fermium

fermium [for Enrico Fermi ], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527°C; b.p. and sp. gr. unknown; valence +2, +3. Fermium is a member of Group 3 of the periodic table . The physical properties of fermium are largely unknown; its chemical properties are believed to be similar to those of the other members of the actinide series . The eighth transuranium element to be discovered, fermium was first identified (1952) as fermium-255 ( half-life about 20 hours) by Albert Ghiorso and his coworkers, who discovered it in residue from the first thermonuclear test explosion in the South Pacific. Twenty isotopes, all of which are radioactive, are known; the most stable is fermium-257, with a half-life of about 100 days. Isotopes of fermium have been produced by neutron bombardment of plutonium.

fermium (symbol Fm) Radioactive metallic transuranic element of the actinide series. US nuclear scientist Albert Ghiorso (1915– ) and colleagues identified it in 1952 as a decay product of U²⁵⁵ from the first large hydrogen bomb explosion. Ten isotopes have subsequently been identified. Properties: at.no. 100; most stable isotope Fm²⁵⁷ (half-life 80 days).

fer·mi·um / ˈfermēəm; ˈfər-/ • n. the chemical element of atomic number 100, a radioactive metal of the actinide series. Fermium does not occur naturally and was discovered in 1953 in the debris of the first hydrogen bomb explosion. (Symbol: Fm)