Editing Thorium (section)

==History==
[[File:Mårten Eskil Winge - Tor's Fight with the Giants - Google Art Project.jpg|thumb|upright|alt=Thor raising his hammer in a battle against the giants|''[[Thor's Fight with the Giants]]'' (1872) by [[Mårten Eskil Winge]]; [[Thor]], the [[Norse god]] of thunder, raising his hammer [[Mjölnir]] in a battle against the [[Jötunn|giants]].<ref>{{Cite web|url=https://artsandculture.google.com/asset/tor-s-fight-with-the-giants/3gGd_ynWqGjGfQ?hl=en|title=Tor's Fight with the Giants |publisher=[[Google Arts & Culture]]|language=en|access-date=26 June 2016}}</ref>]]

===Erroneous report===

In 1815, the Swedish chemist [[Jöns Jacob Berzelius]] analysed an unusual sample of [[gadolinite]] from a copper mine in [[Falun]], central Sweden. He noted impregnated traces of a white mineral, which he cautiously assumed to be an earth ([[oxide]] in modern chemical nomenclature) of an unknown element. Berzelius had already discovered two elements, [[cerium]] and [[selenium]], but he had made a public mistake once, announcing a new element, ''gahnium'', that turned out to be [[zinc oxide]].<ref name="Lost" /> Berzelius privately named the putative element "thorium" in 1817<ref>{{cite book |last1=Ryabchikov |first1=D. I. |last2=Gol'braikh |first2=E. K. |date=2013 |title=The Analytical Chemistry of Thorium: International Series of Monographs on Analytical Chemistry |publisher=[[Elsevier]] |page=1 |isbn=978-1-4831-5659-0}}</ref> and its supposed oxide "thorina" after [[Thor]], the [[Norse god]] of thunder.<ref>{{cite book |last=Thomson |first=T. |date=1831 |title=A System of Chemistry of Inorganic Bodies |volume=1 |publisher=Baldwin & Cradock and [[William Blackwood]] |page=475}}</ref> In 1824, after more deposits of the same mineral in [[Vest-Agder]], Norway, were discovered, he retracted his findings, as the mineral (later named [[xenotime]]) proved to be mostly [[yttrium phosphate|yttrium orthophosphate]].{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}}<ref name="Lost">{{cite book|ref=Fontani|last1=Fontani|first1=M.|last2=Costa|first2=M.|last3=Orna|first3=V.|title=The Lost Elements: The Periodic Table's Shadow Side|publisher=Oxford University Press|year=2014|page=73|isbn=978-0-19-938334-4}}</ref><ref>{{cite journal |last=Berzelius |first=J. J. |author-link=Jöns Jakob Berzelius |date=1824 |title=Undersökning af några Mineralier. 1. Phosphorsyrad Ytterjord. |trans-title=Examining some minerals. 1st phosphoric yttria. |journal=Kungliga Svenska Vetenskapsakademiens Handlingar |volume=2 |pages=334–338 |language=sv}}</ref><ref name="Mindat">{{cite web |url=http://www.mindat.org/min-4333.html |title=Xenotime-(Y) |publisher=Mindat database |access-date=7 October 2017 |archive-date=16 March 2017 |archive-url=https://web.archive.org/web/20170316030444/http://www.mindat.org/min-4333.html |url-status=live }}</ref>

