Fermium (100Fm) is a synthetic element, and thus a standard atomic weight 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 4 nuclear isomers, 247mFm, 250mFm, 251mFm, and 253mFm. The longest-lived isotope is 257Fm with a half-life of 100.5 days, and the longest-lived isomer is 247mFm with a half-life of 5.1 seconds.
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List of isotopes
Nuclide [n 1] | Z | N | Isotopic mass (Da) [n 2][n 3] | Half-life | Decay mode [n 4] | Daughter isotope | Spin and parity [n 5][n 6] | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy | |||||||||||||||||||
241Fm | 100 | 141 | 241.07421(32)# | 730(60) μs | SF | (various) | 5/2+# | ||||||||||||
α (<14%) | 237Cf | ||||||||||||||||||
242Fm | 100 | 142 | 242.07343(43)# | <4 μs[2] | SF | (various) | 0+ | ||||||||||||
243Fm[3] | 100 | 143 | 243.07447(23)# | 231(9) ms | α (91%) | 239Cf | (7/2−) | ||||||||||||
SF (9%) | (various) | ||||||||||||||||||
β+ (<10%) | 243Es | ||||||||||||||||||
244Fm[2] | 100 | 144 | 244.07404(22)# | 3.12(8) ms | SF | (various) | 0+ | ||||||||||||
α (<1%) | 240Cf | ||||||||||||||||||
245Fm[4] | 100 | 145 | 245.07535(21)# | 5.5(7) s | α (88.5%) | 241Cf | (1/2+) | ||||||||||||
β+ (11.5%) | 245Es | ||||||||||||||||||
SF (<0.3%)[3] | (various) | ||||||||||||||||||
246Fm[5] | 100 | 146 | 246.075350(17) | 1.54(4) s | α (93.2%) | 242Cf | 0+ | ||||||||||||
SF (6.8%) | (various) | ||||||||||||||||||
β+ (<1.3%) | 246Es | ||||||||||||||||||
247Fm[6] | 100 | 147 | 247.07695(12)# | 31(1) s | α (64%) | 243Cf | (7/2+) | ||||||||||||
β+ (36%) | 247Es | ||||||||||||||||||
247mFm | 45(7) keV | 5.1(2) s | α (88%) | 243Cf | (1/2+) | ||||||||||||||
IT (12%) | 247Fm | ||||||||||||||||||
β+? | 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+ (84.4%) | 249Es | (7/2+) | ||||||||||||
α (15.6%)[7] | 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 | IT | 251Fm | (5/2+) | ||||||||||||||
252Fm | 100 | 152 | 252.082467(6) | 25.39(4) h | α (99.99%)[n 7] | 248Cf | 0+ | ||||||||||||
SF (.0023%) | (various) | ||||||||||||||||||
253Fm | 100 | 153 | 253.085185(4) | 3.00(12) d | EC (88%) | 253Es | (1/2)+ | ||||||||||||
α (12%) | 249Cf | ||||||||||||||||||
253mFm[8] | ~351 keV | 0.56(6) μs | IT | 253Fm | (11/2-) | ||||||||||||||
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 8] | 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 9][n 10] | 100 | 160 | 260.10281(55)# | 4 ms | SF | (various) | 0+ | ||||||||||||
This table header & footer: |
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) |
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. S2CID 250839471.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (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
- Half-life, spin, and isomer data selected from the following sources.
- G. Audi; F. G. Kondev; M. Wang; B. Pfeiffer; X. Sun; J. Blachot; M. MacCormick (2012). "The NUBASE2012 evaluation of nuclear properties" (PDF). Chinese Physics C. 36 (12): 1157–1286. Bibcode:2012ChPhC..36....1A. doi:10.1088/1674-1137/36/12/001. Archived from the original (PDF) on 2014-02-22.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (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.x database". Brookhaven National Laboratory.
- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.
- M. Thoennessen (2012). "Discovery of Isotopes of Elements with Z≥100". Atomic Data and Nuclear Data Tables. 99 (3): 312–344. arXiv:1203.2105. Bibcode:2013ADNDT..99..312T. doi:10.1016/j.adt.2012.03.003. S2CID 94982856.
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