Extinct radionuclide
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An extinct radionuclide is one which was thought to have been formed by a primordial process such as stellar nucleogenesis in the supernova(s) which contributed radioisotopes to the early solar system, about 4.6 billion years ago. Generally, radioisotopes with a decay half-life shorter than about 100 million years are not found in nature, unless known to be generated continuously by a natural process, such as cosmic rays, or a decay chain of much longer lived isotopes, such as uranium or thorium. These short-lived isotopes are thus seen only as extinct radionuclides, presenting now as only a superabundance of their stable decay products.
Examples of extinct radionuclides include iodine-129 (the first to be noted in 1960, and inferred from excess xenon-129 concentrations in meteorites, in the xenon-iodine dating system) and aluminium-26 (also inferred from extra magnesium-26 found in meteorites).
[edit] List of extinct radionuclides
A partial list of radionuclides which are not found in nature, but for which decay products are found, is:
| Isotope | Halflife (Myr) |
|---|---|
| Samarium-146 | 103 |
| Curium-247 | 16 |
| Lead-205 | 15 |
| Hafnium-182 | 9 |
| Palladium-107 | 7 |
| Caesium-135 | 3 |
| Technetium-97 | 3 |
| Gadolinium-150 | 2 |
| Zirconium-93 | 2 |
| Technetium-98 | 2 |
| Dysprosium-154 | 1 |
Some notable isotopes with shorter lives still being produced on Earth include:
- Manganese-53 and beryllium-10 are produced by cosmic ray spallation on dust in the upper atmosphere.
- Uranium-236 is produced in uranium ores by neutrons from other radioactives.
- Iodine-129 is produced from tellurium-130 by cosmic-ray muons and from cosmic ray spallation of stable xenon isotopes in the atmosphere.
Radioactives with half-lives shorter than one million years are also produced: for example, carbon-14 by cosmic ray production in the atmosphere (half life 5730 years).
