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| {{about|the chemical element|the ancient city located in Cyprus|Kourion}}
| | Hello from Netherlands. I'm glad to came here. My first name is Aida. <br>I live in a small city called Zelhem in east Netherlands.<br>I was also born in Zelhem 20 years ago. Married in March year 2010. I'm working at the post office.<br><br>My website: [http://www.thealaskalife.com/ knives] |
| {{good article}}
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| {{infobox curium}}
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| '''Curium''' is a [[transuranic element|transuranic]] [[radioactive decay|radioactive]] [[chemical element]] with the symbol '''Cm''' and [[atomic number]] 96. This element of the [[actinide]] series was named after [[Marie Curie|Marie Skłodowska-Curie]] and [[Pierre Curie]] – both were known for their research on radioactivity. Curium was first intentionally produced and identified in July 1944 by the group of [[Glenn T. Seaborg]] at the [[University of California, Berkeley]]. The discovery was kept secret and only released to the public in November 1945. Most curium is produced by bombarding [[uranium]] or [[plutonium]] with [[neutron]]s in [[nuclear reactor]]s – one [[tonne]] of spent [[nuclear fuel]] contains about 20 grams of curium.
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| Curium is a hard, dense, silvery metal with a relatively high melting point and boiling point for an actinide. Whereas it is [[paramagnetism|paramagnetic]] at [[Standard conditions for temperature and pressure|ambient conditions]], it becomes [[antiferromagnetism|antiferromagnetic]] upon cooling, and other magnetic transitions are also observed for many curium compounds. In compounds, curium usually exhibits [[valence (chemistry)|valence]] +3 and sometimes +4, and the +3 valence is predominant in solutions. Curium readily oxidizes, and its oxides are a dominant form of this element. It forms strongly [[fluorescence|fluorescent]] complexes with various organic compounds, but there is no evidence of its incorporation into [[bacteria]] and [[archaea]]. When introduced into the human body, curium accumulates in the bones, lungs and liver, where it promotes [[cancer]].
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| All known [[isotope]]s of curium are radioactive and have a small [[critical mass]] for a sustained [[nuclear chain reaction]]. They predominantly emit [[alpha radiation|α-particles]], and the heat released in this process can potentially produce electricity in [[radioisotope thermoelectric generator]]s. This application is hindered by the scarcity, high cost and radioactivity of curium isotopes. Curium is used in production of heavier actinides and of the <sup>238</sup>Pu [[radionuclide]] for power sources in [[artificial pacemaker]]s. It served as the [[alpha radiation|α-source]] in the [[alpha particle X-ray spectrometer]]s installed on the [[Mars Pathfinder|Sojourner]], [[Mars rover|Mars]], [[Mars 96]], [[Mars Exploration Rover|Athena]], [[Spirit rover|Spirit]] and [[Opportunity rover]]s as well as the [[Mars Science Laboratory]] to analyze the composition and structure of the rocks on the surface of [[Mars]] and the [[Moon]]. Such a spectrometer will also be used by the [[Philae lander]] of the [[Rosetta (spacecraft)|Rosetta]] spacecraft to probe the surface of the [[67P/Churyumov-Gerasimenko]] [[comet]].
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| ==History==
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| [[File:Glenn Seaborg - 1964.jpg|thumb|left|upright|Glenn T. Seaborg]]
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| [[File:Berkeley 60-inch cyclotron.gif|thumb|left|upright|The {{convert|60|in|cm|adj=on}} cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley, in August 1939.]]
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| Although curium had likely been produced in previous nuclear experiments, it was [[discoveries of the chemical elements|first intentionally synthesized]], isolated and identified in 1944, at the [[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|year = 2000|pages = 8–9|isbn = 978-0-521-45224-3|url = http://books.google.com/books?id=U4rnzH9QbT4C&pg=PA8}}</ref>
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| Curium was chemically identified at the Metallurgical Laboratory (now [[Argonne National Laboratory]]) at the [[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 unknown at the time.<ref name="E96">Seaborg, G. T.; James, R. A. and Ghiorso, A.: "The New Element Curium (Atomic Number 96)", NNES PPR ''(National Nuclear Energy Series, Plutonium Project Record)'', Vol. 14 B, ''The Transuranium Elements: Research Papers'', Paper No. 22.2, McGraw-Hill Book Co., Inc., New York, 1949; [http://www.osti.gov/cgi-bin/rd_accomplishments/display_biblio.cgi?id=ACC0049&numPages=13&fp=N Abstract]; [http://www.osti.gov/accomplishments/documents/fullText/ACC0049.pdf Full text (January 1948)].</ref><ref name="Morrs"/>
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| The sample was prepared as follows: first [[plutonium]] nitrate solution was coated on a [[platinum]] foil of about 0.5 cm<sup>2</sup> area, the solution was evaporated and the residue was converted into plutonium dioxide (PuO<sub>2</sub>) by [[annealing (metallurgy)|annealing]]. Following cyclotron irradiation of the oxide, the coating was dissolved with [[nitric acid]] and then precipitated as the hydroxide using concentrated aqueous [[ammonium hydroxide|ammonia solution]]. The residue was dissolved in [[perchloric acid]], and further separation was carried out 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. [http://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><ref>{{OEtymD|pandemonium}}</ref><ref>{{OEtymD|delirium}}</ref>
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| The curium-242 isotope was produced in July–August 1944 by bombarding <sup>239</sup>Pu with [[alpha radiation|α-particles]] to produce curium with the release of a [[neutron]]:
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| : <math>\mathrm{^{239\!\,}_{\ 94}Pu\ +\ ^{4}_{2}He\ \longrightarrow \ ^{242}_{\ 96}Cm\ +\ ^{1}_{0}n}</math>
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| Curium-242 was unambiguously identified by the characteristic energy of the α-particles emitted during the decay:
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| : <math>\mathrm{^{242}_{\ 96}Cm\ \longrightarrow \ ^{238}_{\ 94}Pu\ +\ ^{4}_{2}He}</math>
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| The [[half-life]] of this [[alpha decay]] was first measured as 150 days and then corrected to 162.8 days.<ref name="nubase"/>
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| Another isotope <sup>240</sup>Cm was produced in a similar reaction in March 1945:
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| : <math>\mathrm{^{239}_{\ 94}Pu\ +\ ^{4}_{2}He\ \longrightarrow \ ^{240}_{\ 96}Cm\ +\ 3\ ^{1}_{0}n}</math>
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| The half-life of the <sup>240</sup>Cm α-decay was correctly determined as 26.7 days.<ref name="nubase"/>
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| The discovery of curium, as well as americium, in 1944 was closely related to the [[Manhattan Project]], 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 of the listeners asked whether any new transuranium 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|accessdate = 07-12-2008| first = Rachel Sheremeta|last = Pepling|year = 2003}}</ref> The discovery of curium (<sup>242</sup>Cm and <sup>240</sup>Cm), their production and compounds were 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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| {{double image|left|Marie Curie (Nobel-Chem).png|150|Curie-pierre.jpg|150|Marie and Pierre Curie}}
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| The new element was named after [[Marie Curie|Marie Skłodowska-Curie]] and her husband [[Pierre Curie]] who are noted 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 the [[rare earth element]]s [[Johan Gadolin]]:<ref>Greenwood, p. 1252</ref>
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| ::''"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 base 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"/>''
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| The first curium samples were barely visible, and were identified by their radioactivity. Louis Werner and [[Isadore Perlman]] created the first substantial sample of 30 µg curium-242 hydroxide at the University of California 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. 14 B, ''The Transuranium Elements: Research Papers'', Paper No. 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 |date= |accessdate=2011-03-25}}</ref> Macroscopic amounts of [[curium 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 1951 by reduction of curium fluoride with [[barium]].<ref name="CM_METALL">{{cite journal|first = J. C.|last = Wallmann|coauthors = Crane, W. W. T.; Cunningham, B. B.|title = The Preparation and Some Properties of Curium Metal|journal = [[Journal of the American Chemical Society]]|year = 1951|volume =73|issue =1|pages = 493–494|doi = 10.1021/ja01145a537}}</ref><ref>{{cite journal|author =Werner, L. B.; Perlman, I.|title =First Isolation of Curium| journal = Journal of the American Chemical Society|year = 1951| volume =73|issue =1|pages = 5215–5217|doi = 10.1021/ja01155a063}}</ref>
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| ==Characteristics==
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| ===Physical===
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| [[File:Closest packing ABAC.png|thumb|Double-hexagonal close packing with the layer sequence ABAC in the crystal structure of α-curium (A: green, B: blue, C: red)]]
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| [[File:Cm-Fluoreszenz.GIF|thumb|Orange [[fluorescence]] of Cm<sup>3+</sup> ions in a solution of tris(hydrotris)pyrazolylborato-Cm(III) complex, excited at 396.6 nm.]]
