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Isotopes of fermium

Fermium (Fm) has no stable isotopes. A standard atomic mass cannot be given.

Fermium has also been called eka-erbium and centurium.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
²⁴²Fm	100	142	242.07343(43)#	0.8(2) ms	0+
²⁴³Fm	100	143	243.07435(23)#	210(60) ms [0.18(+8-4) s]	7/2-#
²⁴⁴Fm	100	144	244.07408(30)#	3.3(5) ms	0+
²⁴⁵Fm	100	145	245.07539(30)#	4.2(13) s	1/2+#
²⁴⁶Fm	100	146	246.07530(4)	1.1(2) s	0+
²⁴⁷Fm	100	147	247.07685(15)#	29(1) s	(7/2+)
²⁴⁸Fm	100	148	248.077195(13)	36(2) s	0+
²⁴⁹Fm	100	149	249.07903(11)#	2.6(7) min	(7/2+)#
²⁵⁰Fm	100	150	250.079521(13)	30(3) min	0+
^250mFm	1500(300)# keV			1.8(1) s	7,8#
²⁵¹Fm	100	151	251.081575(9)	5.30(8) h	(9/2-)
^251mFm	191(2) keV			15.2(23) µs	(5/2+)
²⁵²Fm	100	152	252.082467(6)	25.39(4) h	0+
²⁵³Fm	100	153	253.085185(4)	3.00(12) d	(1/2)+
²⁵⁴Fm	100	154	254.0868542(30)	3.240(2) h	0+
²⁵⁵Fm	100	155	255.089962(5)	20.07(7) h	7/2+
²⁵⁶Fm	100	156	256.091773(8)	157.6(13) min	0+
²⁵⁷Fm	100	157	257.095105(7)	100.5(2) d	(9/2+)
²⁵⁸Fm	100	158	258.09708(22)#	370(14) µs	0+
²⁵⁹Fm	100	159	259.1006(3)#	1.5(3) s	3/2+#
²⁶⁰Fm	100	160	260.10268(54)#	1# min	0+

Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
The isotopes denoted by an isotope number with an "m" are metastable_isomers.

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.