Isotopes of fermium
List of isotopes
Abbreviations: EC: Electron capture IT: Isomeric transition SF: Spontaneous fission Heaviest nuclide produced via neutron capture Discovery of this isotope is unconfirmed Not directly synthesized, occurs as decay product of ²⁶⁰Md

Isotopes of fermium

Section Title: List of isotopes
Table Section Text: Abbreviations: EC: Electron capture IT: Isomeric transition SF: Spontaneous fission Heaviest nuclide produced via neutron capture Discovery of this isotope is unconfirmed Not directly synthesized, occurs as decay product of ²⁶⁰Md

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin and parity

excitation energy

241Fm	100	141	241.07421(32)#	730(60) µs	SF(>78%)	(various)	5/2#+

α (<14%)	237Cf

242Fm	100	142	242.07343(43)#	0.8(2) ms	SF	(various)	0+

α (rare)	238Cf

243Fm	100	143	243.07447(23)#	231(9) ms	α (91%)	239Cf	7/2−#

SF (9%)	(various)

β+ (rare)	243Es

244Fm	100	144	244.07404(22)#	3.12(8) ms	SF (99%)	(various)	0+

α (1%)	240Cf

245Fm	100	145	245.07535(21)#	4.2(13) s	α (95.7%)	241Cf	1/2+#

β+ (4.2%)	245Es

SF (.13%)	(various)

246Fm	100	146	246.075350(17)	1.54(4) s	α (85%)	242Cf	0+

β+ (10%)	246Es

β+, SF (10%)	(various)

SF (4.5%)	(various)

247Fm	100	147	247.07695(12)#	31(1) s	α (>50%)	243Cf	(7/2+)

β+ (<50%)	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+ (85%)	249Es	(7/2+)#

α (15%)	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	(5/2+)

252Fm	100	152	252.082467(6)	25.39(4) h	α (99.99%)	248Cf	0+

SF (.0023%)	(various)

β+β+ (rare)	252Cf

253Fm	100	153	253.085185(4)	3.00(12) d	EC (88%)	253Es	(1/2)+

α (12%)	249Cf

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	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	100	160	260.10281(55)#	4 ms	SF	(various)	0+

Sentence(s)

There are 20 known isotopes ranging in atomic mass from ²⁴¹Fm to ²⁶⁰Fm.

final_sentence: There are 20 known isotopes ranging in atomic mass from ²⁴¹Fm to ²⁶⁰Fm.