Most of the isotope data on this site has been obtained from the National Nuclear Data Center.
Naturally Occurring Isotopes
Mendelevium has no naturally occurring isotopes.
Known Isotopes
| Mass Number | Half-life | Decay Mode | Branching Percentage |
| 245 | 0.90 milliseconds | Alpha Decay | No Data Available |
| Spontaneous Fission | No Data Available | ||
| 245m | 0.35 seconds | Electron Capture | No Data Available |
| Alpha Decay | No Data Available | ||
| 246 | 0.9 seconds | Alpha Decay | 100.00% |
| Electron Capture | > 77.00% | ||
| Alpha Decay | < 23.00% | ||
| Spontaneous Fission (suspected) | No Data Available | ||
| Electron Capture (suspected) | No Data Available | ||
| 247 | 1.2 seconds | Alpha Decay | 99.90% |
| Spontaneous Fission | < 0.10% | ||
| 247m | 0.25 seconds | Alpha Decay | 79.00% |
| Spontaneous Fission | 21.00% | ||
| 248 | 13 seconds | Alpha Decay | 58.00% |
| Electron Capture | 42.00% | ||
| 249 | 21.7 seconds | Alpha Decay | > 60.00% |
| Electron Capture | <= 40.00% | ||
| 249m | 1.9 seconds | Alpha Decay (suspected) | No Data Available |
| 250 | 25 seconds | Alpha Decay | 7.00% |
| Electron Capture | 93.00% | ||
| 251 | 4.3 minutes | Electron Capture | 90.00% |
| Alpha Decay | 10.00% | ||
| 252 | 2.3 minutes | Electron Capture | <= 100.00% |
| 253 | 6 minutes | Electron Capture | <= 100.00% |
| Alpha Decay | No Data Available | ||
| 254 | 28 minutes | Electron Capture | <= 100.00% |
| Electron Capture | <= 100.00% | ||
| 255 | 27 minutes | Electron Capture | 92.00% |
| Alpha Decay | 8.00% | ||
| Spontaneous Fission | < 0.15% | ||
| 256 | 77 minutes | Electron Capture | 90.80% |
| Alpha Decay | 9.20% | ||
| Spontaneous Fission | < 3.00% | ||
| 257 | 5.52 hours | Electron Capture | 85.00% |
| Alpha Decay | 15.00% | ||
| Spontaneous Fission | < 1.00% | ||
| 258 | 51.5 days | Alpha Decay | 100.00% |
| Spontaneous Fission | No Data Available | ||
| 258m | 57.0 minutes | Electron Capture | >= 70.00% |
| Spontaneous Fission | No Data Available | ||
| 259 | 96 minutes | Alpha Decay | < 1.30% |
| Spontaneous Fission | 100.00% | ||
| 260 | 31.8 days | Spontaneous Fission | >= 42.00% |
| Alpha Decay | <= 25.00% | ||
| Electron Capture | <= 23.00% | ||
| Beta-minus Decay | <= 10.00% | ||
| 261 | No Data Available | Alpha Decay (suspected) | No Data Available |
| 262 | No Data Available | Spontaneous Fission (suspected) | No Data Available |
| Alpha Decay (suspected) | No Data Available |
This page is maintained by Steve Gagnon.