In 1941, the scientists in the Berkeley Laboratory found small amounts of a new element in samples of neptunium. The paper announcing thier discovery was written in the early part of 1941, but it was not published until 1946. At that time, a few selected scientists were called from their university laboratories to participate in a government project known as the Manhattan Project. Under the watchful eyes of the United States security people, plutonium-239 was found to be a fissionable material. It was a much more efficient fissioning agent than uranium-235 and was suitable for building an atomic bomb. A kilogram of plutonium-239 can release the explosive energy of 20,000 tons of TNT, making it the material of choice for fission weaponry. Plutonium was an important ingredient in the development and production of the first atomic bombs.

Plutonium is a highly toxic radioactive silvery element of the actinoid series of metals. It is a transuranium element that has six known allotropic forms. The alpha version is the one that exists at normal environmental temperatures. It is silvery colour that takes on a yellowish hue as it oxidizes in the air.

Plutonium's commercial use is chiefly in electric power reactors. It is extremely dangerous to handle, and operations must be done by remote control and with adequate shielding.