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Technetium is a ; it has symbol Tc and 43. It is the lightest element whose are all . Technetium and are the only radioactive elements whose neighbours in the sense of atomic number are both stable. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous in and ore (the most common source), or the product of in ores. This silvery gray, crystalline lies between and in group 7 of the , and its chemical properties are intermediate between those of both adjacent elements. The most common naturally occurring isotope is 99Tc, in traces only.

Many of technetium's properties had been predicted by before it was discovered; Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese ( Em). In 1937, technetium became the first predominantly artificial element to be produced, hence its name (from the Greek , 'artificial', +

One short-lived –emitting , technetium-99m, is used in for a wide variety of tests, such as bone cancer diagnoses. The ground state of the technetium-99 is used as a gamma ray–free source of . Long-lived technetium isotopes produced commercially are byproducts of the of uranium-235 in and are extracted from nuclear fuel rods. Because even the longest-lived isotope of technetium has a relatively short (4.21 million years), the 1952 detection of technetium in helped to prove that stars can .


History

Early assumptions
From the 1860s through 1871, early forms of the periodic table proposed by contained a gap between (element 42) and (element 44). In 1871, Mendeleev predicted this missing element would occupy the empty place below and have similar chemical properties. Mendeleev gave it the provisional name eka-manganese (from eka, the word for one) because it was one place down from the known element manganese.


Early misidentifications
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. This turned out not to be the case, due to technetium's radioactivity.

1828
1845Niobium–tantalum alloy

1847R. Hermann
1877Serge Kern alloy
1896Prosper Barrière
1908, which was the unknown dvi-manganese


Irreproducible results
German chemists , Otto Berg, and reported the discovery of element 75 and element 43 in 1925, and named element 43 masurium (after in eastern , now in , the region where Walter Noddack's family originated). This name caused significant resentment in the scientific community, because it was interpreted as referring to a series of victories of the German army over the Russian army in the Masuria region during World War I; as the Noddacks remained in their academic positions while the Nazis were in power, suspicions and hostility against their claim for discovering element 43 continued. The group bombarded with a beam of and deduced element 43 was present by examining emission . The of the X-rays produced is related to the atomic number by a formula derived by 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. Still, in 1933, a series of articles on the discovery of elements quoted the name masurium for element 43. Some more recent attempts have been made to rehabilitate the Noddacks' claims, but they are disproved by 's study on the amount of technetium that could have been present in the ores they studied: it could not have exceeded of ore, and thus would have been undetectable by the Noddacks' methods.
(2025). 9780195391312, Oxford University Press.


Official discovery and later history
The discovery of element 43 was finally confirmed in a 1937 experiment at the University of Palermo in Sicily by and Emilio Segrè.
(1992). 9780830630189, TAB Books.
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 inventor to let him take back some discarded cyclotron parts that had become . Lawrence mailed him a foil that had been part of the deflector in the cyclotron.
(1993). 9780520076273, University of California Press. .

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, which they did. University of Palermo officials wanted them to name their discovery panormium, after the Latin name for , Panormus. In 1947, element 43 was named after the 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.

(2025). 9781860940873, University of California Press.

In 1952, the astronomer Paul W. Merrill detected the spectral signature of technetium (specifically of 403.1 , 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type . The stars were near the end of their lives but were rich in the short-lived element, which indicated that it was being produced in the stars by . That evidence bolstered the hypothesis that heavier elements are the product of in stars. More recently, such observations provided evidence that elements are formed by in the .

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 from the in very small quantities (about 0.2 ng/kg), where it originates as a spontaneous fission product of uranium-238. The natural nuclear fission reactor in contains evidence that significant amounts of technetium-99 were produced and have since decayed into ruthenium-99.


Characteristics

Physical properties
Technetium is a silvery-gray radioactive with an appearance similar to , commonly obtained as a gray powder. The crystal structure of the bulk pure metal is hexagonal . Atomic technetium has characteristic emission lines at of 363.3 , 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm.
9780849305955, CRC press.
The unit cell parameters of the orthorhombic Tc metal were reported when Tc is contaminated with carbon ( = 0.2805(4), = 0.4958(8), = 0.4474(5)·nm for Tc-C with 1.38 wt% C and = 0.2815(4), = 0.4963(8), = 0.4482(5)·nm for Tc-C with 1.96 wt% C ). The metal form is slightly , meaning its align with external , but will assume random orientations once the field is removed. Pure, metallic, single-crystal technetium becomes a type-II superconductor at temperatures below . Below this temperature, technetium has a very high magnetic penetration depth, greater than any other element except .


