2014年3月28日金曜日

Iodine-131

Iodine-131

From Wikipedia, the free encyclopedia
Iodine-131
General
Name, symbol Radioiodine,131I
Neutrons 78
Protons 53
Nuclide data
Half-life 8.0197 days
Isotope mass 130.9061246(12) u
Excess energy 971 keV
Iodine-131 (131I), also called radioiodine, is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. It is associated with nuclear energy, medical diagnostic and treatment procedures, and natural gas production. It also plays a major role as a radioactive isotope present in nuclear fission products, and was a significant contributor to the health hazards from open-air atomic bomb testing in the 1950s, and from the Chernobyl disaster, as well as being a large fraction of the contamination hazard in the first weeks in the Fukushima nuclear crisis. This is because I-131 is a major uranium, plutonium fission product, comprising nearly 3% of the total products of fission (by weight). See fission product yield for a comparison with other radioactive fission products. I-131 is also a major fission product of uranium-233, produced from thorium.
Due to its mode of beta decay, iodine-131 is notable for causing mutation and death in cells that it penetrates, and other cells up to several millimeters away. For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation. For example, children treated with moderate dose of I-131 for thyroid adenomas had a detectable increase in thyroid cancer, but children treated with a much higher dose did not. Likewise, most studies of very-high-dose I-131 for treatment of Graves disease have failed to find any increase in thyroid cancer, even though there is linear increase in thyroid cancer risk with I-131 absorption at moderate doses.[1] Thus, iodine-131 is increasingly less employed in small doses in medical use (especially in children), but increasingly is used only in large and maximal treatment doses, as a way of killing targeted tissues. This is known as "therapeutic use."
Iodine-131 can be "seen" by nuclear medicine imaging techniques (i.e., gamma cameras) whenever it is given for therapeutic use, since about 10% of its energy and radiation dose is via gamma radiation. However, since the other 90% of radiation (beta radiation) causes tissue damage without contributing to any ability to see or "image" the isotope, other less-damaging radioisotopes of iodine are preferred in situations when only nuclear imaging is required. The isotope I-131 is still occasionally used for purely diagnostic (i.e., imaging) work, due to its low expense compared to other iodine radioisotopes. Very small medical imaging doses of I-131 have not shown any increase in thyroid cancer. The low-cost availability of I-131, in turn, is due to the relative ease of creating I-131 by neutron bombardment of natural tellurium in a nuclear reactor, then separating I-131 out by various simple methods (i.e., heating to drive off the volatile iodine). By contrast, other iodine radioisotopes are usually created by far more expensive techniques, starting with reactor radiation of expensive capsules of pressurized xenon gas.
Iodine-131 is also one of the most commonly used gamma-emitting radioactive industrial tracer. Radioactive tracer isotopes are injected with hydraulic fracturing fluid to determine the injection profile and location of fractures created by hydraulic fracturing.[2]
Much smaller incidental doses of iodine-131 than those used in medical therapeutic procedures, are thought to be the major cause of increased thyroid cancers after accidental nuclear contamination.[3][4][5][6] These cancers happen from residual tissue radiation damage caused by the I-131, and usually appear years after exposure, long after the I-131 has decayed.[3]

Production

Most I-131 production is from nuclear reactor neutron-irradiation of a natural tellurium target. Irradiation of natural tellurium produces almost entirely I-131 as the only radionuclide with a half-life longer than hours, since most lighter isotopes of tellurium become heavier stable isotopes, or else stable iodine or xenon. However, the heaviest naturally-occurring tellurium nuclide, Te-130 (34% of natural Te) absorbs a neutron to become tellurium-131, which beta-decays with a half-life of 25 minutes, to I-131.
A tellurium compound can be irradiated while bound as an oxide to an ion exchange column, and evolved I-131 then eluted into an alkaline solution.[7] More commonly, powdered elemental tellurium is irradiated and then I-131 separated from it by dry distillation of the iodine, which has a far higher vapor pressure. The element is then dissolved in a mildly alkaline solution in the standard manner, to produce I-131 as iodide and hypoiodate (which is soon reduced to iodide).[8]
131I is a fission product with a yield of 2.878% from uranium-235,[9] and can be released in nuclear weapons tests and nuclear accidents. However, the short half-life means it is not present in significant quantities in cooled spent nuclear fuel, unlike iodine-129 whose half-life is nearly a billion times that of I-131.

