Technetium 30041 move=:edit= 224922620 2008-07-11T00:45:29Z Dirac66 2038644 /* Applications */ Tc-95m uses are not medical but environmental science and biology {{Infobox technetium}} '''Technetium''' ({{pronEng|tɛkˈniːʃɪəm}}) is the lightest [[chemical element]] with no [[stable isotope]]. It is a [[synthetic element]]. It has [[atomic number]] 43 and is given the symbol '''Tc'''. The chemical properties of this silvery grey, crystalline [[transition metal]] are intermediate between [[rhenium]] and [[manganese]]. Its short-lived gamma-emitting [[nuclear isomer]] <sup>99[[nuclear isomer|m]]</sup>Tc ([[technetium-99m]]) is used in [[nuclear medicine]] for a wide variety of diagnostic tests. [[Tc-99|<sup>99</sup>Tc]] is used as a [[gamma ray]]-free source of [[beta particle]]s. The [[pertechnetate]] [[ion]] (TcO<sub>4</sub><sup>-</sup>) has been suggested as a strong anodic [[corrosion]] inhibitor for mild [[steel]] in closed cooling systems. Before the element was discovered, many of the properties of element 43 [[Mendeleev's predicted elements|were predicted]] by [[Dmitri Mendeleev]]. Mendeleev noted a gap in his [[periodic table]] and called the element ''ekamanganese''(Em). In 1937 its isotope <sup>97</sup>Tc became the first predominantly artificial element to be produced, hence its name (from the [[Greek language|Greek]] ''τεχνητός'', meaning "artificial"). Most technetium produced on Earth is a by-product of [[nuclear fission|fission]] of [[uranium-235]] in [[nuclear reactor]]s and is extracted from [[nuclear fuel cycle|nuclear fuel rod]]s. No isotope of technetium has a [[half-life]] longer than 4.2 million years (<sup>98</sup>Tc), so its detection in [[red giant]]s in 1952 helped bolster the theory that stars can produce heavier elements. On Earth, technetium occurs in trace but measurable quantities as a product of [[spontaneous fission]] in uranium ore or by [[neutron capture]] in [[molybdenum]] ores. == Characteristics == Technetium is a silvery-grey radioactive [[metal]] with an appearance similar to [[platinum]]. However, it is commonly obtained as a grey powder. Its position in the periodic table is between [[rhenium]] and [[manganese]] and as predicted by the [[History of the periodic table|periodic law]] its properties are intermediate between those two elements. Technetium is unusual among the lighter elements in that it has no stable [[isotope]]s. Only technetium and [[promethium]] have no stable isotopes, but are followed by elements which do. Technetium is therefore extremely rare on [[Earth]]. Technetium plays no natural biological role and is not normally found in the [[human]] body. The metal form of technetium slowly [[tarnish]]es in moist air. Its [[oxide]]s are Tc[[oxygen|O]]<sub>2</sub> and Tc<sub>2</sub>O<sub>7</sub>. Under oxidizing conditions technetium (VII) will exist as the [[pertechnetate]] [[ion]], TcO<sub>4</sub><sup>-</sup>.<ref>''LANL Periodic Table'', "Technetium" paragraph 3</ref> Common [[oxidation number|oxidation states]] of technetium include 0, +2, +4, +5, +6 and +7.<ref>''The Encyclopedia of the Chemical Elements'', page 691, "Chemical Properties", paragraph 1</ref> Technetium will burn in [[oxygen]] when in powder form.<ref>''The Encyclopedia of the Chemical Elements'', page 692, "Analytical Methods of Determination", paragraph 1</ref> It dissolves in [[aqua regia]], [[nitric acid]], and concentrated [[sulfuric acid]], but it is not soluble in [[hydrochloric acid]]. It has characteristic [[spectral line]]s at 363 [[Nanometre|nm]], 403 nm, 410 nm, 426 nm, 430 nm, and 485 nm.<ref>The CRC Handbook, 85th edition, Line Spectra of the Elements</ref> The metal form is slightly [[paramagnetism|paramagnetic]], meaning its [[dipole|magnetic dipole]]s align with external [[magnetic field]]s even though technetium is not normally magnetic.<ref>''The Encyclopedia of the Chemical Elements'', page 691, paragraph 1</ref> The [[crystal structure]] of the metal is [[hexagonal]] [[close-packed]]. Pure metallic single-crystal technetium becomes a type II [[superconductivity|superconductor]] at 7.46 [[Kelvin|K]]; irregular crystals and trace impurities raise this temperature to 11.2 K for 99.9% pure technetium powder.<ref name="schwochau">Schwochau, ''Technetium''</ref> Below this temperature technetium has a very high [[superconductor#Meissner effect|magnetic penetration depth]], the largest among the elements apart from [[niobium]].