Commonly Encountered Radionuclides
Approximately 2,300 nuclides have been identified; most of them are radioactive.
Which nuclides are radioactive?
Unstable nuclides of any element can exist. However, almost all elements that are heavier than bismuth, which has 83 protons, have an unstable nucleus; they are radioactive and are known as "heavy nuclides. Nuclides with fewer than 83 protons are known as "light nuclides.
While there are hundreds of radionuclides, many of them are rarely encountered. People are much more likely to encounter a few that are used routinely for medical, military, or commercial purposes. The list below and accompanying fact sheets discuss twelve radionuclides. They are the ones most commonly used and most commonly found in Superfund Sites.
Please note: Where an element is listed rather than an individual radionuclide, the element has several radioactive isotopes of interest:
|Fact Sheets on Commonly Encountered Radionuclides|
|* tritium is a specific isotope, H-3.|