Curium

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Though curium had likely been produced in previous nuclear experiments as well as the natural nuclear fission reactor at Oklo, Gabon, it was 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.{{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}}

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.{{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. 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}}

The sample was prepared as follows: first plutonium nitrate solution was coated on a platinum foil of ~0.5 cm² area, the solution was evaporated and the residue was converted into plutonium(IV) oxide (PuO₂) by 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 pandemonium (from Greek for all demons or hell) and delirium (from Latin for madness).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

Curium-242 was made in July–August 1944 by bombarding ²³⁹Pu with α-particles to produce curium with the release of a neutron:{{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}}

: ^{239}_{94}Pu + ^{4}_{2}He -> ^{242}_{96}Cm + ^{1}_{0}n

Curium-242 was unambiguously identified by the characteristic energy of the α-particles emitted during the decay:

: ^{242}_{96}Cm -> ^{238}_{94}Pu + ^{4}_{2}He

The half-life of this alpha decay was first measured as 5 months (150 days) and then corrected to 162.8 days.{{NUBASE2020|name}}

Another isotope ²⁴⁰Cm was produced in a similar reaction in March 1945:

: ^{239}_{94}Pu + ^{4}_{2}He -> ^{240}_{96}Cm + 3^{1}_{0}n

The α-decay half-life of ²⁴⁰Cm was determined as 26.8 days 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.{{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}} The discovery of curium (²⁴²Cm and ²⁴⁰Cm), its production, and its compounds was later patented listing only Seaborg as the inventor.Seaborg, G. T. {{US patent|3161462}} "Element", Filing date: 7 February 1949, Issue date: December 1964

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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 elements Johan Gadolin:Greenwood, p. 1252

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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 basis element 96 is named after the Curies in a manner analogous to the naming of gadolinium, in which the chemist Gadolin was honored.

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 μg curium-242 hydroxide at University of California, Berkeley in 1947 by bombarding americium-241 with neutrons.Hammond C. R. "The elements" in {{RubberBible86th}}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.{{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}} 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 GdF₃ providing the first experimental evidence for the +3 valence of curium in its compounds. Curium metal was produced only in 1950 by reduction of CmF₃ with barium.{{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}}{{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}}

File:Closest packing ABAC.png

File:Cm(HDPA)3·H2O_PL_420_nm.jpg of the Cm(HDPA)₃·H₂O crystal upon irradiation with 420 nm light]]

A synthetic, radioactive element, curium is a hard, dense metal with a silvery-white appearance and physical and chemical properties resembling gadolinium. Its melting point of 1344 °C is significantly higher than that of the previous elements neptunium (637 °C), plutonium (639 °C) and americium (1176 °C). In comparison, gadolinium melts at 1312 °C. Curium boils at 3556 °C. With a density of 13.52 g/cm³, curium is lighter than neptunium (20.45 g/cm³) and plutonium (19.8 g/cm³), but heavier than most other metals. Of two crystalline forms of curium, α-Cm is more stable at ambient conditions. It has a hexagonal symmetry, space group P6₃/mmc, lattice parameters a = 365 pm and c = 1182 pm, and four formula units per unit cell.{{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|date=2003|doi=10.1016/S0022-3115(03)00321-0|bibcode=2003JNuM..322..165M|last2=Winkler|first2=B.|last3=Pickard|first3=C. J.}} The crystal consists of double-hexagonal close packing with the layer sequence ABAC and so is isotypic with α-lanthanum. At pressure >23 GPa, at room temperature, α-Cm becomes β-Cm, which has face-centered cubic symmetry, space group Fm{{overline|3}}m and lattice constant a = 493 pm. On further compression to 43 GPa, curium becomes an orthorhombic γ-Cm structure similar to α-uranium, with no further transitions observed up to 52 GPa. These three curium phases are also called Cm I, II and III.Young, D. A. [https://books.google.com/books?id=F2HVYh6wLBcC&pg=PA227 Phase diagrams of the elements], University of California Press, 1991, {{ISBN|0-520-07483-1}}, p. 227{{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|date=1985|doi=10.1016/0022-5088(85)90108-0}}

