halflife =8.0197 days
Iodine-131 (131I), also called radioiodine, is a
radioisotopeof iodinewhich has medical and pharmaceutical uses.
131I decays with a
half-lifeof 8.0197 days with beta and gamma emissions. This nuclideof iodine atomhas 78 neutrons in nucleus, the stable nuclide 127I has 74 neutrons. On decaying, 131I transforms into 131Xe:
The primary emissions of 131I decay are 364 keV gamma rays (81% abundance) and 606 keV beta particles (89% abundance). [http://hpschapters.org/northcarolina/NSDS/131IPDF.pdf]
131I is a
fission productwith a yield of 2.8336% from uranium-235, and was released in nuclear weapons testsand the Chernobyl accident. However, the short half-life means it is not present in cooled spent nuclear fuel, unlike iodine-129whose 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
thyroidwhere it is needed for the functioning of that gland. When 131I 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 131I is the chance occurrence of radiogenic thyroid cancerin 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 groupFact|date=September 2008.
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. [ Steven L. Simon, André Bouville, Charles E. Land (2006) Fallout from nuclear weapons tests and cancer risks. "American Scientist" 94:48-57. ] The
National Cancer Instituteprovides additional information on the health effects from exposure to 131I in fallout, [cite web |title=Radioactive I-131 from Fallout |url=http://www.cancer.gov/i131 |publisher=National Cancer Institute |accessdate=2007-11-14] 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. [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]
Medical and pharmaceutical uses
It is used in
nuclear medicineboth diagnostically and therapeutically. Examples of its use in radiation therapyinclude the treatment of thyrotoxicosisand 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.
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 pheochromocytomaand neuroblastoma.
Patients receiving radioiodine treatment are warned not to have
sexual intercoursefor one month (or shorter, depending on dose given), and women are told not to become pregnant for six months afterwards. "This is because a theoretical risk to adeveloping 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." [Radioiodine Therapy: Information for Patients. AACE 2004 - http://www.kumc.edu/endocrine/Radioiodine_Therapy.pdf] 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 metredistance to others may be recommendedFact|date=September 2008.
airports now have radiation detectors in order to detect the smugglingof 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.Fact|date=September 2008
* [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 – Iodine, Radioactive]
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Look at other dictionaries:
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