There are 37 known

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...

s of

iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

(₅₃I) from ¹⁰⁸I to ¹⁴⁴I; all undergo radioactive decay except ¹²⁷I, which is stable. Iodine is thus a monoisotopic element. Its longest-lived radioactive isotope, ¹²⁹I, has a half-life of 15.7 million years, which is far too short for it to exist as a primordial nuclide. Cosmogenic sources of ¹²⁹I produce very tiny quantities of it that are too small to affect atomic weight measurements; iodine is thus also a mononuclidic element—one that is found in nature only as a single nuclide. Most ¹²⁹I derived radioactivity on Earth is man-made, an unwanted long-lived byproduct of early nuclear tests and nuclear fission accidents. All other iodine radioisotopes have half-lives less than 60 days, and four of these are used as tracers and therapeutic agents in medicine. These are ¹²³I, ¹²⁴I, ¹²⁵I, and ¹³¹I. All industrial production of radioactive iodine isotopes involves these four useful radionuclides. The isotope ¹³⁵I has a half-life less than seven hours, which is too short to be used in biology. Unavoidable ''in situ'' production of this isotope is important in nuclear reactor control, as it decays to ¹³⁵Xe, the most powerful known neutron absorber, and the nuclide responsible for the so-called iodine pit phenomenon. In addition to commercial production, ¹³¹I (half-life 8 days) is one of the common radioactive fission products of

nuclear fission Nuclear fission is a nuclear reaction, reaction in which the atomic nucleus, nucleus of an atom splits into two or more smaller atomic nucleus, nuclei. The fission process often produces gamma ray, gamma photons, and releases a very large ...

, and is thus produced inadvertently in very large amounts inside

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

s. Due to its volatility, short half-life, and high abundance in fission products, ¹³¹I (along with the short-lived iodine isotope ¹³²I, which is produced from the decay of ¹³²Te with a half-life of 3 days) is responsible for the largest part of

radioactive contamination Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirab ...

during the first week after accidental environmental contamination from the

radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weap ...

from a nuclear power plant. Thus highly dosed iodine supplements (usually potassium iodide) are given to the populace after nuclear accidents or explosions (and in some cases prior to any such incident as a civil defense mechanism) to reduce the uptake of radioactive iodine compounds by the thyroid before the highly radioactive isotopes have had time to decay. AirDoseChernobylVector

