HomeTable of NuclidesFermiumIsotopes

Isotopes of Fermium

List of known isotopes of the element Fermium.

Isotope	t½	%	Spin/parity	Radius	Isotopic mass	Discovery
²⁴¹Fm	0.73 ±6 ms	syn.	—	—	2.41·10⁸ ±322 keV/c²	2008
²⁴²Fm	0.8 ±2 ms	syn.	0+	—	2.42·10⁸ ±430 keV/c²	1975
²⁴³Fm	231 ±9 ms	syn.	(7/2-)	—	2.43·10⁸ ±140 keV/c²	1981
²⁴⁴Fm	3.12 ±8 ms	syn.	0+	—	2.44·10⁸ ±216 keV/c²	1967
²⁴⁵Fm	4.2 ±13 s	syn.	—	—	2.45·10⁸ ±210 keV/c²	1967
²⁴⁶Fm	1.54 ±4 s	syn.	0+	—	2.46·10⁸ ±14.67 keV/c²	1966
²⁴⁷Fm	31 ±1 s	syn.	(7/2+)	—	2.47·10⁸ ±194 keV/c²	1967
²⁴⁸Fm	34.5 ±12 s	syn.	0+	—	2.48·10⁸ ±9.122 keV/c²	1958
²⁴⁹Fm	2.6 ±7 m	syn.	(7/2+)	—	2.49·10⁸ ±6.668 keV/c²	1960
²⁵⁰Fm	30 ±3 m	syn.	0+	—	2.5·10⁸ ±8.468 keV/c²	1954
²⁵¹Fm	5.3 ±8 h	syn.	(9/2-)	—	2.51·10⁸ ±15.34 keV/c²	1957
²⁵²Fm	25.39 ±4 h	syn.	0+	—	2.52·10⁸ ±5.604 keV/c²	1956
²⁵³Fm	3 ±12 d	syn.	1/2+	—	2.53·10⁸ ±1.662 keV/c²	1957
²⁵⁴Fm	3.24 ±2 h	syn.	0+	—	2.54·10⁸ ±1.978 keV/c²	1954
²⁵⁵Fm	20.07 ±7 h	syn.	7/2+	—	2.55·10⁸ ±4.223 keV/c²	1954
²⁵⁶Fm	157.1 ±13 m	syn.	0+	—	2.56·10⁸ ±3.241 keV/c²	1955
²⁵⁷Fm	100.5 ±2 d	syn.	(9/2+)	—	2.57·10⁸ ±4.669 keV/c²	1964
²⁵⁸Fm	370 ±14 us	syn.	0+	—	2.58·10⁸ ±215 keV/c²	1971
²⁵⁹Fm	1.5 ±2 s	syn.	—	—	2.591·10⁸ ±304 keV/c²	1980

241FmFermium-241

Classification	z: 100; n: 141; m: 241
Half life	0.73 ±6 ms
Natural abundance	synthetic nuclide
Decay modes	spontaneous fission; α decay; electron capture (EC)
Discovery	2008
Mass excess	69,220 ±300 keV
Binding energy	7,459 ±1 keV
Single-particle energy	2,294 ±473 keV
Q value for electron capture	5,327 ±378.6 keV

Point at nuclide Decay chain of Fermium-241

242FmFermium-242

Classification	z: 100; n: 142; m: 242
Half life	0.8 ±2 ms
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	spontaneous fission
Discovery	1975
Mass excess	68,400 ±401 keV
Binding energy	7,465 ±2 keV
Single-particle energy	2,783 ±462 keV
Neutron separation energy	8,892 ±500 keV
Q value for electron capture	3,599 ±476.2 keV

Point at nuclide Decay chain of Fermium-242

243FmFermium-243

Classification	z: 100; n: 143; m: 243
Half life	231 ±9 ms
Natural abundance	synthetic nuclide
Spin/parity	(7/2-)
Decay modes	α decay; electron capture + β⁺ decay; spontaneous fission
Discovery	1981
Mass excess	69,310 ±130 keV
Binding energy	7,464 ±1 keV
Single-particle energy	2,774 ±288 keV
Neutron separation energy	7,155 ±421 keV
Q value for electron capture	4,569 ±244.4 keV

Point at nuclide Decay chain of Fermium-243

244FmFermium-244

Classification	z: 100; n: 144; m: 244
Half life	3.12 ±8 ms
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	spontaneous fission; electron capture (EC); α decay
Discovery	1967
Mass excess	68,960 ±201 keV
Binding energy	7,468 ±1 keV
Single-particle energy	3,072 ±288 keV
Neutron separation energy	8,424 ±239 keV
Q value for electron capture	2,938 ±270.4 keV
β⁻ decay energy	-6,634 ±425 keV

