Plutonium Pu

Discovery

Plutonium was first produced in December 1940 at Berkeley by Glenn Seaborg, Edwin McMillan, Joseph Kennedy and Arthur Wahl. They bombarded uranium-238 with deuterons from a cyclotron, forming neptunium-238, which beta-decayed into element 94. Its chemical identification was completed in February 1941. That first isotope was plutonium-238.

Within weeks the team showed that plutonium-239 splits readily with slow neutrons, just like uranium-235. Because the Second World War was under way, the work was kept secret and only published in 1946. The Manhattan Project built large production reactors at Hanford, Washington, to breed plutonium from uranium on an industrial scale.

Plutonium-239 was the core of the device tested at Trinity in New Mexico in July 1945 and of the bomb dropped on Nagasaki that August. During the Cold War the United States and the Soviet Union produced hundreds of tonnes of it, and safeguarding and disposing of that stockpile remains an international problem.

Origin of the name

Following neptunium (Neptune), the element was named after Pluto, then counted as the outermost planet; Pluto is the Roman god of the underworld. Seaborg briefly considered 'plutium' before settling on plutonium. The obvious symbol would have been Pl, but Seaborg jokingly suggested Pu, which recalls the exclamation 'pee-yoo' used for a bad smell, and to his surprise it was accepted without objection.

Main uses

• Nuclear power: In any uranium reactor, some uranium-238 becomes plutonium-239, which then fissions and supplies part of the energy. Some countries recycle separated plutonium into mixed-oxide (MOX) fuel.
• Space power: Plutonium-238 gives off steady heat and has a useful half-life, so it powers radioisotope generators on missions such as Voyager, Cassini, Curiosity and Perseverance.
• Weapons: Plutonium-239 is a principal fissile material in nuclear weapons, which is why the International Atomic Energy Agency tracks plutonium inventories closely.
• Past medical use: In the 1970s a number of heart pacemakers were powered by small plutonium-238 sources.

Isotopes

Plutonium has no stable isotopes. Plutonium-239, the most important, has a half-life of about 24,100 years. Plutonium-238, at about 88 years, releases heat intensely enough to serve as a power source. Plutonium-240 (about 6,560 years) undergoes spontaneous fission readily, and its proportion distinguishes weapons-grade from reactor-grade material. Plutonium-241 (about 14 years) decays into americium-241. The longest-lived isotope is plutonium-244, with a half-life of about 80 million years.

In everyday life

Nobody encounters plutonium in daily life, yet fallout from atmospheric weapons tests between 1945 and 1980 left traces of it in soils worldwide. Its alpha radiation is stopped by a sheet of paper, so it poses little hazard outside the body. Inhaled particles, however, can lodge in the lungs, bone and liver for decades and raise cancer risk, which is why preventing inhalation is the central safety rule wherever it is handled. Storage is also strictly controlled, because too much gathered in one place can trigger a criticality accident.