iodine-131

iodine-131
Background	#fc6
Mass number	131
Num neutrons	78
Num protons	53
Caption	Decay scheme of iodine-131

iodine-131 is a significant radioisotope of the element iodine with important applications in nuclear medicine and a notable component of nuclear fallout. It is a fission product with a half-life of approximately 8.02 days, decaying via beta decay to an excited state of xenon-131. Its unique physical and chemical properties make it both a powerful tool for medical therapy and a serious radiological hazard in the environment, particularly following events like the Chernobyl disaster and the Fukushima Daiichi nuclear disaster.

Properties

Iodine-131 decays with a half-life of 8.02 days, emitting both beta particles and gamma rays. The primary beta particle has a maximum energy of 606 keV, while the accompanying gamma emission has an energy of 364 keV, which is useful for gamma camera imaging. Its decay product is the stable noble gas xenon-131. Chemically, it behaves identically to stable iodine-127, allowing it to be readily incorporated by the thyroid gland through the sodium-iodide symporter. This biochemical pathway is central to its medical utility and its primary hazard as an internal emitter.

Production

Iodine-131 is primarily produced artificially in nuclear reactors as a common fission product of uranium-235 and plutonium-239. It is typically separated from other fission products in spent nuclear fuel through chemical processing. Major production facilities have historically included the Oak Ridge National Laboratory and the Savannah River Site. It can also be generated by neutron irradiation of tellurium targets, such as tellurium-130, in reactors. The International Atomic Energy Agency monitors global production due to its potential for use in radiopharmaceuticals and its proliferation relevance.

Medical applications

In nuclear medicine, iodine-131 is a cornerstone for both diagnosis and therapy, particularly for thyroid conditions. As radioiodine therapy, it is the standard treatment for hyperthyroidism caused by Graves' disease and for ablating residual tissue after thyroidectomy for thyroid cancer. The Mayo Clinic and Johns Hopkins Hospital are among many institutions utilizing this therapy. It is administered orally, often as sodium iodide, and its uptake is assessed using single-photon emission computed tomography. The American Thyroid Association provides guidelines for its clinical use.

Industrial and research uses

Beyond medicine, iodine-131 serves as a radioactive tracer in industrial and research settings. It is used to study fluid dynamics in complex systems like petroleum pipelines and to label compounds in biochemistry research to track metabolic pathways. Historically, it was used in radioisotope thermoelectric generators for remote power, such as those in some Soviet Union lighthouses. Research into its environmental transport often follows incidents at facilities like the Hanford Site.

Health and safety

Exposure to iodine-131 poses significant health risks due to its concentration in the thyroid gland, increasing the risk of thyroid cancer, particularly in children. Protective measures include prophylactic administration of stable potassium iodide, as recommended by the World Health Organization and the U.S. Food and Drug Administration. Handling requires strict radiation protection protocols, including shielding and monitoring, as enforced by agencies like the Nuclear Regulatory Commission. Notable exposures occurred in populations downwind of the Nevada Test Site and among responders to the Windscale fire.

Environmental impact

Iodine-131 is a major short-term component of atmospheric nuclear fallout due to its volatility and moderate half-life. Its release and dispersion have been extensively studied after events like the Chernobyl disaster, the Fukushima Daiichi nuclear disaster, and historical nuclear weapons testing. It enters the food chain rapidly, contaminating pastures and concentrating in milk. Long-term environmental monitoring is conducted by bodies such as the Comprehensive Nuclear-Test-Ban Treaty Organization to track its global dispersion and decay.

Category:Isotopes of iodine Category:Industrial isotopes Category:Nuclear medicine