Most of the isotope data on this site has been obtained from the National Nuclear Data Center.
Naturally Occurring Isotopes
Promethium has no naturally occurring isotopes.
Known Isotopes
| Mass Number | Half-life | Decay Mode | Branching Percentage |
| 126 | No Data Available | Electron Capture (suspected) | No Data Available |
| 127 | No Data Available | Proton Emission (suspected) | No Data Available |
| Electron Capture (suspected) | No Data Available | ||
| 128 | 1.0 seconds | Electron Capture | 100.00% |
| Alpha Decay | No Data Available | ||
| Electron Capture with delayed Proton Emission | No Data Available | ||
| 129 | 2.4 seconds | Electron Capture | 100.00% |
| 130 | 2.6 seconds | Electron Capture | 100.00% |
| Electron Capture with delayed Proton Emission | No Data Available | ||
| 131 | 6.3 seconds | Electron Capture | 100.00% |
| 132 | 6.2 seconds | Electron Capture | 100.00% |
| Electron Capture with delayed Proton Emission | ~ 5.0×10-5 % | ||
| 133 | 13.5 seconds | Electron Capture | 100.00% |
| 133m | < 8.8 seconds | Isomeric Transition | No Data Available |
| Electron Capture | No Data Available | ||
| 134 | ≈ 5 seconds | Electron Capture | 100.00% |
| 134m | 22 seconds | Electron Capture | 100.00% |
| 135 | 49 seconds | Electron Capture | 100.00% |
| 135m | 45 seconds | Electron Capture | 100.00% |
| 136 | 107 seconds | Electron Capture | 100.00% |
| 136m | 47 seconds | Electron Capture | 100.00% |
| 137 | 2.4 minutes | Electron Capture | 100.00% |
| 138 | 10 seconds | Electron Capture | 100.00% |
| 138m | 3.24 minutes | Electron Capture | No Data Available |
| 139 | 4.15 minutes | Electron Capture | 100.00% |
| 139m | 180 milliseconds | Isomeric Transition | 99.94% |
| Electron Capture | 0.06% | ||
| 140 | 9.2 seconds | Electron Capture | 100.00% |
| 140m | 5.95 minutes | Electron Capture | 100.00% |
| 141 | 20.90 minutes | Electron Capture | 100.00% |
| 142 | 40.5 seconds | Electron Capture | 100.00% |
| 142m | 2.0 milliseconds | Isomeric Transition | 100.00% |
| 143 | 265 days | Electron Capture | 100.00% |
| 144 | 363 days | Electron Capture | 100.00% |
| 145 | 17.7 years | Electron Capture | 100.00% |
| Alpha Decay | 2.8×10-7 % | ||
| 146 | 5.53 years | Electron Capture | 66.00% |
| Beta-minus Decay | 34.00% | ||
| 147 | 2.6234 years | Beta-minus Decay | 100.00% |
| 148 | 5.368 days | Beta-minus Decay | 100.00% |
| 148m | 41.29 days | Beta-minus Decay | 95.80% |
| Isomeric Transition | 4.20% | ||
| 149 | 53.08 hours | Beta-minus Decay | 100.00% |
| 150 | 2.68 hours | Beta-minus Decay | 100.00% |
| 151 | 28.40 hours | Beta-minus Decay | 100.00% |
| 152 | 4.12 minutes | Beta-minus Decay | 100.00% |
| 152m | 13.8 minutes | Beta-minus Decay | 100.00% |
| Isomeric Transition | >= 0.00% | ||
| 152m1 | 7.52 minutes | Beta-minus Decay | 100.00% |
| 153 | 5.25 minutes | Beta-minus Decay | 100.00% |
| 154 | 2.68 minutes | Beta-minus Decay | 100.00% |
| 154m | 1.73 minutes | Beta-minus Decay | 100.00% |
| 155 | 41.5 seconds | Beta-minus Decay | 100.00% |
| 156 | 26.70 seconds | Beta-minus Decay | 100.00% |
| 157 | 10.56 seconds | Beta-minus Decay | 100.00% |
| 158 | 4.8 seconds | Beta-minus Decay | 100.00% |
| 159 | 1.5 seconds | Beta-minus Decay | 100.00% |
| 160 | No Data Available | Beta-minus Decay (suspected) | No Data Available |
| 161 | No Data Available | Beta-minus Decay (suspected) | No Data Available |
| 162 | No Data Available | Beta-minus Decay (suspected) | No Data Available |
| 163 | No Data Available | Beta-minus Decay (suspected) | No Data Available |
This page is maintained by Steve Gagnon.