Stable Isotope

Stable Isotope

Stable isotopes are chemical isotopes that are not radioactive, i.e. they do not decay spontaneously.

Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory (see list of nuclides). An additional 164 are theoretically unstable to known types of decay, but no evidence of decay has ever been observed, for a total of 254 nuclides for which there is no evidence of radioactivity. By this definition, there are 254 known stable nuclides of the 80 elements which have one or more stable isotopes. A list of these is given at the end of this article.

Of the 80 elements with one or more stable isotopes, twenty-six have only a single stable isotope, and are thus termed monoisotopic, and the rest have more than one stable isotope. One element (tin) has ten stable isotopes, the largest number known for an element.