What causes atoms to be radioactive?
Atoms found in nature are either stable or unstable. An atom is stable if the forces among the particles that make up the nucleus are balanced. An atom is unstable (radioactive) if these forces are unbalanced–if the nucleus has an excess of internal energy. Unstable atoms are called radionuclides. The instability of a radionuclide’s nucleus may result from an excess of either neutrons or protons. An unstable nucleus will continually vibrate and contort and, sooner or later, attempt to reach stability by some combination of means: • ejecting neutrons, and protons • converting one to the other with the ejection of a beta particle or positron • the release of additional energy by photon (i.e., gamma ray) emission.
