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Isotopes of fermium

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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 nuclear fallout from the Ivy Mike H-bomb test) was 255Fm in 1952. 250Fm was independently synthesized (to establish priority if the former result had to remain classified) shortly after the discovery of 255Fm.

Isotopes of fermium (100Fm)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
252Fm synth 25.39 h α 248Cf
SF –
253Fm synth 3 d ε 253Es
α 249Cf
255Fm synth 20.07 h α 251Cf
SF –
257Fm synth 100.5 d α 253Cf
SF –

There are 20 known radioisotopes ranging in atomic mass from 241Fm to 260Fm (260Fm is unconfirmed), and 5 nuclear isomers. 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.

List of isotopes

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Nuclide
[n 1]		 Z N Isotopic mass (Da)[2]
[n 2][n 3]		 Discovery
year[3][4]		 Half-life[1]
 Decay
mode[1]
[n 4]		 Daughter
isotope
 Spin and
parity[1]
[n 5][n 6]
Excitation energy
241Fm 100 141 241.07431(32)# 2008 730(60) μs SF (various) 5/2+#
α (<14%) 237Cf
β+ (<12%) 241Es
242Fm 100 142 242.07343(43)# 1975 0.8(2) ms SF (various) 0+
243Fm 100 143 243.07441(14)# 1981 231(9) ms α (91%) 239Cf 7/2−#
SF (9%) (various)
244Fm 100 144 244.07404(22)# 1967 3.12(8) ms SF (>97%) (various) 0+
β+ (<2%) 244Es
α (<1%) 240Cf
245Fm 100 145 245.07535(21)# 1967 4.2(13) s α (88.5%) 241Cf 1/2+#
β+ (11.5%)[5] 245Es
SF (<0.3%) (various)
246Fm 100 146 246.075353(15) 1966 1.54(4) s α (93.2%) 242Cf 0+
SF (6.8%) (various)
EC (<1.3%) 246Es
247Fm 100 147 247.07694(19)# 1967 31(1) s α (~64%) 243Cf (7/2+)
β+? (~36%) 247Es
247mFm 49(8) keV 1967 5.1(2) s α (88%) 243Cf (1/2+)
IT? (12%) 247Fm
248Fm 100 148 248.077185(9) 1958 34.5(12) s α (99.9%) 244Cf 0+
SF (0.1%) (various)
248mFm 1200(100)# keV (2010)[n 7] 10.1(6) ms IT? 248Fm 6+#
α? 244Cf
β+? 248Es
249Fm 100 149 249.078926(7) 1959 1.6(1) min β+? (67%) 249Es 7/2+
α (33%) 245Cf
250Fm 100 150 250.079520(8) 1954 31.0(11) min α (99.99%) 246Cf 0+
SF (6.9×10−3%) (various)
250mFm 1199.2(10) keV 1971 1.92(5) s IT 250Fm (8−)
251Fm 100 151 251.081545(15) 1957 5.30(8) h β+ (98.20%) 251Es 9/2−
α (1.80%) 247Cf
251mFm 200.0(1) keV 2006 21.8(8) μs IT 251Fm 5/2+
252Fm 100 152 252.082466(6) 1956 25.39(4) h α (99.99%)[n 8] 248Cf 0+
SF (0.0023%) (various)
253Fm 100 153 253.0851809(17) 1957 3.00(12) d EC (88%) 253Es 1/2+
α (12%) 249Cf
253mFm 351(6) keV 2011 0.56(6) μs IT 253Fm 11/2−#
254Fm 100 154 254.0868524(20) 1954 3.240(2) h α (99.94%) 250Cf 0+
SF (0.0592%) (various)
255Fm 100 155 255.089963(4) 1954 20.07(7) h α 251Cf 7/2+
SF (2.4×10−5%) (various)
256Fm 100 156 256.091772(3) 1955 157.1(13) min SF (91.9%) (various) 0+
α (8.1%) 252Cf
257Fm[n 9] 100 157 257.095105(5) 1964 100.5(2) d α (99.79%) 253Cf 9/2+
SF (0.210%) (various)
258Fm 100 158 258.09708(22)# 1971 370(14) μs SF (various) 0+
259Fm 100 159 259.10060(30)# 1980 1.5(2) s SF (various)
260Fm[n 10][n 11] 100 160 260.10281(47)# (1992) 1# min SF (various) 0+
This table header & footer:
  1. ↑ mFm – Excited nuclear isomer.
  2. ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ↑ Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
    SF:Spontaneous fission
  5. ↑ ( ) spin value – Indicates spin with weak assignment arguments.
  6. ↑ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  7. ↑ Only published in a conference proceeding and not a refereed journal
  8. ↑ Theoretically capable of β+β+ decay to 252Cf
  9. ↑ Heaviest nuclide produced via neutron capture
  10. ↑ Discovery of this isotope is unconfirmed
  11. ↑ Not directly synthesized, occurs as decay product of 260Md

References

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  1. 1 2 3 4 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3) 030001. doi:10.1088/1674-1137/abddae.
  2. ↑ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3) 030003. doi:10.1088/1674-1137/abddaf.
  3. ↑ FRIB Nuclear Data Group. "Discovery of Nuclides Project, Isotope Database". doi:10.11578/frib/2279152.
  4. ↑ FRIB Nuclear Data Group. "Discovery of Nuclides Project, Isomer Database". doi:10.11578/frib/2572219.
  5. ↑ Tezekbayeva, M. S.; Yeremin, A. V.; Svirikhin, A. I.; Lopez-Martens, A.; Chelnokov, M. L.; Chepigin, V. I.; Isaev, A. V.; Izosimov, I. N.; Karpov, A. V.; Kuznetsova, A. A.; Malyshev, O. N.; Mukhin, R. S.; Popeko, A. G.; Popov, Yu. A.; Rachkov, V. A.; Sailaubekov, B. S.; Sokol, E. A.; Hauschild, K.; Jacob, H.; Chakma, R.; Dorvaux, O.; Forge, M.; Gall, B.; Kessaci, K.; Andel, B.; Antalic, S.; Bronis, A.; Mosat, P. (24 March 2022). "Study of the production and decay properties of neutron-deficient nobelium isotopes". The European Physical Journal A. 58 (3): 52. arXiv:2203.15659. Bibcode:2022EPJA...58...52T. doi:10.1140/epja/s10050-022-00707-9. ISSN 1434-601X. S2CID 247720708. Retrieved 24 June 2023.
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