Technetium is a chemical element with symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive; none are stable, excluding the fully ionized state of 97Tc. Nearly all technetium is produced synthetically, and only about 18,000 tons can be found at any given time in the Earth's crust. Naturally occurring technetium is a spontaneous fission product in uranium ore and thorium ore, the most common source, or the product of neutron capture in molybdenum ores. This silvery gray, crystalline transition metal lies between rhenium and manganese in group 7 of the periodic table, and its chemical properties are intermediate between those of these two adjacent elements. The most common naturally occurring isotope is 99Tc.
Many of technetium's properties were predicted by Dmitri Mendeleev before the element was discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937, technetium (specifically the technetium-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek τεχνητός, meaning "synthetic or artificial", + -ium).
One short-lived gamma ray-emitting nuclear isomer of technetium—technetium-99m—is used in nuclear medicine for a wide variety of diagnostic tests, such as bone cancer diagnoses. The ground state of this nuclide, technetium-99, is used as a gamma-ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of the fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. Because no isotope of technetium has a half-life longer than 4.21 million years (technetium-97), the 1952 detection of technetium in red giants helped to prove that stars can produce heavier elements.
|Appearance||shiny gray metal|
|Mass number||97 (most stable isotope)|
|Technetium in the periodic table|
|Atomic number (Z)||43|
|Element category||transition metal|
|Electron configuration||[Kr] 4d5 5s2|
Electrons per shell
|2, 8, 18, 13, 2|
|Phase at STP||solid|
|Melting point||2430 K (2157 °C, 3915 °F)|
|Boiling point||4538 K (4265 °C, 7709 °F)|
|Density (near r.t.)||11 g/cm3|
|Heat of fusion||33.29 kJ/mol|
|Heat of vaporization||585.2 kJ/mol|
|Molar heat capacity||24.27 J/(mol·K)|
|Vapor pressure (extrapolated)|
|Oxidation states||−3, +1, +2, +3, +4, +5, +6, +7 (a strongly acidic oxide)|
|Electronegativity||Pauling scale: 1.9|
|Atomic radius||empirical: 136 pm|
|Covalent radius||147±7 pm|
Spectral lines of technetium
|Natural occurrence||from decay|
|Crystal structure|| hexagonal close-packed (hcp)|
|Speed of sound thin rod||16,200 m/s (at 20 °C)|
|Thermal expansion||7.1 µm/(m·K) (at r.t.)|
|Thermal conductivity||50.6 W/(m·K)|
|Electrical resistivity||200 nΩ·m (at 20 °C)|
|Magnetic susceptibility||+270.0·10−6 cm3/mol (298 K)|
|Prediction||Dmitri Mendeleev (1871)|
|Discovery and first isolation||Emilio Segrè and Carlo Perrier (1937)|
|Main isotopes of technetium|
From the 1860s through 1871, early forms of the periodic table proposed by Dmitri Mendeleev contained a gap between molybdenum (element 42) and ruthenium (element 44). In 1871, Mendeleev predicted this missing element would occupy the empty place below manganese and have similar chemical properties. Mendeleev gave it the provisional name ekamanganese (from eka-, the Sanskrit word for one) because the predicted element was one place down from the known element manganese.
Many early researchers, both before and after the periodic table was published, were eager to be the first to discover and name the missing element. Its location in the table suggested that it should be easier to find than other undiscovered elements.
|Year||Claimant||Suggested name||Actual material|
|1846||R. Hermann||Ilmenium||Niobium-tantalum alloy|
|1847||Heinrich Rose||Pelopium||Niobium-tantalum alloy|
|1877||Serge Kern||Davyum||Iridium-rhodium-iron alloy|
|1908||Masataka Ogawa||Nipponium||Rhenium, which was the then unknown dvi-manganese|
German chemists Walter Noddack, Otto Berg, and Ida Tacke reported the discovery of element 75 and element 43 in 1925, and named element 43 masurium (after Masuria in eastern Prussia, now in Poland, the region where Walter Noddack's family originated). The group bombarded columbite with a beam of electrons and deduced element 43 was present by examining X-ray emission spectrograms. The wavelength of the X-rays produced is related to the atomic number by a formula derived by Henry Moseley in 1913. The team claimed to detect a faint X-ray signal at a wavelength produced by element 43. Later experimenters could not replicate the discovery, and it was dismissed as an error for many years. Still, in 1933, a series of articles on the discovery of elements quoted the name masurium for element 43.[note 1] Whether the 1925 team actually did discover element 43 is still debated.