Radioactive decay

Iodine-131 decay scheme (simplified)
I-131 decays with a half-life of 8.02 days with beta minus and gamma emissions. This nuclide of iodine has 78 neutrons in its nucleus, while the only stable nuclide, 127I, has 74. On decaying, 131I most often (89% of the time) expends its 971 keV of decay energy by transforming into the stable 131Xe (Xenon) in two steps, with gamma decay following rapidly after beta decay:
{^{131}_{53}\mathrm{I}} \rightarrow \beta + \bar{\nu_e} + {^{131}_{54}\mathrm{Xe}^*} + 606 keV
{^{131}_{54}\mathrm{Xe}^*} \rightarrow {^{131}_{54}\mathrm{Xe}} + \gamma + 364 keV
The primary emissions of 131I decay are thus electrons with a maximal energy of 606 keV (89% abundance, others 248–807 keV) and 364 keV gamma rays (81% abundance, others 723 keV).[10] Beta decay also produces an antineutrino, which carries off variable amounts of the beta decay energy. The electrons, due to their high mean energy (190 keV, with typical beta-decay spectra present) have a tissue penetration of 0.6 to 2 mm.[11]

Effects of exposure

Per capita thyroid doses in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951-1962. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that nuclear fallout might have led to approximately 11,000 excess deaths, most caused by thyroid cancer linked to exposure to iodine-131.[12]
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 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 cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis.[1]
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.[1]
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 the face and chest and lowering the relative proportion of radioactive iodine. However, such supplements were not distributed to the population living nearest to the Chernobyl nuclear power plant after the disaster,[13] though they were widely distributed to children in Poland.
Within the USA, the highest 131I fallout doses occurred during the 1950s and early 1960s to children having consumed fresh sources of milk contaminated as the result of above-ground testing of nuclear weapons.[3] The National Cancer Institute provides additional information on the health effects from exposure to 131I in fallout,[14] as well as individualized estimates, for those born before 1971, for each of the 3070 counties in the USA. The calculations are taken from data collected regarding fallout from the nuclear weapons tests conducted at the Nevada Test Site.[15]
On 27 March 2011, the Massachusetts Department of Public Health reported that 131I was detected in very low concentrations in rainwater from samples collected in Massachusetts, USA, and that this likely originated from the Fukushima power plant.[16] Farmers near the plant dumped raw milk, while testing in the United States found 0.8 pico-curies per liter of iodine-131 in a milk sample, but the radiation levels were 5,000 times lower than the FDA's "defined intervention level." The levels were expected to drop relatively quickly[17]

