Isotopes of fermium

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Isotopes of fermium  (100Fm)
Main isotopes [1] Decay
abun­dance half-life (t1/2) mode pro­duct
252Fm synth 25.39 h SF –
α 248Cf
253Fmsynth3 d ε 253Es
α 249Cf
255Fmsynth20.07 hSF–
α 251Cf
257Fmsynth100.5 dα 253Cf
SF–

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.

Contents

List of isotopes


Nuclide
[n 1] 		Z N Isotopic mass (Da) [2]
[n 2] [n 3] 		Half-life [1]
Decay
mode [1]
[n 4] 		Daughter
isotope
Spin and
parity [1]
[n 5] [n 6]
Excitation energy
241Fm100141241.07431(32)#730(60) μs SF?(various)5/2+#
α (<14%)237Cf
β+ (<12%)241Es
242Fm100142242.07343(43)#0.8(2) msSF(various)0+
α?238Cf
243Fm [3] 100143243.07441(14)#231(9) msα (91%)239Cf(7/2−)
SF (9%)(various)
β+?243Es
244Fm100144244.07404(22)#3.12(8) msSF (>97%)(various)0+
β+ (<2%)244Es
α (<1%)240Cf
245Fm [4] 100145245.07535(21)#4.2(13) sα (88.5%)241Cf(1/2+)
β+ (11.5%)245Es
SF (<0.3%) [3] (various)
246Fm100146246.075350(17)1.54(4) sα (93.2%)242Cf0+
SF (6.8%)(various)
EC (<1.3%)246Es
247Fm100147247.07694(19)#31(1) sα (~64%)243Cf(7/2+)
β+? (~36%)247Es
247mFm49(8) keV5.1(2) sα (88%)243Cf(1/2+)
IT?247Fm
β+?247Es
248Fm100148248.0771855(91)34.5(12) sα (99.9%)244Cf0+
SF (0.1%)(various)
β+?248Es
248mFm1200(100)# keV10.1(6) msIT?248Fm6+#
α?244Cf
β+?248Es
249Fm100149249.0789260(67)1.6(1) minβ+? (67%)249Es7/2+
α (33%)245Cf
250Fm100150250.0795198(85)31.0(11) minα (99.99%)246Cf0+
SF (6.9×10−3%)(various)
EC?250Es
250mFm1199.2(10) keV1.92(5) sIT250Fm(8−)
α?246Cf
β+?250Es
SF?(various)
251Fm100151251.081545(15)5.30(8) hβ+ (98.20%)251Es9/2−
α (1.80%)247Cf
251mFm200.0(1) keV21.8(8) μsIT251Fm5/2+
252Fm100152252.0824660(56)25.39(4) hα (99.99%) [n 7] 248Cf0+
SF (.0023%)(various)
253Fm100153253.0851809(16)3.00(12) dEC (88%)253Es1/2+
α (12%)249Cf
253mFm351(6) keV0.56(6) μsIT253Fm11/2-#
254Fm100154254.0868524(20)3.240(2) hα (99.94%)250Cf0+
SF (0.0592%)(various)
255Fm100155255.0899635(42)20.07(7) hα251Cf7/2+
SF (2.4×10−5%)(various)
256Fm100156256.0917717(32)157.1(13) minSF (91.9%)(various)0+
α (8.1%)252Cf
257Fm [n 8] 100157257.0951054(47)100.5(2) dα (99.79%)253Cf9/2+
SF (.210%)(various)
258Fm100158258.09708(22)#370(14) μsSF(various)0+
α?254Cf
259Fm100159259.10060(30)#1.5(2) sSF(various)3/2+#
260Fm [n 9] [n 10] 100160260.10281(47)#1# minSF(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. ↑ Theoretically capable of β+β+ decay to 252Cf
  8. ↑ Heaviest nuclide produced via neutron capture
  9. ↑ Discovery of this isotope is unconfirmed
  10. ↑ Not directly synthesized, occurs as decay product of 260Md

Chronology of isotope discovery

IsotopeDiscoveredReaction
241Fm2008204Pb(40Ar,3n)
242Fm1975204Pb(40Ar,2n), 206Pb(40Ar,4n)
243Fm1981206Pb(40Ar,3n)
244Fm1967233U(16O,5n)
245Fm1967233U(16O,4n)
246Fm1966235U(16O,5n)
247Fm1967239Pu(12C,4n)
248Fm1958240Pu(12C,4n)
249Fm1960238U(16O,5n)
250Fm1954238U(16O,4n)
251Fm1957249Cf(α,2n)
252Fm1956249Cf(α,n)
253Fm1957252Cf(α,3n)
254Fm1954Neutron capture
255Fm1954Neutron capture
256Fm1955Neutron capture
257Fm1964Neutron capture
258Fm1971257Fm(d,p)
259Fm1980257Fm(t,p)
260Fm?1992?254Es+18O, 22Ne — transfer (EC of 260Md)

260Fm was not confirmed in 1997.

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References

  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. 1 2 Khuyagbaatar, J.; Heßberger, F. P.; Hofmann, S.; Ackermann, D.; Burkhard, H. G.; Heinz, S.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R.; Maurer, J.; Nishio, K. (12 October 2020). "α decay of Fm 243 143 and Fm 245 145 , and of their daughter nuclei". Physical Review C. 102 (4): 044312. doi:10.1103/PhysRevC.102.044312. ISSN   2469-9985. S2CID   241259726 . Retrieved 24 June 2023.
  4. ↑ 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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