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| A synthetic, radioactive element, curium is a hard dense metal with silvery-white appearance and physical and chemical properties resembling those of [[gadolinium]]. Its melting point of 1340 °C is significantly higher than that of the previous transuranic elements neptunium (637 °C), plutonium (639 °C) and americium (1173 °C). In comparison, gadolinium melts at 1312 °C. The boiling point of curium is 3110 °C. With a density of 13.52 g/cm<sup>3</sup>, curium is significantly lighter than neptunium (20.45 g/cm<sup>3</sup>) and plutonium (19.8 g/cm<sup>3</sup>), but is heavier than most other metals. Between two crystalline forms of curium, the α-Cm is more stable at ambient conditions. It has a hexagonal symmetry, [[space group]] P6<sub>3</sub>/mmc, lattice parameters ''a'' = 365 [[picometer|pm]] and ''c'' = 1182 pm, and four [[formula unit]]s per [[unit cell]].<ref name="Milman">{{cite journal|last1=Milman|first1=V|title=Crystal structures of curium compounds: an ab initio study|journal=Journal of Nuclear Materials|volume=322|issue=2–3|page=165|year=2003|doi=10.1016/S0022-3115(03)00321-0|bibcode=2003JNuM..322..165M|last2=Winkler|first2=B|last3=Pickard|first3=C.J}}</ref> The crystal consists of a double-[[Close-packing of spheres|hexagonal close packing]] with the layer sequence ABAC and so is isotypic with α-lanthanum. At pressures above 23 [[Pascal (unit)|GPa]], at room temperature, α-Cm transforms into β-Cm, which has a [[Cubic crystal system|face-centered cubic]] symmetry, space group Fm{{overline|3}}m and the lattice constant ''a'' = 493 pm.<ref name = "Milman"/> Upon further compression to 43 GPa, curium transforms to an [[Orthorhombic crystal system|orthorhombic]] γ-Cm structure similar to that of α-uranium, with no further transitions observed up to 52 GPa. These three curium phases are also referred to as Cm I, II and III.<ref>Young, D. A. [http://books.google.com/books?id=F2HVYh6wLBcC&pg=PA227 Phase diagrams of the elements], University of California Press, 1991, ISBN 0-520-07483-1p. 227</ref><ref>{{cite journal|last1=Haire|first1=R|last2=Peterson|first2=J|last3=Benedict|first3=U|last4=Dufour|first4=C|last5=Itie|first5=J|title=X-ray diffraction of curium-248 metal under pressures of up to 52 GPa|journal=Journal of the Less Common Metals|volume=109|issue=1|page=71|year=1985|doi=10.1016/0022-5088(85)90108-0}}</ref>
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| Curium has peculiar magnetic properties. Whereas its neighbor element americium shows no deviation from [[Curie–Weiss law|Curie-Weiss]] [[paramagnetism]] in the entire temperature range, α-Cm transforms to an [[Antiferromagnetism|antiferromagnetic]] state upon cooling to 65–52 K,<ref>{{cite journal|last1=Kanellakopulos|first1=B|title=The magnetic susceptibility of Americium and curium metal|journal=Solid State Communications|volume=17|issue=6|page=713|year=1975|doi=10.1016/0038-1098(75)90392-0|bibcode = 1975SSCom..17..713K|last2=Blaise|first2=A.|last3=Fournier|first3=J.M.|last4=Müller|first4=W. }}</ref><ref>{{cite journal|last1=Fournier|first1=J|title=Curium: A new magnetic element|journal=Physica B+C|volume=86–88|page=30|year=1977|doi=10.1016/0378-4363(77)90214-5|bibcode = 1977PhyBC..86...30F|last2=Blaise|first2=A.|last3=Muller|first3=W.|last4=Spirlet|first4=J.-C. }}</ref> and β-Cm exhibits a [[Ferrimagnetism|ferrimagnetic]] transition at about 205 K. Meanwhile, curium pnictides show [[Ferromagnetism|ferromagnetic]] transitions upon cooling: <sup>244</sup>CmN and <sup>244</sup>CmAs at 109 K, <sup>248</sup>CmP at 73 K and <sup>248</sup>CmSb at 162 K. Similarly, the lanthanide analogue of curium, gadolinium, as well as its pnictides also show magnetic transitions upon cooling, but the transition character is somewhat different: Gd and GdN become ferromagnetic, and GdP, GdAs and GdSb show antiferromagnetic ordering.<ref>Nave, S. E.; Huray, P. G.; Peterson, J. R. and Damien, D. A. [http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=ECF73C70531D64E8B663048ECE8C10F9?purl=/6263633-jkoGGI/ Magnetic susceptibility of curium pnictides], Oak Ridge National Laboratory</ref>
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| In accordance with magnetic data, electrical resistivity of curium increases with temperature – about twice between 4 and 60 K – and then remains nearly constant up to room temperature. There is a significant increase in resistvity over time (about 10 µΩ·cm/h) due to self-damage of the crystal lattice by alpha radiation. This makes uncertain the absolute resistivity value for curium (about 125 µΩ·cm). The resistivity of curium is similar to that of gadolinium and of the actinides plutonium and neptunium, but is significantly higher than that of americium, uranium, [[polonium]] and [[thorium]].<ref name=res/><ref>{{cite journal|last1=Schenkel|first1=R|title=The electrical resistivity of 244Cm metal|journal=Solid State Communications|volume=23|issue=6|page=389|year=1977|doi=10.1016/0038-1098(77)90239-3|bibcode = 1977SSCom..23..389S }}</ref>
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| Under ultraviolet illumination, curium(III) ions exhibit strong and stable yellow-orange [[fluorescence]] with a maximum in the range about 590–640 nm depending on their environment.<ref name="denecke">{{cite journal|last1=Denecke|first1=Melissa A.|last2=Rossberg|first2=André|last3=Panak|first3=Petra J.|last4=Weigl|first4=Michael|last5=Schimmelpfennig|first5=Bernd|last6=Geist|first6=Andreas|title=Characterization and Comparison of Cm(III) and Eu(III) Complexed with 2,6-Di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine Using EXAFS, TRFLS, and Quantum-Chemical Methods|journal=Inorganic Chemistry|volume=44|issue=23|year=2005|pmid=16270980|doi=10.1021/ic0511726|pages=8418–25}}</ref> The fluorescence originates from the transitions from the first excited state <sup>6</sup>D<sub>7/2</sub> and the ground state <sup>8</sup>S<sub>7/2</sub>. Analysis of this fluorescence allows monitoring interactions between Cm(III) ions in organic and inorganic complexes.<ref name=plb>Bünzli, J.-C. G. and Choppin, G. R. ''Lanthanide probes in life, chemical, and earth sciences: theory and practice'', Elsevier, Amsterdam, 1989 ISBN 0-444-88199-9</ref>
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| ===Chemical===
