Summary Table For Numbers of Each Class of Nuclides
This is a summary table from List of nuclides. Note that numbers are not exact, and may change slightly in the future, as nuclides are observed to be radioactive, or new half-lives are determined to some precision. Note that only the 254 have any claim to stability, but that only 90 nuclides from the first 40 elements are theoretically stable to any process but proton decay.
| Type of nuclide by stability class. | Number of nuclides in class (exact number may change). | Running total of nuclides in all classes to this point. | 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. Considered stable until radioactivity confirmed. | 164 | 254 | Spontaneous fission possible for "stable" nuclides > niobium-93. Other mechanisms possible for heavier nuclides. Total is the classically stable nuclides |
| Radioactive primordial nuclides. | 34 | 288 | Total primordials include Bi, U, Th, Pu, plus all stable nuclides. |
| Radioactive nonprimordial, but naturally occurring on Earth. | ~ 51 | ~ 339 | Cosmogenic nuclides from cosmic rays; daughters of radioactive primordials such as francium, etc. |
Read more about this topic: Stable Isotope
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