Treatment and prevention

See also: Potassium iodide
A common treatment method for preventing iodine-131 exposure is by saturating the thyroid with regular, non-radioactive iodine-127, as an iodide or iodate salt. Free elemental iodine should not be used for saturating the thyroid because it is a corrosive oxidant and therefore is toxic to ingest in the necessary quantities[citation needed]. The thyroid will absorb very little of the radioactive iodine-131 after it is saturated with non-radioactive iodide, thereby avoiding the damage caused by radiation from radioiodine. The most common method of treatment is to give potassium iodide to those at risk. The dosage for adults is 130 mg potassium iodide per day, given in one dose, or divided into portions of 65 mg twice a day. This is equivalent to 100 mg of iodide, and is about 7000 times bigger than the nutritional dose of iodide, which is 0.015 mg per day (150 micrograms per day). See potassium iodide for more information on prevention of radioiodine absorption by the thyroid during nuclear accident, or for nuclear medical reasons. The FDA-approved dosing of potassium iodide for this purpose are as follows: infants less than 1 month old, 16 mg; children 1 month to 3 years, 32 mg; children 3 years to 18 years, 65 mg; adults 130 mg.[18] However, some sources recommend alternative dosing regimens.[19]
The World Health Organizations daily recommended Dosage for Radiological Emergencies involving radioactive iodine[20]
Age KI in mg KIO3 in mg
Over 12 years old 130 170
3 – 12 years old 65 85
1 – 36 months old 32 42
< 1 month old 16 21
The ingestion of prophylaxis iodide & iodate is not without its dangers, There is reason for caution about taking potassium iodide or iodine supplements, as their unnecessary use can cause conditions such as the Jod-Basedow phenomena, and the Wolff-Chaikoff effect, trigger and/or worsen hyperthyroidism and hypothyroidism respectively, and ultimately cause temporary or even permanent thyroid conditions. It can also cause sialadenitis (an inflammation of the salivary gland), gastrointestinal disturbances, allergic reactions and rashes. Potassium iodide is also not recommended for those who have had an allergic reaction to iodine, and people with dermatitis herpetiformis and hypocomplementemic vasculitis, conditions that are linked to a risk of iodine sensitivity.[21]
The use of a particular 'Iodine tablet' used in portable water purification has also been determined as somewhat effective at reducing radioiodine uptake. In a small study on human subjects, who for each of their 90 day trial, ingested four 20 milligram tetraglycine hydroperiodide(TGHP) water tablets, with each tablet releasing 8 milligrams (ppm) of free titratable iodine;[22] it was found that the biological uptake of radioactive iodine in these human subjects dropped to, and remained at, a value of less than 2% the radioiodine uptake rate of that observed in control subjects who went fully exposed to radioiodine without treatment.[23]
The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, (whether it be the nutritional non-radioactive iodine-127 or radioactive iodine, radioiodine - most commonly iodine-131, as the body cannot discern between different iodine isotopes). Perchlorate ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodine uptake and thus is classified as a goitrogen. Perchlorate ions are a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate begins to temporarily inhibit the thyroid gland’s ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen).[24] The reduction of the iodide pool by perchlorate has dual effects—reduction of excess hormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.[25]
Treatment of thyrotoxicosis (including Graves' disease) with 600-2,000 mg potassium perchlorate (430-1,400 mg perchlorate) daily for periods of several months or longer was once common practice, particularly in Europe,[24][26] and perchlorate use at lower doses to treat thryoid problems continues to this day.[27] Although 400 mg of potassium perchlorate divided into four or five daily doses was used initially and found effective, higher doses were introduced when 400 mg/day was discovered not to control thyrotoxicosis in all subjects.[24][25]
Current regimens for treatment of thyrotoxicosis (including Graves' disease), when a patient is exposed to additional sources of iodine, commonly include 500 mg potassium perchlorate twice per day for 18–40 days.[24][28]
Prophylaxis with perchlorate containing water at concentrations of 17 ppm, which corresponds to 0.5 mg/kg-day personal intake, if one is 70 kg and consumes two litres of water per day, was found to reduce baseline radioiodine uptake by 67%[24] This is equivalent to ingesting a total of just 35 mg of perchlorate ions per day. In another related study were subjects drank just 1 litre of perchlorate containing water per day at a concentration of 10 ppm, i.e. daily 10 mg of perchlorate ions were ingested, an average 38% reduction in the uptake of iodine was observed.[29]
However when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0.5 mg/kg-day, as in the above paragraph, a 67% reduction of iodine uptake would be expected. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine.[30] this may well be attributable to sufficient daily exposure or intake of healthy iodine-127 among the workers and the short 8 hr biological half life of perchlorate in the body.[24]
To completely block the uptake of iodine-131 by the purposeful addition of perchlorate ions to a populaces water supply, aiming at dosages of 0.5 mg/kg-day, or a water concentration of 17 ppm, would therefore be grossly inadequate at truly reducing radioiodine uptake. Perchlorate ion concentrations in a regions water supply, would therefore need to be much higher, with at least a total dosage of 7.15 mg/kg of body weight per day needing to be aimed for, with this being achievable for most adults by consuming 2 liters of water per day with a water concentration of 250 mg/kg of water or 250 ppm of perchlorate ions per liter, only at this level would perchlorate consumption offer adequate protection, and be truly beneficial to the population at preventing bioaccumulation when exposed to a radioiodine environment.[24][28] This being entirely independent of the availability of iodate or iodide drugs.
The continual addition of perchlorate to the water supply would need to continue for no less than 80–90 days, beginning immediately after the initial release of radioiodine was detected, after 80–90 days had passed released radioactive iodine-131 would have decayed to less than 0.1% of its initial quantity and thus the danger from biouptake of iodine-131 is essentially over.[31]
In the event of a radioiodine release the ingestion of prophylaxis potassium iodide or iodate, if available, would rightly take precedence over perchlorate administration and would be the first line of defense in protecting the population from a radioiodine release. However in the event of a radioiodine release too massive and widespread to be controlled by the limited stock of iodide & iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.
The ingestion of goitrogen drugs is, much like potassium iodide is also not without its dangers, such as hypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions were radioiodine has sufficiently contaminatated the environment.