List of isotopes

, - , rowspan=3, ¹⁰⁸I , rowspan=3 style="text-align:right" , 53 , rowspan=3 style="text-align:right" , 55 , rowspan=3, 107.94348(39)# , rowspan=3, 36(6) ms , α (90%) , ¹⁰⁴Sb , rowspan=3, (1)# , rowspan=3, , rowspan=3, , - , β⁺ (9%) , ¹⁰⁸Te , - , p (1%) , ¹⁰⁷Te , - , rowspan=2, ¹⁰⁹I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 56 , rowspan=2, 108.93815(11) , rowspan=2, 103(5) µs , p (99.5%) , ¹⁰⁸Te , rowspan=2, (5/2+) , rowspan=2, , rowspan=2, , - , α (.5%) , ¹⁰⁵Sb , - , rowspan=4, ¹¹⁰I , rowspan=4 style="text-align:right" , 53 , rowspan=4 style="text-align:right" , 57 , rowspan=4, 109.93524(33)# , rowspan=4, 650(20) ms , β⁺ (70.9%) , ¹¹⁰Te , rowspan=4, 1+# , rowspan=4, , rowspan=4, , - , α (17%) , ¹⁰⁶Sb , - , β⁺, p (11%) , ¹⁰⁹Sb , - , β⁺, α (1.09%) , ¹⁰⁶Sn , - , rowspan=2, ¹¹¹I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 58 , rowspan=2, 110.93028(32)# , rowspan=2, 2.5(2) s , β⁺ (99.92%) , ¹¹¹Te , rowspan=2, (5/2+)# , rowspan=2, , rowspan=2, , - , α (.088%) , ¹⁰⁷Sb , - , rowspan=4, ¹¹²I , rowspan=4 style="text-align:right" , 53 , rowspan=4 style="text-align:right" , 59 , rowspan=4, 111.92797(23)# , rowspan=4, 3.42(11) s , β⁺ (99.01%) , ¹¹²Te , rowspan=4, , rowspan=4, , rowspan=4, , - , β⁺, p (.88%) , ¹¹¹Sb , - , β⁺, α (.104%) , ¹⁰⁸Sn , - , α (.0012%) , ¹⁰⁸Sb , - , rowspan=3, ¹¹³I , rowspan=3 style="text-align:right" , 53 , rowspan=3 style="text-align:right" , 60 , rowspan=3, 112.92364(6) , rowspan=3, 6.6(2) s , β⁺ (100%) , ¹¹³Te , rowspan=3, 5/2+# , rowspan=3, , rowspan=3, , - , α (3.3×10⁻⁷%) , ¹⁰⁹Sb , - , β⁺, α , ¹⁰⁹Sn , - , rowspan=2, ¹¹⁴I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 61 , rowspan=2, 113.92185(32)# , rowspan=2, 2.1(2) s , β⁺ , ¹¹⁴Te , rowspan=2, 1+ , rowspan=2, , rowspan=2, , - , β⁺, p (rare) , ¹¹³Sb , - , rowspan=2 style="text-indent:1em" , ^114mI , rowspan=2 colspan="3" style="text-indent:2em" , 265.9(5) keV , rowspan=2, 6.2(5) s , β⁺ (91%) , ¹¹⁴Te , rowspan=2, (7) , rowspan=2, , rowspan=2, , - , IT (9%) , ¹¹⁴I , - , ¹¹⁵I , style="text-align:right" , 53 , style="text-align:right" , 62 , 114.91805(3) , 1.3(2) min , β⁺ , ¹¹⁵Te , (5/2+)# , , , - , ¹¹⁶I , style="text-align:right" , 53 , style="text-align:right" , 63 , 115.91681(10) , 2.91(15) s , β⁺ , ¹¹⁶Te , 1+ , , , - , style="text-indent:1em" , ^116mI , colspan="3" style="text-indent:2em" , 400(50)# keV , 3.27(16) µs , , , (7−) , , , - , ¹¹⁷I , style="text-align:right" , 53 , style="text-align:right" , 64 , 116.91365(3) , 2.22(4) min , β⁺ , ¹¹⁷Te , (5/2)+ , , , - , ¹¹⁸I , style="text-align:right" , 53 , style="text-align:right" , 65 , 117.913074(21) , 13.7(5) min , β⁺ , ¹¹⁸Te , 2− , , , - , rowspan=2 style="text-indent:1em" , ^118mI , rowspan=2 colspan="3" style="text-indent:2em" , 190.1(10) keV , rowspan=2, 8.5(5) min , β⁺ , ¹¹⁸Te , rowspan=2, (7−) , rowspan=2, , rowspan=2, , - , IT (rare) , ¹¹⁸I , - , ¹¹⁹I , style="text-align:right" , 53 , style="text-align:right" , 66 , 118.91007(3) , 19.1(4) min , β⁺ , ¹¹⁹Te , 5/2+ , , , - , ¹²⁰I , style="text-align:right" , 53 , style="text-align:right" , 67 , 119.910048(19) , 81.6(2) min , β⁺ , ¹²⁰Te , 2− , , , - , style="text-indent:1em" , ^120m1I , colspan="3" style="text-indent:2em" , 72.61(9) keV , 228(15) ns , , , (1+, 2+, 3+) , , , - , style="text-indent:1em" , ^120m2I , colspan="3" style="text-indent:2em" , 320(15) keV , 53(4) min , β⁺ , ¹²⁰Te , (7−) , , , - , ¹²¹I , style="text-align:right" , 53 , style="text-align:right" , 68 , 120.907367(11) , 2.12(1) h , β⁺ , ¹²¹Te , 5/2+ , , , - , style="text-indent:1em" , ^121mI , colspan="3" style="text-indent:2em" , 2376.9(4) keV , 9.0(15) µs , , , , , , - , ¹²²I , style="text-align:right" , 53 , style="text-align:right" , 69 , 121.907589(6) , 3.63(6) min , β⁺ , ¹²²Te , 1+ , , , - , ¹²³IHas medical uses , style="text-align:right" , 53 , style="text-align:right" , 70 , 122.905589(4) , 13.2235(19) h , EC , ¹²³Te , 5/2+ , , , - , ¹²⁴I , style="text-align:right" , 53 , style="text-align:right" , 71 , 123.9062099(25) , 4.1760(3) d , β⁺ , ¹²⁴Te , 2− , , , - , ¹²⁵I , style="text-align:right" , 53 , style="text-align:right" , 72 , 124.9046302(16) , 59.400(10) d , EC , ¹²⁵Te , 5/2+ , , , - , rowspan=2, ¹²⁶I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 73 , rowspan=2, 125.905624(4) , rowspan=2, 12.93(5) d , β⁺ (56.3%) , ¹²⁶Te , rowspan=2, 2− , rowspan=2, , rowspan=2, , - , β⁻ (43.7%) , ¹²⁶Xe , - , ¹²⁷I Fission product , style="text-align:right" , 53 , style="text-align:right" , 74 , 126.904473(4) , colspan=3 align=center, StableTheoretically capable of spontaneous fission , 5/2+ , 1.0000 , , - , rowspan=2, ¹²⁸I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 75 , rowspan=2, 127.905809(4) , rowspan=2, 24.99(2) min , β⁻ (93.1%) , ¹²⁸Xe , rowspan=2, 1+ , rowspan=2, , rowspan=2, , - , β⁺ (6.9%) , ''¹²⁸Te'' , - , style="text-indent:1em" , ^128m1I , colspan="3" style="text-indent:2em" , 137.850(4) keV , 845(20) ns , , , 4− , , , - , style="text-indent:1em" , ^128m2I , colspan="3" style="text-indent:2em" , 167.367(5) keV , 175(15) ns , , , (6)− , , , - , ¹²⁹ICan be used to date certain early events in Solar System history and some use for dating groundwater , style="text-align:right" , 53 , style="text-align:right" , 76 , 128.904988(3) , 1.57(4)×10⁷ y , β⁻ , ¹²⁹Xe , 7/2+ , Trace Cosmogenic nuclide, also found as nuclear contamination , , - , ¹³⁰I , style="text-align:right" , 53 , style="text-align:right" , 77 , 129.906674(3) , 12.36(1) h , β⁻ , ¹³⁰Xe , 5+ , , , - , rowspan=2 style="text-indent:1em" , ^130m1I , rowspan=2 colspan="3" style="text-indent:2em" , 39.9525(13) keV , rowspan=2, 8.84(6) min , IT (84%) , ¹³⁰I , rowspan=2, 2+ , rowspan=2, , rowspan=2, , - , β⁻ (16%) , ¹³⁰Xe , - , style="text-indent:1em" , ^130m2I , colspan="3" style="text-indent:2em" , 69.5865(7) keV , 133(7) ns , , , (6)− , , , - , style="text-indent:1em" , ^130m3I , colspan="3" style="text-indent:2em" , 82.3960(19) keV , 315(15) ns , , , - , , , - , style="text-indent:1em" , ^130m4I , colspan="3" style="text-indent:2em" , 85.1099(10) keV , 254(4) ns , , , (6)− , , , - , ¹³¹I , style="text-align:right" , 53 , style="text-align:right" , 78 , 130.9061246(12) , 8.02070(11) d , β⁻ , ¹³¹Xe , 7/2+ , , , - , ¹³²I , style="text-align:right" , 53 , style="text-align:right" , 79 , 131.907997(6) , 2.295(13) h , β⁻ , ¹³²Xe , 