===Discovery===
In 1828, [[Morten Thrane Esmark]] found a black mineral on [[Løvøya, Telemark|Løvøya]] island, [[Telemark]] county, Norway. He was a Norwegian [[priest]] and amateur [[mineralogist]] who studied the minerals in Telemark, where he served as [[vicar]]. He commonly sent the most interesting specimens, such as this one, to his father, [[Jens Esmark]], a noted mineralogist and professor of mineralogy and geology at the [[Royal Frederick University]] in Christiania (today called [[Oslo]]).<ref name="snl">{{cite encyclopedia|year=2007|title=Morten Thrane Esmark|encyclopedia=[[Store norske leksikon]]<!--|editor-last=Henriksen |editor-first=P. is this correct? -->|first=R. S.|last=Selbekk|publisher=[[Kunnskapsforlaget]]|url=http://www.snl.no/Morten_Thrane_Esmark|access-date=16 May 2009|language=no|archive-date=28 April 2021|archive-url=https://web.archive.org/web/20210428144944/https://snl.no/Morten_Thrane_Esmark|url-status=live}}</ref> The elder Esmark determined that it was not a known mineral and sent a sample to Berzelius for examination. Berzelius determined that it contained a new element.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}} He published his findings in 1829, having isolated an impure sample by reducing {{chem2|K[ThF5]}} (potassium pentafluorothorate(IV)) with [[potassium]] metal.<ref name="Weeks" /><ref>{{cite journal|last=Berzelius|first=J. J.|language=de|date=1829|url=http://gallica.bnf.fr/ark:/12148/bpt6k151010.pleinepage.r=Annalen+der+Physic.f395.langFR|title=Untersuchung eines neues Minerals und einer darin erhalten zuvor unbekannten Erde|trans-title=Investigation of a new mineral and of a previously unknown earth contained therein|journal=Annalen der Physik und Chemie|volume=16|pages=385–415|doi=10.1002/andp.18290920702|bibcode=1829AnP....92..385B|issue=7|archive-date=27 April 2021|access-date=20 July 2009|archive-url=https://web.archive.org/web/20210427143538/https://gallica.bnf.fr/ark:/12148/bpt6k151010.pleinepage.r=Annalen+der+Physic.f395.langFR|url-status=live}} (modern citation: ''Annalen der Physik'', vol. 92, no. 7, pp. 385–415).</ref><ref>{{cite journal|last=Berzelius |first=J. J. |date= 1829|title=Undersökning af ett nytt mineral (Thorit), som innehåller en förut obekant jord |trans-title=Investigation of a new mineral (thorite), as contained in a previously unknown earth|journal=Kungliga Svenska Vetenskaps Akademiens Handlingar |pages=1–30 |language=sv}}</ref> Berzelius reused the name of the previous supposed element discovery<ref name="Weeks">{{cite journal |doi= 10.1021/ed009p1231|bibcode= 1932JChEd...9.1231W |title= The discovery of the elements. XI. Some elements isolated with the aid of potassium and sodium: Zirconium, titanium, cerium, and thorium |date= 1932 |last1= Weeks |first1= M. E. |author-link1=Mary Elvira Weeks| journal= Journal of Chemical Education |volume= 9 |issue= 7 |page= 1231}}</ref><ref>{{cite journal |doi= 10.1002/ange.19020153703 |title= Die eigentlichen Thorit-Mineralien (Thorit und Orangit) |trans-title= The actual thoritic minerals (thorite and orangite) |language= de |date= 1902 |last1= Schilling |first1= J. |journal= Zeitschrift für Angewandte Chemie |volume= 15 |issue= 37 |pages= 921–929 |bibcode= 1902AngCh..15..921S |url= https://zenodo.org/record/1424433 |archive-date= 13 April 2023 |access-date= 24 August 2019 |archive-url= https://web.archive.org/web/20230413111147/https://zenodo.org/record/1424433 |url-status= live }}</ref> and named the source mineral thorite.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}}

[[File:J J Berzelius.jpg|thumb|upright|alt=Jöns Jacob Berzelius|[[Jöns Jacob Berzelius]], who first identified thorium as a new element]]

Berzelius made some initial characterisations of the new metal and its chemical compounds: he correctly determined that the thorium–oxygen mass ratio of thorium oxide was 7.5 (its actual value is close to that, ~7.3), but he assumed the new element was divalent rather than tetravalent, and so calculated that the atomic mass was 7.5 times that of oxygen (120 [[atomic mass unit|amu]]); it is actually 15 times as large.{{efn|At the time, the [[rare-earth element]]s, among which thorium was found and with which it is closely associated in nature, were thought to be divalent; the rare earths were given [[atomic weight]] values two-thirds of their actual ones, and thorium and uranium are given values half of the actual ones.}} He determined that thorium was a very [[Electronegativity#Electropositivity|electropositive]] metal, ahead of cerium and behind zirconium in electropositivity.<ref name="leach2">{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=453 |title=The Internet Database of Periodic Tables: Berzelius' Electronegativity Table |last=Leach |first=M. R. |access-date=16 July 2016 |archive-date=28 April 2021 |archive-url=https://web.archive.org/web/20210428202351/https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=453 |url-status=live }}</ref> Metallic thorium was isolated for the first time in 1914 by Dutch entrepreneurs Dirk Lely Jr. and Lodewijk Hamburger.{{efn|The main difficulty in isolating thorium lies not in its chemical electropositivity, but in the close association of thorium in nature with the rare-earth elements and uranium, which collectively are difficult to separate from each other. Swedish chemist [[Lars Fredrik Nilson]], the discoverer of scandium, had previously made an attempt to isolate thorium metal in 1882, but was unsuccessful at achieving a high degree of purity.<ref>{{cite journal |last=Nilson |first=L. F. |date=1882 |title=Über metallisches Thorium |trans-title=About metallic thorium |journal=Berichte der Deutschen Chemischen Gesellschaft |volume=15 |issue=2 |pages=2537–2547 |doi=10.1002/cber.188201502213 |language=de |url=https://zenodo.org/record/1425272 |archive-date=13 April 2023 |access-date=24 August 2019 |archive-url=https://web.archive.org/web/20230413114159/https://zenodo.org/record/1425272 |url-status=live }}</ref> Lely and Hamburger obtained 99% pure thorium metal by reducing thorium chloride with sodium metal.<ref name="Meister" /> A simpler method leading to even higher purity was discovered in 1927 by American engineers John Marden and Harvey Rentschler, involving the reduction of thorium oxide with calcium in presence of calcium chloride.<ref name="Meister">{{cite report |year=1948 |last=Meister |first=G. |url=http://www.lm.doe.gov/Considered_Sites/F/Foote_Mineral_Co_-_PA_27/PA_27-3.pdf |title=Production of Rarer Metals |publisher=[[United States Atomic Energy Commission]] |access-date=22 September 2017 |archive-date=24 February 2017 |archive-url=https://web.archive.org/web/20170224180301/https://www.lm.doe.gov/Considered_Sites/F/Foote_Mineral_Co_-_PA_27/PA_27-3.pdf }}</ref>}}

