Isotopes of fermium
From Wikipedia, the free encyclopedia
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 19 known radioisotopes ranging in atomic mass from 242Fm to 260Fm, 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.
[edit] Table
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[1][n 1] |
daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| excitation energy | |||||||
| 242Fm | 100 | 142 | 242.07343(43)# | 0.8(2) ms | SF | (various) | 0+ |
| α (rare) | 238Cf | ||||||
| 243Fm | 100 | 143 | 243.07435(23)# | 210(60) ms [0.18(+8-4) s] |
α (60%) | 239Cf | 7/2-# |
| β+ (40%) | 243Es | ||||||
| SF (.57%) | (various) | ||||||
| 244Fm | 100 | 144 | 244.07408(30)# | 3.3(5) ms | SF (99%) | (various) | 0+ |
| α (1%) | 240Cf | ||||||
| 245Fm | 100 | 145 | 245.07539(30)# | 4.2(13) s | α (95.7%) | 241Cf | 1/2+# |
| β+ (4.2%) | 245Es | ||||||
| SF (.13%) | (various) | ||||||
| 246Fm | 100 | 146 | 246.07530(4) | 1.1(2) s | α (85%) | 242Cf | 0+ |
| β+ (10%) | 246Es | ||||||
| β+, SF (10%) | (various) | ||||||
| SF (4.5%) | (various) | ||||||
| 247Fm | 100 | 147 | 247.07685(15)# | 29(1) s | α (50%) | 243Cf | (7/2+) |
| β+ (50%) | 247Es | ||||||
| 248Fm | 100 | 148 | 248.077195(13) | 36(2) s | α (99%) | 244Cf | 0+ |
| β+ (1%) | 248Es | ||||||
| SF (.05%) | (various) | ||||||
| 249Fm | 100 | 149 | 249.07903(11)# | 2.6(7) min | β+ (85%) | 249Es | (7/2+)# |
| α (15%) | 245Cf | ||||||
| 250Fm | 100 | 150 | 250.079521(13) | 30(3) min | α (90%) | 246Cf | 0+ |
| EC (10%) | 250Es | ||||||
| SF (6×10−4%) | (various) | ||||||
| 250mFm | 1500(300)# keV | 1.8(1) s | IT | 250Fm | 7,8# | ||
| 251Fm | 100 | 151 | 251.081575(9) | 5.30(8) h | β+ (98.2%) | 251Es | (9/2-) |
| α (1.8%) | 247Cf | ||||||
| 251mFm | 191(2) keV | 15.2(23) µs | (5/2+) | ||||
| 252Fm | 100 | 152 | 252.082467(6) | 25.39(4) h | α (99.99%) | 248Cf | 0+ |
| SF (.0023%) | (various) | ||||||
| β+β+ (rare) | 252Cf | ||||||
| 253Fm | 100 | 153 | 253.085185(4) | 3.00(12) d | EC (88%) | 253Es | (1/2)+ |
| α (12%) | 249Cf | ||||||
| 254Fm | 100 | 154 | 254.0868542(30) | 3.240(2) h | α (99.94%) | 250Cf | 0+ |
| SF (.06%) | (various) | ||||||
| 255Fm | 100 | 155 | 255.089962(5) | 20.07(7) h | α | 251Cf | 7/2+ |
| SF (2×10−5%) | (various) | ||||||
| 256Fm | 100 | 156 | 256.091773(8) | 157.6(13) min | SF (91.9%) | (various) | 0+ |
| α (8.1%) | 252Cf | ||||||
| 257Fm[n 2] | 100 | 157 | 257.095105(7) | 100.5(2) d | α (99.79%) | 253Cf | (9/2+) |
| SF (.21%) | (various) | ||||||
| 258Fm | 100 | 158 | 258.09708(22)# | 370(14) µs | SF | (various) | 0+ |
| 259Fm | 100 | 159 | 259.1006(3)# | 1.5(3) s | SF | (various) | 3/2+# |
| 260Fm | 100 | 160 | 260.10268(54)# | 1# min | 0+ | ||
- ^ Abbreviations:
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission - ^ Heaviest nuclide produced via neutron capture
[edit] 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.
[edit] References
- Isotope masses from:
- 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. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- 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. http://www.iupac.org/publications/pac/75/6/0683/pdf/.
- 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. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary.
- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- 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. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. 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 978-0849304859.
| Isotopes of einsteinium | Isotopes of fermium | Isotopes of mendelevium |
| Index to isotope pages · Table of nuclides | ||