The discovery of element 43 was finally confirmed in a 1937 experiment at the University of Palermo in Sicily by Carlo Perrier and Emilio Segrè. In mid-1936, Segrè visited the United States, first Columbia University in New York and then the Lawrence Berkeley National Laboratory in California. He persuaded cyclotron inventor Ernest Lawrence to let him take back some discarded cyclotron parts that had become radioactive. Lawrence mailed him a molybdenum foil that had been part of the deflector in the cyclotron.
Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the molybdenum activity was indeed from an element with the atomic number 43. In 1937 they succeeded in isolating the isotopes technetium-95m and technetium-97. University of Palermo officials wanted them to name their discovery "panormium", after the Latin name for Palermo, Panormus. In 1947 element 43 was named after the Greek word τεχνητός, meaning "artificial", since it was the first element to be artificially produced. Segrè returned to Berkeley and met Glenn T. Seaborg. They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually.
In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium (specifically wavelengths of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants. The stars were near the end of their lives, yet were rich in this short-lived element, indicating that it was being produced in the stars by nuclear reactions. This evidence bolstered the hypothesis that heavier elements are the product of nucleosynthesis in stars. More recently, such observations provided evidence that elements are formed by neutron capture in the s-process.
Since that discovery, there have been many searches in terrestrial materials for natural sources of technetium. In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in extremely small quantities (about 0.2 ng/kg); there it originates as a spontaneous fission product of uranium-238. The Oklo natural nuclear fission reactor contains evidence that significant amounts of technetium-99 were produced and have since decayed into ruthenium-99.
Technetium is a silvery-gray radioactive metal with an appearance similar to platinum, commonly obtained as a gray powder. The crystal structure of the pure metal is hexagonal close-packed. Atomic technetium has characteristic emission lines at these wavelengths of light: 363.3 nm, 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm.
The metal form is slightly paramagnetic, meaning its magnetic dipoles align with external magnetic fields, but will assume random orientations once the field is removed. Pure, metallic, single-crystal technetium becomes a type-II superconductor at temperatures below 7.46 K.[note 2] Below this temperature, technetium has a very high magnetic penetration depth, greater than any other element except niobium.
Technetium is located in the seventh group of the periodic table, between rhenium and manganese. As predicted by the periodic law, its chemical properties are between those two elements. Of the two, technetium more closely resembles rhenium, particularly in its chemical inertness and tendency to form covalent bonds. Unlike manganese, technetium does not readily form cations (ions with a net positive charge). Technetium exhibits nine oxidation states from −1 to +7, with +4, +5, and +7 being the most common. Technetium dissolves in aqua regia, nitric acid, and concentrated sulfuric acid, but it is not soluble in hydrochloric acid of any concentration.
Technetium can catalyse the destruction of hydrazine by nitric acid, and this property is due to its multiplicity of valencies. This caused a problem in the separation of plutonium from uranium in nuclear fuel processing, where hydrazine is used as a protective reductant to keep plutonium in the trivalent rather than the more stable tetravalent state. The problem was exacerbated by the mutually-enhanced solvent extraction of technetium and zirconium at the previous stage, and required a process modification.
Related to pertechnetate is heptoxide. This pale-yellow, volatile solid is produced by oxidation of Tc metal and related precursors:
Technetium forms a dioxide, disulfide, diselenide, and ditelluride. An ill-defined Tc2S7 forms upon treating pertechnate with hydrogen sulfide. It thermally decomposes into disulfide and elemental sulfur. Similarly the dioxide can be produced by reduction of the Tc2O7.
The following binary (containing only two elements) technetium halides are known: TcF6, TcF5, TcCl4, TcBr4, TcBr3, α-TcCl3, β-TcCl3, TcI3, α-TcCl2, and β-TcCl2. The oxidation states range from Tc(VI) to Tc(II). Technetium halides exhibit different structure types, such as molecular octahedral complexes, extended chains, layered sheets, and metal clusters arranged in a three-dimensional network. These compounds are produced by combining the metal and halogen or by less direct reactions.
TcCl4 is obtained by chlorination of Tc metal or Tc2O7 Upon heating, TcCl4 gives the corresponding Tc(III) and Tc(II) chlorides.
