Summary Table For Classes of Nuclides, "stable" and Radioactive
Following is a summary table for the total list of nuclides with half-lives greater than one hour. Ninety of these 905 nuclides are theoretically stable, except to proton-decay (which has never been observed). About 255 nuclides have never been observed to decay, and are classically considered stable.
The remaining 650 radionuclides have half-lives longer than 1 hour, and are well characterized (see list of nuclides for a complete tabulation). They include 27 nuclides with measured half-lives longer than the estimated age of the universe (13.7 billion years), and another 6 nuclides with half-lives long enough (> 80 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the solar system, about 4.6 billion years ago. Another ~51 short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.
Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.
This is a summary table for the 905 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.
| 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. | 165 | 255 | Total of classically stable nuclides. |
| Radioactive primordial nuclides. | 33 | 288 | Total primordial elements include uranium, thorium, bismuth, rubidium-97, potassium-40 plus all stable nuclides. |
| Radioactive nonprimordial, but naturally occurring on Earth. | ~ 51 | ~ 339 | Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc. |
| Radioactive synthetic (half-life > 1.0 hour). Includes most useful radiotracers. | 556 | 905 | These 905 nuclides are listed in the article List of nuclides. |
| Radioactive synthetic (half-life < 1.0 hour). | >2400 | >3300 | Includes all well-characterized synthetic nuclides. |
Read more about this topic: Radionuclide
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