The primary emissions of 131I decay are 364 keV gamma rays (81% abundance) and 606 keV beta particles (89% abundance).
131I is a fission product with a yield of 2.8336% from uranium-235, and was released in nuclear weapons tests and the Chernobyl accident. However, the short half-life means it is not present in cooled spent nuclear fuel, unlike iodine-129 whose halflife is nearly a billion times that of I-131.
The risk of thyroid cancer in later life appears to diminish with increasing age at time of exposure. Most risk estimates are based on studies in which radiation exposures occurred in children or teenagers. When adults are exposed, it has been difficult for epidemiologists to detect a statistically significant difference in the rates of thyroid disease above that of a similar but otherwise unexposed group.
The risk can be mitigated by taking iodine supplements, raising the total amount of iodine in the body and therefore reducing uptake and retention in tissues and lowering the relative proportion of radioactive iodine. Such supplements were distributed to the population living nearest to the Chernobyl nuclear power plant after the disaster.
Within the USA, the highest 131I fallout doses occurred during the 1950s and early 1960s to children who consumed fresh sources of milk contaminated as the result of above ground testing of nuclear weapons. The National Cancer Institute provides additional information on the health effects from exposure to 131I in fallout, as well as individualized estimates, for those born before 1971, for each of the 3070 counties in the USA from the nuclear weapons tests conducted at the Nevada Test Site.
131I is also used as a radioactive label for radiopharmaceuticals that can be used for imaging and therapy e.g. 131I-metaiodobenzylguanidine (131I-MIBG) for imaging and treating pheochromocytoma and neuroblastoma.
Many airports now have radiation detectors in order to detect the smuggling of radioactive materials that may be used in nuclear weapons manufacture. Patients should be warned that if they choose to travel by air, they may set off radiation detectors at airports up to 12 weeks after their treatment with 131I.
Iodine-131/thyrotropin-[Alpha]: Increased Uptake and Half-Life of Iodine-131 Leading to Grade 3 Haematological Side Effects in a Patient with Thyroid Hormone Secreting Metastases: Case Report
Jun 09, 2012; A 64-year-old woman with follicular thyroid cancer developed grade 3 haematological side effects due to an increased uptake and...