Curium has peculiar magnetic properties. Its neighbor element americium shows no deviation from Curie-Weiss paramagnetism in the entire temperature range, but α-Cm transforms to an antiferromagnetic state upon cooling to 65–52 K,{{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|date=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. }}{{cite journal|last1=Fournier|first1=J.|title=Curium: A new magnetic element|journal=Physica B+C|volume=86–88|page=30|date=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. }} and β-Cm exhibits a ferrimagnetic transition at ~205 K. Curium pnictides show ferromagnetic transitions upon cooling: ²⁴⁴CmN and ²⁴⁴CmAs at 109 K, ²⁴⁸CmP at 73 K and ²⁴⁸CmSb at 162 K. The lanthanide analog of curium, gadolinium, and 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.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

In accordance with magnetic data, electrical resistivity of curium increases with temperature – about twice between 4 and 60 K – and then is nearly constant up to room temperature. There is a significant increase in resistivity over time (~{{val|10|u=μΩ·cm/h}}) due to self-damage of the crystal lattice by alpha decay. This makes uncertain the true resistivity of curium (~{{val|125|u=μΩ·cm}}). Curium's resistivity is similar to that of gadolinium, and the actinides plutonium and neptunium, but significantly higher than that of americium, uranium, polonium and thorium.

Under ultraviolet illumination, curium(III) ions show strong and stable yellow-orange fluorescence with a maximum in the range of 590–640 nm depending on their environment.{{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|date=2005|pmid=16270980|doi=10.1021/ic0511726|pages=8418–8425}} The fluorescence originates from the transitions from the first excited state ⁶D_7/2 and the ground state ⁸S_7/2. Analysis of this fluorescence allows monitoring interactions between Cm(III) ions in organic and inorganic complexes.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}}

File:Curium-248.png

Curium ion in solution almost always has a +3 oxidation state, the most stable oxidation state for curium.Penneman, p. 24 A +4 oxidation state is seen mainly in a few solid phases, such as CmO₂ and CmF₄.{{cite journal|last1=Keenan|first1=Thomas K.|title=First Observation of Aqueous Tetravalent Curium|journal=Journal of the American Chemical Society|volume=83|issue=17|page=3719|date=1961|doi=10.1021/ja01478a039|bibcode=1961JAChS..83.3719K }} 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 itself. Chemical behavior of curium is different from the actinides thorium and uranium, and is similar to americium and many lanthanides. In aqueous solution, the Cm³⁺ ion is colorless to pale green;Greenwood, p. 1265 Cm⁴⁺ ion is pale yellow.Holleman, p. 1956 The optical absorption of Cm³⁺ ion contains three sharp peaks at 375.4, 381.2 and 396.5 nm and their strength can be directly converted into the concentration of the ions.Penneman, pp. 25–26 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 beta decay of americium-242 in the americium(V) ion {{chem|242|AmO|2|+}}. Failure to get Cm(VI) from oxidation of Cm(III) and Cm(IV) may be due to the high Cm⁴⁺/Cm³⁺ ionization potential and the instability of Cm(V).{{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|date = 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|isbn = 978-1-4020-3555-5|access-date = 2013-10-18|archive-date = 2018-01-17|archive-url = https://web.archive.org/web/20180117190715/http://radchem.nevada.edu/classes/rdch710/files/neptunium.pdf|url-status = dead}}

Curium ions are hard Lewis acids and thus form most stable complexes with hard bases.{{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|date=2002|pmid=12175247|doi=10.1021/ja0178620|pages=9870–9877|bibcode=2002JAChS.124.9870J |url=https://figshare.com/articles/Comparison_of_Covalency_in_the_Complexes_of_Trivalent_Actinide_and_Lanthanide_Cations/3640428|url-access=subscription}} The bonding is mostly ionic, with a small covalent component.{{cite journal|last1=Seaborg |first1=Glenn T. |title=Overview of the Actinide and Lanthanide (the f) Elements|journal=Radiochimica Acta|date=1993|volume=61|issue=3–4 |pages=115–122|doi=10.1524/ract.1993.61.34.115 |s2cid=99634366 }} Curium in its complexes commonly exhibits a 9-fold coordination environment, with a tricapped trigonal prismatic molecular geometry.Greenwood, p. 1267