Medical and pharmaceutical uses

A pheochromocytoma tumor is seen as a dark sphere in the center of the body (it is in the left adrenal gland). The image is by MIBG scintigraphy, showing the tumor by radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. The image of the thyroid in the neck is due to unwanted uptake of radioiodine (as iodide) by the thyroid, after breakdown of the radioactive iodine-containing medication. Accumulation at the sides of the head is from salivary gland due to uptake of I-131 mIBG by the sympathetic neuronal elements in the salivary glands.Meta-[I-131]iodobenzylguanidine is a radio-labeled analog of the adrenergic blocking agent guanethidine.Radioactivity is also seen from uptake by the liver, and excretion by the kidneys with accumulation in the bladder.
It is used in nuclear medicine therapeutically and can also be seen with diagnostic scanners if it has been used therapeutically. Use of the 131I as iodide salt exploits the mechanism of absorption of iodine by the normal cells of the thyroid gland. Examples of its use in radiation therapy are those where tissue destruction is desired after iodine uptake by the tissue.
Major uses of 131I include the treatment of thyrotoxicosis (hyperthyroidism) and some types of thyroid cancer that absorb iodine. The 131I is thus used as direct radioisotope therapy to treat hyperthyroidism due to Graves' disease, and sometimes hyperactive thyroid nodules (abnormally active thyroid tissue that is not malignant). The therapeutic use of radioiodine to treat hyperthyroidism from Graves' disease was first reported by Saul Hertz in 1941.
The 131I isotope is also used as a radioactive label for certain radiopharmaceuticals that can be used for therapy, e.g. 131I-metaiodobenzylguanidine (131I-MIBG) for imaging and treating pheochromocytoma and neuroblastoma. In all of these therapeutic uses, 131I destroys tissue by short-range beta radiation. About 90% of its radiation damage to tissue is via beta radiation, and the rest occurs via its gamma radiation (at a longer distance from the radioisotope). It can be seen in diagnostic scans after its use as therapy, because 131I is also a gamma-emitter.
Because of the carcinogenicity of its beta radiation in the thyroid in small doses, I-131 is rarely used primarily or solely for diagnosis (although in the past this was more common due to this isotope's relative ease of production and low expense). Instead the more purely gamma-emitting radioiodine iodine-123 is used in diagnostic testing (nuclear medicine scan of the thyroid). The longer half-lived iodine-125 is also occasionally used when a longer half-life radioiodine is needed for diagnosis, and, in brachytherapy treatment (isotope confined in small seed-like metal capsules), where the low-energy gamma radiation without a beta component, makes iodine-125 useful. The other radioisotopes of iodine are never used in brachytherapy.
The use of 131I as a medical isotope has been blamed for a routine shipment of biosolids being rejected from crossing the Canada—U.S. border.[32] Such material can enter the sewers directly from the medical facilities, or by being excreted by patients after a treatment.

