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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 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.1
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.
Cluster decay was discovered in 1984 when researchers at Oxford University detected that 223Ra emits one 14C nucleus for every billion (109) alpha decays.2
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
- ^ Baum, E. M. et al. (2002). Nuclides and Isotopes: Chart of the nuclides 16th ed.. Knolls Atomic Power Laboratory (Lockheed Martin).
- ^ Rose, H. J. and Jones, G. A. (1984-01-19). "A new kind of natural radioactivity". Nature 307: 245–247. doi:, http://www.nature.com/nature/journal/v307/n5948/abs/307245a0.html.
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- This page was last modified on 9 November 2008, at 22:03.
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