<ref>''Technetium as a Material for AC Superconductivity Applications''</ref> Technetium is produced in quantity by nuclear fission, and spreads more readily than many radionuclides. In spite of the importance of understanding its toxicity in animals and humans, experimental evidence is scant. It appears to have low chemical toxicity. Its radiological toxicity (per unit of mass) is a function of compound, type of radiation for the isotope in question, and the isotope half-life. [[Technetium-99m]] is particularly attractive for medical applications, as the radiation from this isotope is a gamma ray with the same wavelength as X-rays used for common medical diagnostic X-ray applications, giving it adequate penetration while causing minimal damage for a gamma photon. This, plus the extremely short half-life of this metastable [[nuclear isomer]], followed by the relatively long half-life of the daughter isotope Tc-99 which allows it to be eliminated from the body before it decays. This leads to a relatively low dose of administered radiation in biologically dose-equivalent amounts ([[sievert]]s) for a typical Tc-99m based nuclear scan (see more on this subject below).<ref name="schwochau"/> 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. Soft [[X-ray]]s are emitted when the beta particles are stopped, but as long as the body is kept more than 30 cm away these should pose no problem. 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; a [[glove box]] is not needed.<ref name="schwochau"/> == Applications == ===Nuclear medicine=== <sup>99m</sup>Tc ("m" indicates that this is a [[Nuclear isomer#Metastable isomers|metastable]] [[nuclear isomer]]) is used in radioactive isotope [[nuclear medicine|medical tests]], for example as a [[radioactive tracer]] that medical equipment can detect in the human body.<ref>Reference for whole <sup>99m</sup>Tc medical use discussion except where specific cites are given: ''Nature's Building Blocks'', page 423, "Medical Element", paragraphs 2&ndash;4</ref> It is well suited to the role because it emits readily detectable 140 [[Electronvolt|keV]] [[gamma ray]]s, and its half-life is 6.01 hours (meaning that about seven eighths of it decays to <sup>99</sup>Tc in 24 hours).<ref>''The Encyclopedia of the Chemical Elements'', page 693, "Applications", paragraph 3 and ''Guide to the Elements'', page 123, paragraph 3 </ref> Klaus Schwochau's book ''Technetium'' lists 31 [[radiopharmaceuticals]] based on <sup>99m</sup>Tc for imaging and functional studies of the [[brain]], [[myocardium]], [[thyroid]], [[lung]]s, [[liver]], [[gallbladder]], [[kidney]]s, [[skeleton]], [[blood]], and [[tumor]]s.<ref name="schwochau"/> [[Immunoscintigraphy]] incorporates <sup>99m</sup>Tc into a [[monoclonal antibody]], an [[immune system]] [[protein]] capable of binding to [[cancer]] cells. A few hours after injection, medical equipment is used to detect the gamma rays emitted by the <sup>99m</sup>Tc; higher concentrations indicate where the tumor is. This technique is particularly useful for detecting hard-to-find cancers, such as those affecting the [[intestine]]. These modified antibodies are sold by the German company [[Hoechst AG|Hoechst]] (now part of [[Sanofi-Aventis]]) under the name "Scintium".<ref>''Nature's Building Blocks'', page 423, "Medical Element", paragraph 2</ref> When <sup>99m</sup>Tc is combined with a [[tin]] compound it binds to [[red blood cell]]s and can therefore be used to map [[circulatory system]] disorders. It is commonly used to detect gastrointestinal bleeding sites. A [[phosphate|pyrophosphate]] ion with <sup>99m</sup>Tc adheres to [[calcium]] deposits in damaged [[heart]] muscle, making it useful to gauge damage after a [[Myocardial infarction|heart attack]].<ref name="heartscan">''Technetium heart scan''</ref> The [[sulfur]] colloid of <sup>99m</sup>Tc is scavenged by the [[spleen]], making it possible to image the structure of the spleen.<ref>''The Encyclopedia of the Chemical Elements'', page 693, "Applications", paragraph 3</ref> [[Radioactive contamination|Radiation exposure]] due to diagnostic treatment involving Tc-99m can be kept low. Because <sup>99m</sup>Tc has a short half-life and high energy gamma (allowing small amounts to be easily detected), its quick decay into the far-less radioactive <sup>99</sup>Tc results in relatively less total radiation dose to the patient, per unit of initial activity after administration. In the form administered in these medical tests (usually pertechnetate) both isotopes are quickly eliminated from the body, generally within a few days.<ref name="heartscan"/> Technetium for nuclear medicine purposes is usually extracted from [[technetium-99m generator]]s, because of its short 6 hour half-life. ===Environmental science and biology=== The longer-lived isotope <sup>95m</sup>Tc, 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.<ref name="schwochau"/> ===Industrial/Chemical=== Technetium-99 decays almost entirely by [[beta decay]], emitting beta particles with consistent low energies and no accompanying [[gamma ray]]s. 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, used for equipment calibration.<ref name="schwochau"/> Technetium-99 has also been proposed for use in optoelectric and [[nanotechnology|nanoscale]] [[nuclear battery|nuclear batteries]].