isotope /ī″sətōp/ [Gk, isos + topos, place] , one of two or more forms of an atom having the same number of protons in the atomic nucleus but different numbers of neutrons and thus a different atomic mass. For example, two common isotopes of carbon are 12C, which has six neutrons, and 14C, which has eight. Many isotopes are used in diagnostic and therapeutic procedures.