{{see also|Isotopes of curium}}

About 19 radioisotopes and 7 nuclear isomers, ²³³Cm to ²⁵¹Cm, are known; none are stable. The longest half-lives are 15.6 million years (²⁴⁷Cm) and 348,000 years (²⁴⁸Cm). Other long-lived ones are ²⁴⁵Cm (8500 years), ²⁵⁰Cm (8300 years) and ²⁴⁶Cm (4760 years). Curium-250 is unusual: it mostly (~86%) decays by spontaneous fission. The most commonly used isotopes are ²⁴²Cm and ²⁴⁴Cm with the half-lives 162.8 days and 18.11 years, respectively.{{NUBASE2020|name}}

All isotopes ranging from ²⁴²Cm to ²⁴⁸Cm, as well as ²⁵⁰Cm, undergo a self-sustaining nuclear chain reaction and thus in principle can be a nuclear fuel in a reactor. As in most transuranic elements, nuclear fission cross section is especially high for the odd-mass curium isotopes ²⁴³Cm, ²⁴⁵Cm and ²⁴⁷Cm. These can be used in thermal-neutron reactors, whereas a mixture of curium isotopes is only suitable for fast breeder reactors since the even-mass isotopes are not fissile in a thermal reactor and accumulate as burn-up increases.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"] {{webarchive |url=https://web.archive.org/web/20110519171204/http://ec.europa.eu/energy/nuclear/transport/doc/irsn_sect03_146.pdf |date=May 19, 2011 }}, p. 16 The mixed-oxide (MOX) fuel, which is to be used in power reactors, should contain little or no curium because neutron activation of ²⁴⁸Cm will create californium. Californium is a strong neutron emitter, and would pollute the back end of the fuel cycle and increase the dose to reactor personnel. Hence, if 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.{{cite book|author=National Research Council (U.S.). Committee on Separations Technology and Transmutation Systems|title=Nuclear wastes: technologies for separations and transmutation|url=https://books.google.com/books?id=iRI7Cx2D4e4C&pg=PA231|access-date=19 April 2011|date=1996|publisher=National Academies Press|isbn=978-0-309-05226-9|pages=231–}}

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The adjacent table lists the critical masses for curium isotopes for a sphere, without moderator or 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 grams for ²⁴⁵Cm, 155 grams for ²⁴³Cm and 1550 grams for ²⁴⁷Cm. There is significant uncertainty in these critical mass values. While it is usually on the order of 20%, the values for ²⁴²Cm and ²⁴⁶Cm were listed as large as 371 kg and 70.1 kg, respectively, by some research groups.{{cite journal|author=Okundo, H.|author2=Kawasaki, H.|name-list-style=amp |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|date=2002|volume=39|pages=1072–1085|doi=10.3327/jnst.39.1072|issue=10|doi-access=free}}

Curium is not currently used as nuclear fuel due to its low availability and high price.[http://bundesrecht.juris.de/atg/__2.html § 2 Begriffsbestimmungen (Atomic Energy Act)] (in German) ²⁴⁵Cm and ²⁴⁷Cm have very small critical mass and so could be used in tactical nuclear weapons, but none are known to have been made. Curium-243 is not suitable for such, due to its short half-life and strong α emission, which would cause excessive heat.{{cite book|author1=Jukka Lehto|author2=Xiaolin Hou|title=Chemistry and Analysis of Radionuclides: Laboratory Techniques and Methodology|url=https://books.google.com/books?id=v2iRJaO3SMIC&pg=PA303|access-date=19 April 2011|date=2 February 2011|publisher=Wiley-VCH|isbn=978-3-527-32658-7|pages=303–}} Curium-247 would be highly suitable due to its long half-life, which is 647 times longer than plutonium-239 (used in many existing nuclear weapons).

File:Ivy Mike - mushroom cloud.jpg nuclear test.]]