4+ , , , - , rowspan=2 style="text-indent:1em" , ^132mI , rowspan=2 colspan="3" style="text-indent:2em" , 104(12) keV , rowspan=2, 1.387(15) h , IT (86%) , ¹³²I , rowspan=2, (8−) , rowspan=2, , rowspan=2, , - , β⁻ (14%) , ¹³²Xe , - , ¹³³I , style="text-align:right" , 53 , style="text-align:right" , 80 , 132.907797(5) , 20.8(1) h , β⁻ , ¹³³Xe , 7/2+ , , , - , style="text-indent:1em" , ^133m1I , colspan="3" style="text-indent:2em" , 1634.174(17) keV , 9(2) s , IT , ¹³³I , (19/2−) , , , - , style="text-indent:1em" , ^133m2I , colspan="3" style="text-indent:2em" , 1729.160(17) keV , ~170 ns , , , (15/2−) , , , - , ¹³⁴I , style="text-align:right" , 53 , style="text-align:right" , 81 , 133.909744(9) , 52.5(2) min , β⁻ , ¹³⁴Xe , (4)+ , , , - , rowspan=2 style="text-indent:1em" , ^134mI , rowspan=2 colspan="3" style="text-indent:2em" , 316.49(22) keV , rowspan=2, 3.52(4) min , IT (97.7%) , ¹³⁴I , rowspan=2, (8)− , rowspan=2, , rowspan=2, , - , β⁻ (2.3%) , ¹³⁴Xe , - , ¹³⁵IProduced as a decay product of ¹³⁵Te in nuclear reactors, in turn decays to ¹³⁵Xe, which, if allowed to build up, can shut down reactors due to the iodine pit phenomenon , style="text-align:right" , 53 , style="text-align:right" , 82 , 134.910048(8) , 6.57(2) h , β⁻ , ¹³⁵Xe , 7/2+ , , , - , ¹³⁶I , style="text-align:right" , 53 , style="text-align:right" , 83 , 135.91465(5) , 83.4(10) s , β⁻ , ''¹³⁶Xe'' , (1−) , , , - , style="text-indent:1em" , ^136mI , colspan="3" style="text-indent:2em" , 650(120) keV , 46.9(10) s , β⁻ , ''¹³⁶Xe'' , (6−) , , , - , rowspan=2, ¹³⁷I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 84 , rowspan=2, 136.917871(30) , rowspan=2, 24.13(12) s , β⁻ (92.86%) , ¹³⁷Xe , rowspan=2, (7/2+) , rowspan=2, , rowspan=2, , - , β⁻, n (7.14%) , ''¹³⁶Xe'' , - , rowspan=2, ¹³⁸I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 85 , rowspan=2, 137.92235(9) , rowspan=2, 6.23(3) s , β⁻ (94.54%) , ¹³⁸Xe , rowspan=2, (2−) , rowspan=2, , rowspan=2, , - , β⁻, n (5.46%) , ¹³⁷Xe , - , rowspan=2, ¹³⁹I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 86 , rowspan=2, 138.92610(3) , rowspan=2, 2.282(10) s , β⁻ (90%) , ¹³⁹Xe , rowspan=2, 7/2+# , rowspan=2, , rowspan=2, , - , β⁻, n (10%) , ¹³⁸Xe , - , rowspan=2, ¹⁴⁰I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 87 , rowspan=2, 139.93100(21)# , rowspan=2, 860(40) ms , β⁻ (90.7%) , ¹⁴⁰Xe , rowspan=2, (3)(−#) , rowspan=2, , rowspan=2, , - , β⁻, n (9.3%) , ¹³⁹Xe , - , rowspan=2, ¹⁴¹I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 88 , rowspan=2, 140.93503(21)# , rowspan=2, 430(20) ms , β⁻ (78%) , ¹⁴¹Xe , rowspan=2, 7/2+# , rowspan=2, , rowspan=2, , - , β⁻, n (22%) , ¹⁴⁰Xe , - , rowspan=2, ¹⁴²I , rowspan=2 style="text-align:right" , 53 , rowspan=2 style="text-align:right" , 89 , rowspan=2, 141.94018(43)# , rowspan=2, ~200 ms , β⁻ (75%) , ¹⁴²Xe , rowspan=2, 2−# , rowspan=2, , rowspan=2, , - , β⁻, n (25%) , ¹⁴¹Xe , - , ¹⁴³I , style="text-align:right" , 53 , style="text-align:right" , 90 , 142.94456(43)# , 100# ms 300 ns, β⁻ , ¹⁴³Xe , 7/2+# , , , - , ¹⁴⁴I , style="text-align:right" , 53 , style="text-align:right" , 91 , 143.94999(54)# , 50# ms 300 ns, β⁻ , ¹⁴⁴Xe , 1−# , ,

