Iodine-131 or ¹³¹I, also commonly known as radioiodine is a radioactive form of Iodine, which is harmful in any exposure allowing it to enter the body. Iodine-131 is the most stable form of iodine in an isotope. Iodine-131, when inside the human body, is absorbed by the thyroid, and is harmful in decay, when it decays into ¹³¹Xenon. Iodine-131 will also be airborne in the event of nuclear fallout. Taking high doses of uncontaminated iodine can prevent the thyroid from absorbing the radioactive iodine, and the harmful isotope simply passes through the body, without the effect of thyroid cancer. Such uses of iodine in heavy doses after nuclear incidents were used in Chernobyl, Ukraine (Then Chernobyl, U.S.S.R.) in 1986. This prevented some people from being contaminated with thyroid cancer, but an estimated 2,300 were unable to get iodine in time, and later in life suffered thyroid cancer induced by exposure to airborne iodine-131. The half-life of this isotope is slightly more than eight days.