Most of the isotope data on this site has been obtained from the National Nuclear Data Center.
Naturally Occurring Isotopes
Americium has no naturally occurring isotopes.
Known Isotopes
| Mass Number | Half-life | Decay Mode | Branching Percentage |
| 230 | ≈ 17 seconds | Electron Capture | 100.00% |
| 231 | No Data Available | Alpha Decay (suspected) | No Data Available |
| Electron Capture (suspected) | No Data Available | ||
| 232 | 79 seconds | Electron Capture | ~ 97.00% |
| Alpha Decay | ~ 3.00% | ||
| 233 | 3.2 minutes | Alpha Decay | > 3.00% |
| Electron Capture | No Data Available | ||
| 234 | 2.32 minutes | Electron Capture | 100.00% |
| Alpha Decay | No Data Available | ||
| 235 | 10.3 minutes | Alpha Decay | 0.40% |
| Electron Capture | 99.60% | ||
| 236 | 3.6 minutes | Alpha Decay | No Data Available |
| Electron Capture | No Data Available | ||
| 236m | 2.9 minutes | Alpha Decay | No Data Available |
| Electron Capture | No Data Available | ||
| 237 | 73.6 minutes | Electron Capture | 99.97% |
| Alpha Decay | 0.03% | ||
| 238 | 98 minutes | Electron Capture | 100.00% |
| Alpha Decay | 1.0×10-4 % | ||
| 239 | 11.9 hours | Alpha Decay | 0.01% |
| Electron Capture | 99.99% | ||
| 240 | 50.8 hours | Electron Capture | 100.00% |
| Alpha Decay | 1.9×10-4 % | ||
| 240m | 0.94 milliseconds | Spontaneous Fission | <= 100.00% |
| 241 | 432.6 years | Alpha Decay | 100.00% |
| Spontaneous Fission | 4×10-10 % | ||
| 242 | 16.02 hours | Beta-minus Decay | 82.70% |
| Electron Capture | 17.30% | ||
| 242m | 141 years | Isomeric Transition | 99.55% |
| Alpha Decay | 0.45% | ||
| Spontaneous Fission | < 4.7×10-9 % | ||
| 242m1 | 14.0 milliseconds | Spontaneous Fission | 100.00% |
| Isomeric Transition | No Data Available | ||
| Alpha Decay | < 5.0×10-3 % | ||
| 243 | 7370 years | Alpha Decay | 100.00% |
| Spontaneous Fission | 3.7×10-9 % | ||
| 244 | 10.1 hours | Beta-minus Decay | 100.00% |
| 244m | 0.90 milliseconds | Spontaneous Fission | <= 100.00% |
| 244m1 | 26 minutes | Beta-minus Decay | 99.96% |
| Electron Capture | 0.04% | ||
| 245 | 2.05 hours | Beta-minus Decay | 100.00% |
| 246 | 39 minutes | Beta-minus Decay | 100.00% |
| 246m | 25.0 minutes | Beta-minus Decay | 100.00% |
| Isomeric Transition | < 0.02% | ||
| 247 | 23.0 minutes | Beta-minus Decay | 100.00% |
| 248 | ≈ 10 minutes | Beta-minus Decay | 100.00% |
| 249 | No Data Available | Beta-minus Decay (suspected) | No Data Available |
This page is maintained by Steve Gagnon.