Two polymorphs of technetium trichloride exist, α- and β-TcCl3. The α polymorph is also denoted as Tc3Cl9. It adopts a confacial bioctahedral structure. It is prepared by treating the chloro-acetate Tc2(O2CCH3)4Cl2 with HCl. Like Re3Cl9, the structure of the α-polymorph consists of triangles with short M-M distances. β-TcCl3 features octahedral Tc centers, which are organized in pairs, as seen also for molybdenum trichloride. TcBr3 does not adopt the structure of either trichloride phase. Instead it has the structure of molybdenum tribromide, consisting of chains of confacial octahedra with alternating short and long Tc—Tc contacts. TcI3 has the same structure as the high temperature phase of TiI3, featuring chains of confacial octahedra with equal Tc—Tc contacts.
Several anionic technetium halides are known. The binary tetrahalides can be converted to the hexahalides [TcX6]2− (X = F, Cl, Br, I), which adopt octahedral molecular geometry. More reduced halides form anionic clusters with Tc–Tc bonds. The situation is similar for the related elements of Mo, W, Re. These clusters have the nuclearity Tc4, Tc6, Tc8, and Tc13. The more stable Tc6 and Tc8 clusters have prism shapes where vertical pairs of Tc atoms are connected by triple bonds and the planar atoms by single bonds. Every technetium atom makes six bonds, and the remaining valence electrons can be saturated by one axial and two bridging ligand halogen atoms such as chlorine or bromine.
Technetium forms a variety of compounds with Tc–C bonds, i.e. organotechnetium complexes. Prominent members of this class are complexes with CO, arene, and cyclopentadienyl ligands. The binary carbonyl Tc2(CO)10 is a white volatile solid. In this molecule, two technetium atoms are bound to each other; each atom is surrounded by octahedra of five carbonyl ligands. The bond length between technetium atoms, 303 pm, is significantly larger than the distance between two atoms in metallic technetium (272 pm). Similar carbonyls are formed by technetium's congeners, manganese and rhenium. Interest in organotechnetium compounds has also been motivated by applications in nuclear medicine. Unusual for other metal carbonyls, Tc forms aquo-carbonyl complexes, prominent being [Tc(CO)3(H2O)3]+.
Technetium, with atomic number (denoted Z) 43, is the lowest-numbered element in the periodic table for which all isotopes are radioactive. The second-lightest exclusively radioactive element, promethium, has an atomic number of 61. Atomic nuclei with an odd number of protons are less stable than those with even numbers, even when the total number of nucleons (protons + neutrons) is even, and odd numbered elements have fewer stable isotopes.
The most stable radioactive isotopes are technetium-97 with a half-life of 4.21 million years, technetium-98 with 4.2 million years , and technetium-99 with 211,100 years. Thirty other radioisotopes have been characterized with mass numbers ranging from 85 to 118. Most of these have half-lives that are less than an hour, the exceptions being technetium-93 (half-life: 2.73 hours), technetium-94 (half-life: 4.88 hours), technetium-95 (half-life: 20 hours), and technetium-96 (half-life: 4.3 days).
The primary decay mode for isotopes lighter than technetium-98 (98Tc) is electron capture, producing molybdenum (Z = 42). For technetium-98 and heavier isotopes, the primary mode is beta emission (the emission of an electron or positron), producing ruthenium (Z = 44), with the exception that technetium-100 can decay both by beta emission and electron capture.
Technetium also has numerous nuclear isomers, which are isotopes with one or more excited nucleons. Technetium-97m (97mTc; 'm' stands for metastability) is the most stable, with a half-life of 91 days (0.0965 MeV). This is followed by technetium-95m (half-life: 61 days, 0.03 MeV), and technetium-99m (half-life: 6.01 hours, 0.142 MeV). Technetium-99m emits only gamma rays and decays to technetium-99.
Technetium-99 (99Tc) is a major product of the fission of uranium-235 (235U), making it the most common and most readily available isotope of technetium. One gram of technetium-99 produces 6.2×108 disintegrations a second (that is, 0.62 GBq/g).
Technetium occurs naturally in the Earth's crust in minute concentrations of about 0.003 parts per trillion. This totals about 18000 tonnes at any given time, assuming the mass of the Earth's crust is 6×1021 kilograms. Technetium is so rare because technetium-98's half-life is only 4.2 million years. More than a thousand of such periods have passed since the formation of the Earth, so the probability for the survival of even one atom of primordial technetium is effectively zero. However, small amounts exist as spontaneous fission products in uranium ores. A kilogram of uranium contains an estimated 1 nanogram (10−9 g) of technetium. Some red giant stars with the spectral types S-, M-, and N contain a spectral absorption line indicating the presence of technetium. These red-giants are known informally as technetium stars.
