Isotopes of fermium

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.

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

|-id=Fermium-241 | rowspan=3|²⁴¹Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 141 | rowspan=3|241.07431(32)# | rowspan=3 style="text-align:center" | 2008 | rowspan=3|730 us | SF | (various) | rowspan=3|5/2+# |- | α (<14%) | ²³⁷Cf |- | β⁺ (<12%) | ²⁴¹Es |-id=Fermium-242 | ²⁴²Fm | style="text-align:right" | 100 | style="text-align:right" | 142 | 242.07343(43)# | style="text-align:center" | 1975 | 0.8 ms | SF | (various) | 0+ |-id=Fermium-243 | rowspan=2|²⁴³Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 143 | rowspan=2|243.07441(14)# | rowspan=2 style="text-align:center" | 1981 | rowspan=2|231 ms | α (91%) | ²³⁹Cf | rowspan=2|7/2−# |- | SF (9%) | (various) |-id=Fermium-244 | rowspan=3|²⁴⁴Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 144 | rowspan=3|244.07404(22)# | rowspan=3 style="text-align:center" | 1967 | rowspan=3|3.12 ms | SF (>97%) | (various) | rowspan=3|0+ |- | β⁺ (<2%) | ²⁴⁴Es |- | α (<1%) | ²⁴⁰Cf |-id=Fermium-245 | rowspan=3|²⁴⁵Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 145 | rowspan=3|245.07535(21)# | rowspan=3 style="text-align:center" | 1967 | rowspan=3|4.2 s | α (88.5%) | ²⁴¹Cf | rowspan=3|1/2+# |- | β⁺ (11.5%)^[1] | ²⁴⁵Es |- | SF (<0.3%) | (various) |-id=Fermium-246 | rowspan=3|²⁴⁶Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 146 | rowspan=3|246.075353(15) | rowspan=3 style="text-align:center" | 1966 | rowspan=3|1.54 s | α (93.2%) | ²⁴²Cf | rowspan=3|0+ |- | SF (6.8%) | (various) |- | EC (<1.3%) | ²⁴⁶Es |-id=Fermium-247 | rowspan=2|²⁴⁷Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 147 | rowspan=2|247.07694(19)# | rowspan=2 style="text-align:center" | 1967 | rowspan=2|31 s | α (~64%) | ²⁴³Cf | rowspan=2|(7/2+) |- | β⁺? (~36%) | ²⁴⁷Es |-id=Fermium-247m | rowspan=2 style="text-indent:1em" | ^247mFm | rowspan=2 colspan="3" style="text-indent:2em" | 49(8) keV | rowspan=2 style="text-align:center" | 1967 | rowspan=2| 5.1 s | α (88%) | ²⁴³Cf | rowspan=2|(1/2+) |- | IT? (12%) | ²⁴⁷Fm |-id=Fermium-248 | rowspan=2|²⁴⁸Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 148 | rowspan=2|248.077185(9) | rowspan=2 style="text-align:center" | 1958 | rowspan=2|34.5 s | α (99.9%) | ²⁴⁴Cf | rowspan=2|0+ |- | SF (0.1%) | (various) |-id=Fermium-248m | rowspan=3 style="text-indent:1em" | ^248mFm | rowspan=3 colspan="3" style="text-indent:2em" | 1200(100)# keV | rowspan=3 style="text-align:center" | (2010)^{[n 1]} | rowspan=3| 10.1 ms | IT? | ²⁴⁸Fm | rowspan=3|6+# |- | α? | ²⁴⁴Cf |- | β⁺? | ²⁴⁸Es |-id=Fermium-249 | rowspan=2|²⁴⁹Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 149 | rowspan=2|249.078926(7) | rowspan=2 style="text-align:center" | 1959 | rowspan=2|1.6 min | β⁺? (67%) | ²⁴⁹Es | rowspan=2|7/2+ |- | α (33%) | ²⁴⁵Cf |-id=Fermium-250 | rowspan=2|²⁵⁰Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 150 | rowspan=2|250.079520(8) | rowspan=2 style="text-align:center" | 1954 | rowspan=2|31.0 min | α (99.99%) | ²⁴⁶Cf | rowspan=2|0+ |- | SF (6.9×10⁻³%) | (various) |-id=Fermium-250m | style="text-indent:1em" | ^250mFm | colspan="3" style="text-indent:2em" | 