Fermium

Author: Robert Husted, Mollie Boorman

History

(Enrico Fermi) Fermium, the eighth discovered transuranium element of the actinide series, was identified by Ghiorso and co-workers in 1952 in the debris from a thermonuclear explosion in the pacific during work involving the University of California Radiation Laboratory, Argonne National Laboratory, and Los Alamos National 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 alpha-emitter, which they ascribed to ²⁵⁰Fm, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed.

Properties

The chemical properties of fermium have been studied solely with tracer amounts. In normal aqueous media, only the (III) oxidation state appears to exist.

Isotopes

²⁵⁴Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached.

Sixteen isotopes 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 minutes, has been shown to be a decay product of element ²⁵⁴No. Chemical identification of ²⁵⁰Fm confirmed the production of element 102 (nobelium).