Iodine-131(I-131 or RAI) is a radioactive isotope commonly used in the treatment

Iodine-131(I-131 or RAI) is a radioactive isotope commonly used in the treatment of thyroid cancer. It is used for its specific affinity for the thyroid gland, which allows it to be targeted to treat thyroid cancer cells. I-131 is a form of internal radiation and there are precautions taken to avoid radiation exposure to others. After undergoing treatment, patients are instructed to isolate themselves for a short period of time from family, friends, and the general public. I-131 has a half-life of 8 days and decays by beta-particle and gamma emissions.
References
National Center for Environmental Health (NCEH). (2018, April 4). Radioisotope Brief: Iodine-131 (I-131). Centers for Disease Control and Prevention.https://www.cdc.gov/nceh/radiation/emergencies/isotopes/iodine.htmLinks to an external site.
Mumtaz, M., Lin, L. S., Hui, K. C., & Mohd Khir, A. S. (2009). Radioiodine I-131 for the therapy of graves’ disease. The Malaysian journal of medical sciences : MJMS, 16(1), 25–33.