Plutonium

Plutonium is the most important synthetic element: the material used in nuclear weapons and a fuel for some nuclear reactors. Produced in 1940 at Berkeley, it was manufactured in enormous quantities during the Manhattan Project. Plutonium-239 has a half-life of 24,100 years and is fissile, making it ideal for both weapons and reactors.

  • Atomic Number9494 protons, 94 electrons
  • Atomic Mass244.06420 u94× heavier than hydrogen
  • State at Room TempSolidSolid
  • Density19.84 g/cm³
  • Melting / Boiling639.9°C / 3227.8°C
  • Discovered1940

What is Plutonium?

Plutonium has 94 protons. Pu-239 is the primary fissile material in nuclear weapons and also used in mixed oxide (MOX) fuel in some reactors. Named after Pluto (then considered a planet). Produced in 1940 by Glenn Seaborg, Edwin McMillan, Joseph Kennedy and Arthur Wahl at Berkeley.

Fact Plutonium is element 94, symbol Pu. As an actinide, it is part of the f-block of the periodic table: one of 15 radioactive elements from actinium (89) to lawrencium (103). All actinides are radioactive; none has a stable isotope. They are produced in nuclear reactors and by decay of heavier elements, and their chemistry has been studied using only microgram or nanogram quantities.

Where you find Plutonium

On Earth

Plutonium does not occur in significant natural abundance. It is produced only artificially, by bombarding heavier actinide targets with neutrons or lighter ions in nuclear reactors or particle accelerators. World production is measured in micrograms or milligrams per year.

How we use Plutonium

Plutonium has 94 protons

How it was discovered

Plutonium has 94 protons. Pu-239 is the primary fissile material in nuclear weapons and also used in mixed oxide (MOX) fuel in some reactors. Named after Pluto (then considered a planet). Produced in 1940 by Glenn Seaborg, Edwin McMillan, Joseph Kennedy and Arthur Wahl at Berkeley.

Deeper dive: plutonium and the actinide series

The actinides (elements 89-103) form the lower of the two rows below the main body of the periodic table. They represent the filling of the 5f electron subshell. Unlike the lanthanides (the upper row), the actinides show greater variety in their chemistry because the 5f, 6d and 7s orbitals are close in energy. The early actinides, thorium through neptunium, can show many different oxidation states (e.g. uranium from +3 to +6). The heavier actinides increasingly resemble the lanthanides in preferring the +3 state.

All actinides beyond bismuth (83) are radioactive. The lightest, thorium, protactinium and uranium, have long enough half-lives to survive from the formation of the solar system. Neptunium and beyond are almost entirely synthetic, produced in nuclear reactors or accelerators. The transuranic elements were created at remarkable facilities including Oak Ridge National Laboratory, the Berkeley Cyclotron, the GSI in Darmstadt and JINR in Dubna.

Moving to 95 protons brings us to the next element on the periodic table.