The longest-lived isotope, ²⁴⁷Cm, has half-life 15.6 million years; so any primordial curium, that is, present on Earth when it formed, should have decayed by now. Its past presence as an extinct radionuclide is detectable as an excess of its primordial, long-lived daughter ²³⁵U.{{cite news |url=https://phys.org/news/2016-03-cosmochemists-evidence-unstable-heavy-element.html |title=Cosmochemists find evidence for unstable heavy element at solar system formation |date=2016 |publisher=University of Chicago |website=phys.org |access-date=6 June 2022}} Traces of ²⁴²Cm may occur naturally in uranium minerals due to neutron capture and beta decay (²³⁸U → ²³⁹Pu → ²⁴⁰Pu → ²⁴¹Am → ²⁴²Cm), though the quantities would be tiny and this has not been confirmed: even with "extremely generous" estimates for neutron absorption possibilities, the quantity of ²⁴²Cm present in 1 × 10⁸ kg of 18% uranium pitchblende would not even be one atom.{{Cite web|url=https://www.livescience.com/39915-facts-about-curium.html|title=Facts About Curium|last=Earth|first=Live Science Staff 2013-09-24T21:44:13Z Planet|website=livescience.com|date=24 September 2013|language=en|access-date=2019-08-10}}{{Cite web|url=http://www.rsc.org/periodic-table/element/96/curium|title=Curium - Element information, properties and uses {{!}} Periodic Table|website=www.rsc.org|access-date=2019-08-10}} Traces of ²⁴⁷Cm are also probably brought to Earth in cosmic rays, but this also has not been confirmed.{{cite journal |last1=Thornton |first1=Brett F. |last2=Burdette |first2=Shawn C. |date=2019 |title=Neutron stardust and the elements of Earth |url=https://www.nature.com/articles/s41557-018-0190-9 |journal=Nature Chemistry |volume=11 |issue=1 |pages=4–10 |doi=10.1038/s41557-018-0190-9 |pmid=30552435 |bibcode=2019NatCh..11....4T |s2cid=54632815 |access-date=19 February 2022|url-access=subscription }} There is also the possibility of ²⁴⁴Cm being produced as the double beta decay daughter of natural ²⁴⁴Pu.{{Cite journal

|last1=Tretyak |first1=V.I.

|last2=Zdesenko |first2=Yu.G.

|year=2002

|title=Tables of Double Beta Decay Data — An Update

|journal=At. Data Nucl. Data Tables |volume=80 |issue=1 |pages=83–116

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|bibcode=2002ADNDT..80...83T }}

Curium is made artificially in small amounts for research purposes. It also occurs as one of the waste products in spent nuclear fuel.{{cite journal |vauthors = Chaplin J, Warwick P, Cundy A, Bochud F, Froidevaux P |title=Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments |journal=Analytical Chemistry |date=25 August 2021 |volume=93 |issue=35 |pages=11937–11945 |doi=10.1021/acs.analchem.1c01342 |pmid=34432435 |s2cid=237307309 |doi-access=free }}{{cite journal |vauthors = Chaplin J, Christl M, Straub M, Bochud F, Froidevaux P |title=Passive Sampling Tool for Actinides in Spent Nuclear Fuel Pools |journal=ACS Omega |date=2 June 2022 |volume=7 |issue=23 |pages=20053−20058 |doi=10.1021/acsomega.2c01884 |pmid=35722008 |pmc=9202248 |hdl=20.500.11850/554631 |url=https://doi.org/10.1021/acsomega.2c01884}} Curium is present in nature in some areas used for nuclear weapons testing.[http://www.lenntech.de/pse/pse.htm Curium] (in German) Analysis of the debris at the test site of the United States' first thermonuclear weapon, Ivy Mike (1 November 1952, Enewetak Atoll), besides einsteinium, fermium, plutonium and americium also revealed isotopes of berkelium, californium and curium, in particular ²⁴⁵Cm, ²⁴⁶Cm and smaller quantities of ²⁴⁷Cm, ²⁴⁸Cm and ²⁴⁹Cm.{{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=Glenn T.|display-authors=3|title=Transplutonium Elements in Thermonuclear Test Debris|date=1956|journal=Physical Review|volume=102|issue=1|pages=180–182|doi=10.1103/PhysRev.102.180|bibcode=1956PhRv..102..180F}}

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.