Administration of therapeutic I-131

Because the total radioactivity of a dose of I-131 is usually high, and because the local beta radiation of nearby stomach tissue from an undissolved capsule is high, I-131 is usually administered to human patients in a small drink containing a few ounces of fluid. This is often slowly and carefully sucked out of a shielded container to prevent spillage.[33] For administration to animals (for example, cats with hyperthyroidism) for practical reasons the isotope must be administered by injection.

Post-treatment isolation

Patients receiving I-131 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 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."[34] These guidelines vary from hospital to hospital and will depend also on the dose of radiation given. Some also advise not to hug or hold children when the radiation is still high, and a one or two metre distance to others may be recommended.[35]
I-131 will be eliminated from the body over the next several weeks after it is given. The majority of I-131 will be eliminated from the human body in 3–5 days, through natural decay, and through excretion in sweat and urine. Smaller amounts will continue to be released over the next several weeks, as the body processes thyroid hormones created with the I-131. For this reason, it is advised to regularly clean toilets, sinks, bed sheets and clothing used by the person who received the treatment. Patients may also be advised to wear slippers or socks at all times, and themselves physically isolated from others. This minimizes accidental exposure by family members, especially children.[36] Use of a decontaminant specially made for radioactive iodine removal may be advised. The use of chlorine bleach solutions, or cleaners that contain chlorine bleach for cleanup, are not advised, since radioactive elemental iodine gas may be released.[37] Airborne I-131 may cause a greater risk of second-hand exposure, spreading contamination over a wide area.
Many airports now have radiation detectors to detect the smuggling of radioactive materials that may be used in nuclear weapons manufacture. Patients should be warned that if they travel by air, they may trigger radiation detectors at airports up to 95 days after their treatment with 131I.[38]

Industrial radioactive tracer uses

Used for the first time in 1951 to localize leaks in a drinking water supply system of Munich, Germany, iodine-131 became one of the most commonly used gamma-emitting industrial radioactive tracer with applications in isotope hydrology and leak detection.[39][40][41][42]
Since late 1940s, radioactive tracers have been used by the oil industry. Tagged at the surface, water is then tracked downhole, using the appropriated gamma detector, to determine flows and detect underground leaks. I-131 has been the most widely used tagging isotope in an aqueous solution of sodium iodine.[2][43][44] It is used to characterize the hydraulic fracturing fluid to help determine the injection profile and location of fractures created by hydraulic fracturing.[45][46][47]

See also

References

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  2. Reis, John C. (1976). "Radioactive materials". Environmental Control in Petroleum Engineering. Gulf Professional Publishers. p. 55. ISBN 978-0-88415-273-6.
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  19. https://www.eanm.org/scientific_info/guidelines/gl_paed_mibg.pdf?PHPSESSID=46d05b62d235c36a12166bf939b656c7
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48. The Journal of Nuclear Medicine, Salivary gland uptake of Meta-[I131]Iodobenzylguanidine by M. Nakajo, B. Shapiro, J.C. Sisson, D.P. Swanson, and W.H. Beierwaltes University of Michigan, Ann Arbor, Michigan. J Nucl Med 25:2-6, 1984

