Editing Curium (section)

==History==
[[File:Glenn Seaborg - 1964.jpg|thumb|left|upright|[[Glenn T. Seaborg]]]]
[[File:Berkeley 60-inch cyclotron.jpg|thumb|left|upright|The {{convert|60|in|cm|adj=on}} cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley, in August 1939.]]
Though curium had likely been produced in previous nuclear experiments as well as the [[natural nuclear fission reactor]] at Oklo, Gabon, it was [[timeline of chemical element discoveries|first intentionally synthesized]], isolated and identified in 1944, at [[University of California, Berkeley]], by [[Glenn T. Seaborg]], [[Ralph A. James]], and [[Albert Ghiorso]]. In their experiments, they used a {{convert|60|in|cm|adj=on}} [[cyclotron]].<ref>{{cite book|title = The New Chemistry: A Showcase for Modern Chemistry and Its Applications|first = Nina|last = Hall|publisher = Cambridge University Press|date = 2000|pages = [https://archive.org/details/newchemistry00hall/page/8 8]–9|isbn = 978-0-521-45224-3|url = https://archive.org/details/newchemistry00hall|url-access = registration}}</ref>

Curium was chemically identified at the Metallurgical Laboratory (now [[Argonne National Laboratory]]), [[University of Chicago]]. It was the third [[transuranium element]] to be discovered even though it is the fourth in the series – the lighter element [[americium]] was still unknown.<ref name="E96">{{cite journal|last1=Seaborg|first1=Glenn T. |last2=James |first2=R. A. |last3=Ghiorso|first3=A.|title=The New Element Curium (Atomic Number 96)|journal=NNES PPR (National Nuclear Energy Series, Plutonium Project Record)|volume=14 B|series=The Transuranium Elements: Research Papers, Paper No.&nbsp;22.2 |year=1949|osti=4421946|url=http://www.osti.gov/accomplishments/documents/fullText/ACC0049.pdf|archive-url=https://web.archive.org/web/20071012083344/http://www.osti.gov/accomplishments/documents/fullText/ACC0049.pdf|archive-date=12 October 2007}}</ref><ref name="Morrs" />

The sample was prepared as follows: first [[plutonium]] nitrate solution was coated on a [[platinum]] foil of ~0.5&nbsp;cm<sup>2</sup> area, the solution was evaporated and the residue was converted into [[plutonium(IV) oxide]] (PuO<sub>2</sub>) by [[annealing (materials science)|annealing]]. Following cyclotron irradiation of the oxide, the coating was dissolved with [[nitric acid]] and then precipitated as the hydroxide using concentrated aqueous [[ammonia solution]]. The residue was dissolved in [[perchloric acid]], and further separation was done by [[ion exchange]] to yield a certain isotope of curium. The separation of curium and americium was so painstaking that the Berkeley group initially called those elements ''[[wikt:pandemonium|pandemonium]]'' (from Greek for ''all demons'' or ''hell'') and ''[[wikt:delirium|delirium]]'' (from Latin for ''madness'').<ref name="radio" /><ref>Krebs, Robert E. [https://books.google.com/books?id=yb9xTj72vNAC&pg=PA322 The history and use of our earth's chemical elements: a reference guide], Greenwood Publishing Group, 2006, {{ISBN|0-313-33438-2}} p. 322</ref>

Curium-242 was made in July–August 1944 by bombarding <sup>239</sup>Pu with [[alpha decay|α-particles]] to produce curium with the release of a [[neutron]]:<ref name="E96"/><ref>{{Cite web |title=Curium {{!}} Radioactive, Synthetic, Actinide {{!}} Britannica |url=https://www.britannica.com/science/curium-chemical-element |access-date=2025-02-15 |website=www.britannica.com |language=en}}</ref>
: <chem>^{239}_{94}Pu + ^{4}_{2}He -> ^{242}_{96}Cm + ^{1}_{0}n</chem>

Curium-242 was unambiguously identified by the characteristic energy of the α-particles emitted during the decay:
: <chem>^{242}_{96}Cm -> ^{238}_{94}Pu + ^{4}_{2}He</chem>
The [[half-life]] of this [[alpha decay]] was first measured as 5 months (150 days)<ref name="E96"/> and then corrected to 162.8 days.{{NUBASE2020|name}}