Point at nuclide Decay chain of Fermium-244

245FmFermium-245

Classification	z: 100; n: 145; m: 245
Half life	4.2 ±13 s
Natural abundance	synthetic nuclide
Decay modes	α decay
Discovery	1967
Mass excess	70,190 ±195 keV
Binding energy	7,465 ±1 keV
Single-particle energy	3,123 ±266 keV
Neutron separation energy	6,843 ±280 keV
Q value for electron capture	3,877 ±255.4 keV
β⁻ decay energy	-5,133 ±325 keV
β⁻ decay energy with neutron	-13,480 ±422 keV

Point at nuclide Decay chain of Fermium-245

246FmFermium-246

Classification	z: 100; n: 146; m: 246
Half life	1.54 ±4 s
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	α decay; spontaneous fission; electron capture (EC)
Discovery	1966
Mass excess	70,190 ±13.67 keV
Binding energy	7,467 ±0.0556 keV
Single-particle energy	3,413 ±166 keV
Neutron separation energy	8,072 ±196 keV
Q value for electron capture	2,372 ±90.95 keV
β⁻ decay energy	-5,924 ±260 keV
β⁻ decay energy with neutron	-13,210 ±260 keV

Point at nuclide Decay chain of Fermium-246

247FmFermium-247

Classification	z: 100; n: 147; m: 247
Half life	31 ±1 s
Natural abundance	synthetic nuclide
Spin/parity	(7/2+)
Decay modes	α decay; electron capture + β⁺ decay
Discovery	1967
Mass excess	71,670 ±181 keV
Binding energy	7,464 ±1 keV
Single-particle energy	3,435 ±202 keV
Neutron separation energy	6,590 ±181 keV
Q value for electron capture	3,093 ±182 keV
β⁻ decay energy	-4,263 ±275 keV
β⁻ decay energy with neutron	-12,520 ±317 keV

Point at nuclide Decay chain of Fermium-247

248FmFermium-248

Classification	z: 100; n: 148; m: 248
Half life	34.5 ±12 s
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	α decay; electron capture (EC); spontaneous fission
Discovery	1958
Mass excess	71,890 ±8.497 keV
Binding energy	7,465 ±0.0343 keV
Single-particle energy	3,969 ±21.21 keV
Neutron separation energy	7,846 ±181 keV
Q value for electron capture	1,598 ±52.69 keV
β⁻ decay energy	-5,050 ±184 keV
β⁻ decay energy with neutron	-12,110 ±208 keV

Point at nuclide Decay chain of Fermium-248

249FmFermium-249

Classification	z: 100; n: 149; m: 249
Half life	2.6 ±7 m
Natural abundance	synthetic nuclide
Spin/parity	(7/2+)
Decay modes	electron capture + β⁺ decay; α decay
Discovery	1960
Mass excess	73,510 ±6.212 keV
Binding energy	7,461 ±0.0249 keV
Single-particle energy	4,069 ±53 keV
Neutron separation energy	6,449 ±10.47 keV
Q value for electron capture	2,344 ±30.63 keV
β⁻ decay energy	-3,662 ±164.5 keV
β⁻ decay energy with neutron	-11,500 ±184 keV

Point at nuclide Decay chain of Fermium-249

250FmFermium-250

Classification	z: 100; n: 150; m: 250
Half life	30 ±3 m
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	α decay; electron capture (EC); spontaneous fission
Discovery	1954
Mass excess	74,070 ±7.888 keV
Binding energy	7,462 ±0.0316 keV
Single-particle energy	4,392 ±31 keV
Neutron separation energy	7,518 ±9.967 keV
Q value for electron capture	847.1 ±100.3 keV
β⁻ decay energy	-4,327 ±91.26 keV
β⁻ decay energy with neutron	-11,190 ±164.6 keV

Point at nuclide Decay chain of Fermium-250

251FmFermium-251

Classification	z: 100; n: 151; m: 251
Half life	5.3 ±8 h
Natural abundance	synthetic nuclide
Spin/parity	(9/2-)
Decay modes	electron capture + β⁺ decay; α decay
Discovery	1957
Mass excess	75,950 ±14.29 keV
Binding energy	7,457 ±0.0569 keV
Single-particle energy	4,555 ±101 keV
Neutron separation energy	6,184 ±16.32 keV
Q value for electron capture	1,447 ±15.23 keV
β⁻ decay energy	-3,008 ±23.71 keV
β⁻ decay energy with neutron	-10,520 ±92.03 keV