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Radionuclide

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A radionuclide, or a radioactive nuclide, is an atom with an unstable nucleus, characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or via internal conversion. During this process, the radionuclide is said to undergo radioactive decay, resulting in the emission of gamma ray(s) and/or subatomic particles such as alpha or beta particles.[1] These emissions constitute ionizing radiation. Radionuclides occur naturally, or can be produced artificially.
Radionuclides are often referred to by chemists and physicists as radioactive isotopes or radioisotopes. Radioisotopes with suitable half-lives play an important part in a number of technologies (for example, nuclear medicine). Radionuclides can also present both real and perceived dangers to health.
The number of radionuclides is uncertain because the number of very short-lived radionuclides that have yet to be characterized is extremely large and potentially unquantifiable. Even the number of long-lived radionuclides is uncertain (to a lesser degree), because many "stable" nuclides are calculated to have half-lives so long that their decay has not been experimentally measured. The total list of nuclides contains 90 nuclides that are, in theory, stable, and 254 total stable nuclides that have not been observed to decay. In addition, however, there exist 34 primordial radionuclides that exist from the creation of the solar system, plus another 50 radionuclides detectable in nature as daughters of these, plus a few produced by cosmic radiation. Including artificial radionuclides, about 650 radionuclides that have been experimentally observed to decay, with half-lives longer than 60 minutes (see list of nuclides for this list). Of all these, less than a hundred natural radionuclides are known (they have been observed on Earth, but not as a consequence of human activity).
Including artificially produced nuclides, more than 3300 nuclides are known (including ~3000 radionuclides), many of which (> ~2400) with decay half-lives shorter than 60 minutes. This list expands as new radionuclides with very short half-lives are characterized.
All elements form a number of radionuclides, although the half-lives of many are too short for them to be observed in nature. Even the lightest element, hydrogen, has a well-known radioisotope, tritium. The heaviest elements (heavier than bismuth) exist only as radionuclides. For every chemical element, many radioisotopes that do not occur in nature (due to short half lives or the lack of an ongoing natural production mechanism), have been produced artificially.

Origin

Naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides. Primordial radionuclides, such as uranium and thorium, originate mainly from the interiors of stars and are still present as their half-lives are so long they have not yet completely decayed. Secondary radionuclides are radiogenic isotopes derived from the decay of primordial radionuclides. They have shorter half-lives than primordial radionuclides. Cosmogenic isotopes, such as carbon-14, are present because they are continually being formed in the atmosphere due to cosmic rays.[2]
Artificially produced radionuclides can be produced by nuclear reactors, particle accelerators or by radionuclide generators:
  • Radioisotopes produced with nuclear reactors exploit the high flux of neutrons present. These neutrons activate elements placed within the reactor. A typical product from a nuclear reactor is thallium-201 and iridium-192. The elements that have a large propensity to take up the neutrons in the reactor are said to have a high neutron cross-section.
  • Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons accelerate protons at a target to produce positron-emitting radionuclides, e.g., fluorine-18.
  • Radionuclide generators contain a parent radionuclide that decays to produce a radioactive daughter. The parent is usually produced in a nuclear reactor. A typical example is the technetium-99m generator used in nuclear medicine. The parent produced in the reactor is molybdenum-99.
  • Radionuclides are produced as an unavoidable side-effect of nuclear and thermonuclear explosions.
Trace radionuclides are those that occur in tiny amounts in nature either due to inherent rarity or due to half-lives that are significantly shorter than the age of the Earth. Synthetic isotopes are inherently not naturally occurring on Earth, but can be created by nuclear reactions.

Uses

Radionuclides are used in two major ways: for their chemical properties and as sources of radiation. Radionuclides of familiar elements such as carbon can serve as radioactive tracers because they are chemically very similar to the nonradioactive nuclides, so most chemical, biological, and ecological processes treat them in a nearly identical way. One can then examine the result with a radiation detector, such as a Geiger counter, to determine where the provided atoms ended up. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive.
In nuclear medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays or positrons can provide diagnostic information about a person's internal anatomy and the functioning of specific organs. This is used in some forms of tomography: single-photon emission computed tomography and positron emission tomography scanning and Cerenkov luminescence imaging.
Radioisotopes are also a method of treatment in hemopoietic forms of tumors; the success for treatment of solid tumors has been limited. More powerful gamma sources sterilise syringes and other medical equipment.
In biochemistry and genetics, radionuclides label molecules and allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport.
In food preservation, radiation is used to stop the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables.
In industry, and in mining, radionuclides examine welds, to detect leaks, to study the rate of wear, erosion and corrosion of metals, and for on-stream analysis of a wide range of minerals and fuels.
Radionuclides are also used to trace and analyze pollutants, to study the movement of surface water, and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers. Natural radionuclides are used in geology, archaeology, and paleontology to measure ages of rocks, minerals, and fossil materials.