The transuranium elements from americium to fermium, including curium, occurred naturally in the natural nuclear fission reactor at Oklo, but no longer do so.{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|date=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7}}

Curium, and other non-primordial actinides, have also been suspected to exist in the spectrum of Przybylski's Star.{{cite journal |last1=Gopka |first1=V. F. |last2=Yushchenko |first2=A. V. |last3=Yushchenko |first3=V. A. |last4=Panov |first4=I. V. |last5=Kim |first5=Ch. |title=Identification of absorption lines of short half-life actinides in the spectrum of Przybylski's star (HD 101065) |journal=Kinematics and Physics of Celestial Bodies |date=15 May 2008 |volume=24 |issue=2 |pages=89–98 |doi=10.3103/S0884591308020049 |bibcode = 2008KPCB...24...89G |s2cid=120526363 }}

Curium is made in small amounts in nuclear reactors, and by now only kilograms of ²⁴²Cm and ²⁴⁴Cm have been accumulated, and grams or even milligrams for heavier isotopes. Hence the high price of curium, which has been quoted at 160–185 USD per milligram, with a more recent estimate at US$2,000/g for ²⁴²Cm and US$170/g for ²⁴⁴Cm. In nuclear reactors, curium is formed from ²³⁸U in a series of nuclear reactions. In the first chain, ²³⁸U captures a neutron and converts into ²³⁹U, which via β⁻ decay transforms into ²³⁹Np and ²³⁹Pu.

{{NumBlk|:|^{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 (the times are half-lives).|{{EquationRef|1}}}}

Further neutron capture followed by β⁻-decay gives americium (²⁴¹Am) which further becomes ²⁴²Cm:

{{NumBlk|:|^{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.|{{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 ²⁴⁴Cm: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}}.

{{NumBlk|:|^{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|{{EquationRef|3}}}}

Curium-244 alpha decays to ²⁴⁰Pu, but it also absorbs neutrons, hence a small amount of heavier curium isotopes. Of those, ²⁴⁷Cm and ²⁴⁸Cm are popular in scientific research due to their long half-lives. But the production rate of ²⁴⁷Cm in thermal neutron reactors is low because it is prone to fission due to thermal neutrons. Synthesis of ²⁵⁰Cm by neutron capture is unlikely due to the short half-life of the intermediate ²⁴⁹Cm (64 min), which β⁻ decays to the berkelium isotope ²⁴⁹Bk.

{{NumBlk|:|$\backslash ce\{^\backslash mathit\{A\}\_\{96\}Cm\{\}\; +\; ^\{1\}\_\{0\}n\; ->\; ^\{\backslash mathit\{A\}+1\}\_\{96\}Cm\{\}\; +\; \backslash gamma\}\; \backslash \; (\backslash text\{for\; \}\; 244\; \backslash le\; A\; \backslash le\; 248)$|{{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 ²⁵²Cf, which is available in relatively large amounts due to its long half-life (2.65 years). About 35–50 mg of ²⁴⁸Cm is produced thus, per year. The associated reaction produces ²⁴⁸Cm with isotopic purity of 97%.{{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

}}

{{NumBlk|:|$\backslash begin\{matrix\}\{\}\backslash \backslash$

\ce{^{252}_{98}Cf ->[\alpha][2.645\ \ce{yr}] ^{248}_{96}Cm}\\{}

\end{matrix}|{{EquationRef|5}}}}

Another isotope, ²⁴⁵Cm, can be obtained for research, from α-decay of ²⁴⁹Cf; the latter isotope is produced in small amounts from β⁻-decay of ²⁴⁹Bk.

{{NumBlk|:|

^{249}_{97}Bk ->[\beta^-][330\ \ce{d}] ^{249}_{98}Cf ->[\alpha][351\ \ce{yr}] ^{245}_{96}Cm

|{{EquationRef|6}}}}

File:Elutionskurven Tb Gd Eu und Bk Cm Am.png 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 oxides, 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 (Plutonium – URanium EXtraction) 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.Penneman, pp. 34–48 Bis-triazinyl bipyridine complex has been recently proposed as such reagent which is highly selective to curium.{{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}} 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.Penneman, p. 25

Metallic curium is obtained by 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.{{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}}{{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}}Gmelin Handbook of Inorganic Chemistry, System No. 71, Volume 7 a, transuranics, Part B 1, pp. 67–68.

