from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A synthetic transuranic metallic element having over 20 isotopes and isomers with mass numbers ranging from 242 to 260. The longest-lived isotope has mass number 257 and a half-life of approximately 100 days. Atomic number 100; melting point 1527°C; valence 3. cross-reference: Periodic Table.

from the GNU version of the Collaborative International Dictionary of English.

  • noun the transuranic element of atomic number 100; symbol Fm. The atomic weight of the most stable isotope, having a half-life of about 80 days, is 257. The first isotope, Fm255 was discovered in 1952 in the debris of a thermonuclear explosion. Other istopes have been produced in nuclear reactors and by decay of other transuranic elements.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun A transuranic chemical element (symbol Fm) with an atomic number of 100.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a radioactive transuranic metallic element produced by bombarding plutonium with neutrons


from The American Heritage® Dictionary of the English Language, 4th Edition

[After Enrico Fermi.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

Named for Enrico Fermi.


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  • The first glimpse at 112 lasted for only a third of a millisecond, until it decayed first into element 110 (darmstaditium) and then into four different short-lived elements until researchers lost its trail at element 110 (fermium).

    unknown title 2009


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  • Fm.

    December 16, 2007