#radioisotope  a radioactive isotope of an element; produced either naturally or artificially
  supertype:  isotope  one of two or more atoms with the same atomic number but with different numbers of neutrons
  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

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