Plutonium (specifically Pu-238) is first isolated at Berkeley, California.

Plutonium is a chemical element; it has symbol Pu and atomic number 94. It was initially discovered and named Hesperium by Enrico Fermi in 1934. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous.

Plutonium-238 is a radioactive isotope of plutonium that has a half-life of 87.7 years.