In contrast to the rare natural occurrence, bulk quantities of technetium-99 are produced each year from spent nuclear fuel rods, which contain various fission products. The fission of a gram of uranium-235 in nuclear reactors yields 27 mg of technetium-99, giving technetium a fission product yield of 6.1%. Other fissile isotopes produce similar yields of technetium, such as 4.9% from uranium-233 and 6.21% from plutonium-239. An estimated 49,000 TBq (78 metric tons) of technetium was produced in nuclear reactors between 1983 and 1994, by far the dominant source of terrestrial technetium. Only a fraction of the production is used commercially.[note 3]
Technetium-99 is produced by the nuclear fission of both uranium-235 and plutonium-239. It is therefore present in radioactive waste and in the nuclear fallout of fission bomb explosions. Its decay, measured in becquerels per amount of spent fuel, is the dominant contributor to nuclear waste radioactivity after about 104 to 106 years after the creation of the nuclear waste. From 1945 to 1994, an estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment during atmospheric nuclear tests. The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is on the order of 1000 TBq (about 1600 kg), primarily by nuclear fuel reprocessing; most of this was discharged into the sea. Reprocessing methods have reduced emissions since then, but as of 2005 the primary release of technetium-99 into the environment is by the Sellafield plant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea. From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year. Discharge of technetium into the sea resulted in contamination of some seafood with minuscule quantities of this element. For example, European lobster and fish from west Cumbria contain about 1 Bq/kg of technetium.[note 4]
Because used fuel is allowed to stand for several years before reprocessing, all molybdenum-99 and technetium-99m is decayed by the time that the fission products are separated from the major actinides in conventional nuclear reprocessing. The liquid left after plutonium–uranium extraction (PUREX) contains a high concentration of technetium as TcO−
4 but almost all of this is technetium-99, not technetium-99m.
The vast majority of the technetium-99m used in medical work is produced by irradiating dedicated highly enriched uranium targets in a reactor, extracting molybdenum-99 from the targets in reprocessing facilities, and recovering at the diagnostic center the technetium-99m produced upon decay of molybdenum-99. Molybdenum-99 in the form of molybdate MoO2−
4 is adsorbed onto acid alumina (Al
3) in a shielded column chromatograph inside a technetium-99m generator ("technetium cow", also occasionally called a "molybdenum cow"). Molybdenum-99 has a half-life of 67 hours, so short-lived technetium-99m (half-life: 6 hours), which results from its decay, is being constantly produced. The soluble pertechnetate TcO−
4 can then be chemically extracted by elution using a saline solution. A drawback of this process is that it requires targets containing uranium-235, which are subject to the security precautions of fissile materials.
Almost two-thirds of the world's supply comes from two reactors; the National Research Universal Reactor at Chalk River Laboratories in Ontario, Canada, and the High Flux Reactor at Nuclear Research and Consultancy Group in Petten, Netherlands. All major reactors that produce technetium-99m were built in the 1960s and are close to the end of life. The two new Canadian Multipurpose Applied Physics Lattice Experiment reactors planned and built to produce 200% of the demand of technetium-99m relieved all other producers from building their own reactors. With the cancellation of the already tested reactors in 2008, the future supply of technetium-99m became problematic.
The Chalk River reactor was shut down for maintenance in August 2009, and reopened in August 2010. The Petten reactor had a 6-month scheduled maintenance shutdown on Friday, February 19, 2010, and reopened September 2010. With millions of procedures relying on technetium-99m every year, the low supply has left a gap, leaving some practitioners to revert to techniques not used for 20 years. Somewhat allaying this issue is an announcement from the Polish Maria research reactor that they have developed a technique to isolate technetium.
The long half-life of technetium-99 and its potential to form anionic species creates a major concern for long-term disposal of radioactive waste. Many of the processes designed to remove fission products in reprocessing plants aim at cationic species such as caesium (e.g., caesium-137) and strontium (e.g., strontium-90). Hence the pertechnetate escapes through those processes. Current disposal options favor burial in continental, geologically stable rock. The primary danger with such practice is the likelihood that the waste will contact water, which could leach radioactive contamination into the environment. The anionic pertechnetate and iodide tend not to adsorb into the surfaces of minerals, and are likely to be washed away. By comparison plutonium, uranium, and caesium tend to bind to soil particles. Technetium could be immobilized by some environments, such as microbial activity in lake bottom sediments, and the environmental chemistry of technetium is an area of active research.
