Radioactive contamination
Some organs concentrate certain elements and hence radionuclide variants of those elements. This action may lead to much lower removal rates. For instance, the thyroid gland takes up a large percentage of any iodine that enters the body. Large quantities of inhaled or ingested radioactive iodine may impair or destroy the thyroid, while other tissues are affected to a lesser extent. Radioactive iodine-131 is a common fission product; it was a major component of the radioactivity released from the Chernobyl disaster, leading to nine fatal cases of pediatric thyroid cancer and hypothyroidism. On the other hand, radioactive iodine is used in the diagnosis and treatment of many diseases of the thyroid precisely because of the thyroid's selective uptake of iodine.
Iodine-125
To isolate radioiodine, the irradiated capsule is first cooled (to collect free iodine gas on the capsule sides) and the remaining Xe gas is allowed to escape. The inner walls of the capsule are then rinsed with dilute NaOH solution to collect iodine as soluble iodide and hypoiodite OI, according to the standard disproportionation reaction of halogens in alkaline solutions. Any cesium immediately oxidizes and passes into the water as Cs. In order to eliminate any long-lived Cs and Cs which may be present in small amounts, the solution is passed through a cation-exchange column, which exchanges Cs for another non-radioactive cation. The radioiodine (as anion I or OI ) remains in solution as iodide/hypoiodite.