A radioactive iodine isotope; beta and gamma emitter with a half-life of 8.1 days; used as a tracer in thyroid studies, as therapy in hyperthyroidism and thyroid cancer, and as a label in immunoassay and imaging; formerly used as therapy in heart disease.
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iodine-131 -.wən-.thərt-ē-'wən n a heavy radioactive isotope of iodine that has the mass number 131 and a half-life of eight days, emits beta particles and gamma rays, and is used esp. in the form of its sodium salt in the diagnosis of thyroid disease and the treatment of goiter
Medical dictionary. 2011.