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| Curium ions in solution almost exclusively assume the [[oxidation state]] of +3, which is the most stable oxidation state for curium.<ref>Penneman, p. 24</ref> The +4 oxidation state is observed mainly in a few solid phases, such as CmO<sub>2</sub> and CmF<sub>4</sub>.<ref>{{cite journal|last1=Keenan|first1=Thomas K.|journal=Journal of the American Chemical Society|volume=83|issue=17|page=3719|year=1961|doi=10.1021/ja01478a039}}</ref><ref name = "asprey"/> Aqueous curium(IV) is only known in the presence of strong oxidizers such as [[potassium persulfate]], and is easily reduced to curium(III) by [[radiolysis]] and even by water.<ref name=Lumetta/> The chemical behavior of curium is different from the actinides thorium and uranium, and is similar to that of americium and many [[lanthanides]]. In aqueous solution, the Cm<sup>3+</sup> ion is colorless to pale green,<ref name=g1265>Greenwood, p. 1265</ref> and Cm<sup>4+</sup> ion is pale yellow.<ref name="HOWI_1956">Holleman, p. 1956</ref> The optical absorption of Cm<sup>3+</sup> ions contains three sharp peaks at 375.4, 381.2 and 396.5 nanometers and their strength can be directly converted into the concentration of the ions.<ref>Penneman, pp. 25–26</ref> The +6 oxidation state has only been reported once in solution in 1978, as the curyl ion ({{chem|CmO|2|2+}}): this was prepared from the [[beta decay]] of [[americium-242]] in the americium(V) ion {{chem|242|AmO|2|+}}.<ref name=CmO3/> Failure to obtain Cm(VI) from oxidation of Cm(III) and Cm(IV) may be due to the high Cm<sup>4+</sup>/Cm<sup>3+</sup> [[ionization potential]] and the instability of Cm(V).<ref name=Lumetta>{{cite book|first1 = Lumetta|last1 = Gregg J.|first2 = Major C.|last2 = Thompson|first3 = Robert A.|last3 = Penneman|first4 = P. Gary|last4=Eller|contribution = Curium|title = The Chemistry of the Actinide and Transactinide Elements|editor1-first = Lester R.|editor1-last = Morss|editor2-first = Norman M.|editor2-last = Edelstein|editor3-first = Jean|editor3-last = Fuger|edition = 3rd|year = 2006|volume = 3|publisher = Springer|location = Dordrecht, the Netherlands|pages = 1397–1443|url = http://radchem.nevada.edu/classes/rdch710/files/neptunium.pdf|doi = 10.1007/1-4020-3598-5_9}}</ref>
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| Curium ions are [[HSAB theory|hard Lewis acids]] and thus form most stable complexes with hard bases.<ref>{{cite journal|last1=Jensen|first1=Mark P.|last2=Bond|first2=Andrew H.|title=Comparison of Covalency in the Complexes of Trivalent Actinide and Lanthanide Cations|journal=Journal of the American Chemical Society|volume=124|issue=33|year=2002|pmid=12175247|doi=10.1021/ja0178620|pages=9870–7}}</ref> The bonding is mostly ionic, with a small covalent component.<ref>{{cite journal|author=Seaborg, G. T. |title=Overview of the Actinide and Lanthanide (the ''f'') Elements|journal=Radiochimica Acta|year=1993|volume=61|pages=115–122}}</ref> Curium in its complexes commonly exhibits a 9-fold coordination environment, within a tricapped [[trigonal prismatic geometry|trigonal prismatic]] geometry.<ref>Greenwood, p. 1267</ref>
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| ===Isotopes===
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| <div style="float:right; margin:0; font-size:85%;">
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| {| class="wikitable"
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| !colspan="7"| [[Thermal neutron]] [[Neutron cross-section|cross sections]] ([[Barn (unit)|barns]])<ref>Pfennig, G.; Klewe-Nebenius, H. and Seelmann Eggebert, W. (Eds.): Karlsruhe [[nuclide]], 6th Ed. 1998</ref>
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| | ||<sup>242</sup>Cm||<sup>243</sup>Cm||<sup>244</sup>Cm||<sup>245</sup>Cm||<sup>246</sup>Cm||<sup>247</sup>Cm
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| |-
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| |Fission||5||617||1.04||2145||0.14||81.90
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| |-
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| |Capture||16||130||15.20||369||1.22||57
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| |-
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| |C/F ratio||3.20||0.21||14.62||0.17||8.71||0.70
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| |-
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| !colspan="7"| [[low enriched uranium|LEU]] [[spent fuel]] 20 years after 53 MWd/kg [[burnup]]<ref>{{cite journal|doi=10.1080/08929880500357682|last1=Kang|year=2005|page=169|issue=3|volume=13|journal=Science and Global Security|url=http://www.princeton.edu/sgs/publications/sgs/pdf/13_3%20Kang%20vonhippel.pdf|first1=Jungmin|last2=Von Hippel|first2=Frank|title=Limited Proliferation-Resistance Benefits from Recycling Unseparated Transuranics and Lanthanides from Light-Water Reactor Spent Fuel}}</ref>
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| |-
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| |colspan="2" |3 common isotopes ||51||3700||390|| ||
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| |-
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| !colspan="7"| [[Fast reactor]] [[MOX fuel]] (avg 5 samples, [[burnup]] 66-120GWd/t)<ref>{{cite journal|doi=10.3327/jnst.38.912|url=http://web.archive.org/web/20070703191508/http://wwwsoc.nii.ac.jp/aesj/publication/JNST2001/No.10/38_912-914.pdf|format=PDF|title=Analysis of Curium Isotopes in Mixed Oxide Fuel Irradiated in Fast Reactor|journal=Journal of Nuclear Science and Technology|volume=38|year=2001|issue=10|pages=912–914|author=Osaka, M. ''et al.''}}</ref>
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| |-
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| |colspan="2" |Total curium 3.09{{e|-3}}% ||27.64%||70.16%||2.166%||0.0376%||0.000928%
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| |}
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| {| Class = "wikitable"
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| |-
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| | Isotope||<sup>242</sup>Cm||<sup>243</sup>Cm||<sup>244</sup>Cm||<sup>245</sup>Cm||<sup>246</sup>Cm||<sup>247</sup>Cm||<sup>248</sup>Cm||<sup>250</sup>Cm
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| |-
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| |[[Critical mass]], kg|| 25|| 7.5||33||6.8||39||7||40.4||23.5
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| |}
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| </div>
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| {{see also|Isotopes of curium}}
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| About 20 [[Radionuclide|radioisotopes]] and 7 [[nuclear isomer]]s between <sup>233</sup>Cm and <sup>252</sup>Cm are known for curium, and no stable [[isotope]]s. The longest half-lives have been reported for <sup>247</sup>Cm (15.6 million years) and <sup>248</sup>Cm (348,000 years). Other long-lived isotopes are <sup>245</sup>Cm (half-life 8500 years), <sup>250</sup>Cm (8,300 years) and <sup>246</sup>Cm (4,760 years). Curium-250 is unusual in that it predominantly (about 86%) decays via [[spontaneous fission]]. The most commonly used curium isotopes are <sup>242</sup>Cm and <sup>244</sup>Cm with the half-lives of 162.8 days and 18.1 years, respectively.<ref name="nubase">{{cite journal|last1=Audi|first1=G|doi=10.1016/S0375-9474(97)00482-X|title=The N? evaluation of nuclear and decay properties|year=1997|page=1|issue=1|volume=624|journal=Nuclear Physics A|url=http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf|bibcode=1997NuPhA.624....1A|last2=Bersillon|first2=O.|last3=Blachot|first3=J.|last4=Wapstra|first4=A.H.}}</ref>
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| [[File:Sasahara.svg|thumb|325px|Transmutation flow between <sup>238</sup>Pu and <sup>244</sup>Cm in LWR.<ref>{{cite journal|url=http://nuclear.ee.duth.gr/upload/A11%20%20%20200401.pdf|title=Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels|journal=Journal of Nuclear Science and Technology|volume=41|issue=4|pages=448–456|year=2004|doi=10.3327/jnst.41.448|author=Sasahara, Akihiro|last2=Matsumura|first2=Tetsuo|last3=Nicolaou|first3=Giorgos|last4=Papaioannou|first4=Dimitri}}</ref><br>Fission percentage is 100 minus shown percentages.<br>Total rate of transmutation varies greatly by nuclide.<br><sup>245</sup>Cm–<sup>248</sup>Cm are long-lived with negligible decay.]]
