Discovered | Name | Characteristics

Fermium is a member of the actinide series, which stretches from actinium (Ac) to lawrencium (Lr). Fermium is a synthetic element; none occurs naturally on earth.

Albert Ghiorso and his coworkers (including Glenn Seaborg) first detected the element in the residue of the first thermonuclear or hydrogen bomb, which was exploded in 1952. It is produced in a chain of reactions beginning with plutonium--239. One arrives at fermium by building up successive elements by neutron bombardment followed by beta decay. For example, in the last step, californium--253 decays to einsteinium--253

253Cf 253Es + b

and neutron capture by the 253Es nucleus, and subsequent beta decay, give fermium.

254Es + 1n 254Es

254Es 254Fm + b

This chain of neutron capture reactions occurred in the intense neutron flux of an atomic explosion.

The element is named for Enrico Fermi (1901-1954), the Italian physicist who first experimentally observed nuclear fission.

At least 16 isotopes of Fm are known, ranging from mass numbers of 243 to 258. The most stable isotope is 257Fm, which has a half-life of about 100 days.

Little is known about its chemistry. However, it is thought that its compounds have oxidation numbers of +2 and +3, with +3 being the more stable.