Notable radioisotopes

Radioisotopes of iodine are called radioactive iodine or radioiodine. Dozens exist, but about a half dozen are the most notable in applied sciences such as the life sciences and nuclear power, as detailed below. Mentions of radioiodine in

health care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health ...

contexts refer more often to iodine-131 than to other isotopes. Of the many isotopes of iodine, only two are typically used in a medical setting: iodine-123 and iodine-131. Since ¹³¹I has both a beta and gamma decay mode, it can be used for radiotherapy or for imaging. ¹²³I, which has no beta activity, is more suited for routine nuclear medicine imaging of the thyroid and other medical processes and less damaging internally to the patient. There are some situations in which iodine-124 and iodine-125 are also used in medicine. Due to preferential uptake of iodine by the thyroid, radioiodine is extensively used in imaging of and, in the case of ¹³¹I, destroying dysfunctional thyroid tissues. Other types of tissue selectively take up certain iodine-131-containing tissue-targeting and killing radiopharmaceutical agents (such as MIBG). Iodine-125 is the only other iodine radioisotope used in radiation therapy, but only as an implanted capsule in brachytherapy, where the isotope never has a chance to be released for chemical interaction with the body's tissues.

Iodine-123 and iodine-125

The gamma-emitting isotopes iodine-123 (half-life 13 hours), and (less commonly) the longer-lived and less energetic iodine-125 (half-life 59 days) are used as

nuclear imaging Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...

tracers to evaluate the anatomic and physiologic function of the thyroid. Abnormal results may be caused by disorders such as Graves' disease or Hashimoto's thyroiditis. Both isotopes decay by electron capture (EC) to the corresponding tellurium nuclides, but in neither case are these the

metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...

nuclides ^123mTe and ^125mTe (which are of higher energy, and are not produced from radioiodine). Instead, the excited tellurium nuclides decay immediately (half-life too short to detect). Following EC, the excited ¹²³Te from ¹²³I emits a high-speed 127 keV

internal conversion Internal conversion is a non-radioactive, atomic decay process where an excited nucleus interacts electromagnetically with one of the orbital electrons of an atom. This causes the electron to be emitted (ejected) from the atom. Thus, in interna ...

electron (not a beta ray) about 13% of the time, but this does little cellular damage due to the nuclide's short half-life and the relatively small fraction of such events. In the remainder of cases, a 159 keV gamma ray is emitted, which is well-suited for gamma imaging. Excited ¹²⁵Te resulting from electron capture of ¹²⁵I also emits a much lower-energy internal conversion electron (35.5 keV), which does relatively little damage due to its low energy, even though its emission is more common. The relatively low-energy gamma from ¹²⁵I/¹²⁵Te decay is poorly suited for imaging, but can still be seen, and this longer-lived isotope is necessary in tests that require several days of imaging, for example, fibrinogen scan imaging to detect blood clots. Both ¹²³I and ¹²⁵I emit copious low energy Auger electrons after their decay, but these do not cause serious damage (double-stranded DNA breaks) in cells, unless the nuclide is incorporated into a medication that accumulates in the nucleus, or into DNA (this is never the case is clinical medicine, but it has been seen in experimental animal models). Iodine-125 is also commonly used by radiation oncologists in low dose rate brachytherapy in the treatment of cancer at sites other than the thyroid, especially in

prostate cancer Prostate cancer is cancer of the prostate. Prostate cancer is the second most common cancerous tumor worldwide and is the fifth leading cause of cancer-related mortality among men. The prostate is a gland in the male reproductive system that su ...

. When ¹²⁵I is used therapeutically, it is encapsulated in titanium seeds and implanted in the area of the tumor, where it remains. The low energy of the gamma spectrum in this case limits radiation damage to tissues far from the implanted capsule. Iodine-125, due to its suitable longer half-life and less penetrating gamma spectrum, is also often preferred for laboratory tests that rely on iodine as a tracer that is counted by a gamma counter, such as in radioimmunoassaying. I is used as the radiolabel in investigating which

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...

s go to which

plant pattern recognition receptor Pattern recognition receptors (PRRs) play a crucial role in the proper function of the innate immune system. PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. They are proteins expressed, mainly, by cells of ...

s (PRRs).