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| All isotopes between <sup>242</sup>Cm and <sup>248</sup>Cm, as well as <sup>250</sup>Cm, undergo a self-sustaining [[nuclear chain reaction]] and thus in principle can act as a [[nuclear fuel]] in a reactor. As in most transuranic elements, the [[nuclear fission]] cross section is especially high for the odd-mass curium isotopes<sup>243</sup>Cm, <sup>245</sup>Cm and <sup>247</sup>Cm. These can be used in [[thermal-neutron reactor]]s, whereas a mixture of curium isotopes is only suitable for [[fast breeder reactor]]s since the even-mass isotopes are not fissile in a thermal reactor and accumulate as burn-up increases.<ref name="irsn">Institut de Radioprotection et de Sûreté Nucléaire: [http://ec.europa.eu/energy/nuclear/transport/doc/irsn_sect03_146.pdf "Evaluation of nuclear criticality safety. data and limits for actinides in transport"], p. 16</ref> The mixed-oxide (MOX) fuel, which is to be used in power reactors, should contain little or no curium because the neutron activation of <sup>248</sup>Cm will create [[californium]]. This is strong [[neutron]] emitter, and would pollute the back end of the fuel cycle and increase the dose to reactor personnel. Hence, if the [[minor actinides]] are to be used as fuel in a thermal neutron reactor, the curium should be excluded from the fuel or placed in special fuel rods where it is the only actinide present.<ref>{{cite book|author=National Research Council (U.S.). Committee on Separations Technology and Transmutation Systems|title=Nuclear wastes: technologies for separations and transmutation|url=http://books.google.com/books?id=iRI7Cx2D4e4C&pg=PA231|accessdate=19 April 2011|year=1996|publisher=National Academies Press|isbn=978-0-309-05226-9|pages=231–}}</ref>
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| The table to the right lists the [[critical mass]]es for curium isotopes for a sphere, without a moderator and reflector. With a metal reflector (30 cm of steel), the critical masses of the odd isotopes are about 3–4 kg. When using water (thickness ~20–30 cm) as the reflector, the critical mass can be as small as 59 gram for <sup>245</sup>Cm, 155 gram for <sup>243</sup>Cm and 1550 gram for <sup>247</sup>Cm. There is a significant uncertainty in these critical mass values. Whereas it is usually of the order 20%, the values for <sup>242</sup>Cm and <sup>246</sup>Cm were listed as large as 371 kg and 70.1 kg, respectively, by some research groups.<ref name="irsn"/><ref>{{cite journal|author=Okundo, H. and Kawasaki, H. |title=Critical and Subcritical Mass Calculations of Curium-243 to −247 Based on JENDL-3.2 for Revision of ANSI/ANS-8.15|journal=Journal of Nuclear Science and Technology|year=2002|volume=39|pages=1072–1085|doi=10.3327/jnst.39.1072|issue=10}}</ref>
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| Currently, curium is not used as a nuclear fuel owing to its low availability and high price.<ref>[http://bundesrecht.juris.de/atg/__2.html § 2 Begriffsbestimmungen (Atomic Energy Act)] (in German)</ref> <sup>245</sup>Cm and <sup>247</sup>Cm have a very small critical mass and therefore could be used in portable [[nuclear weapon]]s, but none have been reported thus far. Curium-243 is not suitable for this purpose because of its short half-life and strong α emission which would result in excessive heat.<ref>{{cite book|author1=Jukka Lehto|author2=Xiaolin Hou|title=Chemistry and Analysis of Radionuclides: Laboratory Techniques and Methodology|url=http://books.google.com/books?id=v2iRJaO3SMIC&pg=PA303|accessdate=19 April 2011|date=2 February 2011|publisher=Wiley-VCH|isbn=978-3-527-32658-7|pages=303–}}</ref> Curium-247 would be highly suitable, having a half-life 647 times that of plutonium-239.
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| ===Occurrence===
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| [[File:Ivy Mike - mushroom cloud.jpg|thumb|Several isotopes of curium were detected in the fallout from the ''Ivy Mike'' nuclear test.]]
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| The longest-lived isotope of curium, <sup>247</sup>Cm, has a half-life of 15.6 million years. Therefore, all [[primordial nuclide|primordial]] curium, that is curium present on the Earth during its formation, should have decayed by now. Curium is produced artificially, in small quantities for research purposes. Furthermore, it occurs in spent [[nuclear fuel]]. Curium is present in nature in certain areas used for the atmospheric [[nuclear weapons testing|nuclear weapons tests]], which were conducted between 1945 and 1980.<ref name="lenntech">[http://www.lenntech.de/pse/pse.htm Curium] (in German)</ref> So the analysis of the debris at the testing site of the first U.S. [[hydrogen bomb]], [[Ivy Mike]], (1 November 1952, [[Enewetak Atoll]]), beside [[einsteinium]], [[fermium]], [[plutonium]] and [[americium]] also revealed isotopes of berkelium, californium and curium, in particular <sup>245</sup>Cm, <sup>246</sup>Cm and smaller quantities of <sup>247</sup>Cm, <sup>248</sup>Cm and <sup>249</sup>Cm. For reasons of military secrecy, this result was published only in 1956.<ref>{{cite journal|last1=Fields|first1=P. R.|last2=Studier|first2=M. H.|last3=Diamond|first3=H.|last4=Mech|first4=J. F.|last5=Inghram|first5=M. G.|last6=Pyle|first6=G. L.|last7=Stevens|first7=C. M.|last8=Fried|first8=S.|last9=Manning|first9=W. M.|last10=Ghiorso|first10=A.|last11=Thompson|first11=S. G.|last12=Higgins|first12=G. H.|last13=Seaborg|first13=G. T.|displayauthors=3|title=Transplutonium Elements in Thermonuclear Test Debris|year=1956|journal=Physical Review|volume=102|issue=1|pages=180–182|doi=10.1103/PhysRev.102.180|bibcode=1956PhRv..102..180F}}</ref>
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| Atmospheric curium compounds are poorly soluble in common solvents and mostly adhere to soil particles. Soil analysis revealed about 4,000 times higher concentration of curium at the sandy soil particles than in water present in the soil pores. An even higher ratio of about 18,000 was measured in [[loam]] soils.<ref name=LA2/>
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| A few atoms of curium can be produced by [[Neutron capture|neutron capture reactions]] and [[beta decay]] in very highly concentrated [[uranium]]-bearing deposits.<ref name="emsley">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7}}</ref>
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| ==Synthesis==
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| ===Isotope preparation===
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| Curium is produced in small quantities in [[nuclear reactor]]s, and by now only kilograms of it have been accumulated for the <sup>242</sup>Cm and <sup>244</sup>Cm and grams or even milligrams for heavier isotopes. This explains the high price of curium, which has been be quoted at 160–185 [[United States dollar|USD]] per milligram,<ref name=CRC/> with a more recent estimate at 2,000 USD/g for <sup>242</sup>Cm and 170 USD/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.