An alternative disposal method, transmutation, has been demonstrated at CERN for technetium-99. In this process, the technetium (technetium-99 as a metal target) is bombarded with neutrons to form the short-lived technetium-100 (half-life = 16 seconds) which decays by beta decay to ruthenium-100. If recovery of usable ruthenium is a goal, an extremely pure technetium target is needed; if small traces of the minor actinides such as americium and curium are present in the target, they are likely to undergo fission and form more fission products which increase the radioactivity of the irradiated target. The formation of ruthenium-106 (half-life 374 days) from the 'fresh fission' is likely to increase the activity of the final ruthenium metal, which will then require a longer cooling time after irradiation before the ruthenium can be used.
The actual separation of technetium-99 from spent nuclear fuel is a long process. During fuel reprocessing, it comes out as a component of the highly radioactive waste liquid. After sitting for several years, the radioactivity reduces to a level where extraction of the long-lived isotopes, including technetium-99, becomes feasible. A series of chemical processes yields technetium-99 metal of high purity.
Molybdenum-99, which decays to form technetium-99m, can be formed by the neutron activation of molybdenum-98. When needed, other technetium isotopes are not produced in significant quantities by fission, but are manufactured by neutron irradiation of parent isotopes (for example, technetium-97 can be made by neutron irradiation of ruthenium-96).
The feasibility of technetium-99m production with the 22-MeV-proton bombardment of a molybdenum-100 target in medical cyclotrons following the reaction 100Mo(p,2n)99mTc was demonstrated in 1971. The recent shortages of medical technetium-99m reignited the interest in its production by proton bombardment of isotopically-enriched (>99.5%) molybdenum-100 targets. Other techniques are being investigated for obtaining molybdenum-99 from molybdenum-100 via (n,2n) or (γ,n) reactions in particle accelerators.
Technetium-99m ("m" indicates that this is a metastable nuclear isomer) is used in radioactive isotope medical tests. For example, Technetium-99m is a radioactive tracer that medical imaging equipment tracks in the human body. It is well suited to the role because it emits readily detectable 140 keV gamma rays, and its half-life is 6.01 hours (meaning that about 94% of it decays to technetium-99 in 24 hours). The chemistry of technetium allows it to be bound to a variety of biochemical compounds, each of which determines how it is metabolized and deposited in the body, and this single isotope can be used for a multitude of diagnostic tests. More than 50 common radiopharmaceuticals are based on technetium-99m for imaging and functional studies of the brain, heart muscle, thyroid, lungs, liver, gall bladder, kidneys, skeleton, blood, and tumors.
Technetium-99 decays almost entirely by beta decay, emitting beta particles with consistent low energies and no accompanying gamma rays. Moreover, its long half-life means that this emission decreases very slowly with time. It can also be extracted to a high chemical and isotopic purity from radioactive waste. For these reasons, it is a National Institute of Standards and Technology (NIST) standard beta emitter, and is used for equipment calibration. Technetium-99 has also been proposed for optoelectronic devices and nanoscale nuclear batteries.
Like rhenium and palladium, technetium can serve as a catalyst. In processes such as the dehydrogenation of isopropyl alcohol, it is a far more effective catalyst than either rhenium or palladium. However, its radioactivity is a major problem in safe catalytic applications.
When steel is immersed in water, adding a small concentration (55 ppm) of potassium pertechnetate(VII) to the water protects the steel from corrosion, even if the temperature is raised to 250 °C (523 K). For this reason, pertechnetate has been used as an anodic corrosion inhibitor for steel, although technetium's radioactivity poses problems that limit this application to self-contained systems. While (for example) CrO2−
4 can also inhibit corrosion, it requires a concentration ten times as high. In one experiment, a specimen of carbon steel was kept in an aqueous solution of pertechnetate for 20 years and was still uncorroded. The mechanism by which pertechnetate prevents corrosion is not well understood, but seems to involve the reversible formation of a thin surface layer (passivation). One theory holds that the pertechnetate reacts with the steel surface to form a layer of technetium dioxide which prevents further corrosion; the same effect explains how iron powder can be used to remove pertechnetate from water. The effect disappears rapidly if the concentration of pertechnetate falls below the minimum concentration or if too high a concentration of other ions is added.
