Isotopes of fermium

Fermium (Fm) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered (in fallout from nuclear testing) was ²⁵⁵Fm in 1952. ²⁵⁰Fm was independently synthesized shortly after the discovery of ²⁵⁵Fm. There are 20 known radioisotopes ranging in atomic mass from ²⁴¹Fm to ²⁶⁰Fm (²⁶⁰Fm is unconfirmed), and 2 nuclear isomers, ^250mFm and ^251mFm. The longest-lived isotope is ²⁵⁷Fm with a half-life of 100.5 days, and the longest-lived isomer is ^250mFm with a half-life of 1.8 seconds.

Table

1. ↑ Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
   SF: Spontaneous fission
2. ↑ Heaviest nuclide produced via neutron capture
3. ↑ Discovery of this isotope is unconfirmed
4. ↑ Not directly synthesized, occurs as decay product of ²⁶⁰Md

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
• The isotopes denoted by an isotope number with an "m" are metastable isomers.

Chronology of isotope discovery

²⁶⁰Fm? was not confirmed in 1997.

References

1. ↑ http://www.nucleonica.net/unc.aspx
2. ↑ see mendelevium

• Isotope masses from:
  • M. Wang, G. Audi, A.H. Wapstra, F.G. Kondev, M. MacCormick, X. Xu, et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references.". Chinese Physics C, 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003. 
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. 
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. 
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary. 
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi, F.G. Kondev, M. Wang, B. Pfeiffer, X. Sun, J. Blachot, and M. MacCormick (2012). "The NUBASE2012 evaluation of nuclear properties.". Chinese Physics C, 36 (12): 1157–1286. 
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. 
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. 
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9. 
  • M. Thoennessen (2012). "Discovery of Isotopes of Elements with Z≥100". National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA. Retrieved July 2012.