Isotopes of fermium
(Redirected from Fermium-250)
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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 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 1.92 seconds.
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(>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 7] | 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 8][n 9] | 100 | 160 | 260.10281(55)# | 4 ms | SF | (various) | 0+ | ||||||||||||
This table header & footer: |
- ^ mFm – Excited nuclear isomer.
- ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- ^
Modes of decay:
EC: Electron capture IT: Isomeric transition SF: Spontaneous fission - ^ ( ) spin value – Indicates spin with weak assignment arguments.
- ^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- ^ Heaviest nuclide produced via neutron capture
- ^ Discovery of this isotope is unconfirmed
- ^ Not directly synthesized, occurs as decay product of 260Md
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.
- 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
- Isotopic compositions and standard atomic masses from:
- de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
- Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.
- "News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
- 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.