As noted, the radioactive nature of technetium (3 MBq/L at the concentrations required) makes this corrosion protection impractical in almost all situations. Nevertheless, corrosion protection by pertechnetate ions was proposed (but never adopted) for use in boiling water reactors.
Technetium plays no natural biological role and is not normally found in the human body. Technetium is produced in quantity by nuclear fission, and spreads more readily than many radionuclides. It appears to have low chemical toxicity. For example, no significant change in blood formula, body and organ weights, and food consumption could be detected for rats which ingested up to 15 µg of technetium-99 per gram of food for several weeks. The radiological toxicity of technetium (per unit of mass) is a function of compound, type of radiation for the isotope in question, and the isotope's half-life.
All isotopes of technetium must be handled carefully. The most common isotope, technetium-99, is a weak beta emitter; such radiation is stopped by the walls of laboratory glassware. The primary hazard when working with technetium is inhalation of dust; such radioactive contamination in the lungs can pose a significant cancer risk. For most work, careful handling in a fume hood is sufficient, and a glove box is not needed.
ATC code V09 Diagnostic radiopharmaceuticals is a therapeutic subgroup of the Anatomical Therapeutic Chemical Classification System, a system of alphanumeric codes developed by the WHO for the classification of drugs and other medical products. Subgroup V09 is part of the anatomical group V Various.
Codes for veterinary use (ATCvet codes) can be created by placing the letter Q in front of the human ATC code: for example, QV09. National issues of the ATC classification may include additional codes not present in this list, which follows the WHO version.Bectumomab
Bectumomab (marketed under the trade name LymphoScan) is a mouse monoclonal antibody labelled with the radioactive isotope technetium-99m. It is used to detect non-Hodgkin's lymphoma.Group 7 element
Group 7, numbered by IUPAC nomenclature, is a group of elements in the periodic table. They are manganese (Mn), technetium (Tc), rhenium (Re), and bohrium (Bh). All known elements of group 7 are transition metals.
Like other groups, the members of this family show patterns in their electron configurations, especially the outermost shells resulting in trends in chemical behavior.Isotopes of technetium
Technetium (43Tc) is the first of the two elements lighter than bismuth that have no stable isotopes; the other such element is promethium. It is primarily artificial, with only trace quantities (about 16 thousand metric tonnes) existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are 97Tc (half-life of 4.21 million years), 98Tc (half-life: 4.2 million years) and 99Tc (half-life: 211,100 years).Thirty-three other radioisotopes have been characterized with atomic masses ranging from 85Tc to 120Tc. Most of these have half-lives that are less than an hour; the exceptions are 93Tc (half-life: 2.75 hours), 94Tc (half-life: 4.883 hours), 95Tc (half-life: 20 hours), and 96Tc (half-life: 4.28 days).Technetium also has numerous meta states. 97mTc is the most stable, with a half-life of 91.0 days (0.097 MeV). This is followed by 95mTc (half-life: 61 days, 0.038 MeV), and 99mTc (half-life: 6.04 hours, 0.143 MeV). 99mTc only emits gamma rays, subsequently decaying to 99Tc.For isotopes lighter than the most stable isotope, 98Tc, the primary decay mode is electron capture to isotopes of molybdenum. For the heavier isotopes, the primary mode is beta emission to isotopes of ruthenium, with the exception that 100Tc can decay both by beta emission and electron capture.Technetium-99 is the most common and most readily available isotope, as it is a major fission product from fission of actinides like uranium and plutonium with a fission product yield of 6% or more, and in fact the most significant long-lived fission product. Lighter isotopes of technetium are almost never produced in fission because the initial fission products normally have a higher neutron/proton ratio than is stable for their mass range, and therefore undergo beta decay until reaching the ultimate product. Beta decay of fission products of mass 95–98 stops at the stable isotopes of molybdenum of those masses and does not reach technetium. For mass 100 and greater, the technetium isotopes of those masses are very short-lived and quickly beta decay to isotopes of ruthenium. Therefore, the technetium in spent nuclear fuel is practically all 99Tc.