===Initial chemical classification===
In the periodic table published by [[Dmitri Mendeleev]] in 1869, thorium and the rare-earth elements were placed outside the main body of the table, at the end of each vertical period after the [[alkaline earth metal]]s. This reflected the belief at that time that thorium and the rare-earth metals were divalent. With the later recognition that the rare earths were mostly trivalent and thorium was tetravalent, Mendeleev moved cerium and thorium to group IV in 1871, which also contained the modern [[carbon group]] (group 14) and titanium group (group 4), because their maximum oxidation state was +4.<ref name="leach">{{cite web |url=http://www.meta-synthesis.com/webbook//35_pt/pt_database.php |title=The Internet Database of Periodic Tables |last=Leach |first=M. R. |access-date=14 May 2012 |archive-date=24 March 2016 |archive-url=https://web.archive.org/web/20160324070522/http://www.meta-synthesis.com/webbook/35_pt/pt_database.php |url-status=live }}</ref><ref name="Jensen">{{cite journal|author1-link=William B. Jensen |last1=Jensen |first1=William B. |title=The Place of Zinc, Cadmium, and Mercury in the Periodic Table |journal=Journal of Chemical Education |date=August 2003 |volume=80 |issue=8 |page=952 |doi=10.1021/ed080p952 |bibcode=2003JChEd..80..952J }}</ref> Cerium was soon removed from the main body of the table and placed in a separate lanthanide series; thorium was left with group 4 as it had similar properties to its supposed lighter congeners in that group, such as [[titanium]] and zirconium.<ref name="Masterton" />{{efn|Thorium also appears in the 1864 table by British chemist [[John Newlands (chemist)|John Newlands]] as the last and heaviest element, as it was initially thought that uranium was a trivalent element with an atomic weight of around 120: this is half of its actual value, since uranium is predominantly hexavalent. It also appears as the heaviest element in the 1864 table by British chemist [[William Odling]] under titanium, zirconium, and [[tantalum]]. It does not appear in the periodic systems published by French geologist [[Alexandre-Émile Béguyer de Chancourtois]] in 1862, German-American musician [[Gustav Hinrichs]] in 1867, or German chemist [[Julius Lothar Meyer]] in 1870, all of which exclude the rare earths and thorium.<ref name="leach" />}}

===First uses===
[[File:Old thorium dioxide gas mantle - oblong shape.JPG|thumb|alt=Gas mantle|[[World War II]] thorium dioxide gas mantle]]
While thorium was discovered in 1828 its first application dates only from 1885, when Austrian chemist [[Carl Auer von Welsbach]] invented the [[gas mantle]], a portable source of light which produces light from the incandescence of thorium oxide when heated by burning gaseous fuels.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}} Many applications were subsequently found for thorium and its compounds, including ceramics, carbon arc lamps, heat-resistant crucibles, and as catalysts for industrial chemical reactions such as the oxidation of ammonia to nitric acid.{{sfn|Wickleder|Fourest|Dorhout|2006|p=52}}