Iodine-124

Iodine-124 is a proton-rich isotope of iodine with a half-life of 4.18 days. Its modes of decay are: 74.4% electron capture, 25.6% positron emission. ¹²⁴I decays to ¹²⁴Te. Iodine-124 can be made by numerous nuclear reactions via a

cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: J ...

. The most common starting material used is ¹²⁴Te. Iodine-124 as the iodide salt can be used to directly image the thyroid using

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

(PET). Iodine-124 can also be used as a PET radiotracer with a usefully longer half-life compared with fluorine-18. In this use, the nuclide is chemically bonded to a pharmaceutical to form a positron-emitting radiopharmaceutical, and injected into the body, where again it is imaged by PET scan.

Iodine-129

Iodine-129 (¹²⁹I; half-life 15.7 million years) is a product of cosmic ray spallation on various isotopes of xenon in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

, in

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our ow ...

muon interaction with tellurium-130, and also uranium and

plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhib ...

fission, both in subsurface rocks and nuclear reactors. Artificial nuclear processes, in particular nuclear fuel reprocessing and atmospheric nuclear weapons tests, have now swamped the natural signal for this isotope. Nevertheless, it now serves as a groundwater tracer as indicator of nuclear waste dispersion into the natural environment. In a similar fashion, ¹²⁹I was used in rainwater studies to track fission products following the

Chernobyl disaster The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the No. 4 nuclear reactor, reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian Soviet Socialist Republic, Ukrainia ...

. In some ways, ¹²⁹I is similar to ³⁶Cl. It is a soluble halogen, exists mainly as a non-sorbing anion, and is produced by cosmogenic, thermonuclear, and in-situ reactions. In hydrologic studies, ¹²⁹I concentrations are usually reported as the ratio of ¹²⁹I to total I (which is virtually all ¹²⁷I). As is the case with ³⁶Cl/Cl, ¹²⁹I/I ratios in nature are quite small, 10⁻¹⁴ to 10⁻¹⁰ (peak thermonuclear ¹²⁹I/I during the 1960s and 1970s reached about 10⁻⁷). ¹²⁹I differs from ³⁶Cl in that its half-life is longer (15.7 vs. 0.301 million years), it is highly biophilic, and occurs in multiple ionic forms (commonly, I⁻ and IO₃⁻), which have different chemical behaviors. This makes it fairly easy for ¹²⁹I to enter the biosphere as it becomes incorporated into vegetation, soil, milk, animal tissue, etc. Excesses of stable ¹²⁹Xe in meteorites have been shown to result from decay of "primordial" iodine-129 produced newly by the supernovas that created the dust and gas from which the solar system formed. This isotope has long decayed and is thus referred to as "extinct". Historically, ¹²⁹I was the first extinct radionuclide to be identified as present in the early

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

. Its decay is the basis of the I-Xe iodine-xenon

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

scheme, which covers the first 85 million years of

evolution.

Iodine-131

Iodine-131 () is a beta-emitting isotope with a half-life of eight days, and comparatively energetic (190 keV average and 606 keV maximum energy) beta radiation, which penetrates 0.6 to 2.0 mm from the site of uptake. This beta radiation can be used for the destruction of thyroid nodules or hyperfunctioning thyroid tissue and for elimination of remaining thyroid tissue after surgery for the treatment of Graves' disease. The purpose of this therapy, which was first explored by Dr. Saul Hertz in 1941, is to destroy thyroid tissue that could not be removed surgically. In this procedure, ¹³¹I is administered either intravenously or orally following a diagnostic scan. This procedure may also be used, with higher doses of radio-iodine, to treat patients with

thyroid cancer Thyroid cancer is cancer that develops from the tissues of the thyroid gland. It is a disease in which cells grow abnormally and have the potential to spread to other parts of the body. Symptoms can include swelling or a lump in the neck. C ...

