Editing Technetium (section)

==Occurrence and production==
Technetium occurs naturally in the Earth's [[Crust (geology)|crust]] in minute concentrations of about 0.003 parts per trillion. Technetium is so rare because the [[half-life|half-lives]] of <sup>97</sup>Tc and <sup>98</sup>Tc are only {{nobr|4.2 million years.}} More than a thousand of such periods have passed since the formation of the [[Earth]], so the probability of survival of even one atom of [[primordial nuclide|primordial]] technetium is effectively zero. However, small amounts exist as spontaneous [[fission product]]s in [[uranium ore]]s. A kilogram of uranium contains an estimated 1&nbsp;[[Orders of magnitude (mass)|nanogram]] {{nobr|({{10^|−9}} g)}}, equivalent to ten trillion atoms, of technetium.<ref name=blocks/><ref>
{{cite journal
 |last1=Dixon    |first1=P.        |last2=Curtis  |first2=David B.
 |last3=Musgrave |first3=John      |last4=Roensch |first4=Fred
 |last5=Roach    |first5=Jeff      |last6=Rokop   |first6=Don
 |date=1997
 |title=Analysis of naturally produced technetium and plutonium in geologic materials
 |journal=Analytical Chemistry
 |volume=69 |issue=9 |pages=1692–1699
 |doi=10.1021/ac961159q  |pmid=21639292
}}
</ref><ref>
{{cite journal
 |last1=Curtis |first1=D.         |last2=Fabryka-Martin |first2=June
 |last3=Dixon  |first3=Paul       |last4=Cramer   |first4=Jan
 |date=1999
 |title=Nature's uncommon elements: Plutonium and technetium
 |journal=Geochimica et Cosmochimica Acta
 |volume=63 |issue=2 |page=275
 |bibcode=1999GeCoA..63..275C
 |doi=10.1016/S0016-7037(98)00282-8
 |url=https://digital.library.unt.edu/ark:/67531/metadc704244/
}}
</ref>
Some [[red giant]] stars with the spectral types S, M, and N display a spectral absorption line indicating the presence of technetium.{{sfn|Hammond|2004|p={{page needed|date=June 2021}}}}<ref>{{cite journal|doi=10.1126/science.114.2951.59|date=1951 |last1=Moore|first1=C. E.|title=Technetium in the Sun|journal=Science |volume=114 |issue=2951 |pages=59–61 |pmid=17782983|bibcode=1951Sci...114...59M}}</ref><!--Technetium in Red Giant Stars P Merrill&nbsp;— Science, 1952--> These red giants are known informally as [[technetium star]]s.

===Fission waste product===
In contrast to 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 products. The fission of a gram of [[uranium-235]] in [[nuclear reactor]]s yields 27&nbsp;mg of technetium-99, giving technetium a [[fission product yield]] of 6.1%.<ref name="enc" /> Other [[fissile]] isotopes produce similar yields of technetium, such as 4.9% from [[uranium-233]] and 6.21% from [[plutonium-239]].{{sfn|Schwochau|2000|pp=374–404}} An estimated 49,000&nbsp;T[[Becquerel|Bq]] (78&nbsp;[[tonne|metric tons]]) of technetium was produced in nuclear reactors between 1983 and 1994, by far the dominant source of terrestrial technetium.<ref name=yoshihara>
{{cite book
 |last=Yoshihara   |first=K.
 |date=1996
 |chapter=Technetium in the environment
 |editor1-last=Yoshihara  |editor1-first=K.
 |editor2-last=Omori      |editor2-first=T.
 |title=Technetium and Rhenium: Their chemistry and its applications
 |series=Topics in Current Chemistry |volume=176
 |publisher=Springer-Verlag
 |location=Berlin / Heidelberg, DE
 |isbn=978-3-540-59469-7
 |doi=10.1007/3-540-59469-8_2
 |pages=17–35
}}
</ref><ref name=leon/>
Only a fraction of the production is used commercially.{{efn|
{{As of|2005}}, technetium-99 in the form of [[ammonium pertechnetate]] is available to holders of an [[Oak Ridge National Laboratory]] permit.{{sfn|Hammond|2004|p={{page needed|date=June 2021}}}}
}}