Common examples

Americium-241

Americium-241 container in a smoke detector.
Americium-241 capsule as found in smoke detector. The circle of darker metal in the center is americium-241, the surrounding casing is aluminium.
Most household smoke detectors contain americium produced in nuclear reactors. The radioisotope used is americium-241. The element americium is created by bombarding plutonium with neutrons in a nuclear reactor. Its isotope, Am-241 decays by emitting alpha particles and gamma radiation to become neptunium-237. Most common household smoke detectors use a very small quantity of Am-241 (about 0.29 micrograms per smoke detector) in the form of americium dioxide. Smoke detectors use Am-241 since the alpha particles it emits collide with oxygen and nitrogen particles in the air. This occurs in the detector's ionization chamber where it produces charged particles or ions. Then, these charged particles are collected by a small electric voltage that will create an electric current that will pass between two electrodes. Then, the ions that are flowing between the electrodes will be neutralized when coming in contact with smoke, thereby decreasing the electric current between the electrodes, which will activate the detector's alarm.[3][4]

Steps for creating americium-241

The plutonium-241 is formed in any nuclear reactor by neutron capture from uranium-238.
  1. 238U + n → 239U
  2. 239U → 239Np + e− + ν
    e
  3. 239Np → 239Pu + e− + ν
    e
  4. 239Pu + n → 240Pu
  5. 240Pu + n → 241Pu
This will decay both in the reactor and subsequently to form Am-241, which has a half-life of 432.2 years.[5][6]

Gadolinium-153

The Gd-153 isotope is used in X-ray fluorescence and osteoporosis screening. It is a gamma-emitter with an 8-month half-life, making it easier to use for medical purposes. In nuclear medicine, it serves to calibrate the equipment needed like single-photon emission computed tomography systems (SPECT) to make x-rays. It ensures that the machines work correctly to produce images of radioisotope distribution inside the patient. This isotope is produced in a nuclear reactor from europium or enriched gadolinium.[7] It can also detect the loss of calcium in the hip and back bones, allowing the ability to diagnose osteoporosis.[8]

Dangers

Radionuclides that find their way into the environment may cause harmful effects as radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways exposed to living beings, by radiation poisoning. Potential health damage from exposure to radionuclides depends on a number of factors, and "can damage the functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not show up until years, or even decades, after exposure."[9]

Summary table for classes of nuclides, "stable" and radioactive

Following is a summary table for the total list of nuclides with half-lives greater than one hour. Ninety of these 905 nuclides are theoretically stable, except to proton-decay (which has never been observed). About 254 nuclides have never been observed to decay, and are classically considered stable.
The remaining 650 radionuclides have half-lives longer than 1 hour, and are well-characterized (see list of nuclides for a complete tabulation). They include 28 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years[10]), and another 6 nuclides with half-lives long enough (> 80 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the solar system, about 4.6 billion years ago. Another ~51 short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.
Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.
This is a summary table [11] for the 905 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.
Stability class Number of nuclides Running total Notes on running total
Theoretically stable to all but proton decay 90 90 Includes first 40 elements. Proton decay yet to be observed.
Energetically unstable to one or more known decay modes, but no decay yet seen. Spontaneous fission possible for "stable" nuclides > niobium-93; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected. 164 254 Total of classically stable nuclides.
Radioactive primordial nuclides. 34 288 Total primordial elements include uranium, thorium, bismuth, rubidium-87, potassium-40 plus all stable nuclides.
Radioactive nonprimordial, but naturally occurring on Earth. ~ 51 ~ 339 Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc.
Radioactive synthetic (half-life > 1.0 hour). Includes most useful radiotracers. 556 905 These 905 nuclides are listed in the article List of nuclides.
Radioactive synthetic (half-life < 1.0 hour). >2400 >3300 Includes all well-characterized synthetic nuclides.