===Radioactivity===
Thorium was first observed to be radioactive in 1898, by the German chemist [[Gerhard Carl Schmidt]] and later that year, independently, by the Polish-French physicist [[Marie Curie]]. It was the second element that was found to be radioactive, after the 1896 discovery of radioactivity in uranium by French physicist [[Henri Becquerel]].<ref>{{cite journal|last=Curie |first=M. |author-link=Marie Curie |date=1898|title= Rayons émis par les composés de l'uranium et du thorium |trans-title=Rays emitted by compounds of uranium and thorium|journal=Comptes Rendus|volume= 126| pages= 1101–1103|ol=24166254M |language=fr}}</ref><ref>{{cite journal |last=Schmidt |first=G. C. |author-link=Gerhard Carl Schmidt |date=1898 |title=Über die vom Thorium und den Thoriumverbindungen ausgehende Strahlung |trans-title=On the radiation emitted by thorium and thorium compounds |journal=Verhandlungen der Physikalischen Gesellschaft zu Berlin |volume=17 |pages=14–16 |language=de |url=http://digital.slub-dresden.de/id507751434-18980000/24 }}</ref><ref>{{cite journal |last=Schmidt |first=G. C. |url=http://gallica.bnf.fr/ark:/12148/bpt6k153068.image.r=Annalen+der+Physic.f149.langFR |title=Über die von den Thorverbindungen und einigen anderen Substanzen ausgehende Strahlung |trans-title=On the radiation emitted by thorium compounds and some other substances |journal=Annalen der Physik und Chemie |volume=65 |issue=5 |pages=141–151 |date=1898 |language=de |bibcode=1898AnP...301..141S |doi=10.1002/andp.18983010512 |archive-date=28 April 2021 |access-date=19 July 2009 |archive-url=https://web.archive.org/web/20210428101106/https://gallica.bnf.fr/ark:/12148/bpt6k153068.image.r=Annalen+der+Physic.f149.langFR |url-status=live }} (modern citation: ''Annalen der Physik'', vol. 301, pp. 141–151 (1898)).</ref> Starting from 1899, the New Zealand physicist [[Ernest Rutherford]] and the American electrical engineer [[Robert Bowie Owens]] studied the radiation from thorium; initial observations showed that it varied significantly. It was determined that these variations came from a short-lived gaseous daughter of thorium, which they found to be a new element. This element is now named [[radon]], the only one of the rare radioelements to be discovered in nature as a daughter of thorium rather than uranium.<ref>{{cite journal|author=Rutherford, E.|author-link=Ernest Rutherford|author2=Owens, R. B.|author2-link=Robert Bowie Owens|title=Thorium and uranium radiation|journal=Trans. R. Soc. Can.|volume=2|date= 1899|pages= 9–12}}: "The radiation from thorium oxide was not constant, but varied in a most capricious manner", whereas "All the compounds of Uranium give out a radiation which is remarkably constant."</ref>

After accounting for the contribution of radon, Rutherford, now working with the British physicist [[Frederick Soddy]], showed how thorium decayed at a fixed rate over time into a series of other elements in work dating from 1900 to 1903. This observation led to the identification of the [[half-life]] as one of the outcomes of the [[alpha particle]] experiments that led to the disintegration theory of [[radioactivity]].<ref>{{cite book|last=Simmons|first=J. G.|title=The Scientific 100: A Ranking of the Most Influential Scientists, Past and Present|url=https://archive.org/details/scientific100ran00simm|url-access=registration|page=[https://archive.org/details/scientific100ran00simm/page/19 19]|date=1996|publisher=Carol|isbn=978-0-8065-2139-8}}</ref> The biological effect of radiation was discovered in 1903.<ref>{{cite web |url=https://www.nobelprize.org/nobel_prizes/themes/physics/curie/ |title=Marie and Pierre Curie and the Discovery of Polonium and Radium |last=Fröman |first=N. |date=1996 |website=nobelprize.org |publisher=[[Nobel Media AB]] |access-date=11 May 2017 |archive-date=7 August 2018 |archive-url=https://web.archive.org/web/20180807095032/https://www.nobelprize.org/nobel_prizes/themes/physics/curie/ |url-status=live }}</ref> The newly discovered phenomenon of radioactivity excited scientists and the general public alike. In the 1920s, thorium's radioactivity was promoted as a cure for [[rheumatism]], [[diabetes]], and [[sexual impotence]]. In 1932, most of these uses were banned in the United States after a federal investigation into the health effects of radioactivity.<ref name="Burns1987" /> 10,000 individuals in the United States had been injected with thorium during X-ray diagnosis; they were later found to suffer health issues such as leukaemia and abnormal chromosomes.<ref name="Emsley2011" /> Public interest in radioactivity had declined by the end of the 1930s.<ref name="Burns1987">{{cite book|last=Burns|first=M.|title=Low-Level Radioactive Waste Regulation-Science, Politics and Fear|year=1987|publisher=CRC Press|isbn=978-0-87371-026-8|pages=24–25}}</ref>

[[File:Seaborg in lab - restoration.jpg|thumb|upright|alt=Glenn T. Seaborg|[[Glenn T. Seaborg]], who settled thorium's location in the f-block]]