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| :<math>\mathrm{^{238}_{\ 92}U\ \xrightarrow {(n,\gamma)} \ ^{239}_{\ 92}U\ \xrightarrow [23.5 \ min]{\beta^-} \ ^{239}_{\ 93}Np\ \xrightarrow [2.3565 \ d]{\beta^-} \ ^{239}_{\ 94}Pu}</math> <small>(the times are [[half-life|half-lives]])</small>.
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| Further neutron capture followed by β<sup>–</sup>-decay produces the <sup>241</sup>Am isotope of [[americium]] which further converts into <sup>242</sup>Cm:
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| :<math>\mathrm{^{239}_{\ 94}Pu\ \xrightarrow {2(n,\gamma)} \ ^{241}_{\ 94}Pu\ \xrightarrow [14.35 \ yr]{\beta^-} \ ^{241}_{\ 95}Am\ \xrightarrow {(n,\gamma)} \ ^{242}_{\ 95}Am\ \xrightarrow [16.02 \ h]{\beta^-} \ ^{242}_{\ 96}Cm}</math>.
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| For research purposes, curium is obtained by irradiating not uranium but plutonium, which is available in large amounts from spent nuclear fuel. 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>
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| :<math>\mathrm{^{239}_{\ 94}Pu\ \xrightarrow {4(n,\gamma)} \ ^{243}_{\ 94}Pu\ \xrightarrow [4,956 \ h]{\beta^-} \ ^{243}_{\ 95}Am\ \xrightarrow {(n,\gamma)} \ ^{244}_{\ 95}Am\ \xrightarrow [10.1 \ h]{\beta^-} \ ^{244}_{\ 96}Cm}</math>
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| :<math>\mathrm{^{244}_{\ 96}Cm\ \xrightarrow [18.11 \ yr]{\alpha} \ ^{240}_{\ 94}Pu}</math>
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| Curium-244 decays into <sup>240</sup>Pu by emission of alpha particle, but it also absorbs neutrons resulting in a small amount of heavier curium isotopes. Among those, <sup>247</sup>Cm and <sup>248</sup>Cm are popular in scientific research because of their long half-lives. However, the production rate of <sup>247</sup>Cm in thermal neutron reactors is relatively low because of it is prone to undergo fission induced by thermal neutrons.<ref name=haire/> Synthesis of <sup>250</sup>Cm via [[neutron absorption]] is also rather unlikely because of the short half-life of the intermediate product <sup>249</sup>Cm (64 min), which converts by β<sup>–</sup> decay to the [[berkelium]] isotope <sup>249</sup>Bk.<ref name=haire/>
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| <!-- 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}} -->
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| :<math>\mathrm{^{A}_{96}Cm\ +\ ^{1}_{0}n\ \longrightarrow \ ^{A+1}_{\ \ 96}Cm\ +\ \gamma}</math> <small>(for A = 244–248)</small>
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| The above cascade of (n,γ) reactions produces a mixture of different curium isotopes. Their post-synthesis separation is cumbersome, and therefore a selective synthesis is desired. Curium-248 is favored for research purposes because of its long half-life. The most efficient preparation method of this isotope is via α-decay of the [[californium]] isotope <sup>252</sup>Cf, which is available in relatively large quantities due to its long half-life (2.65 years). About 35–50 mg of <sup>248</sup>Cm is being produced by this method every year. The associated reaction produces <sup>248</sup>Cm with isotopic purity of 97%.<ref name=haire>{{cite book
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| | title = The Chemistry of the Actinide and Transactinide Elements
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| | editor1-last = Morss|editor2-first = Norman M.
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| | editor2-last = Edelstein
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| | editor3-last = Fuger|editor3-first = Jean
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| | last = Haire|first = Richard G.
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| | chapter = Curium|url=http://radchem.nevada.edu/classes/rdch710/files/curium.pdf|page=1401
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| | publisher = [[Springer Science+Business Media]]
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| | year = 2006
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| | isbn = 1-4020-3555-1
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| | location = Dordrecht, The Netherlands
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| | edition = 3rd
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| }}</ref>
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| :<math>\mathrm{^{252}_{\ 98}Cf\ \xrightarrow [2.645 \ yr]{\alpha} \ ^{248}_{\ 96}Cm}</math>
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| Another interesting for research isotope <sup>245</sup>Cm can be obtained from the α-decay of <sup>249</sup>Cf, and the latter isotope is produced in minute quantities from the β<sup>–</sup>-decay of the [[berkelium]] isotope <sup>249</sup>Bk.
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| :<math>\mathrm{^{249}_{\ 97}Bk\ \xrightarrow [330 \ d]{\beta^-} \ ^{249}_{\ 98}Cf\ \xrightarrow [351 \ yr]{\alpha} \ ^{245}_{\ 96}Cm}</math>
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| ===Metal preparation===
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| [[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.]]
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| Most synthesis routines yield a mixture of different actinide isotopes as [[oxide]]s, from which a certain 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 [[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, Christiansen B, Foreman MRS, Geist A, Glatz JP, Malmbeck R, Modolo G, Serrano-Purroy D and Sorel C|journal = Solvent Extraction and Ion Exchange|year = 2009|volume = 27|issue = 2|page = 97|doi = 10.1080/07366290802672204|title = Demonstration of a SANEX Process in [[centrifugal extractor|Centrifugal Contactors]] using the CyMe4-BTBP Molecule on a Genuine Fuel Solution}}</ref> Separation of curium from a very similar americium can also be achieved 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; whereas americium oxidizes to soluble Am(IV) complexes, curium remains unchanged and can thus be isolated by repeated centrifugation.<ref>Penneman, p. 25</ref>
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| Metallic curium is obtained by [[Redox|reduction]] of its compounds. Initially, curium(III) fluoride was used for this purpose. The reaction was conducted in the environment free from water and oxygen, in the 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|year=1964|doi=10.1016/0022-1902(64)80069-5}}</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|year=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>
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| :<math>\mathrm{CmF_3\ +\ 3\ Li\ \longrightarrow \ Cm\ +\ 3\ LiF}</math>
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| Another possibility is the 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|year=1969|doi=10.1016/0020-1650(69)80221-7|last2=Thompson|first2=M.C.}}</ref>
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| ==Compounds and reactions==
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| {{category see also|Curium compounds}}
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| ===Oxides===
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| Curium readily reacts with oxygen forming mostly Cm<sub>2</sub>O<sub>3</sub> and CmO<sub>2</sub> oxides,<ref name="lenntech"/> but the divalent oxide CmO is also known.<ref name="HOWI_1972">Holleman, p. 1972</ref> Black CmO<sub>2</sub> can be obtained by burning curium [[oxalate]] (Cm<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>), nitrate (Cm(NO<sub>3</sub>)<sub>3</sub>) or hydroxide in pure oxygen.<ref Name="asprey"/><ref name=g1268>Greenwood, p. 1268</ref> Upon heating to 600–650 °C in vacuum (about 0.01 [[Pascal (unit)|Pa]]), it transforms into the whitish Cm<sub>2</sub>O<sub>3</sub>:<ref name="asprey">{{cite journal|last1=Asprey|first1=L. B.|last2=Ellinger|first2=F. H.|last3=Fried|first3=S.|last4=Zachariasen|first4=W. H.|journal=Journal of the American Chemical Society|volume=77|issue=6|page=1707|year=1955|doi=10.1021/ja01611a108}}</ref><ref>{{cite journal|last1=Noe|first1=M|title=Self-radiation effects on the lattice parameter of 244CmO2|journal=Inorganic and Nuclear Chemistry Letters|volume=7|issue=5|page=421|year=1971|doi=10.1016/0020-1650(71)80177-0|last2=Fuger|first2=J.}}</ref>
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| : <math>\mathrm{4\ CmO_2\ \xrightarrow {\Delta T} \ 2\ Cm_2O_3\ +\ O_2}</math>.