Chemical properties
Technetium is located in group 7 of the periodic table, between and . 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 . This is consistent with the tendency of period 5 elements to resemble their counterparts in period 6 more than period 4 due to the lanthanide contraction. Unlike manganese, technetium does not readily form ( with net positive charge). Technetium exhibits nine from −1 to +7, with +4, +5, and +7 being the most common. Technetium dissolves in , , and concentrated , but not in hydrochloric acid of any concentration.

Metallic technetium slowly in moist air and, in powder form, burns in . When reacting with at high pressure, it forms the non-stoichiometric hydride TcH and while reacting with it forms TcC, with cell parameter 0.398 nm.

Technetium can catalyse the destruction of by , 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.


Compounds

Pertechnetate and other derivatives
The most prevalent form of technetium that is easily accessible is sodium pertechnetate, NaTcO4. The majority of this material is produced by radioactive decay from 99MoO42−:

() is only weakly hydrated in aqueous solutions, and it behaves analogously to perchlorate anion, both of which are tetrahedral. Unlike (), it is only a weak .

Related to pertechnetate is technetium heptoxide. This pale-yellow, volatile solid is produced by oxidation of Tc metal and related precursors:

It is a molecular metal oxide, analogous to manganese heptoxide. It adopts a structure with two types of Tc−O bonds with 167 and 184 pm bond lengths.

Technetium heptoxide hydrolyzes to pertechnetate and pertechnetic acid, depending on the pH:

(1977). 9780070443273, McGraw-Hill.

HTcO4 is a strong acid. In concentrated , TcO4 converts to the octahedral form TcO3(OH)(H2O)2, the conjugate base of the hypothetical tri TcO3(H2O)3+.


Other chalcogenide derivatives
Technetium forms a dioxide, disulfide, di, and ditelluride. An ill-defined Tc2S7 forms upon treating with hydrogen sulfide. It thermally decomposes into disulfide and elemental sulfur. Similarly the dioxide can be produced by reduction of the Tc2O7.

Unlike the case for rhenium, a trioxide has not been isolated for technetium. However, TcO3 has been identified in the gas phase using mass spectrometry.


Simple hydride and halide complexes
Technetium forms the complex . The potassium salt is with . At high pressure formation of TcH1.3 from elements was also reported.

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 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.

The structure of TcCl4 is composed of infinite zigzag chains of edge-sharing TcCl6 octahedra. It is isomorphous to transition metal tetrachlorides of , , and .

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 TcX62− (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 halogen atoms such as or .


Coordination and organometallic complexes
Technetium forms a variety of coordination complexes with organic ligands. Many have been well-investigated because of their relevance to .

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 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 are formed by technetium's congeners, manganese and rhenium. Interest in organotechnetium compounds has also been motivated by applications in .

(2025). 9783642131844
Technetium also forms aquo-carbonyl complexes, one prominent complex being Tc(CO)3(H2O)3+, which are unusual compared to other metal carbonyls.


Isotopes
Technetium, with Z = 43, is the lowest-numbered element in the periodic table for which all isotopes are . The second-lightest exclusively radioactive element, , has atomic number 61. with an odd number of are less stable than those with even numbers, even when the total number of (protons + ) is even,
(1983). 9780226109534, University of Chicago Press. .
and odd numbered elements have fewer stable .

The most stable are technetium-97 with a of  million years and technetium-98 with  million years; current measurements of their half-lives give overlapping confidence intervals corresponding to one standard deviation and therefore do not allow a definite assignment of technetium's most stable isotope. The next most stable isotope is technetium-99, which has a half-life of 211,100 years. Thirty-four other radioisotopes have been characterized with ranging from 86 to 122. Most of these have half-lives that are less than an hour, the exceptions being technetium-93 (2.75 hours), technetium-94 (4.88 hours), technetium-95 (19.26 hours), and technetium-96 (4.28 days).

The primary for isotopes lighter than technetium-98 (98Tc) is , producing ( Z = 42). For technetium-98 and heavier isotopes, the primary mode is (the emission of an or ), producing ( Z = 44), with the exception that technetium-100 can decay both by beta emission and electron capture.

Technetium also has numerous , which are isotopes with one or more nucleons. Technetium-97m (97mTc; "m" stands for ) is the most stable, with a half-life of 91.1 days and 0.097 MeV, followed by technetium-95m (62.0 days, 0.039 MeV), and technetium-99m (6.01 hours, 0.143 MeV).

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, and the only one detected in nature. One gram of technetium-99 produces per second (in other words, the specific activity of 99Tc is 0.62 G/g).