===Further classification===
Up to the late 19th century, chemists unanimously agreed that thorium and uranium were the heaviest members of group 4 and [[group 6 element|group 6]] respectively; the existence of the lanthanides in the sixth row was considered to be a one-off fluke. In 1892, British chemist Henry Bassett postulated a second extra-long periodic table row to accommodate known and undiscovered elements, considering thorium and uranium to be analogous to the lanthanides. In 1913, Danish physicist [[Niels Bohr]] published a [[Bohr model|theoretical model]] of the atom and its electron orbitals, which soon gathered wide acceptance. The model indicated that the seventh row of the periodic table should also have f-shells filling before the d-shells that were filled in the transition elements, like the sixth row with the lanthanides preceding the 5d transition metals.<ref name="leach" /> The existence of a second inner transition series, in the form of the actinides, was not accepted until similarities with the electron structures of the lanthanides had been established;<ref>{{cite book|last=van Spronsen |first=J. W. |year=1969 |title=The periodic system of chemical elements |publisher=Elsevier |pages=315–316 |isbn=978-0-444-40776-4}}.</ref> Bohr suggested that the filling of the 5f orbitals may be delayed to after uranium.<ref name="leach" />

It was only with the discovery of the first [[transuranic element]]s, which from plutonium onward have dominant +3 and +4 oxidation states like the lanthanides, that it was realised that the actinides were indeed filling f-orbitals rather than d-orbitals, with the transition-metal-like chemistry of the early actinides being the exception and not the rule.<ref>{{cite book |last=Rhodes |first=R. |title=The Making of the Atomic Bomb |edition=25th Anniversary |date=2012 |publisher=[[Simon & Schuster]] |isbn=978-1-4516-7761-4 |pages=221–222, 349}}</ref> In 1945, when American physicist [[Glenn T. Seaborg]] and his team had discovered the transuranic elements americium and curium, he proposed the [[actinide concept]], realising that thorium was the second member of an f-block actinide series analogous to the lanthanides, instead of being the heavier congener of [[hafnium]] in a fourth d-block row.<ref name="Masterton">{{cite book |last1=Masterton|first1=W. L. |last2=Hurley|first2=C. N.|last3=Neth|first3=E. J.|title=Chemistry: Principles and reactions|publisher=[[Cengage Learning]]|edition=7th|isbn=978-1-111-42710-8|page=173|year=2011 }}</ref>{{efn|The filling of the 5f subshell from the beginning of the actinide series was confirmed when the 6d elements were reached in the 1960s, proving that the 4f and 5f series are of equal length. [[Lawrencium]] has only +3 as an oxidation state, breaking from the trend of the late actinides towards the +2 state; it thus fits as a heavier congener of [[lutetium]]. Even more importantly, the next element, [[rutherfordium]], was found to behave like hafnium and show only a +4 state.<ref name=johnson/><ref>{{cite journal |doi= 10.1016/S0925-8388(98)00072-3 |title= Evidence for relativistic effects in the chemistry of element 104 |first9= D. |last10= Timokhin |first10= S. N. |last11= Yakushev |first11= A. B. |last12= Zvara |first12= I. |last9= Piguet |first8= V. Ya. |last8= Lebedev |first7= D. T. |last7= Jost |first6= S. |last6= Hübener |first5= M. |last5= Grantz |first4= H. W. |last4= Gäggeler |first3= B. |last3= Eichler |first2= G. V. |date= 1998 |last2= Buklanov |last1= Türler| first1= A. |journal= Journal of Alloys and Compounds |volume= 271–273 |pages= 287–291| display-authors=3}}</ref> Today, thorium's similarities to hafnium are still sometimes acknowledged by calling it a "pseudo group 4 element".<ref name="Pershina">{{cite book |last1=Kratz |first1=J. V. |last2=Nagame |first2=Y. |editor1-last=Schädel |editor1-first=M. |editor2-last=Shaughnessy |editor2-first=D. |chapter=Liquid-Phase Chemistry of Superheavy Elements |date=2014 |edition=2nd |title=The Chemistry of Superheavy Elements |publisher=Springer-Verlag |page=335 |isbn=978-3-642-37465-4 |doi=10.1007/978-3-642-37466-1 |s2cid=122675117 |chapter-url=https://cds.cern.ch/record/643991 |archive-date=17 April 2021 |access-date=21 June 2023 |archive-url=https://web.archive.org/web/20210417211550/http://cds.cern.ch/record/643991 |url-status=live }}</ref>}}

