Editing Curium (section)

==Synthesis==
===Isotope preparation===
Curium is made in small amounts in [[nuclear reactor]]s, and by now only kilograms of <sup>242</sup>Cm and <sup>244</sup>Cm have been accumulated, and grams or even milligrams for heavier isotopes. Hence the high price of curium, which has been quoted at 160–185 [[United States dollar|USD]] per milligram,<ref name="CRC" /> with a more recent estimate at US$2,000/g for <sup>242</sup>Cm and US$170/g for <sup>244</sup>Cm.<ref name="lect" /> In nuclear reactors, curium is formed from <sup>238</sup>U in a series of nuclear reactions. In the first chain, <sup>238</sup>U captures a neutron and converts into <sup>239</sup>U, which via [[beta decay|β<sup>−</sup> decay]] transforms into <sup>239</sup>Np and <sup>239</sup>Pu.

{{NumBlk|:|<chem>^{238}_{92}U->[\ce{(n,\gamma)}] {^{239}_{92}U} ->[\beta^-][23.5\ \ce{min}] ^{239}_{93}Np ->[\beta^-][2.3565\ \ce{d}] ^{239}_{94}Pu</chem> <small>(the times are [[half-life|half-lives]])</small>.|{{EquationRef|1}}}}

Further neutron capture followed by β<sup>−</sup>-decay gives [[americium]] (<sup>241</sup>Am) which further becomes <sup>242</sup>Cm:
{{NumBlk|:|<chem>^{239}_{94}Pu->[\ce{2(n,\gamma)}] ^{241}_{94}Pu ->[\beta^-][14.35\ \ce{yr}] {^{241}_{95}Am} ->[\ce{(n,\gamma)}] ^{242}_{95}Am ->[\beta^-][16.02 \ce{h}] ^{242}_{96}Cm</chem>.|{{EquationRef|2}}}}

For research purposes, curium is obtained by irradiating not uranium but plutonium, which is available in large amounts from spent nuclear fuel. A much higher neutron flux is used for the irradiation that results in a different reaction chain and formation of <sup>244</sup>Cm:<ref name = "Morrs">Morss, L. R.; Edelstein, N. M. and Fugere, J. (eds): ''The Chemistry of the Actinide Elements and transactinides'', volume 3, Springer-Verlag, Dordrecht 2006, {{ISBN|1-4020-3555-1}}.</ref>
{{NumBlk|:|<chem>^{239}_{94}Pu ->[\ce{4(n,\gamma)}] ^{243}_{94}Pu ->[\beta^-][4.956\ \ce{h}] ^{243}_{95}Am ->[(\ce n,\gamma)] ^{244}_{95}Am ->[\beta^-][10.1 \ce{h}] ^{244}_{96}Cm ->[\alpha][18.11\ \ce{yr}] ^{240}_{94}Pu</chem>|{{EquationRef|3}}}}

Curium-244 alpha decays to <sup>240</sup>Pu, but it also absorbs neutrons, hence a small amount of heavier curium isotopes. Of those, <sup>247</sup>Cm and <sup>248</sup>Cm are popular in scientific research due to their long half-lives. But the production rate of <sup>247</sup>Cm in thermal neutron reactors is low because it is prone to fission due to thermal neutrons.<ref name="haire" /> Synthesis of <sup>250</sup>Cm by [[neutron capture]] is unlikely due to the short half-life of the intermediate <sup>249</sup>Cm (64 min), which β<sup>−</sup> decays to the [[berkelium]] isotope <sup>249</sup>Bk.<ref name="haire" />
<!-- Curium-250 is obtained instead from the α-decay of <sup>254</sup>Cf. For this however, the production rate is low as <sup>254</sup>Cf decays mainly by spontaneous fission, and only slightly by emission of α-particles into <sup>250</sup>Cm.{{Citation needed|date=May 2012}} -->
{{NumBlk|:|<math chem>\ce{^\mathit{A}_{96}Cm{} + ^{1}_{0}n -> ^{\mathit{A}+1}_{96}Cm{} + \gamma} \ (\text{for } 244 \le A \le 248)</math>|{{EquationRef|4}}}}

The above cascade of (n,γ) reactions gives a mix of different curium isotopes. Their post-synthesis separation is cumbersome, so a selective synthesis is desired. Curium-248 is favored for research purposes due to its long half-life. The most efficient way to prepare this isotope is by α-decay of the [[californium]] isotope <sup>252</sup>Cf, which is available in relatively large amounts due to its long half-life (2.65 years). About 35–50&nbsp;mg of <sup>248</sup>Cm is produced thus, per year. The associated reaction produces <sup>248</sup>Cm with isotopic purity of 97%.<ref name="haire">{{cite book
| title = The Chemistry of the Actinide and Transactinide Elements
| editor1-last = Morss
| editor2-first = Norman M.
| editor2-last = Edelstein
| editor3-last = Fuger
| editor3-first = Jean
| last1 = Lumetta
| first1 = Gregg J.
| last2 = Thompson
| first2 = Major C.
| last3 = Penneman
| first3 = Robert A.
| last4 = Eller
| first4 = P. Gary
| chapter = Curium
| chapter-url = http://radchem.nevada.edu/classes/rdch710/files/curium.pdf
| page = 1401
| publisher = [[Springer Science+Business Media]]
| date = 2006
| isbn = 978-1-4020-3555-5
| location = Dordrecht, The Netherlands
| edition = 3rd
| url-status = dead
| archive-url = https://web.archive.org/web/20100717154205/http://radchem.nevada.edu/classes/rdch710/files/curium.pdf
| archive-date = 2010-07-17
}}</ref>