1199.2(10) keV | style="text-align:center" | 1971 | 1.92 s | IT | ²⁵⁰Fm | (8−) |-id=Fermium-251 | rowspan=2|²⁵¹Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 151 | rowspan=2|251.081545(15) | rowspan=2 style="text-align:center" | 1957 | rowspan=2|5.30 h | β⁺ (98.20%) | ²⁵¹Es | rowspan=2|9/2− |- | α (1.80%) | ²⁴⁷Cf |-id=Fermium-251m | style="text-indent:1em" | ^251mFm | colspan="3" style="text-indent:2em" | 200.0(1) keV | style="text-align:center" | 2006 | 21.8 us | IT | ²⁵¹Fm | 5/2+ |-id=Fermium-252 | rowspan=2|²⁵²Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 152 | rowspan=2|252.082466(6) | rowspan=2 style="text-align:center" | 1956 | rowspan=2|25.39 h | α (99.99%)^{[n 2]} | ²⁴⁸Cf | rowspan=2|0+ |- | SF (0.0023%) | (various) |-id=Fermium-253 | rowspan=2|²⁵³Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 153 | rowspan=2|253.0851809(17) | rowspan=2 style="text-align:center" | 1957 | rowspan=2|3.00 d | EC (88%) | ²⁵³Es | rowspan=2|1/2+ |- | α (12%) | ²⁴⁹Cf |-id=Fermium-253m | style="text-indent:1em" | ^253mFm | colspan="3" style="text-indent:2em" | 351(6) keV | style="text-align:center" | 2011 | 0.56 us | IT | ²⁵³Fm | 11/2−# |-id=Fermium-254 | rowspan=2|²⁵⁴Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 154 | rowspan=2|254.0868524(20) | rowspan=2 style="text-align:center" | 1954 | rowspan=2|3.240 h | α (99.94%) | ²⁵⁰Cf | rowspan=2|0+ |- | SF (0.0592%) | (various) |-id=Fermium-255 | rowspan=2|²⁵⁵Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 155 | rowspan=2|255.089963(4) | rowspan=2 style="text-align:center" | 1954 | rowspan=2|20.07 h | α | ²⁵¹Cf | rowspan=2|7/2+ |- | SF (2.4×10⁻⁵%) | (various) |-id=Fermium-256 | rowspan=2|²⁵⁶Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 156 | rowspan=2|256.091772(3) | rowspan=2 style="text-align:center" | 1955 | rowspan=2|157.1 min | SF (91.9%) | (various) | rowspan=2|0+ |- | α (8.1%) | ²⁵²Cf |-id=Fermium-257 | rowspan=2|²⁵⁷Fm^{[n 3]} | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 157 | rowspan=2|257.095105(5) | rowspan=2 style="text-align:center" | 1964 | rowspan=2|100.5 d | α (99.79%) | ²⁵³Cf | rowspan=2|9/2+ |- | SF (0.210%) | (various) |-id=Fermium-258 | ²⁵⁸Fm | style="text-align:right" | 100 | style="text-align:right" | 158 | 258.09708(22)# | style="text-align:center" | 1971 | 370 us | SF | (various) | 0+ |-id=Fermium-259 | ²⁵⁹Fm | style="text-align:right" | 100 | style="text-align:right" | 159 | 259.10060(30)# | style="text-align:center" | 1980 | 1.5 s | SF | (various) | |-id=Fermium-260 | ²⁶⁰Fm^{[n 4][n 5]} | style="text-align:right" | 100 | style="text-align:right" | 160 | 260.10281(47)# | style="text-align:center" | (1992) | 1# min | SF | (various) | 0+

Chronology of isotope discovery

²⁶⁰Fm was not confirmed in 1997.

References

1. ^ 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.

• • 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

1. ^ Only published in a conference proceeding and not a refereed journal
2. ^ Theoretically capable of β⁺β⁺ decay to ²⁵²Cf
3. ^ Heaviest nuclide produced via neutron capture
4. ^ Discovery of this isotope is unconfirmed
5. ^ Not directly synthesized, occurs as decay product of ²⁶⁰Md