Nuclide
Summary table for numbers of each class of nuclides
This is a summary table 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.

Nuclide

Section Title: Summary table for numbers of each class of nuclides
Table Section Text: This is a summary table 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 from niobium-93 onwards; other mechanisms possible for heavier nuclides.	163	253	Total of classically stable nuclides.

Radioactive primordial nuclides.	33	286	Total primordial elements include bismuth, thorium, and uranium, plus all stable nuclides.

Radioactive non-primordial, but naturally occurring on Earth.	~ 53	~ 339	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.

Sentence(s)

253 stable nuclides exist on Earth, for a total of about 339 naturally occurring nuclides.

final_sentence: 253 stable nuclides exist on Earth, for a total of about 339 naturally occurring nuclides.