<ref>{{Citation | publication-date = 2006-11-30 | title = University Research Program in Robotics REPORT | publisher = University of Florida | url = http://www.osti.gov/bridge/servlets/purl/895620-n4Nt3U/895620.PDF | accessdate = 2007-10-12 }}</ref> Like [[rhenium]] and [[palladium]], technetium can serve as a catalyst. For certain reactions, for example the [[dehydrogenation]] of [[isopropyl alcohol]], it is a far more effective catalyst than either rhenium or palladium. Of course, its radioactivity is a major problem in finding safe applications.<ref name="schwochau"/> Under certain circumstances, a small concentration (5×10<sup>−5</sup> [[mole (unit)|mol]]/[[litre|L]]) of the pertechnetate ion in water can protect iron and carbon steels from corrosion. For this reason, pertechnetate has been suggested {{Fact|date=May 2008}} as a possible anodic [[corrosion]] inhibitor for [[steel]], although technetium's radioactivity poses problems for strictly chemical uses such as these. While (for example) CrO<sub>4</sub><sup>2−</sup> can also inhibit corrosion, it requires a concentration ten times as high. In one experiment, a test specimen 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. One theory holds that the pertechnetate reacts with the steel surface to form a layer of technetium [[oxide|dioxide]] which prevents further corrosion; the same effect explains how iron powder can be used to remove pertechnetate from water. ([[Activated carbon]] can also be used for the same effect.) 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 M[[Becquerel|Bq]] per liter 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 reactor]]s.<ref name="schwochau"/> == History == ===Search for element 43=== [[Image:Дмитрий Иванович Менделеев 4.gif|thumb|[[Dmitri Mendeleev]] predicted technetium's properties before it was discovered.]] For a number of years there was a gap in the periodic table between [[molybdenum]] (element 42) and [[ruthenium]] (element 44). Many early researchers 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. It was first thought to have been found in [[platinum]] ores in 1828. It was given the name ''[[polinium]]'' but it turned out to be impure [[iridium]]. Then in 1846 the element ''ilmenium'' was claimed to have been discovered but was determined to be impure [[niobium]]. This mistake was repeated in 1847 with the "discovery" of ''pelopium''.<ref name="history-origin">''History of the Origin of the Chemical Elements and Their Discoverers'', Individual Element Names and History, "Technetium"</ref> [[Dmitri Mendeleev]] predicted that this missing element, as part of other predictions, would be chemically similar to [[manganese]] and gave it the name ekamanganese. In 1877, the Russian chemist [[Serge Kern]] reported discovering the missing element in [[platinum]] ore. Kern named what he thought was the new element ''davyum,'' after the noted English chemist Sir [[Humphry Davy]], but it was determined to be a mixture of iridium, rhodium and [[iron]]. Another candidate, ''lucium,'' followed in 1896 but it was determined to be [[yttrium]]. Then in 1908 the Japanese chemist [[Masataka Ogawa]] found evidence in the mineral [[thorianite]] which he thought indicated the presence of element 43. Ogawa named the element '''nipponium''', after [[Japan]] (which is ''Nippon'' in Japanese). In 2004 H. K Yoshihara utilized "a record of X-ray spectrum of Ogawa's nipponium sample from thorianite [which] was contained in a photographic plate preserved by his family. The spectrum was read and indicated the absence of the element 43 and the presence of the ''element 75'' (rhenium)."<ref> {{cite journal|title=Discovery of a new element 'nipponium': re-evaluation of pioneering works of Masataka Ogawa and his son Eijiro Ogawa|journal=Atomic spectroscopy (Spectrochim. acta, Part B)|date=2004|first=H. K.|last=YOSHIHARA|coauthors=|volume=vol. 59|issue=no8|pages=pp. 1305–1310|id= |url=|format=|accessdate=|doi=10.1016/j.sab.2003.12.027}}</ref> German chemists [[Walter Noddack]], [[Otto Berg]] and [[Ida Tacke]] (later Mrs. Noddack) 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).<ref name="multidict"/> The group bombarded [[Ferrocolumbite|columbite]] with a beam of [[electron]]s and deduced element 43 was present by examining [[X-ray]] diffraction [[spectrogram]]s. 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. Contemporary experimenters could not replicate the discovery, and in fact it was dismissed as an error for many years.<ref name="armstrong">{{cite web|author=Armstrong, John T.|url=http://pubs.acs.org/cen/80th/technetium.html|title=Technetium|publisher=Chemical & Engineering News|year=2003}}</ref><ref>Nies, Kevin A. "[http://www.hypatiamaze.org/ida/tacke.html Ida Tacke and the warfare behind the discovery of fission]" (2001).</ref> In 1998 [[John T. Armstrong]] of the [[National Institute of Standards and Technology]] ran "computer simulations" of the 1925 experiments and obtained results quite close to those reported by the Noddack team. He claimed that this was further supported by work published by [[David Curtis]] of the [[Los Alamos National Laboratory]] measuring the (tiny) natural occurrence of technetium.