Point at nuclide Decay chain of Fermium-251

252FmFermium-252

Classification	z: 100; n: 152; m: 252
Half life	25.39 ±4 h
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	α decay; spontaneous fission
Discovery	1956
Mass excess	76,810 ±5.221 keV
Binding energy	7,456 ±0.0207 keV
Single-particle energy	4,983 ±7.318 keV
Neutron separation energy	7,213 ±15.21 keV
Q value for electron capture	-478 ±50.32 keV
β⁻ decay energy	-3,651 ±91.43 keV
β⁻ decay energy with neutron	-10,230 ±19.62 keV

Point at nuclide Decay chain of Fermium-252

253FmFermium-253

Classification	z: 100; n: 153; m: 253
Half life	3 ±12 d
Natural abundance	synthetic nuclide
Spin/parity	1/2+
Decay modes	electron capture (EC); α decay
Discovery	1957
Mass excess	79,340 ±1.549 keV
Binding energy	7,448 ±0.0061 keV
Single-particle energy	5,238 ±50.07 keV
Neutron separation energy	5,542 ±5.243 keV
Q value for electron capture	335 ±1.99 keV
β⁻ decay energy	-1,827 ±31 keV
β⁻ decay energy with neutron	-9,193 ±91.29 keV

Point at nuclide Decay chain of Fermium-253

254FmFermium-254

Classification	z: 100; n: 154; m: 254
Half life	3.24 ±2 h
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	α decay; spontaneous fission
Discovery	1954
Mass excess	80,900 ±1.843 keV
Binding energy	7,444 ±0.0073 keV
Single-particle energy	5,396 ±1.71 keV
Neutron separation energy	6,514 ±1.939 keV
Q value for electron capture	-1,092 ±3.46 keV
β⁻ decay energy	-2,550 ±100 keV
β⁻ decay energy with neutron	-8,342 ±31 keV

Point at nuclide Decay chain of Fermium-254

255FmFermium-255

Classification	z: 100; n: 155; m: 255
Half life	20.07 ±7 h
Natural abundance	synthetic nuclide
Spin/parity	7/2+
Decay modes	α decay; spontaneous fission
Discovery	1954
Mass excess	83,800 ±3.934 keV
Binding energy	7,435 ±0.0154 keV
Single-particle energy	5,482 ±4.648 keV
Neutron separation energy	5,173 ±4.047 keV
Q value for electron capture	-288.8 ±11.51 keV
β⁻ decay energy	-1,042 ±6.717 keV
β⁻ decay energy with neutron	-7,723 ±100 keV

Point at nuclide Decay chain of Fermium-255

256FmFermium-256

Classification	z: 100; n: 156; m: 256
Half life	157.1 ±13 m
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	spontaneous fission; α decay
Discovery	1955
Mass excess	85,480 ±3.02 keV
Binding energy	7,431 ±0.0118 keV
Single-particle energy	5,893 ±11.04 keV
Neutron separation energy	6,386 ±4.514 keV
Q value for electron capture	-1,701 ±100 keV
β⁻ decay energy	-1,971 ±124 keV
β⁻ decay energy with neutron	-7,429 ±6.299 keV

Point at nuclide Decay chain of Fermium-256

257FmFermium-257

Classification	z: 100; n: 157; m: 257
Half life	100.5 ±2 d
Natural abundance	synthetic nuclide
Spin/parity	(9/2+)
Decay modes	α decay; spontaneous fission
Discovery	1964
Mass excess	88,590 ±4.35 keV
Binding energy	7,422 ±0.0169 keV
Single-particle energy	5,884 ±100 keV
Neutron separation energy	4,965 ±4.113 keV
Q value for electron capture	-812.9 ±411 keV
β⁻ decay energy	-402.4 ±4.574 keV
β⁻ decay energy with neutron	-6,937 ±124 keV

Point at nuclide Decay chain of Fermium-257

258FmFermium-258

Classification	z: 100; n: 158; m: 258
Half life	370 ±14 us
Natural abundance	synthetic nuclide
Spin/parity	0+
Decay modes	spontaneous fission
Discovery	1971
Mass excess	90,420 ±200 keV
Binding energy	7,418 ±1 keV
Single-particle energy	6,266 ±457 keV
Neutron separation energy	6,235 ±200 keV
β⁻ decay energy	-1,264 ±200 keV
β⁻ decay energy with neutron	-6,637 ±200 keV

Point at nuclide Decay chain of Fermium-258

259FmFermium-259

Classification	z: 100; n: 159; m: 259
Half life	1.5 ±2 s
Natural abundance	synthetic nuclide
Decay modes	spontaneous fission
Discovery	1980
Mass excess	93,700 ±283 keV
Binding energy	7,407 ±1 keV
Single-particle energy	6,287 ±490 keV
Neutron separation energy	4,793 ±347 keV
β⁻ decay energy	140 ±300 keV
β⁻ decay energy with neutron	-6,058 ±283 keV

Point at nuclide Decay chain of Fermium-259