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 [[nuclear weapon|fission bomb]] explosions. Its decay, measured in [[becquerel]]s per amount of spent fuel, is the dominant contributor to nuclear waste radioactivity after about {{nobr|{{10^|4}}~{{10^|6}} years}} after the creation of the nuclear waste.<ref name=yoshihara/> From 1945–1994, an estimated 160&nbsp;T[[Becquerel|Bq]] (about 250&nbsp;kg) of technetium-99 was released into the environment during atmospheric [[nuclear test]]s.<ref name=yoshihara/><ref>
{{cite book
 |last1=Desmet     |first1=G.
 |last2=Myttenaere |first2=C.
 |date=1986
 |title=Technetium in the Environment
 |publisher=Springer
 |isbn=978-0-85334-421-6
 |page=69
 |url=https://books.google.com/books?id=QLHr-UYWoo8C&pg=PA69
}}
</ref>
The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is on the order of 1000&nbsp;TBq (about 1600&nbsp;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&nbsp;TBq (about 900&nbsp;kg) from 1995 to 1999 into the [[Irish Sea]].<ref name=leon>
{{cite journal
 |last=Garcia-Leon  |first=M.
 |date=2005
 |title={{sup|99}}Tc in the environment: Sources, distribution, and methods
 |journal=Journal of Nuclear and Radiochemical Sciences
 |volume=6 |issue=3 |pages=253–259
 |doi=10.14494/jnrs2000.6.3_253 |doi-access=free
 |url=http://www.radiochem.org/paper/JN63/jn6326.pdf
}}
</ref> 
From 2000 onwards the amount has been limited by regulation to 90&nbsp;TBq (about 140&nbsp;kg) per year.<ref>
{{cite journal
 |first=K.  |last=Tagami
 |date=2000
 |title=Technetium-99 behaviour in the terrestrial environment — field observations and radiotracer experiments
 |journal=Journal of Nuclear and Radiochemical Sciences
 |volume=4  |pages=A1–A8
 |doi=10.14494/jnrs2000.4.a1  |doi-access=free
 |url=https://www.jstage.jst.go.jp/article/jnrs2000/4/1/4_1_A1/_pdf
}}
</ref>
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&nbsp;Bq/kg of technetium.<ref>
{{cite book
 |url=https://books.google.com/books?id=zVmdln2pJxUC&pg=PA403
 |page=403
 |title=Mineral Components in Foods
 |last1=Szefer |first1=P.
 |last2=Nriagu |first2=J.O.
 |publisher=CRC Press
 |date=2006
 |isbn=978-0-8493-2234-1
}}
</ref><ref>
{{cite journal
 |first1=J.D. |last1=Harrison
 |first2=A.   |last2=Phipps
 |date=2001
 |title=Gut transfer and doses from environmental technetium
 |journal=Journal of Radiological Protection
 |volume=21  |issue=1  |pages=9–11
 |doi=10.1088/0952-4746/21/1/004
 |bibcode=2001JRP....21....9H
 |pmid=11281541   |s2cid=250752077
}}
</ref>{{efn|
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 mobility of technetium in industrial wastes and other subsurface environments.<ref>
{{cite journal
 |last1=Francis |first1=A.J.
 |last2=Dodge   |first2=C.J.
 |last3=Meinken |first3=G.E.
 |date=2002 
 |title=Biotransformation of pertechnetate by ''Clostridia''
 |journal=Radiochimica Acta
 |volume=90 |issue=9–11 |pages=791–797
 |doi= 10.1524/ract.2002.90.9-11_2002.791
 |s2cid=83759112
 |url=https://zenodo.org/record/1236279
}}
</ref>
}}

===Fission product for commercial use===
The [[Metastability|metastable]] isotope technetium-99m is continuously produced as a [[fission product]] from the fission of uranium or [[plutonium]] in [[nuclear reactor]]s:

<chem display="block"> ^{238}_{92}U ->[\ce{sf}] ^{137}_{53}I + ^{99}_{39}Y + 2^{1}_{0}n</chem>
<chem display="block"> ^{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</chem>

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 [[actinide]]s in conventional [[nuclear reprocessing]]. The liquid left after plutonium–uranium extraction ([[PUREX]]) contains a high concentration of technetium as {{chem|TcO|4|-}} but almost all of this is technetium-99, not technetium-99m.{{sfn|Schwochau|2000|p=39}}

