Editing Iodine (section)

===Isotopes===
{{main|Isotopes of iodine}}
Of the forty known [[isotopes of iodine]], only one occurs in nature, [[Isotopes of iodine|iodine-127]]. The others are radioactive and have half-lives too short to be [[primordial nuclide|primordial]]. As such, iodine is both [[monoisotopic element|monoisotopic]] and [[mononuclidic element|mononuclidic]] and its atomic weight is known to great precision, as it is a constant of nature.<ref name="Greenwood800" />

The longest-lived of the radioactive isotopes of iodine is [[iodine-129]], which has a half-life of 15.7&nbsp;million&nbsp;years, decaying via [[beta decay]] to stable [[xenon]]-129.<ref name="NUBASE">{{NUBASE 2003}}</ref> Some iodine-129 was formed along with iodine-127 before the formation of the [[Solar System]], but it has by now completely decayed away, making it an [[extinct radionuclide]]. Its former presence may be determined from an excess of its [[decay product|daughter]] xenon-129, but early attempts<ref name="Reynolds1960a">{{Cite journal |last=Reynolds |first=J. H. |date=1 January 1960 |title=Determination of the Age of the Elements |url=https://link.aps.org/doi/10.1103/PhysRevLett.4.8 |journal=Physical Review Letters |language=en |volume=4 |issue=1 |pages=8–10 |doi=10.1103/PhysRevLett.4.8 |bibcode=1960PhRvL...4....8R |issn=0031-9007}}</ref> to use this characteristic to date the supernova source for elements in the Solar System are made difficult by alternative nuclear processes giving iodine-129 and by iodine's volatility at higher temperatures.<ref name="Manuel2002">{{Cite book |last=Manuel |first=O. |date=2002 |editor-last=Manuel |editor-first=O. |chapter=Origin of Elements in the Solar System |title=Origin of Elements in the Solar System<!--yes, the chapter and the book have the same title--> |chapter-url=http://link.springer.com/10.1007/0-306-46927-8_44 |language=en |location=Boston, MA |publisher=Springer US |pages=589–643 |doi=10.1007/0-306-46927-8_44 |isbn=978-0-306-46562-8}}</ref> Due to its mobility in the environment iodine-129 has been used to date very old groundwaters.<ref>{{cite journal | vauthors = Watson JT, Roe DK, Selenkow HA | title = Iodine-129 as a "nonradioactive" tracer | journal = Radiation Research | volume = 26 | issue = 1 | pages = 159–163 | date = September 1965 | pmid = 4157487 | doi = 10.2307/3571805 | bibcode = 1965RadR...26..159W | jstor = 3571805 }}</ref><ref>{{cite journal | vauthors = Snyder G, Fabryka-Martin J | year = 2007 | title = I-129 and Cl-36 in dilute hydrocarbon waters: Marine-cosmogenic, in situ, and anthropogenic sources | journal = Applied Geochemistry | volume = 22 | issue = 3| pages = 692–714 | doi = 10.1016/j.apgeochem.2006.12.011 | bibcode = 2007ApGC...22..692S }}</ref> Traces of iodine-129 still exist today, as it is also a [[cosmogenic nuclide]], formed from [[cosmic ray spallation]] of atmospheric xenon: these traces make up 10<sup>−14</sup> to 10<sup>−10</sup> of all terrestrial iodine. It also occurs from open-air nuclear testing, and is not hazardous because of its very long half-life, the longest of all fission products. At the peak of thermonuclear testing in the 1960s and 1970s, iodine-129 still made up only about 10<sup>−7</sup> of all terrestrial iodine.<ref name="SCOPE50">
[http://www.scopenvironment.org/downloadpubs/scope50 SCOPE 50 - Radioecology after Chernobyl] {{webarchive|url=https://web.archive.org/web/20140513065145/http://www.scopenvironment.org/downloadpubs/scope50/ |date=13 May 2014 }}, the [[Scientific Committee on Problems of the Environment]] (SCOPE), 1993. See table 1.9 in Section 1.4.5.2.</ref> Excited states of iodine-127 and iodine-129 are often used in [[Mössbauer spectroscopy]].<ref name="Greenwood800" />

