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Nuklid
This is a summary table [6] for the 905 nuclides with half-lives longer than one hour, given in list of nuclides. Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.
| Stability class | Number of nuclides | Running total | Notes on running total |
|---|---|---|---|
| Theoretically stable to all but proton decay | 90 | 90 | Includes first 40 elements. Proton decay yet to be observed. |
| Energetically unstable to one or more known decay modes, but no decay yet seen. Spontaneous fission possible for "stable" nuclides > niobium-93; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected. | 164 | 254 | Total of classically stable nuclides. |
| Radioactive primordial nuclides. | 35 | 289 | Total primordial elements include bismuth, uranium, thorium, plutonium, plus all stable nuclides. |
| Radioactive non-primordial, but naturally occurring on Earth. | ~ 51 | ~ 340 | Carbon-14 (and other cosmogenic isotopes generated by cosmic rays); daughters of radioactive primordials, such as francium, etc., and nucleogenic nuclides from natural nuclear reactions that are other than those from cosmic rays (such as neutron absorption from spontaneous nuclear fission or neutron emission). |
| Radioactive synthetic (half-life > 1 hour). Includes most useful radiotracers. | 556 | 905 | |
| Radioactive synthetic (half-life < 1 hour). | >2400 | >3300 | Includes all well-characterized synthetic nuclides. |
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