===Phasing out===
In the 1990s, most applications that do not depend on thorium's radioactivity declined quickly due to safety and environmental concerns as suitable safer replacements were found.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}}<ref name="Furuta">{{cite journal|last1=Furuta|first1=E.|last2=Yoshizawa|first2=Y.|last3=Aburai|first3=T.|date=2000|title=Comparisons between radioactive and non-radioactive gas lantern mantles|journal=J. Radiol. Prot.|volume=20|issue=4|pages=423–431|pmid=11140713|bibcode=2000JRP....20..423F|doi=10.1088/0952-4746/20/4/305|s2cid=7368077 }}</ref> Despite its radioactivity, the element has remained in use for applications where no suitable alternatives could be found. A 1981 study by the [[Oak Ridge National Laboratory]] in the United States estimated that using a thorium gas mantle every weekend would be safe for a person,<ref name="Furuta" /> but this was not the case for the dose received by people manufacturing the mantles or for the soils around some factory sites.<ref>{{cite journal|author=New Jersey Department of Health|date=1996|title=Health and hazardous waste|url=http://www.state.nj.us/health/eoh/hhazweb/hhw_no_3.pdf|journal=A Practitioner's Guide to Patients' Environmental Exposures|volume=1|issue=3|pages=1–8|archive-url=https://web.archive.org/web/20160415153459/http://www.state.nj.us/health/eoh/hhazweb/hhw_no_3.pdf|archive-date=15 April 2016}}</ref> Some manufacturers have changed to other materials, such as yttrium.<ref>{{cite journal |last1=Toepker |first1=Terrence P. |date=1996 |title=Thorium and yttrium in gas lantern mantles |journal=American Journal of Physics |volume=64 |issue=2 |page=109 |doi=10.1119/1.18463 |bibcode=1996AmJPh..64..109T |doi-access=free }}</ref> As recently as 2007, some companies continued to manufacture and sell thorium mantles without giving adequate information about their radioactivity, with some even falsely claiming them to be non-radioactive.<ref name="Furuta" /><ref name="Poljanc">{{cite journal|last1=Poljanc|first1=K.|last2=Steinhauser|first2=G.|last3=Sterba|first3=J. H.|last4=Buchtela|first4=K.|last5=Bichler|first5=M.|display-authors=3|date=2007|title=Beyond low-level activity: on a "non-radioactive" gas mantle|journal=[[Science of the Total Environment]]|volume=374|issue=1|pages=36–42|doi=10.1016/j.scitotenv.2006.11.024|pmid=17270253|bibcode=2007ScTEn.374...36P}}</ref>

===Nuclear power===
{{Main|Thorium-based nuclear power|Thorium fuel cycle}}
[[File:Indian_Point_Nuclear_Power_Plant.jpg|left|thumb|alt=Indian Point Energy Center|The [[Indian Point Energy Center]] ([[Buchanan, New York]], United States), home of the world's first thorium reactor]]