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| Alternatively, Cm<sub>2</sub>O<sub>3</sub> can be obtained by reducing CmO<sub>2</sub> with molecular [[hydrogen]]:<ref>{{cite journal|last1=Haug|first1=H|title=Curium sesquioxide Cm2O3|journal=Journal of Inorganic and Nuclear Chemistry|volume=29|issue=11|page=2753|year=1967|doi=10.1016/0022-1902(67)80014-9}}</ref>
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| : <math>\mathrm{2\ CmO_2\ +\ H_2\ \longrightarrow \ Cm_2O_3\ +\ H_2O}</math>
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| Furthermore, a number of ternary oxides of the type M(II)CmO<sub>3</sub> are known, where M stands for a divalent metal, such as barium.<ref>{{cite journal|last1=Fuger|first1=J|last2=Haire|first2=R|last3=Peterson|first3=J|title=Molar enthalpies of formation of BaCmO3 and BaCfO3|journal=Journal of Alloys and Compounds|volume=200|issue=1–2|page=181|year=1993|doi=10.1016/0925-8388(93)90491-5}}</ref>
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| Thermal oxidation of trace quantities of curium hydride (CmH<sub>2–3</sub>) has been reported to produce a volatile form of CmO<sub>2</sub> and the volatile trioxide CmO<sub>3</sub>, one of the two known examples of the very rare +6 state for curium.<ref name=CmO3/> Another observed species was reported to behave similarly to plutonium tetroxide and was tentatively characterized as CmO<sub>4</sub>, with curium in the extremely rare +8 state only known in this compound.<ref name=CmO4/>
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| ===Halides===
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| The colorless curium(III) fluoride (CmF<sub>3</sub>) can be produced by introducing fluoride ions into curium(III)-containing solutions. The brown tetravalent curium(IV) fluoride (CmF<sub>4</sub>) on the other hand is only obtained by reacting curium(III) fluoride with molecular [[fluorine]]:<ref name = "Morrs"/>
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| : <math>\mathrm{2\ CmF_3\ +\ F_2\ \longrightarrow\ 2\ CmF_4}</math>
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| A series of ternary fluorides are known of the form A<sub>7</sub>Cm<sub>6</sub>F<sub>31</sub>, where A stands for [[alkali metal]].<ref>{{cite journal|last1=Keenan|first1=T|title=Lattice constants of K7Cm6F31 trends in the 1:1 and 7:6 alkali metal-actinide(IV) series|journal=Inorganic and Nuclear Chemistry Letters|volume=3|issue=10|page=391|year=1967|doi=10.1016/0020-1650(67)80092-8}}</ref>
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| The colorless [[curium(III) chloride]] (CmCl<sub>3</sub>) is produced in the reaction of [[curium(III) hydroxide]] (Cm(OH)<sub>3</sub>) with anhydrous [[hydrogen chloride]] gas. It can further be converted into other halides, such as curium(III) bromide (colorless to light green) and curium(III) iodide (colorless), by reacting it with the [[ammonia]] salt of the corresponding halide at elevated temperature of about 400–450 °C:<ref>{{cite journal|last1=Asprey|first1=L. B.|last2=Keenan|first2=T. K.|last3=Kruse|first3=F. H.|journal=Inorganic Chemistry|volume=4|issue=7|page=985|year=1965|doi=10.1021/ic50029a013}}</ref>
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| : <math>\mathrm{CmCl_3\ +\ 3\ NH_4I\ \longrightarrow \ CmI_3\ +\ 3\ NH_4Cl}</math>
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| An alternative procedure is heating curium oxide to about 600 °C with the corresponding acid (such as [[hydrobromic acid|hydrobromic]] for curium bromide).<ref>{{cite journal|last1=Burns|first1=J|title=Crystallographic studies of some transuranic trihalides: 239PuCl3, 244CmBr3, 249BkBr3 and 249CfBr3|journal=Journal of Inorganic and Nuclear Chemistry|volume=37|issue=3|page=743|year=1975|doi=10.1016/0022-1902(75)80532-X|last2=Peterson|first2=J.R.|last3=Stevenson|first3=J.N.}}</ref><ref>{{cite journal|last1=Wallmann|first1=J|title=Crystal structure and lattice parameters of curium trichloride|journal=Journal of Inorganic and Nuclear Chemistry|volume=29|issue=11|page=2745|year=1967|doi=10.1016/0022-1902(67)80013-7|last2=Fuger|first2=J.|last3=Peterson|first3=J.R.|last4=Green|first4=J.L.}}</ref> Vapor phase [[hydrolysis]] of curium(III) chloride results in curium oxychloride:<ref>{{cite journal|last1=Weigel|first1=F|last2=Wishnevsky|first2=V|last3=Hauske|first3=H|title=The vapor phase hydrolysis of PuCl3 and CmCl3: heats of formation of PuOC1 and CmOCl|journal=Journal of the Less Common Metals|volume=56|issue=1|page=113|year=1977|doi=10.1016/0022-5088(77)90224-7}}</ref>
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| : <math>\mathrm{CmCl_3\ +\ \ H_2O\ \longrightarrow \ CmOCl\ +\ 2\ HCl}</math>
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| ===Chalcogenides and pnictides===
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| Sulfides, selenides and tellurides of curium have been obtained by treating curium with gaseous [[sulfur]], [[selenium]] or [[tellurium]] in vacuum at elevated temperature.<ref>Troc, R. [http://books.google.com/books?id=vkzx_t3zLR0C&pg=PA4 Actinide Monochalcogenides, Volume 27], Springer, 2009 ISBN 3-540-29177-6, p. 4</ref><ref>{{cite journal|last1=Damien|first1=D|title=Preparation and lattice parameters of curium sulfides and selenides|journal=Inorganic and Nuclear Chemistry Letters|volume=11|issue=7–8|page=451|year=1975|doi=10.1016/0020-1650(75)80017-1|last2=Charvillat|first2=J.P.|last3=Müller|first3=W.}}</ref> The [[Nitrogen group|pnictides]] of curium of the type CmX are known for the elements [[nitrogen]], [[phosphorus]], [[arsenic]] and [[antimony]].<ref Name="Morrs"/> They can be prepared by reacting either curium(III) hydride (CmH<sub>3</sub>) or metallic curium with these elements at elevated temperatures.<ref name=CuriumChap9>Lumetta, G. J.; Thompson, M. C.; Penneman, R. A.; Eller, P. G. [http://radchem.nevada.edu/classes/rdch710/files/curium.pdf Curium], Chapter Nine in ''Radioanalytical Chemistry'', Springer, 2004, pp. 1420-1421. ISBN 0387341226, ISBN 978-0387 341224</ref>
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| ===Organocurium compounds and biological aspects===
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| [[File:Uranocene-3D-balls.png|thumb|120px|Predicted curocene structure]]
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| Organometallic complexes analogous to [[uranocene]] are known also for other actinides, such as thorium, protactinium, neptunium, plutonium and americium. [[Molecular orbital theory]] predicts a stable "curocene" complex (η<sup>8</sup>-C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>Cm, but it has not been reported experimentally yet.<ref>Elschenbroich, Ch. Organometallic Chemistry, 6th edition, Wiesbaden 2008, ISBN 978-3-8351-0167-8, p. 589</ref><ref>{{cite journal|last1=Kerridge|first1=Andrew|last2=Kaltsoyannis|first2=Nikolas|title=Are the Ground States of the Later Actinocenes Multiconfigurational? All-Electron Spin−Orbit Coupled CASPT2 Calculations on An(η8-C8H8)2(An = Th, U, Pu, Cm)|journal=The Journal of Physical Chemistry A|volume=113|issue=30|year=2009|pmid=19719318|doi=10.1021/jp903912q|pages=8737–45}}</ref>
