Cluster decay
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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 (or more) large fragments and a variable number of neutrons. Spontaneous fission ends up with a probabilistic distribution of daughter products, which sets it apart from cluster decay. In cluster decay the emitted particle is a light nucleus and the decay method 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 | Reference |
|---|---|---|---|
| 114Ba | 12C | ~3.0×10−3 | [1] |
| 221Fr | 14C | 8.14×10−13 | [1] |
| 221Ra | 14C | 1×10−12 | [1] |
| 222Ra | 14C | 3.07×10−10 | [1] |
| 223Ra | 14C | 8.5×10−10 | [1] |
| 224Ra | 14C | 6.1×10−10 | [1] |
| 225Ac | 14C | 6×10−12 | [1] |
| 226Ra | 14C | 2.9×10−11 | [1] |
| 228Th | 20O Ne |
1×10−13 ? |
[1] ? |
| 230Th | 24Ne | 5.6×10−13 | [1] |
| 231Pa | 23F 24Ne |
9.97×10−15 1.34×10−11 |
[1] |
| 232U | 24Ne 28Mg |
2×10−12 1.18×10−13 |
[1] |
| 233U | 24Ne 25Ne 28Mg |
7×10−13 1.3×10−15 |
|
| 234U | 28Mg 24Ne 26Ne |
1×10−13 9×10−14 |
|
| 235U | 24Ne 25Ne 28Mg 29Mg |
8×10−12 1.8×10−12 |
|
| 236U | 24Ne 26Ne 28Mg 30Mg |
9×10−12 2×10−13 |
|
| 236Pu | 28Mg | 2×10−14 | |
| 237Np | 30Mg | 1.8×10−14 | |
| 238Pu | 32Si 28Mg 30Mg |
1.38×10−16 5.62×10−17 |
|
| 240Pu | 34Si | 6×10−15 | |
| 241Am | 34Si | 2.6×10−13 | |
| 242Cm | 34Si | 1×10−16 |
[edit] References
- ^ a b c d e f g h i j k l m 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.
[edit] External links
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