Thorium has been used as a power source on a prototype scale. The earliest thorium-based reactor was built at the [[Indian Point Energy Center]] located in [[Buchanan, New York|Buchanan]], New York, [[United States]] in 1962.<ref>{{cite web|url=http://www.americanscientist.org/issues/feature/thorium-fuel-for-nuclear-energy/2|title=Thorium Fuel for Nuclear Energy|last=Kazimi|first=M.|date=2003|publisher=[[American Scientist]]|archive-url=https://web.archive.org/web/20170101123406/http://www.americanscientist.org/issues/feature/thorium-fuel-for-nuclear-energy/2|archive-date=1 January 2017|access-date=29 September 2017}}</ref> China may be the first to have attempted to commercialise the technology.<ref>{{cite journal |last1=Mallapaty |first1=Smriti |title=China prepares to test thorium-fuelled nuclear reactor |journal=Nature |date=9 September 2021 |volume=597 |issue=7876 |pages=311–312 |doi=10.1038/d41586-021-02459-w |pmid=34504330 |bibcode=2021Natur.597..311M |s2cid=237471852 }}</ref> The country with the largest estimated reserves of thorium in the world is [[India]], which has sparse reserves of uranium. In the 1950s, India targeted achieving energy independence with their [[India's three-stage nuclear power programme|three-stage nuclear power programme]].<ref>{{cite report|last1=Majumdar|first1=S.|last2=Purushotham|first2=D. S. C.|entry=Experience of thorium fuel development in India|title=Thorium fuel utilization: Options and trends|year=1999|publisher=[[International Atomic Energy Agency]]|access-date=7 October 2017|url=http://large.stanford.edu/courses/2012/ph241/bordia2/docs/te_1319_web.pdf|archive-date=12 April 2021|archive-url=https://web.archive.org/web/20210412041730/http://large.stanford.edu/courses/2012/ph241/bordia2/docs/te_1319_web.pdf|url-status=live}}</ref><ref name="World Nuclear Association India">{{Cite web|url=http://www.world-nuclear.org/information-library/country-profiles/countries-g-n/india.aspx|title=Nuclear Power in India|publisher=World Nuclear Association|year=2017|access-date=29 September 2017|archive-date=6 September 2016|archive-url=https://archive.today/20160906112259/http://www.world-nuclear.org/information-library/country-profiles/countries-g-n/india.aspx|url-status=live}}</ref> In most countries, uranium was relatively abundant and the progress of thorium-based reactors was slow; in the 20th century, three reactors were built in India and twelve elsewhere.<ref>{{cite web |url=http://www-pub.iaea.org/MTCD/publications/PDF/TE_1450_web.pdf |publisher=International Atomic Energy Agency |title=IAEA-TECDOC-1450 Thorium Fuel Cycle – Potential Benefits and Challenges |date=2005 |access-date=23 March 2009 |archive-date=4 August 2016 |archive-url=https://web.archive.org/web/20160804054758/http://www-pub.iaea.org/MTCD/publications/PDF/TE_1450_web.pdf |url-status=live }}</ref> Large-scale research was begun in 1996 by the [[International Atomic Energy Agency]] to study the use of thorium reactors; a year later, the [[United States Department of Energy]] started their research. [[Alvin Radkowsky]] of [[Tel Aviv University]] in [[Israel]] was the head designer of [[Shippingport Atomic Power Station]] in Pennsylvania, the first American civilian reactor to breed thorium.<ref name="asme-landmark">{{cite web|url=http://files.asme.org/ASMEORG/Communities/History/Landmarks/5643.pdf|archive-url=https://web.archive.org/web/20150717051921/http://files.asme.org/ASMEORG/Communities/History/Landmarks/5643.pdf|archive-date=17 July 2015|title=Historic Achievement Recognized: Shippingport Atomic Power Station, A National Engineering Historical Landmark|page=4|access-date=24 June 2006|author=Shippingport Atomic Power Station}}</ref> He founded a consortium to develop thorium reactors, which included other laboratories: [[Raytheon]] Nuclear Inc. and [[Brookhaven National Laboratory]] in the United States, and the [[Kurchatov Institute]] in Russia.<ref name="Inc.1997">{{cite journal |last1=Friedman |first1=John S. |title=More power to thorium? |journal=Bulletin of the Atomic Scientists |date=September 1997 |volume=53 |issue=5 |pages=19–20 |doi=10.1080/00963402.1997.11456765 |bibcode=1997BuAtS..53e..19F }}</ref>

In the 21st century, thorium's potential for reducing nuclear proliferation and its [[nuclear waste|waste]] characteristics led to renewed interest in the thorium fuel cycle.<ref>{{cite web|url=http://www-pub.iaea.org/MTCD/publications/PDF/te_1349_web.pdf|title=IAEA-TECDOC-1349 Potential of thorium-based fuel cycles to constrain plutonium and to reduce the long-lived waste toxicity|date=2002|publisher=International Atomic Energy Agency|access-date=24 March 2009|archive-date=28 April 2021|archive-url=https://web.archive.org/web/20210428163855/https://www-pub.iaea.org/MTCD/publications/PDF/te_1349_web.pdf|url-status=live}}</ref><ref>{{cite news|url=http://www.abc.net.au/news/newsitems/200604/s1616391.htm|title=Scientist urges switch to thorium|last=Evans|first=B.|date=2006|publisher=[[ABC News (Australia)|ABC News]]|archive-url=https://web.archive.org/web/20100328211103/http://www.abc.net.au/news/newsitems/200604/s1616391.htm|archive-date=28 March 2010|access-date=17 September 2011}}</ref><ref>{{cite news|url=https://www.wired.com/magazine/2009/12/ff_new_nukes/|title=Uranium is So Last Century – Enter Thorium, the New Green Nuke|last=Martin|first=R.|date=2009|magazine=[[Wired (magazine)|Wired]]|access-date=19 June 2010|archive-date=26 June 2010|archive-url=https://web.archive.org/web/20100626014207/http://www.wired.com/magazine/2009/12/ff_new_nukes/|url-status=live}}</ref> India has projected meeting as much as 30% of its electrical demands through thorium-based [[nuclear power]] by 2050. In February 2014, [[Bhabha Atomic Research Centre]] (BARC), in [[Mumbai]], India, presented their latest design for a "next-generation nuclear reactor" that burns thorium as its fuel core, calling it the [[Advanced Heavy Water Reactor]] (AHWR). In 2009, the chairman of the Indian Atomic Energy Commission said that India has a "long-term objective goal of becoming energy-independent based on its vast thorium resources."