The vast majority of the technetium-99m used in medical work is produced by irradiating dedicated [[enriched uranium#Highly enriched uranium (HEU)|highly enriched uranium]] targets in a reactor, extracting molybdenum-99 from the targets in reprocessing facilities,<ref name="nuclmed">{{cite journal|last=Moore |first=P. W.|title=Technetium-99 in generator systems|journal=Journal of Nuclear Medicine |date=April 1984 |volume=25 |issue=4|pages=499–502 |pmid=6100549|url=http://jnm.snmjournals.org/content/25/4/499.full.pdf |access-date=2012-05-11}}</ref> and recovering at the diagnostic center the technetium-99m produced upon decay of molybdenum-99.<ref>{{cite patent|country=US |number=3799883|title=Silver coated charcoal step |invent1=Hirofumi Arino|assign1= Union Carbide Corporation|gdate=March 26, 1974}}</ref><ref>{{cite book| title = Medical Isotope Production Without Highly Enriched Uranium| author=Committee on Medical Isotope Production Without Highly Enriched Uranium| publisher=National Academies Press|page=vii |isbn=978-0-309-13040-0|date=2009}}</ref> Molybdenum-99 in the form of molybdate {{chem|MoO|4|2-}} is [[adsorption|adsorbed]] onto acid alumina ({{chem|Al|2|O|3}}) in a [[radiation shielding|shielded]] [[column chromatography|column chromatograph]] inside a [[technetium-99m generator]] ("technetium cow", also occasionally called a "molybdenum cow"). Molybdenum-99 has a half-life of 67&nbsp;hours, so short-lived technetium-99m (half-life: 6&nbsp;hours), which results from its decay, is being constantly produced.<ref name="blocks" /> The soluble [[pertechnetate]] {{chem|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.<ref>{{cite news |last=Lützenkirchen |first=K.-R. |title=Nuclear forensics sleuths trace the origin of trafficked material |url=http://arq.lanl.gov/source/orgs/nmt/nmtdo/AQarchive/4thQuarter07/page1.shtml |publisher=Los Alamos National Laboratory |access-date=2009-11-11 |url-status=dead |archive-url=https://web.archive.org/web/20130216114404/http://arq.lanl.gov/source/orgs/nmt/nmtdo/AQarchive/4thQuarter07/page1.shtml |archive-date=2013-02-16}}</ref><ref>{{cite conference|last1=Snelgrove|first1=J. L.|first2=G. L. |last2=Hofman |url=http://www.rertr.anl.gov/MO99/JLS.pdf|title=Development and Processing of LEU Targets for Mo-99 Production| date=1995| access-date=2009-05-05 |work=ANL.gov |conference=1995 International Meeting on Reduced Enrichment for Research and Test Reactors, September 18–21, 1994, Paris, France}}</ref>
[[File:First technetium-99m generator - 1958.jpg|thumb|upright|The first [[technetium-99m generator]], unshielded, 1958. A Tc-99m [[pertechnetate]] solution is being eluted from Mo-99 [[molybdate]] bound to a chromatographic substrate]]
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 [[Petten nuclear reactor|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 (product)|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.<ref>{{cite journal | last1 = Thomas | first1 = Gregory S. | last2 = Maddahi | first2 = Jamshid | title = The technetium shortage | journal = [[Journal of Nuclear Cardiology]] | volume = 17 | pages = 993–8 | date = 2010 | doi = 10.1007/s12350-010-9281-8 | issue = 6 | pmid=20717761| s2cid = 2397919 }}</ref>

===Waste disposal===
The long half-life of technetium-99 and its potential to form [[anionic]] species creates a major concern for long-term [[High-level radioactive waste management|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 [[geological repository|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,<ref>{{cite journal | last1 = German | first1 = Konstantin E. | last2 = Firsova | first2 = E. V. | title = Bioaccumulation of Tc, Pu, and Np on Bottom Sediments in Two Types of Freshwater Lakes of the Moscow Oblast | journal = Radiochemistry | volume = 45 | pages = 250–256 | date = 2003 | issue = 6 | doi = 10.1023/A:1026008108860 | last3 = Peretrukhin | first3 = V. F. | last4 = Khizhnyak | first4 = T. V. | last5 = Simonoff | first5 = M. | bibcode = 2003Radch..45..250G | s2cid = 55030255 }}</ref> and the [[environmental chemistry]] of technetium is an area of active research.<ref>{{cite book|url=https://books.google.com/books?id=eEeJbur_je0C&pg=PA147|page=147|title=Radioactivity in the terrestrial environment|last=Shaw |first=G. |publisher=Elsevier |date=2007 |isbn=978-0-08-043872-6}}</ref>

An alternative disposal method, [[Nuclear transmutation|transmutation]], has been demonstrated at [[CERN]] for technetium-99. In this process, the technetium (technetium-99 as a metal target) is bombarded with [[neutron]]s to form the short-lived technetium-100 (half-life = 16&nbsp;seconds) which decays by beta decay to stable [[ruthenium]]-100. If recovery of usable ruthenium is a goal, an extremely pure technetium target is needed; if small traces of the [[minor actinide]]s such as [[americium]] and [[curium]] are present in the target, they are likely to undergo fission and form more [[fission product]]s which increase the radioactivity of the irradiated target. The formation of ruthenium-106 (half-life 374&nbsp;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.<ref>{{cite book|url=http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000XT88.txt|title=Alternative disposal concepts for high-level and transuranic radioactive waste disposal|publisher=US Environmental Protection Agency|date=1979|author=Altomare, P|last2=Bernardi}}</ref>