. The ¹³¹I is taken up into thyroid tissue and concentrated there. The beta particles emitted by the radioisotope destroys the associated thyroid tissue with little damage to surrounding tissues (more than 2.0 mm from the tissues absorbing the iodine). Due to similar destruction, ¹³¹I is the iodine radioisotope used in other water-soluble iodine-labeled radiopharmaceuticals (such as MIBG) used therapeutically to destroy tissues. The high energy beta radiation (up to 606 keV) from ¹³¹I causes it to be the most carcinogenic of the iodine isotopes. It is thought to cause the majority of excess thyroid cancers seen after nuclear fission contamination (such as bomb fallout or severe nuclear reactor accidents like the

) However, these epidemiological effects are seen primarily in children, and treatment of adults and children with therapeutic ¹³¹I, and epidemiology of adults exposed to low-dose ¹³¹I has not demonstrated carcinogenicity.

Iodine-135

Iodine-135 is an isotope of iodine with a half-life of 6.6 hours. It is an important isotope from the viewpoint of nuclear reactor physics. It is produced in relatively large amounts as a fission product, and decays to xenon-135, which is a nuclear poison with a very large thermal neutron cross section, which is a cause of multiple complications in the control of

s. The process of buildup of xenon-135 from accumulated iodine-135 can temporarily preclude a shut-down reactor from restarting. This is known as xenon poisoning or "falling into an iodine pit".

Iodine-128 and other isotopes

Iodine fission-produced isotopes not discussed above (iodine-128, iodine-130, iodine-132, and iodine-133) have half-lives of several hours or minutes, rendering them almost useless in other applicable areas. Those mentioned are neutron-rich and undergo beta decay to isotopes of xenon. Iodine-128 (half-life 25 minutes) can decay to either tellurium-128 by electron capture or to xenon-128 by beta decay. It has a specific radioactivity of .

Nonradioactive iodide (¹²⁷I) as protection from unwanted radioiodine uptake by the thyroid

Colloquially, radioactive materials can be described as "hot," and non-radioactive materials can be described as "cold." There are instances in which cold iodide is administered to people in order to prevent the uptake of hot iodide by the thyroid gland. For example, blockade of thyroid iodine uptake with potassium iodide is used in

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emit ...

scintigraphy and therapy with some radioiodinated compounds that are not targeted to the thyroid, such as iobenguane ( MIBG), which is used to image or treat neural tissue tumors, or iodinated fibrinogen, which is used in fibrinogen scans to investigate clotting. These compounds contain iodine, but not in the iodide form. However, since they may be ultimately metabolized or break down to radioactive iodide, it is common to administer non-radioactive potassium iodide to insure that metabolites of these radiopharmaceuticals is not sequestered by thyroid gland and inadvertently administer a radiological dose to that tissue. Potassium iodide has been distributed to populations exposed to

accidents such as the

. The iodide solution SSKI, a saturated solution of potassium (K) iodide in water, has been used to block absorption of the radioiodine (it has no effect on other radioisotopes from fission). Tablets containing potassium iodide are now also manufactured and stocked in central disaster sites by some governments for this purpose. In theory, many harmful late-cancer effects of nuclear fallout might be prevented in this way, since an excess of thyroid cancers, presumably due to radioiodine uptake, is the only proven radioisotope contamination effect after a fission accident, or from contamination by fallout from an atomic bomb (prompt radiation from the bomb also causes other cancers, such as leukemias, directly). Taking large amounts of iodide saturates thyroid receptors and prevents uptake of most radioactive

iodine-131 Iodine-131 (131I, I-131) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley. It has a radioactive decay half-life of about eight days. It is associated with nu ...

that may be present from fission product exposure (although it does not protect from other radioisotopes, nor from any other form of direct radiation). The protective effect of KI lasts approximately 24 hours, so must be dosed daily until a risk of significant exposure to radioiodines from fission products no longer exists. Iodine-131 (the most common radioiodine contaminant in fallout) also decays relatively rapidly with a half-life of eight days, so that 99.95% of the original radioiodine has vanished after three months.

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** **

External links

Iodine isotopes data from ''The Berkeley Laboratory Isotopes Project's''Iodine-128, Iodine-130, Iodine-132 data from 'Wolframalpha'
{{Authority control Iodine

Iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

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