<prompt> Radioisotope used for thyroid treatment of metastasis ablation1-1231-131Jan-83Jan-90  <response>: Ans. b 1-131Ref: Sutton 7th1504 Iodine-131 has a radioactive decay half-life of about eight days. Iodine-131 exhibits a beta mode of decay, and leads to death in cells that it penetrates up to several millimeters and hence is useful for thyroid ablation. 1-123 has a half-life of 13.22 hours and is a radioactive isotope of iodine used in nuclear medicine imaging, including single photon emission computed tomography. 