One gram of 99Tc produces 6.2×108 disintegrations a second (that is, 0.62 GBq/g).Technetium has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given.Myocardial perfusion imaging
Myocardial perfusion imaging or scanning (also referred to as MPI or MPS) is a nuclear medicine procedure that illustrates the function of the heart muscle (myocardium).It evaluates many heart conditions, such as coronary artery disease (CAD), hypertrophic cardiomyopathy and heart wall motion abnormalities. It can also detect regions of myocardial infarction by showing areas of decreased resting perfusion. The function of the myocardium is also evaluated by calculating the left ventricular ejection fraction (LVEF) of the heart. This scan is done in conjunction with a cardiac stress test. The diagnostic information is generated by provoking controlled regional ischemia in the heart with variable perfusion.
Planar techniques, such as conventional scintigraphy, are rarely used. Rather, Single-photon emission computed tomography (SPECT) is more common in the US. With multihead SPECT systems, imaging can often be completed in less than 10 minutes. With SPECT, inferior and posterior abnormalities and small areas of infarction can be identified, as well as the occluded blood vessels and the mass of infarcted and viable myocardium. The usual isotopes for such studies are either Thallium-201 or Technetium-99m.Radiopharmacology
Radiopharmacology is radiochemistry applied to medicine and thus the pharmacology of radiopharmaceuticals (medicinal radiocompounds, that is, pharmaceutical drugs that are radioactive). Radiopharmaceuticals are used in the field of nuclear medicine as radioactive tracers in medical imaging and in therapy for many diseases (for example, brachytherapy). Many radiopharmaceuticals use technetium-99m (Tc-99m) which has many useful properties as a gamma-emitting tracer nuclide. In the book Technetium a total of 31 different radiopharmaceuticals based on Tc-99m are listed for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood and tumors.The term radioisotope, which in its general sense refers to any radioactive isotope (radionuclide), has historically been used to refer to all radiopharmaceuticals, and this usage remains common. Technically, however, many radiopharmaceuticals incorporate a radioactive tracer atom into a larger pharmaceutically-active molecule, which is localized in the body, after which the radionuclide tracer atom allows it to be easily detected with a gamma camera or similar gamma imaging device. An example is fludeoxyglucose in which fluorine-18 is incorporated into deoxyglucose. Some radioisotopes (for example gallium-67, gallium-68, and radioiodine) are used directly as soluble ionic salts, without further modification. This use relies on the chemical and biological properties of the radioisotope itself, to localize it within the body.Synthetic radioisotope
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators.Technetium(VII) oxide
Technetium(VII) oxide is the chemical compound with the formula Tc2O7. This yellow volatile solid is a rare example of a molecular binary metal oxide, the other examples being RuO4, OsO4, and the unstable Mn2O7. It adopts a centrosymmetric corner-shared bi-tetrahedral structure in which the terminal and bridging Tc−O bonds are 167pm and 184 pm respectively and the Tc−O−Tc angle is 180°.Technetium(VII) oxide is prepared by the oxidation of technetium at 450–500 °C:
4 Tc + 7 O2 → 2 Tc2O7It is the anhydride of pertechnic acid and the precursor to sodium pertechnetate:
Tc2O7 + 2 NaOH → 2 NaTcO4 + H2OTechnetium-99
Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting beta particles, but no gamma rays. It is the most significant long-lived fission product of uranium fission, producing the largest fraction of the total long-lived radiation emissions of nuclear waste. Technetium-99 has a fission product yield of 6.0507% for thermal neutron fission of uranium-235.
Technetium-99m (99mTc) is a short-lived (half-life about 6 hours) metastable nuclear isomer used in nuclear medicine, produced from molybdenum-99. It decays by isomeric transition to technetium-99, a desirable characteristic, since the very long half-life and type of decay of technetium-99 imposes little further radiation burden on the body.Technetium-99m
Technetium-99m is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical radioisotope.
Technetium-99m is used as a radioactive tracer and can be detected in the body by medical equipment (gamma cameras). It is well suited to the role, because it emits readily detectable gamma rays with a photon energy of 140 keV (these 8.8 pm photons are about the same wavelength as emitted by conventional X-ray diagnostic equipment) and its half-life for gamma emission is 6.0058 hours (meaning 93.7% of it decays to 99Tc in 24 hours). The relatively "short" physical half-life of the isotope and its biological half-life of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly but keep total patient radiation exposure low. The same characteristics make the isotope suitable only for diagnostic but never therapeutic use.
