Iodine-131 (I-131) is a radioactive isotope of iodine that is used in medicine to diagnose and treat diseases of the thyroid gland. The thyroid gland uses iodine to produce thyroid hormones, and I-131 can be used to treat an overactive thyroid, a condition called hyperthyroidism, by destroying the glands cells. It is also used to treat thyroid cancer and other abnormal conditions such as hyperthyroidism. I-131 emits both beta and gamma radiation and can be therapeutically administered as a single capsule that is to be taken orally. I-131 is produced commercially for medical and industrial uses through nuclear fission and is a byproduct of nuclear fission processes in nuclear reactors and weapons testing. It is a major concern in any kind of radiation release from a nuclear accident because it is volatile and highly radioactive, having an 8-day half-life. External exposure to large amounts of I-131 can cause burns to the eyes and skin, while internal exposure can affect the thyroid gland.