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

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:
  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[1]
  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

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

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  2. ^ a b Khuyagbaatar, J.; Hofmann, S.; Heßberger, F. P.; Ackermann, D.; Burkhard, H. G.; Heinz, S.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R.; Maurer, J.; Nishio, K.; Novikov, Yu. (1 August 2008). "Spontaneous fission of neutron-deficient fermium isotopes and the new nucleus 241Fm" (PDF). The European Physical Journal A. 37 (2): 177–183. Bibcode:2008EPJA...37..177K. doi:10.1140/epja/i2008-10608-4. ISSN 1434-601X. S2CID 18977014. Retrieved 24 June 2023.
  3. ^ a b 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.
  5. ^ Venhart, M.; Heßberger, F. P.; Ackermann, D.; Antalic, S.; Gray-Jones, C.; Greenlees, P. T.; Heinz, S.; Herzberg, R. -D.; Hofmann, S.; Ketelhut, S.; Kindler, B.; Kojouharov, I.; Leino, M.; Lommel, B.; Mann, R.; Papadakis, P.; Rostron, D.; Rudolph, D.; Šáro, Š.; Sulignano, B. (4 February 2011). "Decay study of 246Fm at SHIP" (PDF). The European Physical Journal A. 47 (2): 20. Bibcode:2011EPJA...47...20V. doi:10.1140/epja/i2011-11020-9. ISSN 1434-601X. S2CID 119353521. Retrieved 24 June 2023.
  6. ^ Heßberger, F. P.; Hofmann, S.; Ackermann, D.; Antalic, S.; Kindler, B.; Kojouharov, I.; Kuusiniemi, P.; Leino, M.; Lommel, B.; Mann, R.; Nishio, K.; Popeko, A. G.; Sulignano, B.; Saro, S.; Streicher, B.; Venhart, M.; Yeremin, A. V. (1 December 2006). "Alpha-gamma decay studies of 255Rf, 251No and 247Fm" (PDF). The European Physical Journal A - Hadrons and Nuclei. 30 (3): 561–569. Bibcode:2006EPJA...30..561H. doi:10.1140/epja/i2006-10137-2. ISSN 1434-601X. S2CID 123871572. Retrieved 24 June 2023.
  7. ^ Heßberger, F. P.; Antalic, S.; Ackermann, D.; Kalaninová, Z.; Heinz, S.; Hofmann, S.; Streicher, B.; Kindler, B.; Kojouharov, I.; Kuusiniemi, P.; Leino, M.; Lommel, B.; Mann, R.; Nishio, K.; Šáro, Š.; Sulignano, B.; Venhart, M. (29 May 2012). "Alpha-gamma decay studies of 253No and its daughter products 253Md , 249Fm" (PDF). The European Physical Journal A. 48 (5): 75. Bibcode:2012EPJA...48...75H. doi:10.1140/epja/i2012-12075-8. ISSN 1434-601X. S2CID 254111959. Retrieved 25 June 2023.
  8. ^ Antalic, S.; Heßberger, F. P.; Ackermann, D.; Heinz, S.; Hofmann, S.; Kalaninová, Z.; Kindler, B.; Khuyagbaatar, J.; Kojouharov, I.; Kuusiniemi, P.; Leino, M.; Lommel, B.; Mann, R.; Nishio, K.; Šáro, Š.; Streicher, B.; Sulignano, B.; Venhart, M. (20 May 2011). "Isomeric states in 253No and 253Fm" (PDF). The European Physical Journal A. 47 (5): 62. Bibcode:2011EPJA...47...62A. doi:10.1140/epja/i2011-11062-y. ISSN 1434-601X. S2CID 121080273. Retrieved 25 June 2023.
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