Technetium-99m was discovered as a product of cyclotron bombardment of molybdenum. This procedure produced molybdenum-99, a radionuclide with a longer half-life (2.75 days), which decays to Tc-99m. At present, molybdenum-99 (Mo-99) is used commercially as the easily transportable source of medically used Tc-99m. In turn, this Mo-99 is usually created commercially by fission of highly enriched uranium in aging research and material testing nuclear reactors in several countries.Technetium (99mTc) arcitumomab
Technetium (99mTc) arcitumomab is a drug used for the diagnostic imaging of colorectal cancers, marketed by Immunomedics. It consists of the Fab' fragment of a monoclonal antibody (arcitumomab, trade name CEA-Scan) and a radionuclide, technetium-99m.Technetium (99mTc) fanolesomab
Technetium (99mTc) fanolesomab (trade name NeutroSpec, manufactured by Palatin Technologies) is a mouse monoclonal antibody formerly used to aid in the diagnosis of appendicitis. It is labeled with a radioisotope, technetium-99m (99mTc).Technetium (99mTc) nofetumomab merpentan
Technetium (99mTc) nofetumomab merpentan (trade name Verluma) is a mouse monoclonal antibody derivative used in the diagnosis of lung cancer, gastrointestinal, breast, ovary, pancreas, kidney, cervix, and bladder carcinoma. The antibody part, nofetumomab, is attached to the chelator merpentan, which links it to the radioisotope technetium-99m (99mTc).Technetium (99mTc) pintumomab
Technetium (99mTc) pintumomab (INN) is a mouse monoclonal antibody for the imaging of adenocarcinoma. It is labelled with the radioisotope technetium-99m.Technetium (99mTc) sestamibi
Technetium (99mTc) sestamibi (INN) (commonly sestamibi; USP: technetium Tc 99m sestamibi; trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex consisting of the radioisotope technetium-99m bound to six (sesta=6) methoxyisobutylisonitrile (MIBI) ligands. The anion is not defined. The generic drug became available late September 2008. A scan of a patient using MIBI is commonly known as a "MIBI scan".
Sestamibi is mainly used to image the myocardium (heart muscle). It is also used in the work-up of primary hyperparathyroidism to identify parathyroid adenomas, for radioguided surgery of the parathyroid and in the work-up of possible breast cancer.Technetium (99mTc) sulesomab
Technetium (99mTc) sulesomab (trade name LeukoScan) is a mouse monoclonal antibody labelled with technetium-99m, a radionuclide, for imaging with a gamma camera.
It is approved for the imaging of infections and inflammations in patients with suspected osteomyelitis, and is being investigated for other purposes like the detection of soft tissue infections.Technetium (99mTc) votumumab
Technetium (99mTc) votumumab (trade name HumaSPECT) is a human monoclonal antibody labelled with the radionuclide technetium-99m. It was developed for the detection of colorectal tumors, but has never been marketed.The target of votumumab is CTAA16.88, a complex of cytokeratin polypeptides in the molecular weight range of 35 to 43 kDa, which is expressed in colorectal tumors.Technetium hexafluoride
Technetium hexafluoride or technetium(VI) fluoride (TcF6) is a yellow inorganic compound with a low melting point. It was first identified in 1961. In this compound, technetium has an oxidation state of +6, the highest oxidation state found in the technetium halides. The other such compound is technetium(VI) chloride, TcCl6. In this respect, technetium differs from rhenium, which forms a heptafluoride, ReF7. Technetium hexafluoride occurs as an impurity in uranium hexafluoride, as technetium is a fission product of uranium.Technetium star
A technetium star, or more properly a Tc-rich star, is a star whose stellar spectrum contains absorption lines of the light radioactive metal technetium. The most stable isotope of technetium is 98Tc with a half-life of 4.2 million years, which is too short a time to allow the metal to be material from before the star's formation. Therefore, the detection in 1952 of technetium in stellar spectra provided unambiguous proof of nucleosynthesis in stars, one of the more extreme cases being R Geminorum.Stars containing technetium belong to the class of asymptotic giant branch stars (AGB)—stars that are like red giants, but with a slightly higher luminosity, and which burn hydrogen in an inner shell. Members of this class of stars switch to helium shell burning with an interval of some 100,000 years, in "dredge-ups". Technetium stars belong to the classes M, MS, S, SC and C-N. They are most often variable stars of the long period variable types.
Current research indicate that the presence of technetium in AGB stars occurs after some evolution, and that a significant number of these stars do not exhibit the metal in their spectra. The presence of technetium seems to be related to the "third dredge-up" in the history of the stars.