<ref name="armstrong"/><ref name="armstrong quote">Using first-principles X-ray-emission spectral-generation algorithms developed at NIST, I simulated the X-ray spectra that would be expected for Van Assche's initial estimates of the Noddacks' residue compositions. The first results were surprisingly close to their published spectrum! Over the next couple of years, we refined our reconstruction of their analytical methods and performed more sophisticated simulations. The agreement between simulated and reported spectra improved further. Our calculation of the amount of element 43 required to produce their spectrum is quite similar to the direct measurements of natural technetium abundance in uranium ore published in 1999 by Dave Curtis and colleagues at Los Alamos. We can find no other plausible explanation for the Noddacks' data than that they did indeed detect fission "masurium.#Armstrong, John T. "[http://pubs.acs.org/cen/80th/technetium.html Technetium"] ''Chemical & Engineering News'' (2003).</ref> However, the Noddack's experimental results have never been reproduced, and they were unable to isolate any element 43. Debate still exists as to whether the 1925 team actually did discover element 43. ===Official discovery and later history=== [[Discovery of the chemical elements|Discovery]] of element 43 was finally confirmed in a 1937 experiment at the [[University of Palermo]] in Sicily conducted by [[Carlo Perrier]] and [[Emilio Segrè]]. In the summer of 1936 Segrè and his wife visited the United States, first New York at [[Columbia University]], where he had spent time the previous summer, and then [[Berkeley, California|Berkeley]] at [[Ernest O. Lawrence]]'s [[Lawrence Berkeley National Laboratory|Radiation Laboratory]]. He persuaded [[cyclotron]] inventor Lawrence to let him take back some discarded cyclotron parts that had become radioactive. In early 1937 Lawrence mailed him a molybdenum foil that had been part of the deflector in the cyclotron. Segrè enlisted his experienced chemist colleague Perrier to attempt to prove through comparative chemistry that the molybdenum activity was indeed Z = 43, an element not existent in nature because of its instability against nuclear decay. With considerable difficulty they finally succeeded in isolating three distinct decay periods (90, 80, and 50 days) that eventually turned out to be two isotopes, <sup>95</sup>Tc and <sup>97</sup>Tc, of technetium, the name given later by Perrier and Segrè to the first man-made element.<ref>''Nature's Building Blocks'', page 424, paragraph 2 and ''LANL Periodic Table'', "Technetium", paragraph 1</ref> University of Palermo officials wanted them to name their discovery ''panormium'', after the [[Latin]] name for [[Palermo]], ''Panormus''. The researchers instead named element 43 after the [[Greek language|Greek]] word ''τεχνητός'', meaning "artificial", since it was the first element to be artificially produced.<ref name="multidict"> ''Elentymolgy and Elements Multidict'', "Technetium"</ref><ref name="history-origin"/> Segrè returned to Berkeley and immediately sought out [[Glenn T. Seaborg]]. They isolated the technetium-99m isotope which is now used in some 10,000,000 medical diagnostic procedures annually.<ref> {{cite book | coauthors = | title = THE TRANSURANIUM PEOPLE The Inside Story | publisher =University of California, Berkeley & Lawrence Berkeley National Laboratory | date =2000 | location =Chapter 1.2: Early Days at the Berkeley Radiation Laboratory | pages =pp.15 | url =http://www.worldscibooks.com/physics/p074.html | isbn =ISBN 1-86094-087-0 | id = }}</ref> In 1952 astronomer [[Paul W. Merrill]] in [[California]] detected the [[spectroscopy|spectral signature]] of technetium (in particular, light at 403.1 nm, 423.8 nm, 426.8 nm, and 429.7 nm) in light from [[Stellar classification#Class S|S-type]] [[red giant]]s.<ref name="schwochau"/> These massive [[star]]s near the end of their lives were rich in this short-lived element, meaning [[nuclear reaction]]s within the stars must be producing it. This evidence was used to bolster the then unproven [[theory]] that stars are where [[nucleosynthesis]] of the heavier elements occurs.<ref>''Nature's Building Blocks'', page 422, "Cosmic Element", paragraph 1</ref> More recently, such observations provided evidence that elements were being formed by [[neutron capture]] in the [[s-process]].<ref name="schwochau"/> Since its discovery, there have been many searches in terrestrial materials for natural sources. In 1962, technetium-99 was isolated and identified in [[uraninite|pitchblende]] from the [[Belgian Congo]] in extremely small quantities (about 0.2 ng/kg);<ref name="schwochau"/> there it originates as a [[spontaneous fission]] product of [[uranium-238]]. This discovery was made by B.T. Kenna and P.K. Kuroda.