The other iodine radioisotopes have much shorter half-lives, no longer than days.<ref name="NUBASE" /> Some of them have medical applications involving the [[Thyroid|thyroid gland]], where the iodine that enters the body is stored and concentrated. [[Iodine-123]] has a half-life of thirteen hours and decays by [[electron capture]] to [[Isotopes of tellurium|tellurium-123]], emitting [[Gamma ray|gamma radiation]]; it is used in [[Nuclear medicine|nuclear medicine imaging]], including [[Single-photon emission computed tomography|single photon emission computed tomography]] (SPECT) and [[CT scan|X-ray computed tomography]] (X-Ray CT) scans.<ref>{{cite journal | vauthors = Hupf HB, Eldridge JS, Beaver JE | title = Production of iodine-123 for medical applications | journal = The International Journal of Applied Radiation and Isotopes | volume = 19 | issue = 4 | pages = 345–351 | date = April 1968 | pmid = 5650883 | doi = 10.1016/0020-708X(68)90178-6 }}</ref> [[Iodine-125]] has a half-life of fifty-nine days, decaying by electron capture to [[Isotopes of tellurium|tellurium-125]] and emitting low-energy gamma radiation; the second-longest-lived iodine radioisotope, it has uses in [[Assay|biological assays]], [[nuclear medicine|nuclear medicine imaging]] and in [[radiation therapy]] as [[brachytherapy]] to treat a number of conditions, including [[prostate cancer]], [[uveal melanoma]]s, and [[Brain tumor|brain tumours]].<ref>Harper, P.V.; Siemens, W.D.; Lathrop, K.A.; Brizel, H.E.; Harrison, R.W. ''Iodine-125.'' Proc. Japan Conf. Radioisotopes; Vol: 4 January 1, 1961</ref> Finally, [[iodine-131]], with a half-life of eight days, beta decays to an excited state of stable [[Isotopes of xenon|xenon-131]] that then converts to the ground state by emitting gamma radiation. It is a common [[Nuclear fission product|fission product]] and thus is present in high levels in radioactive [[Nuclear fallout|fallout]]. It may then 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 iodine-131 is the chance occurrence of [[Radiogenic nuclide|radiogenic]] [[thyroid cancer]] in later life. Other risks include the possibility of non-cancerous growths and [[thyroiditis]].<ref name="Rivkees">{{cite journal | vauthors = Rivkees SA, Sklar C, Freemark M | title = Clinical review 99: The management of Graves' disease in children, with special emphasis on radioiodine treatment | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 83 | issue = 11 | pages = 3767–3776 | date = November 1998 | pmid = 9814445 | doi = 10.1210/jcem.83.11.5239 | doi-access = free }}</ref>

Protection usually used against the negative effects of iodine-131 is by saturating the thyroid gland with stable iodine-127 in the form of [[potassium iodide]] tablets, taken daily for optimal prophylaxis.<ref>{{cite journal | vauthors = Zanzonico PB, Becker DV | title = Effects of time of administration and dietary iodine levels on potassium iodide (KI) blockade of thyroid irradiation by 131I from radioactive fallout | journal = Health Physics | volume = 78 | issue = 6 | pages = 660–667 | date = June 2000 | pmid = 10832925 | doi = 10.1097/00004032-200006000-00008 | s2cid = 30989865 }}</ref> However, iodine-131 may also be used for medicinal purposes in [[radiation therapy]] for this very reason, when tissue destruction is desired after iodine uptake by the tissue.<ref>{{cite news|title=Medical isotopes the likely cause of radiation in Ottawa waste|url=http://www.cbc.ca/news/canada/medical-isotopes-the-likely-cause-of-radiation-in-ottawa-waste-1.852645|date=4 February 2009|publisher=[[CBC News]]|access-date=30 September 2015|archive-date=19 November 2021|archive-url=https://web.archive.org/web/20211119213013/https://www.cbc.ca/news/canada/medical-isotopes-the-likely-cause-of-radiation-in-ottawa-waste-1.852645|url-status=live}}</ref> Iodine-131 is also used as a [[radioactive tracer]].<ref>{{cite book|vauthors=Moser H, Rauert W|title=Isotopes in the water cycle : past, present and future of a developing science|year=2007|publisher=Springer|location=Dordrecht|isbn=978-1-4020-6671-9|veditors=Aggarwal PK, Gat JR, Froehlich KF|access-date=6 May 2012|page=11|chapter=Isotopic Tracers for Obtaining Hydrologic Parameters|chapter-url=https://books.google.com/books?id=XKk6V_IeJbIC&pg=PA11|archive-date=19 March 2024|archive-url=https://web.archive.org/web/20240319070244/https://books.google.com/books?id=XKk6V_IeJbIC&pg=PA11#v=onepage&q&f=false|url-status=live}}</ref><ref>{{cite book|vauthors=Rao SM|title=Practical isotope hydrology|year=2006|publisher=New India Publishing Agency|location=New Delhi|isbn=978-81-89422-33-2|chapter-url=https://books.google.com/books?id=E7TVDVVji0EC&q=isotope%20hydrology%20iodine&pg=PA11|access-date=6 May 2012|pages=12–13|chapter=Radioisotopes of hydrological interest|archive-date=19 March 2024|archive-url=https://web.archive.org/web/20240319070414/https://books.google.com/books?id=E7TVDVVji0EC&q=isotope%20hydrology%20iodine&pg=PA11|url-status=live}}</ref><ref>{{cite web|title=Investigating leaks in Dams & Reservoirs|url=http://www.iaea.org/technicalcooperation/documents/sheet20dr.pdf|work=IAEA.org|access-date=6 May 2012|archive-url=https://web.archive.org/web/20130730053205/http://www.iaea.org/technicalcooperation/documents/sheet20dr.pdf|archive-date=30 July 2013|url-status=dead}}</ref><ref>{{cite book|vauthors=Araguás LA, Bedmar AP|title=Detection and prevention of leaks from dams|year=2002|publisher=Taylor & Francis|isbn=978-90-5809-355-4|chapter-url=https://books.google.com/books?id=FXB-HMzfBnkC&pg=PA179|access-date=6 May 2012|pages=179–181|chapter=Artificial radioactive tracers|archive-date=19 March 2024|archive-url=https://web.archive.org/web/20240319070244/https://books.google.com/books?id=FXB-HMzfBnkC&pg=PA179#v=onepage&q&f=false|url-status=live}}</ref>