On 16 June 2023 China's National Nuclear Safety Administration issued a licence to the Shanghai Institute of Applied Physics (SINAP) of the Chinese Academy of Sciences to begin operating the [[TMSR-LF1]], 2 MWt liquid fuel thorium-based molten salt experimental reactor which was completed in August 2021.<ref name= carpineti >Dr. Alfredo Carpineti  [https://www.iflscience.com/experimental-molten-salt-nuclear-reactor-gets-go-ahead-in-china-69417 (16 June 2023) Experimental Molten Salt Nuclear Reactor Gets Go-Ahead In China ] {{Webarchive|url=https://web.archive.org/web/20230702021045/https://www.iflscience.com/experimental-molten-salt-nuclear-reactor-gets-go-ahead-in-china-69417 |date=2 July 2023 }}</ref> China is believed to have one of the largest thorium reserves in the world. The exact size of those reserves has not been publicly disclosed, but it is estimated to be enough to meet the country's total energy needs for more than 20,000 years.<ref>{{Cite web|url=https://www.scmp.com/news/china/science/article/3224183/china-gives-green-light-nuclear-reactor-burns-thorium-fuel-could-power-country-20000-years|title=China gives green light to its first thorium-powered nuclear reactor|date=15 June 2023|website=South China Morning Post}}</ref>

===Nuclear weapons===
When gram quantities of [[plutonium]] were first produced in the [[Manhattan Project]], it was discovered that a minor isotope ([[plutonium-240|<sup>240</sup>Pu]]) underwent significant [[spontaneous fission]], which brought into question the viability of a plutonium-fuelled [[Gun-type fission weapon|gun-type nuclear weapon]]. While the [[Project Y|Los Alamos]] team began work on the [[Nuclear weapon design#Implosion-type weapon|implosion-type weapon]] to circumvent this issue, the [[Metallurgical Laboratory|Chicago team]] discussed reactor design solutions. [[Eugene Wigner]] proposed to use the <sup>240</sup>Pu-contaminated plutonium to drive the conversion of thorium into <sup>233</sup>U in a special converter reactor. It was hypothesized that the <sup>233</sup>U would then be usable in a gun-type weapon, though concerns about contamination from <sup>232</sup>U were voiced. Progress on the implosion weapon was sufficient, and this converter was not developed further, but the design had enormous influence on the development of nuclear energy. It was the first detailed description of a highly enriched water-cooled, water-moderated reactor similar to future naval and commercial power reactors.<ref name="First Nuclear Era">{{cite book |last=Weinberg |first=Alvin |author-link=Alvin Weinberg |year=1994 |title=The First Nuclear Era: The life and times of a technological fixer |pages=36–38 |location=New York |publisher=AIP Press |isbn=978-1-56396-358-2}}</ref>

During the [[Cold War]] the United States explored the possibility of using <sup>232</sup>Th as a source of <sup>233</sup>U to be used in a [[nuclear bomb]]; they fired [[Operation Teapot#MET|a test bomb]] in 1955.<ref name="World Nuclear Association Thorium">{{cite web |title=Thorium |publisher=[[World Nuclear Association]] |year=2017 |url=http://www.world-nuclear.org/information-library/current-and-future-generation/thorium.aspx |access-date=21 June 2017 |archive-date=8 May 2017 |archive-url=https://web.archive.org/web/20170508215033/http://www.world-nuclear.org/information-library/current-and-future-generation/thorium.aspx |url-status=live }}</ref> They concluded that a <sup>233</sup>U-fired bomb would be a very potent weapon, but it bore few sustainable "technical advantages" over the contemporary uranium–plutonium bombs,<ref>{{cite report |last=Woods |first=W.K. |date=1966 |title=LRL Interest in U-233 |publisher=[[Battelle Memorial Institute]] |doi=10.2172/79078 |osti=79078 |language=en |url=https://digital.library.unt.edu/ark:/67531/metadc720752/m2/1/high_res_d/79078.pdf |archive-date=10 September 2023 |access-date=24 August 2019 |archive-url=https://web.archive.org/web/20230910145607/https://digital.library.unt.edu/ark:/67531/metadc720752/m2/1/high_res_d/79078.pdf |url-status=live }}</ref> especially since <sup>233</sup>U is difficult to produce in isotopically pure form.<ref name="World Nuclear Association Thorium" />

Thorium metal was used in the [[hohlraum|radiation case]] of at least one nuclear weapon design deployed by the United States (the [[W71]]).<ref>{{cite web |title=Classification Bulletin WNP-118 |publisher=U.S. Department of Energy |date=12 March 2008 |url=https://www.osti.gov/opennet/servlets/purl/1052069/1052069.pdf |access-date=13 September 2019 |archive-date=3 February 2017 |archive-url=https://web.archive.org/web/20170203132623/https://www.osti.gov/opennet/servlets/purl/1052069/1052069.pdf |url-status=live }}</ref>