The actual separation of technetium-99 from spent nuclear fuel is a long process. During [[nuclear reprocessing|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<!--isotopic and chemical?--> purity.{{sfn|Schwochau|2000|pp=87–96}}

===Neutron activation===
[[Molybdenum-99]], which decays to form technetium-99m, can be formed by the [[neutron activation]] of molybdenum-98.<ref name="IAEA TECDOC-1340">{{cite news|title = Manual for reactor produced radioisotopes |url = http://www-pub.iaea.org/MTCD/publications/PDF/te_1340_web.pdf|access-date = 2009-08-27 |publisher = IAEA|date=January 2003}}</ref> 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]]).<ref>{{cite book|url=https://books.google.com/books?id=mQkdSO48rDUC&pg=PA91|page=91 |title=Effluent and environmental radiation surveillance: a symposium|last=Kelly |first=J. J.|publisher=ASTM International|date=1980}}</ref>

===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 <sup>100</sup>Mo(p,2n)<sup>99m</sup>Tc was demonstrated in 1971.<ref>{{cite journal|last1=Beaver|first1=J. E.|last2=Hupf |first2=H. B. |title=Production of <sup>99m</sup>Tc on a Medical Cyclotron: a Feasibility Study|journal=Journal of Nuclear Medicine|date=November 1971 |volume=12|issue=11|pages=739–741 |pmid=5113635|url=http://jnm.snmjournals.org/content/12/11/739.full.pdf}}</ref> The recent shortages of medical technetium-99m reignited the interest in its production by proton bombardment of isotopically enriched (>99.5%) molybdenum-100 targets.<ref name="bbc-20150530">{{cite news |url=https://www.bbc.co.uk/news/magazine-32833599 |title=The element that can make bones glow |author=Laurence Knight |work=BBC News |date=30 May 2015 |access-date=30 May 2015}}</ref><ref>{{cite journal|display-authors=4|author=Guérin B|author2=Tremblay S|author3=Rodrigue S|author4=Rousseau JA |author5=Dumulon-Perreault V|author6=Lecomte R|author7=van Lier JE|author8=Zyuzin A|author9=van Lier EJ |name-list-style=vanc |title=Cyclotron production of <sup>99m</sup>Tc: an approach to the medical isotope crisis|journal=Journal of Nuclear Medicine |date=2010|volume=51|issue=4|pages=13N–6N|pmid=20351346 |url=http://jnm.snmjournals.org/content/51/4/13N.full.pdf}}</ref> Other techniques are being investigated for obtaining molybdenum-99 from molybdenum-100 via (n,2n) or (γ,n) reactions in particle accelerators.<ref>{{cite journal |last1=Scholten|first1=Bernhard|last2=Lambrecht|first2= Richard M.|last3=Cogneau |first3=Michel|last4= Vera Ruiz|first4=Hernan|last5=Qaim|first5=Syed M.|title=Excitation functions for the cyclotron production of <sup>99m</sup>Tc and <sup>99</sup>Mo|journal=Applied Radiation and Isotopes|date=25 May 1999|volume=51|issue=1 |pages=69–80|doi=10.1016/S0969-8043(98)00153-5|bibcode=1999AppRI..51...69S }}</ref><ref>{{cite journal |last1=Takács|first1=S.|last2=Szűcs|first2=Z. |last3=Tárkányi |first3=F. |last4=Hermanne|first4=A. |last5=Sonck|first5=M.|title=Evaluation of proton induced reactions on <sup>100</sup>Mo: New cross sections for production of <sup>99m</sup>Tc and <sup>99</sup>Mo |journal=Journal of Radioanalytical and Nuclear Chemistry|date=1 January 2003|volume=257|issue=1|pages=195–201|doi=10.1023/A:1024790520036|s2cid=93040978}}</ref><ref>{{cite journal|last1=Celler|first1=A.|last2=Hou|first2=X.|last3=Bénard|first3=F. |last4=Ruth |first4=T. |title=Theoretical modeling of yields for proton-induced reactions on natural and enriched molybdenum targets|journal=Physics in Medicine and Biology|date=2011|volume=56|issue=17|pages=5469–5484 |doi=10.1088/0031-9155/56/17/002|pmid=21813960|bibcode=2011PMB....56.5469C|s2cid=24231457 }}</ref>