<ref>''LANL Periodic Table'', "Technetium"</ref> There is also evidence that the [[Oklo]] [[natural nuclear fission reactor]] produced significant amounts of technetium-99, which has since decayed to ruthenium-99.<ref name="schwochau"/> ==Occurrence and production== Since technetium is unstable, only minute traces occur naturally in the [[Earth]]'s crust as a spontaneous [[fission product]] of [[uranium]]. In 1999 David Curtis (see above) estimated that a kilogram of uranium contains 1 nanogram (1×10<sup>−9</sup> g) of technetium.<ref>''Nature's Building Blocks'', page 423, "Element of History", paragraph 2</ref> Extraterrestrial technetium was found in some [[red giant]] stars (S-, M-, and N-types) that contain an absorption line in their spectrum indicating the presence of this element.<ref>''LANL Periodic Table'', "Technetium" paragraph 1</ref> {{Long-lived fission products}} ===Byproduct production of Tc-99 in fission wastes=== In contrast with the rare natural occurrence, bulk quantities of technetium-99 are produced each year from [[spent nuclear fuel|spent]] [[nuclear fuel]] rods, which contain various [[fission product]]s. The fission of a gram of [[uranium-235]] in [[nuclear reactor]]s yields 27 mg of <sup>99</sup>Tc, giving technetium a [[fission product yield]] of 6.1%.<ref>''Encyclopedia of the Chemical Elements'', page 690, "Sources of Technetium", paragraph 1</ref> Other [[fissile]] isotopes also produce similar yields of technetium,<ref name="schwochau"/> e.g. 4.9% from [[uranium-233]] or 6.21% from [[plutonium-239]]. It is estimated that up to 1994, about 49,000 T[[Becquerel|Bq]] (78 [[tonne|metric tons]]) of technetium was produced in nuclear reactors, which is by far the dominant source of terrestrial technetium.<ref name="yoshihara">Topics in current chemistry, vol 176, "Technetium in the environment"</ref> However, only a fraction of the production is used commercially. [[2005|As of 2005]], technetium-99 in the form of ammonium pertechnate is available to holders of an [[Oak Ridge National Laboratory|ORNL]] permit for [[United States dollar|US$]]83/g plus packing charges.<ref>The CRC Handbook of Chemistry and Physics, 85th edition, The Elements</ref> This is higher than the spot price of platinum, which has never been worth more than $72.40 per gram. Since the yield of technetium-99 as a [[Fission product|product]] of the [[nuclear fission]] of both [[uranium]]-235 and [[plutonium]]-239 is moderate, it is present in [[radioactive waste]] of fission reactors and is produced when a [[nuclear weapon|fission bomb]] is detonated. The amount of artificially produced technetium in the environment exceeds its natural occurrence by many orders of magnitude. This is due to release by atmospheric [[nuclear testing]] along with the disposal and processing of high-level [[radioactive waste]]. Due to its high fission yield and relatively high half-life, technetium-99 is one of the main components of nuclear waste. Its decay, measured in becquerels per amount of spent fuel, is dominant at about 10<sup>4</sup> to 10<sup>6</sup> years after the creation of the nuclear waste.<ref name="yoshihara"/> An estimated 160 T[[Becquerel|Bq]] (about 250 kg) of technetium-99 was released into the environment up to 1994 by atmospheric nuclear tests.<ref name="yoshihara"/> The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is estimated to be on the order of 1000 TBq (about 1600 kg), primarily by [[nuclear fuel reprocessing]]; most of this was discharged into the sea. In recent years, reprocessing methods have improved to reduce emissions, 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.<ref>Technetium-99 behaviour in the terrestrial environment</ref> As a result of nuclear fuel reprocessing, technetium has been discharged into the sea in a number of locations, and some seafood contains tiny but measurable quantities. For example, [[European lobster|lobster]] from west [[Cumbria]] contains small amounts of technetium.<ref>''Gut transfer and doses from environmental technetium''</ref> The [[anaerobic organism|anaerobic]], [[endospore|spore]]-forming [[bacteria]] in the ''[[Clostridium]]'' [[genus]] are able to reduce Tc(VII) to Tc(IV). ''Clostridia'' bacteria play a role in reducing iron, [[manganese]] and [[uranium]], thereby affecting these elements' solubility in soil and sediments. Their ability to reduce technetium may determine a large part of Tc's mobility in industrial wastes and other subsurface environments.<ref>Arokiasamy J. Francis, Cleveland J. Dodge, G. E. Meinken. "[http://www.extenza-eps.com/OLD/doi/abs/10.1524/ract.2002.90.9-11_2002.791 Biotransformation of pertechnetate by ''Clostridia'']" ''Radiochimica Acta'' '''90''' 09&ndash;11 (2002): 791.