{{NumBlk|:|<math chem>\begin{matrix}{}\\
\ce{^{252}_{98}Cf ->[\alpha][2.645\ \ce{yr}] ^{248}_{96}Cm}\\{}
\end{matrix}</math>|{{EquationRef|5}}}}

Another isotope, <sup>245</sup>Cm, can be obtained for research, from α-decay of <sup>249</sup>Cf; the latter isotope is produced in small amounts from β<sup>−</sup>-decay of <sup>249</sup>[[berkelium|Bk]].
{{NumBlk|:|<chem>
^{249}_{97}Bk ->[\beta^-][330\ \ce{d}] ^{249}_{98}Cf ->[\alpha][351\ \ce{yr}] ^{245}_{96}Cm
</chem>|{{EquationRef|6}}}}

===Metal preparation===
[[File:Elutionskurven Tb Gd Eu und Bk Cm Am.png|thumb|[[Chromatography|Chromatographic]] [[elution]] curves revealing the similarity between Tb, Gd, Eu lanthanides and corresponding Bk, Cm, Am actinides]]
Most synthesis routines yield a mix of actinide isotopes as [[oxide]]s, from which a given isotope of curium needs to be separated. An example procedure could be to dissolve spent reactor fuel (e.g. [[MOX fuel]]) in [[nitric acid]], and remove the bulk of the uranium and plutonium using a [[PUREX]] ('''P'''lutonium – '''UR'''anium '''EX'''traction) type extraction with [[tributyl phosphate]] in a hydrocarbon. The lanthanides and the remaining actinides are then separated from the aqueous residue ([[raffinate]]) by a diamide-based extraction to give, after stripping, a mixture of trivalent actinides and lanthanides. A curium compound is then selectively extracted using multi-step [[chromatography|chromatographic]] and centrifugation techniques with an appropriate reagent.<ref>Penneman, pp. 34–48</ref> [[BTBP|''Bis''-triazinyl bipyridine]] complex has been recently proposed as such reagent which is highly selective to curium.<ref>{{cite journal|author = Magnusson D|author2 = Christiansen B|author3 = Foreman MRS|author4 = Geist A|author5 = Glatz JP|author6 = Malmbeck R|author7 = Modolo G|author8 = Serrano-Purroy D|author9 = Sorel C|name-list-style = amp|journal = Solvent Extraction and Ion Exchange|date = 2009|volume = 27|issue = 2|page = 97|doi = 10.1080/07366290802672204|title = Demonstration of a SANEX Process in Centrifugal Contactors using the CyMe4-BTBP Molecule on a Genuine Fuel Solution|title-link = centrifugal extractor|s2cid = 94720457}}</ref> Separation of curium from the very chemically similar americium can also be done by treating a slurry of their hydroxides in aqueous [[sodium bicarbonate]] with [[ozone]] at elevated temperature. Both americium and curium are present in solutions mostly in the +3 valence state; americium oxidizes to soluble Am(IV) complexes, but curium stays unchanged and so can be isolated by repeated centrifugation.<ref>Penneman, p. 25</ref>

Metallic curium is obtained by [[Redox|reduction]] of its compounds. Initially, curium(III) fluoride was used for this purpose. The reaction was done in an environment free of water and oxygen, in an apparatus made of [[tantalum]] and [[tungsten]], using elemental [[barium]] or [[lithium]] as reducing agents.<ref name="Morrs" /><ref name = "CM_METALL" /><ref name="cunning">{{cite journal|last1=Cunningham|first1=B. B.|last2=Wallmann|first2=J. C.|title=Crystal structure and melting point of curium metal|journal=Journal of Inorganic and Nuclear Chemistry|volume=26|issue=2|page=271|date=1964|doi=10.1016/0022-1902(64)80069-5|osti=4667421}}</ref><ref>{{cite journal|last1=Stevenson|first1=J.|last2=Peterson|first2=J.|title=Preparation and structural studies of elemental curium-248 and the nitrides of curium-248 and berkelium-249|journal=Journal of the Less Common Metals|volume=66|issue=2|page=201|date=1979|doi=10.1016/0022-5088(79)90229-7}}</ref><ref>''Gmelin Handbook of Inorganic Chemistry'', System No. 71, Volume 7 a, transuranics, Part B 1, pp. 67–68.</ref>
:<math>\mathrm{CmF_3\ +\ 3\ Li\ \longrightarrow \ Cm\ +\ 3\ LiF}</math>

Another possibility is reduction of curium(IV) oxide using a magnesium-zinc alloy in a melt of [[magnesium chloride]] and [[magnesium fluoride]].<ref>{{cite journal|last1=Eubanks|first1=I.|title=Preparation of curium metal|journal=Inorganic and Nuclear Chemistry Letters|volume=5|issue=3|page=187|date=1969|doi=10.1016/0020-1650(69)80221-7|last2=Thompson|first2=M. C.}}</ref>