:$\backslash mathrm\{CmF\_3\backslash \; +\backslash \; 3\backslash \; Li\backslash \; \backslash longrightarrow\; \backslash \; Cm\backslash \; +\backslash \; 3\backslash \; LiF\}$

Another possibility is reduction of curium(IV) oxide using a magnesium-zinc alloy in a melt of magnesium chloride and magnesium fluoride.{{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.}}

{{Main|Curium compounds}}

Curium readily reacts with oxygen forming mostly Cm₂O₃ and CmO₂ oxides, but the divalent oxide CmO is also known.Holleman, p. 1972 Black CmO₂ can be obtained by burning curium oxalate ({{chem|Cm|2|(C|2|O|4|)|3}}), nitrate ({{chem|Cm|(N|O|3|)|3}}), or hydroxide in pure oxygen.Greenwood, p. 1268 Upon heating to 600–650 °C in vacuum (about 0.01 Pa), it transforms into the whitish Cm₂O₃:{{cite journal|last1=Asprey|first1=L. B.|title=Evidence for Quadrivalent Curium: X-Ray Data on Curium Oxides1|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|date=1955|doi=10.1021/ja01611a108|bibcode=1955JAChS..77.1707A }}{{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|date=1971|doi=10.1016/0020-1650(71)80177-0|last2=Fuger|first2=J.}}

: 4CmO2 ->[\Delta T] 2Cm2O3 + O2.

Or, Cm₂O₃ can be obtained by reducing CmO₂ with molecular hydrogen:{{cite journal|last1=Haug|first1=H.|title=Curium sesquioxide Cm2O3|journal=Journal of Inorganic and Nuclear Chemistry|volume=29|issue=11|page=2753|date=1967|doi=10.1016/0022-1902(67)80014-9}}

: 2CmO2 + H2 -> Cm2O3 + H2O

Also, a number of ternary oxides of the type M(II)CmO₃ are known, where M stands for a divalent metal, such as barium.{{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|date=1993|doi=10.1016/0925-8388(93)90491-5|url=https://zenodo.org/record/1258637}}

Thermal oxidation of trace quantities of curium hydride (CmH_2–3) has been reported to give a volatile form of CmO₂ and the volatile trioxide CmO₃, one of two known examples of the very rare +6 state for curium. Another observed species was reported to behave similar to a supposed plutonium tetroxide and was tentatively characterized as CmO₄, with curium in the extremely rare +8 state;{{cite journal |last1=Domanov |first1=V. P. |date=January 2013 |title=Possibility of generation of octavalent curium in the gas phase in the form of volatile tetraoxide CmO₄ |journal=Radiochemistry |volume=55 |issue=1 |pages=46–51 |doi=10.1134/S1066362213010098 |bibcode=2013Radch..55...46D |s2cid=98076989 }} but new experiments seem to indicate that CmO₄ does not exist, and have cast doubt on the existence of PuO₄ as well.{{cite journal|last1=Zaitsevskii|first1=Andréi|last2=Schwarz|first2=W. H. Eugen|date=April 2014|title=Structures and stability of AnO4 isomers, An = Pu, Am, and Cm: a relativistic density functional study.|journal=Physical Chemistry Chemical Physics|volume=2014|issue=16|pages=8997–9001|bibcode=2014PCCP...16.8997Z|doi=10.1039/c4cp00235k|pmid=24695756}}

The colorless curium(III) fluoride (CmF₃) can be made by adding fluoride ions into curium(III)-containing solutions. The brown tetravalent curium(IV) fluoride (CmF₄) on the other hand is only obtained by reacting curium(III) fluoride with molecular fluorine:

: $\backslash mathrm\{2\backslash \; CmF\_3\backslash \; +\backslash \; F\_2\backslash \; \backslash longrightarrow\backslash \; 2\backslash \; CmF\_4\}$

A series of ternary fluorides are known of the form A₇Cm₆F₃₁ (A = alkali metal).{{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|date=1967|doi=10.1016/0020-1650(67)80092-8}}

The colorless curium(III) chloride (CmCl₃) is made by reacting curium hydroxide (Cm(OH)₃) with anhydrous hydrogen chloride gas. It can be further turned 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 temperatures of ~400–450 °C:{{cite journal|title=Crystal Structures of the Trifluorides, Trichlorides, Tribromides, and Triiodides of Americium and Curium|last1=Asprey|first1=L. B.|last2=Keenan|first2=T. K.|last3=Kruse|first3=F. H.|journal=Inorganic Chemistry|volume=4|issue=7|page=985|date=1965|doi=10.1021/ic50029a013|s2cid=96551460 |url=https://digital.library.unt.edu/ark:/67531/metadc1035960/}}

