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 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.

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 –

view talk edit

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: view

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

1. 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. 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. 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.

• 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. S2CID 250839471.
  • 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
• 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). (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. S2CID 94982856.