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History

Fermium (after Enrico Fermi) was first discovered by a team led by Albert Ghiorso in 1952.  The team found ²⁵⁵Fm (half-life ~20 hrs.)  in the debris of the first hydrogen bomb explosion (Operation Ivy).  That isotope was created when ²³⁸U combined with 17 neutrons in the intense temperature and pressure of the explosion (eight beta decays also occurred to create the element). The work was overseen by the University of California Radiation Laboratory, Argonne National Laboratory, and Los Alomos Scientific Laboratory whose team members included Ghiorso, Stanley G. Thompson, Gary H. Higgins, Glenn T. Seaborg (from the Radiation Laboratory and Department of Chemistry of the University of California), Martin H. Studier, P.R. Fields, Sherman M. Fried, H. Diamond, J.F. Mech, G.L. Pyle, John R. Huizenga, A. Hirsch, W.M. Manning (from the Argonne National Laboratory), C.I. Browne, H. Louise Smith, and R.W. Spence (from the Los Alamos Scientific Laboratory). Samples of sea coral impacted from the first thermonuclear explosion of November 1952 were used.

Enrico Fermi

All these findings were kept secret until 1955 due to Cold War tensions.  In late 1953 and early 1954 a team from the Nobel Institute of Physics in Stockholm bombarded a ²³⁸U target with ¹⁶O ions, producing an alpha-emitter with an atomic weight of ~250 and with 100 protons (in other words, element ²⁵⁰100).  The Nobel team did not claim discovery but the isotope they produced was later positively identified as ²⁵⁰Fm.

Characteristics

Only tracer amounts of fermium have ever been produced or isolated. Thus relatively little is known about its chemical properties. Only the (III) oxidation state of the element appears to exist in aqueous solution. ²⁵⁴Fm and heavier isotopes can be synthesized by intense neutron bombardment of lighter elements (especially uranium and plutonium).  During this, successive neutron captures mixed with beta decays build the fermium isotope. The intense neutron bombardment conditions needed to create fermium exist in thermonuclear explosions and can be replicated in the laboratory (such as in the High Flux Isotope Reactor at Oak Ridge National Laboratory).  The synthesis of element nobelium-102 was confirmed when ²⁵⁰Fm was chemically identified.   There are no known uses of fermium outside of basic research.  Fermium is the eighth transuranic element.

Occurrence

Fermium does not exist naturally on Earth today but it has occurred in the past, produced in natural reactor deposits.  Annual world production of fermium probably totals less than a milllonth of a gram.

Today, fermium is produced though a lengthy chain of nuclear reactions that involves bombarding each isotope in the chain with neutrons and then allowing the resulting isotope to undergo beta decay.  Fermium doesn't occur naturally, and has not been found in the earth's crust, so there is no reason to consider its health hazards.  Due to the small amounts produced and its short half-life, there are currently no uses for fermium outside of basic scientific research.

Isotopes

19 radioisotopes of fermium have been characterized, with the most stable being ²⁵⁷Fm with a half-life of 100.5 days, ²⁵³Fm with a half-life of 3 days, ²⁵²Fm with a half-life of 25.39 hours, and ²⁵⁵Fm with a half-life of 20.07 hours.  All of the remaining radioactive isotopes have half-lifes that are less than 5.4 hours, and the majority of these have half lifes that are less than 3 minutes. This element also has 1 meta state, ^250mFm (t_½ 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 amu (²⁴²Fm) to 259.101 amu (²⁵⁹Fm).

Fermium's most stable isotope, fermium-257, decays into californium-253 through alpha decay or decays through spontaneous fission.

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.

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.