Iodine-131 1884846 224286709 2008-07-08T04:26:19Z Binksternet 4967956 delete grocer's apostrophes {{Infobox isotope | alternate_names =Radioiodine | symbol =I | mass_number =131 | mass = | num_neutrons =78 | num_protons =53 | abundance = | halflife =8.0197 days | error_halflife = | background =#c9F | text_color = | image = | decay_product = | decay_symbol = | decay_mass = | decay_mode1 = | decay_energy1 = | decay_mode2 = | decay_energy2 = | decay_mode3 = | decay_energy3 = | decay_mode4 = | decay_energy4 = | parent = | parent_symbol = | parent_mass = | parent_decay = | parent2 = | parent2_symbol = | parent2_mass = | parent2_decay = | spin = | excess_energy = | error1 = | binding_energy = | error2 = }}'''Iodine-131 (<sup>131</sup>I)''', also called '''radioiodine''', is a [[radioisotope]] of [[iodine]] which has medical and pharmaceutical uses. ==Radioactive decay== <sup>131</sup>I decays with a [[half-life]] of 8.0197 days with [[beta particle|beta]] and [[gamma ray|gamma]] emissions. This [[nuclide]] of iodine [[atom]] has 78 [[neutron]]s in nucleus, the stable nuclide <sup>127</sup>I has 74 neutrons. On decaying, <sup>131</sup>I transforms into [[xenon|<sup>131</sup>Xe]]: <math> {^{131}_{53}I} \rightarrow \beta + {^{131}_{54}Xe} </math> <sup>131</sup>I 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. ==Effects of exposure== Iodine in food is absorbed by the body and preferentially concentrated in the [[thyroid]] where it is needed for the functioning of that gland. When <sup>131</sup>I is present in high levels in the environment from radioactive [[fallout]], it can be absorbed through contaminated food, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid. The primary risk from exposure to high levels of <sup>131</sup>I is the chance occurrence of radiogenic thyroid cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis. 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 disaster|Chernobyl]] nuclear power plant after the disaster. Within the USA, the highest <sup>131</sup>I 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.<ref> Steven L. Simon, André Bouville, Charles E. Land (2006) Fallout from nuclear weapons tests and cancer risks. ''American Scientist'' '''94''':48-57. </ref> The [[National Cancer Institute]] provides additional information on the health effects from exposure to <sup>131</sup>I in fallout,<ref>{{cite web |title=Radioactive I-131 from Fallout |url=http://www.cancer.gov/i131 |publisher=National Cancer Institute |accessdate=2007-11-14}}</ref> 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]].<ref>{{cite web |title=Individual Dose and Risk Calculator for Nevada Test Site fallout |url=http://ntsi131.nci.nih.gov/ |date=10/01/07 |publisher=National Cancer Institute |accessdate=2007-11-14}}</ref> ==Medical and pharmaceutical uses== It is used in [[nuclear medicine]] both diagnostically and therapeutically. Examples of its use in [[radiation therapy]] include the treatment of [[thyrotoxicosis]] and [[thyroid cancer]]. Diagnostic tests exploit the mechanism of absorption of iodine by the normal cells of the thyroid gland. As an example iodine-131 is one of the radioactive isotopes of iodine that can be used to test how well the thyroid gland is functioning. <sup>131</sup>I is also used as a radioactive label for [[radiopharmaceutical]]s that can be used for imaging and therapy e.g. <sup>131</sup>I-[[metaiodobenzylguanidine]] (<sup>131</sup>I-MIBG) for imaging and treating [[pheochromocytoma]] and [[neuroblastoma]]. ===Post-treatment isolation=== Patients receiving radioiodine treatment are warned not to have [[sexual intercourse]] for one month (or shorter, depending on dose given), and women are told not to become [[pregnancy|pregnant]] for six months afterwards. "This is because a theoretical risk to a developing fetus exists, even though the amount of radioactivity retained may be small and there is no medical proof of an actual risk from radioiodine treatment. Such a precaution would essentially eliminate direct fetal exposure to radioactivity and markedly reduce the possibility of conception with sperm that might theoretically have been damaged by exposure to radioiodine."<ref>Radioiodine Therapy: Information for Patients. AACE 2004 - http://www.kumc.edu/endocrine/Radioiodine_Therapy.pdf</ref> These guidelines vary from hospital to hospital and will depend also on the dose of radiation given. One also advises not to hug or hold children when the radiation is still high, and a one or two [[metre]] distance to others may be recommended. Many [[airport]]s now have radiation detectors in order to detect the [[smuggling]] of radioactive materials that may be used in [[nuclear weapon]]s 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 <sup>131</sup>I. A [[physician]]'s letter does not exempt one from interrogation by airport security personnel, because these letters are easily forged. For [[security through obscurity|security]] reasons, there is no information available in the public domain on which airports use radiation detectors. ==References== {{Reflist}} == External links == *[http://www.ead.anl.gov/pub/doc/iodine.pdf ANL factsheet] *[http://www.radiologyinfo.org/en/info.cfm?pg=radioiodine RadiologyInfo - The radiology information resource for patients: Radioiodine (I -131) Therapy] *[http://www.atsdr.cdc.gov/HEC/CSEM/iodine/index.html Case Studies in Environmental Medicine: Radiation Exposure from Iodine 131] *[http://rsna2004.rsna.org/rsna2004/V2004/conference/event_display.cfm?em_id=4407767 Sensitivity of Personal Homeland Security Radiation Detectors to Medical Radionuclides and Implications for Counseling of Nuclear Medicine Patients] *[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+iodine,+radioactive NLM Hazardous Substances Databank &ndash; Iodine, Radioactive] {{Isotope|element=iodine |lighter=[[Iodine-130|<sup>130</sup>I]] |heavier=[[Iodine-132|<sup>132</sup>I]] |before=[[Tellurium-131|<sup>131</sup>Te]] '''([[beta decay|β<sup>-</sup>]]) |after=[[Xenon-131|<sup>131</sup>Xe]] '''(β<sup>-</sup>) }} [[Category:Isotopes of iodine]] [[Category:Antithyroid drugs]] [[Category:Fission products]] [[de:Radioiodtherapie]]