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| Formation of the complexes of the type Cm(n-C<sub>3</sub>H<sub>7</sub>-BTP)<sub>3</sub>, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing n-C<sub>3</sub>H<sub>7</sub>-BTP and Cm<sup>3+</sup> ions has been confirmed by [[Extended X-ray absorption fine structure|EXAFS]]. Some of these BTP-type complexes selectively interact with curium and therefore are useful in its selective separation from lanthanides and another actinides.<ref name="denecke"/><ref>{{cite journal|last1=Girnt|first1=Denise|last2=Roesky|first2=Peter W.|last3=Geist|first3=Andreas|last4=Ruff|first4=Christian M.|last5=Panak|first5=Petra J.|last6=Denecke|first6=Melissa A.|title=6-(3,5-Dimethyl-1H-pyrazol-1-yl)-2,2′-bipyridine as Ligand for Actinide(III)/Lanthanide(III) Separation|journal=Inorganic Chemistry|volume=49|issue=20|year=2010|pmid=20849125|doi=10.1021/ic101309j|pages=9627–35}}</ref> Dissolved Cm<sup>3+</sup> ions bind with many organic compounds, such as [[hydroxamic acid]],<ref name=pl1>{{cite journal|last1=Glorius|first1=M.|last2=Moll|first2=H.|last3=Bernhard|first3=G.|title=Complexation of curium(III) with hydroxamic acids investigated by time-resolved laser-induced fluorescence spectroscopy|journal=Polyhedron|volume=27|issue=9–10|page=2113|year=2008|doi=10.1016/j.poly.2008.04.002}}</ref> [[urea]],<ref name=pl2>{{cite journal|last1=Heller|first1=Anne|last2=Barkleit|first2=Astrid|last3=Bernhard|first3=Gert|last4=Ackermann|first4=Jörg-Uwe|title=Complexation study of europium(III) and curium(III) with urea in aqueous solution investigated by time-resolved laser-induced fluorescence spectroscopy|journal=Inorganica Chimica Acta|volume=362|issue=4|page=1215|year=2009|doi=10.1016/j.ica.2008.06.016}}</ref> [[fluorescein]]<ref name=pl3>{{cite journal|last1=Moll|first1=Henry|last2=Johnsson|first2=Anna|last3=Schäfer|first3=Mathias|last4=Pedersen|first4=Karsten|last5=Budzikiewicz|first5=Herbert|last6=Bernhard|first6=Gert|title=Curium(III) complexation with pyoverdins secreted by a groundwater strain of Pseudomonas fluorescens|journal=BioMetals|volume=21|issue=2|year=2007|pmid=17653625|doi=10.1007/s10534-007-9111-x|pages=219–28}}</ref> and [[adenosine triphosphate]].<ref name=pl4>{{cite journal|last1=Moll|first1=Henry|last2=Geipel|first2=Gerhard|last3=Bernhard|first3=Gert|title=Complexation of curium(III) by adenosine 5′-triphosphate (ATP): A time-resolved laser-induced fluorescence spectroscopy (TRLFS) study|journal=Inorganica Chimica Acta|volume=358|issue=7|page=2275|year=2005|doi=10.1016/j.ica.2004.12.055}}</ref> Many of these compounds are related to biological activity of various [[microorganism]]s. The resulting complexes exhibit strong yellow-orange emission under UV light excitation, which is convenient not only for their detection, but also for studying the interactions between the Cm<sup>3+</sup> ion and the ligands via changes in the half-life (of the order ~0.1 ms) and spectrum of the fluorescence.<ref name=plb/><ref name=pl1/><ref name=pl2/><ref name=pl3/><ref name=pl4/>
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| Curium has no biological significance.<ref>{{cite web|url=http://umbbd.msi.umn.edu/periodic/elements/cm.html |title=Biochemical Periodic Table – Curium |publisher=Umbbd.msi.umn.edu |date=2007-06-08 |accessdate=2011-03-25}}</ref> There are a few reports on [[biosorption]] of Cm<sup>3+</sup> by [[bacteria]] and [[archaea]], however no evidence for incorporation of curium into them.<ref>{{cite journal|doi=10.1021/es0301166|last1=Moll|first1=H|last2=Stumpf|first2=T|last3=Merroun|first3=M|last4=Rossberg|first4=A|last5=Selenska-Pobell|first5=S|last6=Bernhard|first6=G|title=Time-resolved laser fluorescence spectroscopy study on the interaction of curium(III) with Desulfovibrio äspöensis DSM 10631T|journal=Environmental Science & Technology|volume=38|issue=5|pages=1455–9|year=2004|pmid=15046347|bibcode = 2004EnST...38.1455M }}</ref><ref>{{cite journal|author=Ozaki, T. ''et al.''|url=http://sciencelinks.jp/j-east/article/200305/000020030503A0110480.php|title=Association of Eu(III) and Cm(III) with Bacillus subtilis and Halobacterium salinarium|journal=Journal of Nuclear Science and Technology|year=2002|volume=Suppl. 3|pages=950–953}}</ref>
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| ==Applications==
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| ===Radionuclides===
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| [[File:Curium self-glow radiation.jpg|thumb|right|The radiation from curium is so strong that the metal glows purple in the dark.]]
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| Curium is one of the most radioactive isolable elements. Its two most common isotopes <sup>242</sup>Cm and <sup>244</sup>Cm are strong alpha emitters (energy 6 MeV); they have relatively short half-lives of 162.8 days and 18.1 years, and produce as much as 120 W/g and 3 W/g of thermal energy, respectively.<ref name=CRC/><ref name="Binder">Binder, Harry H.: ''Lexikon der chemischen Elemente'', S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3, pp. 174–178.</ref><ref>''Gmelin Handbook of Inorganic Chemistry'', System No. 71, Volume 7a, transuranics, Part A2, p. 289</ref> Therefore, curium can be used in its common oxide form in [[radioisotope thermoelectric generator]]s like those in spacecraft. This application has been studied for the <sup>244</sup>Cm isotope, while <sup>242</sup>Cm was abandoned due to its prohibitive price of around 2000 USD/g. Curium-243 with a ~30 year half-life and good energy yield of ~1.6 W/g could make for a suitable fuel, but it produces significant amounts of harmful [[Gamma ray|gamma]] and [[Beta ray|beta]] radiation from radioactive decay products. Though as an α-emitter, <sup>244</sup>Cm requires a much thinner radiation protection shielding, it has a high spontaneous fission rate, and thus the neutron and gamma radiation rate are relatively strong. As compared to a competing thermoelectric generator isotope such as <sup>238</sup>Pu, <sup>244</sup>Cm emits a 500 time greater fluence of neutrons, and its higher gamma emission requires a shield that is 20 times thicker — about 2 inches of lead for a 1 kW source, as compared to 0.1 in for <sup>238</sup>Pu. Therefore this application of curium is currently considered impractical.<ref name=lect>[http://fti.neep.wisc.edu/neep602/SPRING00/lecture5.pdf Basic elements of static RTGs], G.L. Kulcinski, NEEP 602 Course Notes (Spring 2000), Nuclear Power in Space, University of Wisconsin Fusion Technology Institute (see last page)</ref>
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| A more promising application of <sup>242</sup>Cm is to produce <sup>238</sup>Pu, a more suitable radioisotope for thermoelectric generators such as in cardiac pacemakers. The alternative routes to <sup>238</sup>Pu use the (n,γ) reaction of <sup>237</sup>Np, or the [[deuteron]] bombardment of uranium, which both always produce <sup>236</sup>Pu as an undesired by-product — since the latter decays to <sup>208</sup>Tl with strong gamma emission.<ref>[http://www.kronenberg.kernchemie.de/ Kronenberg, Andreas], [http://www.kernenergie-wissen.de/pu-batterien.html Plutonium-Batterien] (in German)</ref>
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| Curium is also a common starting material for the production of higher [[transuranic elements]] and [[transactinides]]. Thus, bombardment of <sup>248</sup>Cm with oxygen (<sup>18</sup>O) or magnesium (<sup>26</sup>Mg) yielded certain isotopes of [[seaborgium]] (<sup>265</sup>Sg) and [[hassium]] (<sup>269</sup>Hs and <sup>270</sup>Hs).<ref name="HOWI_1980">Holleman, pp. 1980–1981.</ref> Californium was discovered when a microgram-sized target of curium-242 was irradiated with 35 MeV [[alpha particle]]s using the {{convert|60|in|cm|adj=on}} cyclotron at Berkeley:
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| :{{Nuclide|curium|242}} + {{Nuclide|helium|4}} → {{Nuclide|californium|245}} + {{su|b=0|p=1}}{{SubatomicParticle|neutron}}
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| Only about 5,000 atoms of californium were produced in this experiment.<ref>{{cite book|title=One Hundred Years after the Discovery of Radioactivity|editor=Adloff, J. P.|last=Seaborg|first=G. T.|page=82|year=1996|publisher=Oldenbourg Wissenschaftsverlag|isbn=978-3-486-64252-0}}</ref>