</ref> The long half-life of technetium-99 and its ability to form an [[anionic]] species makes it (along with [[Iodine-129|<sup>129</sup>I]]) a major concern when considering long-term disposal of high-level radioactive waste. In addition, many of the processes designed to remove fission products from medium-active process streams in reprocessing plants are designed to remove [[cationic]] species like [[caesium]] (''e.g.,'' [[caesium-137|<sup>137</sup>Cs]]) and [[strontium]] (''e.g.,'' [[strontium-90|<sup>90</sup>Sr]]). Hence the pertechnetate is able to escape through these treatment processes. Current disposal options favor [[geological repository|burial in geologically stable rock]]. The primary danger with such a course is that the waste is likely to come into contact with water, which could leach radioactive contamination into the environment. The anionic pertechnetate and [[iodide]] are less able to absorb onto the surfaces of minerals so they are likely to be more mobile. By comparison [[plutonium]], [[uranium]], and [[caesium]] are much more able to bind to soil particles. For this reason, the environmental chemistry of technetium is an active area of research. An alternative disposal method, [[Nuclear transmutation|transmutation]], has been demonstrated at [[CERN]] for technetium-99. This transmutation process is one in which the technetium (<sup>99</sup>Tc as a [[metal]] target) is bombarded with [[neutrons]] to form the shortlived <sup>100</sup>Tc (half life = 16 seconds) which decays by [[beta decay]] to [[ruthenium]] (<sup>100</sup>Ru). 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 <sup>106</sup>Ru (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 production of technetium-99 from spent nuclear fuel is a long process. During fuel reprocessing, it appears in the waste liquid, which is highly radioactive. After sitting for several years, the radioactivity has fallen to a point where extraction of the long-lived isotopes, including technetium-99, becomes feasible. Several chemical extraction processes are used yielding technetium-99 metal of high purity.<ref name="schwochau"/> ===Neutron activation of molybdenum or other pure elements=== The [[Nuclear isomer|meta stable]] (a state where the nucleus is in an excited state) isotope <sup>99m</sup>Tc is produced as a [[fission product]] from the fission of [[uranium]] or [[plutonium]] in [[nuclear reactor]]s. Because used fuel is allowed to stand for several years before reprocessing, all <sup>99</sup>Mo and <sup>99m</sup>Tc will have decayed by the time that the fission products are separated from the [[major actinides]] in conventional nuclear reprocessing. The PUREX [[raffinate]] will contain a high concentration of technetium as TcO<sub>4</sub><sup>-</sup> but almost all of this will be <sup>99</sup>Tc. The vast majority of the <sup>99m</sup>Tc used in medical work is formed from <sup>99</sup>Mo which is formed by the [[neutron]] activation of <sup>98</sup>Mo. <sup>99</sup>Mo has a half-life of 67 hours, so short-lived <sup>99m</sup>Tc (half-life: 6 hours), which results from its decay, is being constantly produced.<ref>''Nature's Building Blocks'', page 423, paragraph 2</ref> The hospital then chemically extracts the technetium from the solution by using a [[technetium-99m generator]] ("technetium cow", also occasionally called a "molybdenum cow"). The normal technetium cow is an [[alumina]] column which contains molybdenum-98; in as much as aluminium has a small neutron cross section, it is convenient for an alumina column bearing inactive <sup>98</sup>Mo to be irradiated with neutrons to make the radioactive Mo-99 column for the technetium cow.<ref>''The radiochemical manual''</ref> By working in this way, there is no need for the complex chemical steps which would be required to separate molybdenum from a fission product mixture. This alternative method requires that an enriched [[uranium]] target be irradiated with [[neutrons]] to form <sup>99</sup>Mo as a [[fission product]], then separated.<ref>J. L. Snelgrove ''et al.,'' "[http://www.rertr.anl.gov/MO99/JLS.pdf Development and Processing of LEU Targets for Mo-99 Production]" (1995).</ref> Other technetium isotopes are not produced in significant quantities by fission; when needed, they are manufactured by neutron irradiation of parent isotopes (for example, <sup>97</sup>Tc can be made by neutron irradiation of <sup>96</sup>Ru). == Isotopes == {{main|isotopes of technetium}} Technetium is one of the two elements in the first 82 that have no stable [[isotope]]s (in fact, it is the lowest-numbered element that is exclusively radioactive); the other such element is [[promethium]].<ref>''LANL Periodic Table'', "Technetium" paragraph 2</ref> The most stable [[Radionuclide|radioisotope]]s are <sup>98</sup>Tc ([[half-life]] of 4.2 [[Annum|Ma]]), <sup>97</sup>Tc (half-life: 2.6 Ma) and <sup>99</sup>Tc (half-life: 211.1 [[annum|ka]]).<ref name="environmentalchemistry"> EnvironmentalChemistry.com, "Technetium", Nuclides / Isotopes</ref> Twenty-two other radioisotopes have been characterized with [[atomic mass]]es ranging from 87.933 [[atomic mass unit|u]] (<sup>88</sup>Tc) to 112.931 u (<sup>113</sup>Tc). Most of these have half-lives that are less than an hour; the exceptions are <sup>93</sup>Tc (half-life: 2.75 hours), <sup>94</sup>Tc (half-life: 4.883 hours), <sup>95</sup>Tc (half-life: 20 hours), and <sup>96</sup>Tc (half-life: 4.28 days).