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
nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[1][n 1] |
daughter isotope(s) |
nuclear spin |
---|---|---|---|---|---|---|---|
excitation energy | |||||||
241Fm | 100 | 141 | 241.07421(32)# | 730(60) µs | SF(>78%) | (various) | 5/2#+ |
α (<14%) | 237Cf | ||||||
242Fm | 100 | 142 | 242.07343(43)# | 0.8(2) ms | SF | (various) | 0+ |
α (rare) | 238Cf | ||||||
243Fm | 100 | 143 | 243.07447(23)# | 231(9) ms | α (91%) | 239Cf | 7/2-# |
SF (9%) | (various) | ||||||
β+ (rare) | 243Es | ||||||
244Fm | 100 | 144 | 244.07404(22)# | 3.12(8) ms | SF (99%) | (various) | 0+ |
α (1%) | 240Cf | ||||||
245Fm | 100 | 145 | 245.07535(21)# | 4.2(13) s | α (95.7%) | 241Cf | 1/2+# |
β+ (4.2%) | 245Es | ||||||
SF (.13%) | (various) | ||||||
246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | α (85%) | 242Cf | 0+ |
β+ (10%) | 246Es | ||||||
β+, SF (10%) | (various) | ||||||
SF (4.5%) | (various) | ||||||
247Fm | 100 | 147 | 247.07695(12)# | 31(1) s | α (>50%) | 243Cf | (7/2+) |
β+ (<50%) | 247Es | ||||||
248Fm | 100 | 148 | 248.077186(9) | 35.1(8) s | α (93%) | 244Cf | 0+ |
β+ (7%) | 248Es | ||||||
SF (.10%) | (various) | ||||||
249Fm | 100 | 149 | 249.078928(7) | 1.6(1) min | β+ (85%) | 249Es | (7/2+)# |
α (15%) | 245Cf | ||||||
250Fm | 100 | 150 | 250.079521(9) | 30.4(15) min | α (90%) | 246Cf | 0+ |
EC (10%) | 250Es | ||||||
SF (6.9×10−3%) | (various) | ||||||
250mFm | 1199.2(10) keV | 1.92(5) s | IT | 250Fm | (8-) | ||
251Fm | 100 | 151 | 251.081540(16) | 5.30(8) h | β+ (98.2%) | 251Es | (9/2-) |
α (1.8%) | 247Cf | ||||||
251mFm | 200.09(11) keV | 21.1(16) 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 | 254.0868544(30) | 3.240(2) h | α (99.94%) | 250Cf | 0+ |
SF (.0592%) | (various) | ||||||
255Fm | 100 | 155 | 255.089964(5) | 20.07(7) h | α | 251Cf | 7/2+ |
SF (2.4×10−5%) | (various) | ||||||
256Fm | 100 | 156 | 256.091774(8) | 157.6(13) min | SF (91.9%) | (various) | 0+ |
α (8.1%) | 252Cf | ||||||
257Fm[n 2] | 100 | 157 | 257.095106(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[n 3][n 4] | 100 | 160 | 260.10281(55)# | 1# min | 0+ |
- ^ Abbreviations:
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission - ^ Heaviest nuclide produced via neutron capture
- ^ Discovery of this isotope is unconfirmed
- ^ 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
Isotope | Discovered | Reaction |
---|---|---|
241Fm | 2008 | 204Pb(40Ar,3n) |
242Fm | 1975 | 204Pb(40Ar,2n), 206Pb(40Ar,4n) |
243Fm | 1981 | 206Pb(40Ar,3n) |
244Fm | 1967 | 233U(16O,5n) |
245Fm | 1967 | 233U(16O,4n) |
246Fm | 1966 | 235U(16O,5n) |
247Fm | 1967 | 239Pu(12C,4n) |
248Fm | 1958 | 240Pu(12C,4n) |
249Fm | 1960 | 238U(16O,5n) |
250Fm | 1954 | 238U(16O,4n) |
251Fm | 1957 | 249Cf(α,2n) |
252Fm | 1956 | 249Cf(α,n) |
253Fm | 1957 | 252Cf(α,3n) |
254Fm | 1954 | Neutron capture |
255Fm | 1954 | Neutron capture |
256Fm | 1955 | Neutron capture |
257Fm | 1964 | Neutron capture |
258Fm | 1971 | 257Fm(d,p) |
259Fm | 1980 | 257Fm(t,p) |
260Fm? | 1992? | 254Es+18O, 22Ne — transfer (EC of 260Md) [2] |
260Fm? was not confirmed in 1997.
References
- 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" (PDF). Chinese Physics C,. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003.
{{cite journal}}
: Explicit use of et al. in:|author=
(help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) - G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
{{cite journal}}
: CS1 maint: multiple names: authors list (link)
- 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" (PDF). Chinese Physics C,. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003.
- 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.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - 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.
{{cite journal}}
: Unknown parameter|laysummary=
ignored (help)
- 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.
- 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" (PDF). Chinese Physics C,. 36 (12): 1157–1286. doi:10.1088/1674-1137/36/12/001.
{{cite journal}}
: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) - G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
{{cite web}}
: Check date values in:|accessdate=
(help) - N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.
{{cite book}}
: Unknown parameter|nopp=
ignored (|no-pp=
suggested) (help) - 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.
{{cite web}}
: Check date values in:|accessdate=
(help)
- G. Audi, F.G. Kondev, M. Wang, B. Pfeiffer, X. Sun, J. Blachot, and M. MacCormick (2012). "The NUBASE2012 evaluation of nuclear properties" (PDF). Chinese Physics C,. 36 (12): 1157–1286. doi:10.1088/1674-1137/36/12/001.