Another isotope <sup>240</sup>Cm was produced in a similar reaction in March 1945:
: <chem>^{239}_{94}Pu + ^{4}_{2}He -> ^{240}_{96}Cm + 3^{1}_{0}n</chem>
The α-decay half-life of <sup>240</sup>Cm was determined as 26.8 days<ref name="E96"/> and later revised to 30.4 days.{{NUBASE2020|name}}

The discovery of curium and americium in 1944 was closely related to the [[Manhattan Project]], so the results were confidential and declassified only in 1945. Seaborg leaked the synthesis of the elements 95 and 96 on the U.S. radio show for children, the ''[[Quiz Kids]]'', five days before the official presentation at an [[American Chemical Society]] meeting on November 11, 1945, when one listener asked if any new transuranic element beside plutonium and [[neptunium]] had been discovered during the war.<ref name="radio">{{cite web|url = http://pubs.acs.org/cen/80th/americium.html|title = Chemical & Engineering News: It's Elemental: The Periodic Table – Americium|access-date = 2008-12-07| first = Rachel Sheremeta|last = Pepling|date = 2003}}</ref> The discovery of curium (<sup>242</sup>Cm and <sup>240</sup>Cm), its production, and its compounds was later patented listing only Seaborg as the inventor.<ref>Seaborg, G. T. {{US patent|3161462}} "Element", Filing date: 7 February 1949, Issue date: December 1964</ref>

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The element was named after [[Marie Curie]] and her husband [[Pierre Curie]], who are known for discovering [[radium]] and for their work in [[radioactivity]]. It followed the example of [[gadolinium]], a [[lanthanide]] element above curium in the periodic table, which was named after the explorer of [[rare-earth element]]s [[Johan Gadolin]]:<ref>Greenwood, p. 1252</ref>
::<blockquote>As the name for the element of atomic number 96 we should like to propose "curium", with symbol Cm. The evidence indicates that element 96 contains seven 5f electrons and is thus analogous to the element gadolinium, with its seven 4f electrons in the regular rare earth series. On this basis element 96 is named after the Curies in a manner analogous to the naming of gadolinium, in which the chemist Gadolin was honored.<ref name="E96" /></blockquote>

The first curium samples were barely visible, and were identified by their radioactivity. Louis Werner and [[Isadore Perlman]] made the first substantial sample of 30&nbsp;μg curium-242 hydroxide at University of California, Berkeley in 1947 by bombarding [[americium]]-241 with neutrons.<ref name="CRC">Hammond C. R. "The elements" in {{RubberBible86th}}</ref><ref>L. B. Werner, I. Perlman: "Isolation of Curium", NNES PPR (''National Nuclear Energy Series, Plutonium Project Record''), Vol.&nbsp;14&nbsp;B, ''The Transuranium Elements: Research Papers'', Paper No.&nbsp;22.5, McGraw-Hill Book Co., Inc., New York, 1949.</ref><ref>{{cite web|url=http://www.nap.edu/readingroom.php?book=biomems&page=iperlman.html |title=National Academy of Sciences. Isadore Perlman 1915–1991 |publisher=Nap.edu |access-date=2011-03-25}}</ref> Macroscopic amounts of [[curium(III) fluoride]] were obtained in 1950 by W. W. T. Crane, J. C. Wallmann and B. B. Cunningham. Its magnetic susceptibility was very close to that of GdF<sub>3</sub> providing the first experimental evidence for the +3 valence of curium in its compounds.<ref name="CRC" /> Curium metal was produced only in 1950 by reduction of CmF<sub>3</sub> with [[barium]].<ref name="CM_METALL">{{cite journal|first1 = J. C.|last1 = Wallmann|first2 = W. W. T.|last2 = Crane|first3 = B. B.|last3 = Cunningham|title = The Preparation and Some Properties of Curium Metal|journal = [[Journal of the American Chemical Society]]|date = 1951|volume =73|issue =1|pages = 493–494|doi = 10.1021/ja01145a537| bibcode=1951JAChS..73..493W |hdl = 2027/mdp.39015086479790|url = https://cloudfront.escholarship.org/dist/prd/content/qt51t3d12j/qt51t3d12j.pdf}}</ref><ref>{{cite journal|author =Werner, L. B.|author2 =Perlman, I.|title =First Isolation of Curium| journal = Journal of the American Chemical Society|date = 1951| volume =73|issue =1|pages = 5215–5217|doi = 10.1021/ja01155a063|bibcode =1951JAChS..73.5215W|s2cid =95799539}}</ref>