<ref name="environmentalchemistry"/> Technetium also has numerous [[nuclear isomer|meta states]]. <sup>97m</sup>Tc is the most stable, with a half-life of 90.1 days (0.097 MeV). This is followed by <sup>95m</sup>Tc (half life: 61 days, 0.038 MeV), and <sup>99m</sup>Tc (half-life: 6.01 hours, 0.143 MeV). <sup>99m</sup>Tc only emits [[gamma ray]]s, subsequently decaying to <sup>99</sup>Tc.<ref name="environmentalchemistry"/> For isotopes lighter than the most stable isotope, <sup>98</sup>Tc, the primary [[decay mode]] is [[electron capture]], giving [[molybdenum]]. For the heavier isotopes, the primary mode is [[Beta decay|beta emission]], giving [[ruthenium]], with the exception that <sup>100</sup>Tc can decay both by beta emission and electron capture.<ref name="environmentalchemistry"/><ref>CRC Handbook, 85th edition, table of the isotopes</ref> Technetium-99 is the most common and most readily available isotope, as it is a major product of the fission of uranium-235. One gram of <sup>99</sup>Tc produces 6.2×10<sup>8</sup> disintegrations a second (that is, 0.62 G[[Becquerel|Bq]]/g).<ref>''The Encyclopedia of the Chemical Elements'', page 693, "Toxicology", paragraph 2</ref> === Stability of technetium isotopes === Technetium and [[promethium]] are unusual light elements in that they have no stable isotopes. The reason for this is somewhat complicated. <ref>http://book.nc.chalmers.se/KAPITEL/CH03NY3.PDF</ref> Using the [[liquid drop model]] for atomic nuclei, one can derive a semiempirical formula for the binding energy of a nucleus. This formula predicts a "valley of beta stability" along which [[nuclide]]s do not undergo beta decay. Nuclides that lie "up the walls" of the valley tend to decay by beta decay towards the center (by emitting an electron, emitting a [[positron]], or capturing an electron). For a fixed odd number of nucleons ''A'', the graph of binding energies vs. [[atomic number]] (number of protons) is shaped like a [[parabola]] (U-shaped), with the most stable nuclide at the bottom. A single beta decay or electron captures then transforms one nuclide of mass ''A'' into the next or preceding one, if the product has a lower binding energy and the difference in energy is sufficient to drive the decay mode. When there is only one parabola, there can be only one stable isotope lying on that parabola. {{Fact|date=October 2007}} For a fixed even number of nucleons ''A'', the graph is jagged and is better visualized as two separate [[parabola]]s for even and odd atomic numbers, because isotopes with an even number of protons and an even number of neutrons are more stable than isotopes with an odd number of neutrons and an odd number of protons. When there are two parabolas, that is, when the number of [[nucleon]]s is even, it can happen (rarely) that there is a stable nucleus with an odd number of neutrons and an odd number of protons (although there are only 4 truly stable examples as opposed to very long-lived: the light nuclei: <sup>2</sup>H, <sup>6</sup>Li, <sup>10</sup>B, <sup>14</sup>N). However, if this happens, there can be no stable isotope with an even number of neutrons and an even number of protons.{{Fact|date=October 2007}} For technetium (''Z''=43), the valley of beta stability is centered at around 98 nucleons. However, for every number of nucleons from 95 to 102, there is already at least one stable nuclide of either molybdenum (''Z''=42) or ruthenium (''Z''=44).{{Fact|date=October 2007}} <!-- but why? --> For the isotopes with odd numbers of nucleons, this immediately rules out a stable isotope of technetium, since there can be only one stable nuclide with a fixed odd number of nucleons. For the isotopes with an even number of nucleons, since technetium has an odd number of protons, any isotope must also have an odd number of neutrons. In such a case, the presence of a stable nuclide having the same number of nucleons and an even number of protons rules out the possibility of a stable nucleus.