Cluster decay
Cluster decay is a type of nuclear decay in which a radioactive atom emits a cluster of neutrons and protons heavier than an alpha particle. This type of decay happens only in nuclides which decay predominatly by alpha decay, and occurs only a small percentage of the time in all cases. Cluster decay is limited to heavy atoms which have enough nuclear energy to expel a portion of its nucleus.
Cluster decay was discovered in 1987 when researchers at Oxford University detected that 223Ra emits one 14C nucleus for every billion (109) alpha decays.[1]
Cluster decay has an intermediate position between alpha decay (in which a nucleus spits out a 4He nucleus) and spontaneous fission in which a heavy nucleus splits into two large fragments and a variable number of neutrons. In cluster decay the emitted particle is a light nucleus and the decay always emits the same particle. More than 20 nuclei have been found which occasionally decay by emitting clusters.[2]
Tritons and deuterons are also known as radioactive decay products. Helium-6 occasionally decays via deuteron emission and Helium-8 decays a small part of the time with a triton emission. It is possible that other exotic isotopes decay in these methods as helium is studied in particle accelerators to a great degree.
The known cluster emissions are as follows:
| Isotope | Particle emission | Branching ratio |
|---|---|---|
| 221Fr | 14C | 9×10-15 |
| 221Ra | 14C | 1×10-14 |
| 222Ra | 14C | 3.0×10-10 |
| 223Ra | 14C | 8.9×10-10 |
| 224Ra | 14C | 4.0×10-11 |
| 226Ra | 14C | 3.2×10-11 |
| 225Ac | 14C | 6×10-12 |
| 228Th | 20O | 1×10-13 |
| 228Th | Ne | ? |
| 232U | Ne | 9×10-12 |
| 233U | Ne | 7×10-13 |
| 234U | Mg Ne |
1×10-13 9×10-14 |
| 235U | Ne |
8×10-12 8×10-12 |
| 236U | 30Mg | ? |
| 242Cm | 34Si | 1×10-16 |
References
- ↑ Rose, H. J. and Jones, G. A. (1984-01-19). "A new kind of natural radioactivity". Nature. 307: 245–247. doi:10.1038/307245a0.
- ↑ Baum, E. M.; et al. (2002). Nuclides and Isotopes: Chart of the nuclides 16th ed. Knolls Atomic Power Laboratory (Lockheed Martin).