: $\backslash mathrm\{CmCl\_3\backslash \; +\backslash \; 3\backslash \; NH\_4I\backslash \; \backslash longrightarrow\; \backslash \; CmI\_3\backslash \; +\backslash \; 3\backslash \; NH\_4Cl\}$

Or, one can heat curium oxide to ~600°C with the corresponding acid (such as hydrobromic for curium bromide).{{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|date=1975|doi=10.1016/0022-1902(75)80532-X|last2=Peterson|first2=J. R.|last3=Stevenson|first3=J. N.}}{{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|date=1967|doi=10.1016/0022-1902(67)80013-7|last2=Fuger|first2=J.|last3=Peterson|first3=J. R.|last4=Green|first4=J. L.|s2cid=97334114 }} Vapor phase hydrolysis of curium(III) chloride gives curium oxychloride:{{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|date=1977|doi=10.1016/0022-5088(77)90224-7}}

: $\backslash mathrm\{CmCl\_3\backslash \; +\backslash \; \backslash \; H\_2O\backslash \; \backslash longrightarrow\; \backslash \; CmOCl\backslash \; +\backslash \; 2\backslash \; HCl\}$

Sulfides, selenides and tellurides of curium have been obtained by treating curium with gaseous sulfur, selenium or tellurium in vacuum at elevated temperature.Troc, R. [https://books.google.com/books?id=vkzx_t3zLR0C&pg=PA4 Actinide Monochalcogenides, Volume 27], Springer, 2009 {{ISBN|3-540-29177-6}}, p. 4{{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|date=1975|doi=10.1016/0020-1650(75)80017-1|last2=Charvillat|first2=J. P.|last3=Müller|first3=W.}} Curium pnictides of the type CmX are known for nitrogen, phosphorus, arsenic and antimony. They can be prepared by reacting either curium(III) hydride (CmH₃) or metallic curium with these elements at elevated temperature.Lumetta, G. J.; Thompson, M. C.; Penneman, R. A.; Eller, P. G. [http://radchem.nevada.edu/classes/rdch710/files/curium.pdf Curium] {{webarchive|url=https://web.archive.org/web/20100717154205/http://radchem.nevada.edu/classes/rdch710/files/curium.pdf |date=2010-07-17 }}, Chapter Nine in Radioanalytical Chemistry, Springer, 2004, pp. 1420–1421. {{ISBN|0387341226}}, {{ISBN|978-0387 341224}}

File:Uranocene-3D-balls.png

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 (η⁸-C₈H₈)₂Cm, but it has not been reported experimentally yet.Elschenbroich, Ch. Organometallic Chemistry, 6th edition, Wiesbaden 2008, {{ISBN|978-3-8351-0167-8}}, p. 589{{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|date=2009|pmid=19719318|doi=10.1021/jp903912q|pages=8737–8745|bibcode=2009JPCA..113.8737K|url=https://figshare.com/articles/Are_the_Ground_States_of_the_Later_Actinocenes_Multiconfigurational_All_Electron_Spin_Orbit_Coupled_CASPT2_Calculations_on_An_sup_8_sup_C_sub_8_sub_H_sub_8_sub_sub_2_sub_An_Th_U_Pu_Cm_/2840251|url-access=subscription}}

Formation of the complexes of the type {{chem|Cm|(|n-C|3|H|7|-BTP)|3}} (BTP = 2,6-di(1,2,4-triazin-3-yl)pyridine), in solutions containing n-C₃H₇-BTP and Cm³⁺ ions has been confirmed by EXAFS. Some of these BTP-type complexes selectively interact with curium and thus are useful for separating it from lanthanides and another actinides.{{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.|s2cid=978265|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|date=2010|pmid=20849125|doi=10.1021/ic101309j|pages=9627–9635}} Dissolved Cm³⁺ ions bind with many organic compounds, such as hydroxamic acid,{{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|date=2008|doi=10.1016/j.poly.2008.04.002}} urea,{{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|date=2009|doi=10.1016/j.ica.2008.06.016}} fluorescein{{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|date=2007|pmid=17653625|doi=10.1007/s10534-007-9111-x|pages=219–228|s2cid=24565144}} and adenosine triphosphate.{{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|date=2005|doi=10.1016/j.ica.2004.12.055}} Many of these compounds are related to biological activity of various microorganisms. The resulting complexes show strong yellow-orange emission under UV light excitation, which is convenient not only for their detection, but also for studying interactions between the Cm³⁺ ion and the ligands via changes in the half-life (of the order ~0.1 ms) and spectrum of the fluorescence.