<ref>RADIOCHEMISTRY and NUCLEAR CHEMISTRY</ref> ==References== ===Works cited=== <div class="references-small"> ;'''Prose''' *''The Encyclopedia of the Chemical Elements'', edited by Cifford A. Hampel, "Technetium" entry by S. J. Rimshaw (New York; Reinhold Book Corporation; 1968; pages 689–693) Library of Congress Catalog Card Number: 68–29938 *''Nature's Building Blocks: An A-Z Guide to the Elements'', by John Emsley (New York; Oxford University Press; 2001; pages 422–425) ISBN 0-19-850340-7 *The radiochemical Manual, 2nd Ed, edited by B.J. Wilson, 1966. *[http://periodic.lanl.gov/elements/43.html Los Alamos National Laboratory &ndash; Technetium] (viewed [[1 December]] [[2002]] and [[22 April]] [[2005]]) *WebElements.com "Technetium" [http://www.webelements.com/webelements/elements/text/Tc/uses.html Uses] (viewed [[1 December]] [[2002]] and [[22 April]] [[2005]]) *EnvironmentalChemistry.com [http://environmentalchemistry.com/yogi/periodic/Tc-pg2.html Nuclides / Isotopes] (viewed [[1 December]] [[2002]] and [[22 April]] [[2005]]. JavaScript required, browser-restricted access) *[http://www.vanderkrogt.net/elements/elem/tc.html ''Elentymolgy and Elements Multidict'' by Peter van der Krogt, "Technetium"] (viewed [[30 April]] [[2005]]; Last updated [[10 April]] [[2005]] ) *[http://www.nndc.bnl.gov/content/elements.html ''History of the Origin of the Chemical Elements and Their Discoverers''] by Norman E. Holden (viewed [[30 April]] [[2005]]; last updated [[12 March]] [[2004]]) *''[http://www.bnl.gov/magnets/Staff/Gupta/Summer1968/0049.pdf Technetium as a Material for AC Superconductivity Applications]'' by S. H. Autler, Proceedings of the 1968 Summer Study on Superconducting Devices and Accelerators *''[http://www.chclibrary.org/micromed/00067370.html Technetium heart scan]'', Dr. Joseph F. Smith Medical library (viewed [[23 April]] [[2005]]) *''[http://www.iop.org/EJ/abstract/0952-4746/21/1/004 Gut transfer and doses from environmental technetium]'', J D Harrison et al 2001 ''J. Radiol. Prot.'' 21 9–11, Invited Editorial *''[http://www.hypatiamaze.org/ida/tacke.html Ida Tacke and the warfare behind the discovery of fission]'', by Kevin A. Nies (viewed [[23 April]] [[2005]]) *''[http://pubs.acs.org/cen/80th/technetium.html TECHNETIUM]'' by John T. Armstrong (viewed [[23 April]] [[2005]]) *''[http://www.radiochem.org/paper/JN41/j041Tagami.pdf Technetium-99 Behaviour in the Terrestrial Environment - Field Observations and Radiotracer Experiments]'', Keiko Tagami, Journal of Nuclear and Radiochemical Sciences, Vol. 4, No.1, pp. A1-A8, 2003 *''[http://www.superconductors.org/Type2.htm Type 2 superconductors]'' (viewed [[23 April]] [[2005]]) *''[http://www.hbcpnetbase.com/ The CRC Handbook of Chemistry and Physics]'', 85th edition, 2004–2005, CRC Press *K. Yoshihara, "Technetium in the Environment" in "Topics in Current Chemistry: Technetium and Rhenium", vol. 176, K. Yoshihara and T. Omori (eds.), Springer-Verlag, Berlin Heidelberg, 1996. *Schwochau, Klaus, ''Technetium'', Wiley-VCH (2000), ISBN 3-527-29496-1 *''[http://book.nc.chalmers.se/ RADIOCHEMISTRY and NUCLEAR CHEMISTRY]'', Gregory Choppin, Jan-Olov Liljenzin, and Jan Rydberg, 3rd Edition, 2002, [http://book.nc.chalmers.se/KAPITEL/CH03NY3.PDF the chapter on nuclear stability (pdf)] (viewed 5 January 2007) ;'''Table''' *[http://www.webelements.com/webelements/elements/text/Tc/index.html WebElements.com &ndash; Technetium], and [http://environmentalchemistry.com/yogi/periodic/Tc.html EnvironmentalChemistry.com &ndash; Technetium] per the guidelines at [http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Elements Wikipedia's WikiProject Elements] (all viewed [[1 December]] [[2002]]) * [http://www.nndc.bnl.gov/nudat2/index.jsp Nudat 2] nuclide chart from the National Nuclear Data Center, Brookhaven National Laboratory * ''[http://chartofthenuclides.com/default.html Nuclides and Isotopes] Fourteenth Edition: Chart of the Nuclides'', General Electric Company, 1989 </div> ===Notes=== {{reflist}} == External links == {{Commons|Technetium}} {{wiktionary|technetium}} *[http://www.webelements.com/webelements/elements/text/Tc/key.html WebElements.com &ndash; Technetium] *[http://pubs.acs.org/cen/80th/technetium.html pubs.acs.org &ndash; ACS article on validity of Noddack and Tacke's discovery] {{clear}} {{compact periodic table}} [[Category:Chemical elements]] [[Category:Radiobiology]] [[Category:Transition metals]] [[Category:Technetium|*]] [[Category:Synthetic elements]] {{featured article}} {{Link FA|de}} {{Link FA|af}} {{Link FA|es}} <!-- interwiki --> [[af:Tegnesium]] [[ar:تكنيتيوم]] [[az:Texnesium]] [[bn:টেকনেটিয়াম]] [[be:Тэхнецый]] [[bs:Tehnecijum]] [[bg:Технеций]] [[ca:Tecneci]] [[cs:Technecium]] [[co:Tecneziu]] [[da:Technetium]] [[de:Technetium]] [[et:Tehneetsium]] [[el:Τεχνήτιο]] [[es:Tecnecio]] [[eo:Teknecio]] [[eu:Teknezio]] [[fa:تکنسیوم]] [[fr:Technétium]] [[fur:Tecnezi]] [[gv:Çheghnaiçhum]] [[gl:Tecnecio]] [[ko:테크네튬]] [[hy:Տեխնեցիում]] [[hi:टेक्निशियम]] [[hr:Tehnecij]] [[io:Teknecio]] [[id:Teknesium]] [[is:Teknetín]] [[it:Tecnezio]] [[he:טכנציום]] [[sw:Tekineti]] [[ht:Tèknesyòm]] [[ku:Teknesyûm]] [[la:Technetium]] [[lv:Tehnēcijs]] [[lb:Technetium]] [[lt:Technecis]] [[jbo:runjinme]] [[hu:Technécium]] [[ml:ടെക്നീഷ്യം]] [[nl:Technetium]] [[ja:テクネチウム]] [[no:Technetium]] [[nn:Technetium]] [[oc:Tecnèci]] [[uz:Texnetsiy]] [[pl:Technet]] [[pt:Tecnécio]] [[ro:Technetiu-99m]] [[ru:Технеций]] [[scn:Tecnezziu]] [[simple:Technetium]] [[sk:Technécium]] [[sl:Tehnecij]] [[sr:Техницијум]] [[sh:Tehnicijum]] [[fi:Teknetium]] [[sv:Teknetium]] [[ta:டெக்னீசியம்]] [[te:టెక్నీషియమ్]] [[th:เทคนีเชียม]] [[vi:Tecneti]] [[tr:Teknesyum]] [[uk:Технецій]] [[zh:锝]]