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| [[File:MER APXS PIA05113.jpg|thumb|Alpha-particle X-ray spectrometer of a Mars exploration rover]]
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| ===X-ray spectrometer===
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| The most practical application of <sup>244</sup>Cm — though rather limited in total volume — is as α-particle source in the [[alpha particle X-ray spectrometer]]s (APXS). These instruments were installed on the [[Mars Pathfinder|Sojourner]], [[Mars rover|Mars]], [[Mars 96]], [[Spirit rover|Spirit]], [[Mars Exploration Rover|Athena]] and [[Opportunity rover]]s, as well as the [[Mars Science Laboratory]] to analyze the composition and structure of the rocks on the surface of planet [[Mars]].<ref>{{cite journal|bibcode=1996DPS....28.0221R|title=An Alpha Proton X-Ray Spectrometer for Mars-96 and Mars Pathfinder|author=Rieder, R.; Wanke, H.; Economou, T.|journal=Bulletin of the American Astronomical Society|volume=28|page=1062|date=09/1996|last2=Wanke|last3=Economou}}</ref> APXS was also used in the [[Surveyor Program|Surveyor 5–7]] moon probes but with a <sup>242</sup>Cm source.<ref name=LA2>[http://www.ead.anl.gov/pub/doc/curium.pdf Human Health Fact Sheet on Curium], Los Alamos National Laboratory</ref><ref>Leitenberger, Bernd [http://www.bernd-leitenberger.de/surveyor.shtml Die Surveyor Raumsonden] (in German)</ref><ref>{{cite book|url=http://history.nasa.gov/SP-480/ch9.htm |author=Nicks, Oran |
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| chapter=Ch. 9. Essentials for Surveyor|publisher=NASA|year=1985|title=SP-480 Far Travelers: The Exploring Machines}}</ref>
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| An elaborated APXS setup is equipped with a sensor head containing six curium sources having the total radioactive decay rate of several tens of [[curie|millicuries]] (roughly a [[Becquerel|gigabecquerel]]). The sources are collimated on the sample, and the energy spectra of the alpha particles and protons scattered from the sample are analyzed (the proton analysis is implemented only in some spectrometers). These spectra contain quantitative information on all major elements in the samples except for hydrogen, helium and lithium.<ref>[http://web.archive.org/web/20060302040531/http://athena.cornell.edu/pdf/tb_apxs.pdf Alpha Particle X-Ray Spectrometer (APXS)], Cornell University</ref> An APXS will also be used by the [[Philae lander]] of the [[Rosetta (spacecraft)|Rosetta]] spacecraft to probe the surface of the [[67P/Churyumov-Gerasimenko]] [[comet]].<ref>{{cite web|url=http://www.bernd-leitenberger.de/philae.shtml |title=Der Rosetta Lander Philae |publisher=Bernd-leitenberger.de |date=2003-07-01 |accessdate=2011-03-25}}</ref>
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| ==Safety==
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| Owing to its high radioactivity, curium and its compounds must be handled in appropriate laboratories under special arrangements. Whereas curium itself mostly emits α-particles which are absorbed by thin layers of common materials, some of its decay products emit significant fractions of beta and gamma radiation, which require a more elaborate protection.<ref Name="lenntech"/> If consumed, curium is excreted within a few days and only 0.05% is absorbed in the blood. From there, about 45% goes to the [[liver]], 45% to the bones, and the remaining 10% is excreted. In the bone, curium accumulates on the inside of the interfaces to the [[bone marrow]] and does not significantly redistribute with time; its radiation destroys [[bone marrow]] and thus stops [[red blood cell]] creation. The [[biological half-life]] of curium is about 20 years in the liver and 50 years in the bones.<ref Name="lenntech"/><ref name=LA2/> Curium is absorbed in the body much more strongly via inhalation, and the allowed total dose of <sup>244</sup>Cm in soluble form is 0.3 μ[[Curie (unit)|C]].<ref name=CRC/> Intravenous injection of <sup>242</sup>Cm and <sup>244</sup>Cm containing solutions to rats increased the incidence of [[bone tumor]], and inhalation promoted [[Lung|pulmonary]] and [[liver cancer]].<ref name="lenntech"/>
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| Curium isotopes are inevitably present in spent nuclear fuel with a concentration of about 20 g/tonne.<ref>Hoffmann, K. ''Kann man Gold machen? Gauner, Gaukler und Gelehrte. Aus der Geschichte der chemischen Elemente'' (Can you make gold? Crooks, clowns and scholars. From the history of the chemical elements), Urania-Verlag, Leipzig, Jena, Berlin 1979, no ISBN, p. 233</ref> Among them, the <sup>245</sup>Cm–<sup>248</sup>Cm isotopes have decay times of thousands of years and need to be removed to neutralize the fuel for disposal.<ref>Baetslé, L. H. [http://www.ictp.trieste.it/~pub_off/lectures/lns012/Baetsle.pdf Application of Partitioning/Transmutation of Radioactive Materials in Radioactive Waste Management], Nuclear Research Centre of Belgium Sck/Cen, Mol, Belgium, September 2001.</ref> The associated procedure involves several steps, where curium is first separated and then converted by neutron bombardment in special reactors to short-lived nuclides. This procedure, [[nuclear transmutation]], while well documented for other elements, is still being developed for curium.<ref name="denecke"/>
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| == References ==
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| {{Reflist|30em}}
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| ==Bibliography==
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| * {{Greenwood&Earnshaw2nd}}
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| * Holleman, Arnold F. and Wiberg, Nils ''Textbook of Inorganic Chemistry'', 102 Edition, de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1.
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| * Penneman, R. A. and Keenan T. K. [http://www.osti.gov/bridge/purl.cover.jsp?purl=/4187189-IKQUwY/ The radiochemistry of americium and curium], University of California, Los Alamos, California, 1960
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| ==External links==
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| {{Commons|Curium}}
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| {{wiktionary|curium}}
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| * [http://www.periodicvideos.com/videos/096.htm Curium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
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| * [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+curium,+radioactive NLM Hazardous Substances Databank – Curium, Radioactive]
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| {{clear}}
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| {{compact periodic table}}
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| {{Curium compounds}}
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| {{Nuclear Technology}}
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| {{Chemical elements named after scientists}}
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| [[Category:Chemical elements]]
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| [[Category:Actinides]]
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| [[Category:American inventions]]
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| [[Category:Synthetic elements]]
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| [[Category:Curium]]
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| {{link FA|de}}
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