#isotope  one of two or more atoms with the same atomic number but with different numbers of neutrons
  supertype:  atom  (physics and chemistry) the smallest component of an element having the chemical properties of the element
  subtype:  radioisotope  a radioactive isotope of an element; produced either naturally or artificially
     subtype:  tracer  (radiology) any radioactive isotope introduced into the body to study metabolism or other biological processes
     subtype:  label.radioisotope  a radioactive isotope that is used in a compound in order to trace the mechanism of a chemical reaction
     subtype:  iodine-131  heavy radioactive isotope of iodine with a half-life of 8 days; used in a sodium salt to diagnose thyroid disease and to treat goiter
     subtype:  iodine-125  light radioactive isotope of iodine with a half-life of 60 days; used as a tracer in thyroid studies and as a treatment for hyperthyroidism
  subtype:  deuterium__heavy_hydrogen__heavyhydrogen  an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)

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