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Chemical Fact Sheet

Fermium

Chemical Abstract Number (CAS #) 7440-72-4
Analytical Methods 200.8 - 6020
Atomic Symbol Fm

Synopsis from the CRC Handbook of Chemistry and Physics 92nd Edition 2011-2013

Fermium — (Enrico Fermi [1901–1954], nuclear physicist), Fm; at. wt. [257]; at. no. 100; m.p. 1527 °C. Fermium, the eighth transuranium element of the actinide series to be discovered, was identified by Ghiorso and co-workers in 1952 in the debris from a thermonuclear explosion in the Pacific in work involving the University of California Radiation Laboratory, the Argonne National Laboratory, and the Los Alamos Scientific Laboratory. The isotope produced was the 20-hour 255Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded 238U with 16O ions, and isolated a 30-min α-emitter, which they ascribed to 250100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. The chemical properties of fermium have been studied solely with tracer amounts, and in normal aqueous media only the (III) oxidation state appears to exist. The isotope 254Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements such as plutonium by a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. Twenty isotopes and isomers of fermium are known to exist. 257Fm, with a half-life of about 100.5 days, is the longest lived. 250Fm, with a half-life of 30 min, has been shown to be a product of decay of Element 254102. It was by chemical identification of 250Fm that production of Element 102 (nobelium) was confirmed. Fermium would probably have chemical properties resembling erbium.


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