List of commercially available radionuclides

This list covers common isotopes, most of which are available in very small quantities to the general public in most countries. Others that are not publicly accessible are traded commercially in industrial, medical, and scientific fields and are subject to government regulation. For a complete list of all known isotopes for every element (minus activity data), see list of nuclides, and Isotope Lists. For a table see Table of Nuclides.

Gamma emission only

Isotope Activity Half-life Energies (keV)
Barium-133 9694 TBq/kg (262 Ci/g) 10.7 years 81.0, 356.0
Cadmium-109 96200 TBq/kg (2600 Ci/g) 453 days 88.0
Cobalt-57 312280 TBq/kg (8440 Ci/g) 270 days 122.1
Cobalt-60 40700 TBq/kg (1100 Ci/g) 5.27 years 1173.2, 1332.5
Europium-152 6660 TBq/kg (180 Ci/g) 13.5 years 121.8, 344.3, 1408.0
Manganese-54 287120 TBq/kg (7760 Ci/g) 312 days 834.8
Sodium-22 237540 Tbq/kg (6240 Ci/g) 2.6 years 511.0, 1274.5
Zinc-65 304510 TBq/kg (8230 Ci/g) 244 days 511.0, 1115.5
Technetium-99m 1.95×104 TBq/g (5.27 × 107 Ci/g) 6 hours 140

Beta emission only

Isotope Activity Half-life Energies (keV)
Strontium-90 5180 TBq/kg (140 Ci/g) 28.5 years 546.0
Thallium-204 17057 TBq/kg (461 Ci/g) 3.78 years 763.4
Carbon-14 166.5 TBq/kg (4.5 Ci/g) 5730 years 49.5 (average)
Tritium (Hydrogen-3) 357050 TBq/kg (9650 Ci/g) 12.32 years 5.7 (average)

Alpha emission only

Isotope Activity Half-life Energies (keV)
Polonium-210 166500 TBq/kg (4500 Ci/g) 138 days 5304.5
Uranium-238 12580 KBq/kg (0.00000034 Ci/g) 4.468 billion years 4267

Multiple radiation emitters

Isotope Activity Half-life Radiation types Energies (keV)
Caesium-137 3256 TBq/kg (88 Ci/g) 30.1 years Gamma & beta G: 32, 661.6 B: 511.6, 1173.2
Americium-241 129.5 TBq/kg (3.5 Ci/g) 432.2 years Gamma & alpha G: 59.5, 26.3, 13.9 A: 5485, 5443

Bioremediation

Lichens can accumulate radionuclides to a high level.[12]

See also

Notes

  1. R.H. Petrucci, W.S. Harwood and F.G. Herring, General Chemistry (8th ed., Prentice-Hall 2002), p.1025-26
  2. Eisenbud, Merril; Gesell, Thomas F (1997-02-25). Environmental Radioactivity: From Natural, Industrial, and Military Sources. p. 134. ISBN 9780122351549.
  3. Smoke Detectors and Americium
  4. Office of Radiation Protection – Am 241 Fact Sheet – Washington State Department of Health
  5. "Smoke Detectors: Uses of Radioactive Isotopes". Chemistry Tutorial : Radioisotopes in Smoke Detectors. AUS-e-TUTE n.d. Retrieved March 30, 2011.
  6. Reaction in a Smoke Detector
  7. PNNL: Isotope Sciences Program – Gadolinium-153
  8. "Gadolinium". BCIT Chemistry Resource Center. British Columbia Institute of Technology. Retrieved 30 March 2011.
  9. . World Health Organization http://www.who.int/mediacentre/factsheets/fs371/en/. Retrieved January 27, 2014. Missing or empty |title= (help)
  10. "Cosmic Detectives". The European Space Agency (ESA). 2013-04-02. Retrieved 2013-04-15.
  11. Table data is derived by counting members of the list; see WP:CALC. References for the list data itself are given below in the reference section in list of nuclides
  12. Gadd, G. M. (2009). "Metals, minerals and microbes: Geomicrobiology and bioremediation". Microbiology 156 (3): 609. doi:10.1099/mic.0.037143-0.

References

External links


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