Occurrence and production
Technetium occurs naturally in the Earth's crust in minute concentrations of about 0.003 parts per trillion. Technetium is so rare because the of 97Tc and 98Tc are only More than a thousand of such periods have passed since the formation of the , so the probability of survival of even one atom of primordial technetium is effectively zero. However, small amounts exist as spontaneous in . A kilogram of uranium contains an estimated 1 nanogram , equivalent to ten trillion atoms, of technetium.

Some stars with the spectral types S, M, and N display a spectral absorption line indicating the presence of technetium. These red giants are known informally as .


Fission product
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 yields 27 mg of technetium-99, giving technetium a fission product yield of 6.1%. Other isotopes produce similar yields of technetium, such as 4.9% from uranium-233 and 6.21% from plutonium-239. An estimated 49,000 T (78 ) of technetium was produced in nuclear reactors between 1983 and 1994, by far the dominant source of terrestrial technetium.
(1996). 9783540594697, Springer-Verlag.
Only a fraction of the production is used commercially.

Technetium-99 is produced by the of both uranium-235 and plutonium-239. It is therefore present in radioactive waste and in the of explosions. Its decay, measured in per amount of spent fuel, is the dominant contributor to nuclear waste radioactivity after about after the creation of the nuclear waste. From 1945 to 1994, an estimated 160 T (about 250 kg) of technetium-99 was released into the environment during atmospheric .

(1986). 9780853344216, Springer. .
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 plant, which released an estimated 550 TBq (about 900 kg) from 1995 to 1999 into the .

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, and fish from west contain about 1 Bq/kg of technetium.

(2025). 9780849322341, CRC Press. .


Fission product for commercial use
The isotope technetium-99m is continuously produced as a from the fission of uranium or in :

^{238}_{92}U ->\ce{sf} ^{137}_{53}I + ^{99}_{39}Y + 2^{1}_{0}n ^{99}_{39}Y ->\beta^-1.47\,\ce{s} ^{99}_{40}Zr ->\beta^-2.1\,\ce{s} ^{99}_{41}Nb ->\beta^-15.0\,\ce{s} ^{99}_{42}Mo ->\beta^-65.94\,\ce{h} ^{99}_{43}Tc ->\beta^-211,100\,\ce{y} ^{99}_{44}Ru

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 in conventional nuclear reprocessing. The liquid left after plutonium–uranium extraction () contains a high concentration of technetium as 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.

(2025). 9780309130400, National Academies Press.
Molybdenum-99 in the form of molybdate is onto acid alumina () 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 can then be chemically extracted by using a . 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.


Waste disposal
The long half-life of technetium-99 and its potential to form 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 species such as (e.g., caesium-137) and (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 tend not to adsorb into the surfaces of minerals, and are likely to be washed away. By comparison , , and 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.
(2025). 9780080438726, Elsevier. .

An alternative disposal method, transmutation, has been demonstrated at for technetium-99. In this process, the technetium (technetium-99 as a metal target) is bombarded with to form the short-lived technetium-100 (half-life = 16 seconds) which decays by beta decay to stable -100. If recovery of usable ruthenium is a goal, an extremely pure technetium target is needed; if small traces of the such as and are present in the target, they are likely to undergo fission and form more 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.


Neutron activation
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).


Particle accelerators
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.


Applications

Nuclear medicine and biology
Technetium-99m ("m" indicates that this is a metastable nuclear isomer) is used in radioactive isotope . 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  , 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 , heart muscle, , , , , , , , and .

The longer-lived isotope, technetium-95m with a half-life of 61 days, is used as a radioactive tracer to study the movement of technetium in the environment and in plant and animal systems.


Industrial and chemical
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 U.S. 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 .

Like and , technetium can serve as a . In processes such as the 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 from corrosion, even if the temperature is raised to . For this reason, pertechnetate has been used as an anodic inhibitor for steel, although technetium's radioactivity poses problems that limit this application to self-contained systems. While (for example) 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.


Precautions and biological effect
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.
(1986). 9780853344216, Springer. .
In the body, technetium quickly gets converted to the stable ion, which is highly water-soluble and quickly excreted. 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 is sufficient, and a is not needed.

Being close to noble metals, technetium is not very susceptible to corrosion, and during biofouling, its ability to self-cleanse has been recorded due to its radiotoxic effect on biota.


Notes
S. Garg and B. Maheshwari, et al., Atomic Data and Nuclear Data Tables 150, 101546 (2023) https://doi.org/10.1016/j.adt.2022.101546


Bibliography


Further reading


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