glenn T. Seaborg, Edwin McMillan, Joseph W. Kennedy, and Arthur Wahl bombarded uranium with deuterons in the cyclotron at the University of California, Berkeley. The new element was named after the dwarf planet Pluto, continuing the naming convention established by uranium and neptunium. Its potential for use in an atomic bomb was quickly recognized, leading to its large-scale production during the Manhattan Project at sites like the Hanford Site in Washington. The first wartime use of material was in the Trinity test and later in the Fat Man bomb dropped on Nagasaki.

Production

Plutonium is produced primarily by irradiating uranium-238 fuel rods in a nuclear reactor; the U-238 absorbs neutrons to become uranium-239, which decays through neptunium-239 to form the desired isotope. This process occurs in both military production reactors, such as those historically operated at the Savannah River Site, and in commercial power reactors. The irradiated fuel is then processed in facilities like the Sellafield plant or the Mayak complex using the PUREX process to chemically separate it from other actinides and fission products. Major historical producers include the United States, the former Soviet Union, the United Kingdom, and France.

Applications

The principal application is in the cores of nuclear weapons, where the fissile isotope provides the explosive yield in both fission and thermonuclear weapon secondaries. It also serves as a fuel in some types of nuclear reactor, including fast breeder reactors like the BN-800 reactor and in radioisotope thermoelectric generators (RTGs) for deep-space probes such as Cassini–Huygens and Voyager, where the decay heat is converted to electricity. The MOX fuel program, which blends it with uranium dioxide, is used in several countries, including Japan and France, to recycle material from dismantled weapons and spent fuel.

Health and safety

Handling requires stringent precautions due to its high radiotoxicity, particularly if inhaled as a fine particulate, which can lead to lung cancer. Internally, it is a bone-seeking element that concentrates in the liver and skeleton. Major safety incidents include the criticality accident at the Los Alamos National Laboratory involving the Demon Core and the Windscale fire at the Sellafield facility. Its environmental persistence is a long-term concern, as evidenced by contamination studies around the Mayak plant and the Rocky Flats Plant. International safeguards and security measures are governed by treaties like the Treaty on the Non-Proliferation of Nuclear Weapons and monitored by the International Atomic Energy Agency. Category:Actinides Category:Chemical elements Category:Synthetic elements