Fermium, chemical element, symbol Fm; for physical constants see Periodic Table. Fermium was discovered by Albert Ghiorso and co-workers in 1952 from the debris of a thermonuclear bomb exploded in the Pacific. It is a metallic element and a member of the actinide series. It has been produced by intense irradiation of plutonium and other lower elements with neutrons as well as by bombarding uranium-238 with oxygen-16 ions in a cyclotron. All of its 16 known isotopes are radioactive. The chemical identification of fermium-250 as a decay product is confirmation of nobelium-254.