Most of the isotope data on this site has been obtained from the National Nuclear Data Center.
Naturally Occurring Isotopes
Neptunium has no naturally occurring isotopes.
Known Isotopes
| Mass Number | Half-life | Decay Mode | Branching Percentage |
| 225 | No Data Available | Alpha Decay | 100.00% |
| 226 | 35 milliseconds | Alpha Decay | 100.00% |
| 227 | 0.51 seconds | Alpha Decay | 100.00% |
| 228 | 61.4 seconds | Electron Capture | 60.00% |
| Alpha Decay | 40.00% | ||
| 229 | 4.0 minutes | Alpha Decay | 68.00% |
| Electron Capture | 32.00% | ||
| 230 | 4.6 minutes | Electron Capture | <= 97.00% |
| Alpha Decay | >= 3.00% | ||
| 231 | 48.8 minutes | Electron Capture | 98.00% |
| Alpha Decay | 2.00% | ||
| 232 | 14.7 minutes | Electron Capture | 100.00% |
| Alpha Decay | 2.0×10-4 % | ||
| 233 | 36.2 minutes | Electron Capture | 100.00% |
| Alpha Decay | <= 1.0×10-3 % | ||
| 234 | 4.4 days | Electron Capture | 100.00% |
| 235 | 396.1 days | Electron Capture | 100.00% |
| Alpha Decay | 2.6×10-3 % | ||
| 236 | 153×10+3 years | Electron Capture | 86.30% |
| Beta-minus Decay | 13.50% | ||
| Alpha Decay | 0.16% | ||
| 236m | 22.5 hours | Beta-minus Decay | 50.00% |
| Electron Capture | 50.00% | ||
| 237 | 2.144×10+6 years | Alpha Decay | 100.00% |
| Spontaneous Fission | <= 2×10-10 % | ||
| 238 | 2.117 days | Beta-minus Decay | 100.00% |
| 239 | 2.356 days | Beta-minus Decay | 100.00% |
| 240 | 61.9 minutes | Beta-minus Decay | 100.00% |
| 240m | 7.22 minutes | Beta-minus Decay | 99.88% |
| Isomeric Transition | 0.12% | ||
| 241 | 13.9 minutes | Beta-minus Decay | 100.00% |
| 242 | 2.2 minutes | Beta-minus Decay | 100.00% |
| 242m | 5.5 minutes | Beta-minus Decay | 100.00% |
| 243 | 1.85 minutes | Beta-minus Decay | 100.00% |
| 244 | 2.29 minutes | Beta-minus Decay | 100.00% |
| 245 | No Data Available | No Data Available | No Data Available |
This page is maintained by Steve Gagnon.