[Click for Main Data] Proton Emission Neutron Emission Electron Emission Positron Emission
Most of the isotope data on this site has been obtained from the National Nuclear Data Center.
Naturally Occurring Isotopes
Fermium has no naturally occurring isotopes.
Known Isotopes
| Mass Number | Half-life | Decay Mode | Branching Percentage |
| 241 | 0.73 milliseconds | Spontaneous Fission | > 78.00% |
| Alpha Decay | < 14.00% | ||
| Electron Capture | < 12.00% | ||
| 242 | < 4 microseconds | Spontaneous Fission | <= 100.00% |
| 243 | 231 milliseconds | Alpha Decay | 91.00% |
| Spontaneous Fission | 9.00% | ||
| Electron Capture | < 10.00% | ||
| 244 | 3.12 milliseconds | Alpha Decay | < 1.00% |
| Spontaneous Fission | > 97.00% | ||
| Electron Capture | < 2.00% | ||
| 245 | 4.2 seconds | Alpha Decay | <= 100.00% |
| 246 | 1.54 seconds | Alpha Decay | 93.20% |
| Spontaneous Fission | 6.80% | ||
| Electron Capture | <= 1.30% | ||
| 247 | 31 seconds | Alpha Decay | >= 84.00% |
| Electron Capture | <= 16.00% | ||
| 247m | 5.1 seconds | Alpha Decay | 84.00% |
| 248 | 36 seconds | Alpha Decay | 93.00% |
| Electron Capture | 7.00% | ||
| Spontaneous Fission | 0.10% | ||
| 249 | 2.6 minutes | Electron Capture | 67.00% |
| Alpha Decay | 33.00% | ||
| 250 | 30 minutes | Alpha Decay | > 90.00% |
| Electron Capture | < 10.00% | ||
| Spontaneous Fission | 6.9×10-3 % | ||
| 250m | 1.93 seconds | Isomeric Transition | 100.00% |
| 251 | 5.30 hours | Electron Capture | 98.20% |
| Alpha Decay | 1.80% | ||
| 252 | 25.39 hours | Spontaneous Fission | 2.3×10-3 % |
| Alpha Decay | 100.00% | ||
| 253 | 3.00 days | Electron Capture | 88.00% |
| Alpha Decay | 12.00% | ||
| 254 | 3.240 hours | Alpha Decay | 99.94% |
| Spontaneous Fission | 0.06% | ||
| 255 | 20.07 hours | Alpha Decay | 100.00% |
| Spontaneous Fission | 2.4×10-5 % | ||
| 256 | 157.6 minutes | Spontaneous Fission | 91.90% |
| Alpha Decay | 8.10% | ||
| 257 | 100.5 days | Alpha Decay | 99.79% |
| Spontaneous Fission | 0.21% | ||
| 258 | 370 microseconds | Spontaneous Fission | <= 100.00% |
| 259 | 1.5 seconds | Spontaneous Fission | 100.00% |
| 260 | ≈ 4 milliseconds | Spontaneous Fission | 100.00% |
This page is maintained by Steve Gagnon.