It's Elemental

Einsteinium

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Mendelevium

Isotopes of the Element Fermium

[Click for Main Data]

Most of the isotope data on this site has been obtained from the National Nuclear Data Center. Please visit their site for more information.

Naturally Occurring Isotopes

Fermium has no naturally occurring isotopes.

Known Isotopes

Mass NumberHalf-lifeDecay ModeBranching Percentage
2410.73 millisecondsSpontaneous Fission> 78.00%
Alpha Decay< 14.00%
Electron Capture< 12.00%
242< 4 microsecondsSpontaneous Fission<= 100.00%
243231 millisecondsAlpha Decay91.00%
Spontaneous Fission9.00%
Electron Capture< 10.00%
2443.12 millisecondsAlpha Decay< 1.00%
Spontaneous Fission> 97.00%
Electron Capture< 2.00%
2454.2 secondsAlpha Decay<= 100.00%
2461.54 secondsAlpha Decay93.20%
Spontaneous Fission6.80%
Electron Capture<= 1.30%
24731 secondsAlpha Decay>= 84.00%
Electron Capture<= 16.00%
247m5.1 secondsAlpha Decay84.00%
24836 secondsAlpha Decay93.00%
Electron Capture7.00%
Spontaneous Fission0.10%
2492.6 minutesElectron Capture67.00%
Alpha Decay33.00%
25030 minutesAlpha Decay> 90.00%
Electron Capture< 10.00%
Spontaneous Fission6.9×10-3 %
250m1.93 secondsIsomeric Transition100.00%
2515.30 hoursElectron Capture98.20%
Alpha Decay1.80%
25225.39 hoursSpontaneous Fission2.3×10-3 %
Alpha Decay100.00%
2533.00 daysElectron Capture88.00%
Alpha Decay12.00%
2543.240 hoursAlpha Decay99.94%
Spontaneous Fission0.06%
25520.07 hoursAlpha Decay100.00%
Spontaneous Fission2.4×10-5 %
256157.6 minutesSpontaneous Fission91.90%
Alpha Decay8.10%
257100.5 daysAlpha Decay99.79%
Spontaneous Fission0.21%
258370 microsecondsSpontaneous Fission<= 100.00%
2591.5 secondsSpontaneous Fission100.00%
260≈ 4 millisecondsSpontaneous Fission100.00%