There are a few reports on biosorption of Cm³⁺ by bacteria and archaea,{{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=1455–1459|date=2004|pmid=15046347|bibcode = 2004EnST...38.1455M }}{{cite journal|author=Ozaki, T.|display-authors=etal|url=http://sciencelinks.jp/j-east/article/200305/000020030503A0110480.php|archive-url=https://web.archive.org/web/20090225195752/http://sciencelinks.jp/j-east/article/200305/000020030503A0110480.php|url-status=dead|archive-date=2009-02-25|title=Association of Eu(III) and Cm(III) with Bacillus subtilis and Halobacterium salinarium|journal=Journal of Nuclear Science and Technology|date=2002|volume=Suppl. 3|pages=950–953|doi=10.1080/00223131.2002.10875626|bibcode=2002JNST...39S.950O |s2cid=98319565}} and in the laboratory both americium and curium were found to support the growth of methylotrophs.{{cite journal |last1=Remick |first1=Kaleigh |last2=Helmann |first2=John D. |title=The Elements of Life: A Biocentric Tour of the Periodic Table |journal=Advances in Microbial Physiology |publisher=PubMed Central |date=30 January 2023 |volume=82 |pages=1–127 |doi=10.1016/bs.ampbs.2022.11.001 |pmid=36948652 |pmc=10727122 |isbn=978-0-443-19334-7}}

File:Curium self-glow radiation.jpg from curium alpha-radiation creates a purple aura in the dark.]]

Curium is one of the most radioactive isolable elements. Its two most common isotopes ²⁴²Cm and ²⁴⁴Cm are strong alpha emitters (energy 6 MeV); they have fairly short half-lives, 162.8 days and 18.1 years, and give as much as 120 W/g and 3 W/g of heat, respectively.Binder, Harry H.: Lexikon der chemischen Elemente, S. Hirzel Verlag, Stuttgart 1999, {{ISBN|3-7776-0736-3}}, pp. 174–178.Gmelin Handbook of Inorganic Chemistry, System No. 71, Volume 7a, transuranics, Part A2, p. 289 Therefore, curium can be used in its common oxide form in radioisotope thermoelectric generators like those in spacecraft. This application has been studied for the ²⁴⁴Cm isotope, while ²⁴²Cm was abandoned due to its prohibitive price, around 2000 USD/g. ²⁴³Cm with a ~30-year half-life and good energy yield of ~1.6 W/g could be a suitable fuel, but it gives significant amounts of harmful gamma and beta rays from radioactive decay products. As an α-emitter, ²⁴⁴Cm needs much less radiation shielding, but it has a high spontaneous fission rate, and thus a lot of neutron and gamma radiation. Compared to a competing thermoelectric generator isotope such as ²³⁸Pu, ²⁴⁴Cm emits 500 times more neutrons, and its higher gamma emission requires a shield that is 20 times thicker—{{convert|2|in|mm}} of lead for a 1 kW source, compared to {{convert|0.1|in|mm}} for ²³⁸Pu. Therefore, this use of curium is currently considered impractical.[http://fti.neep.wisc.edu/neep602/SPRING00/lecture5.pdf Basic elements of static RTGs] {{Webarchive|url=https://web.archive.org/web/20130215003518/http://fti.neep.wisc.edu/neep602/SPRING00/lecture5.pdf |date=2013-02-15 }}, G.L. Kulcinski, NEEP 602 Course Notes (Spring 2000), Nuclear Power in Space, University of Wisconsin Fusion Technology Institute (see last page)

A more promising use of ²⁴²Cm is for making ²³⁸Pu, a better radioisotope for thermoelectric generators such as in heart pacemakers. The alternate routes to ²³⁸Pu use the (n,γ) reaction of ²³⁷Np, or deuteron bombardment of uranium, though both reactions always produce ²³⁶Pu as an undesired by-product since the latter decays to ²³²U with strong gamma emission.[http://www.kronenberg.kernchemie.de/ Kronenberg, Andreas], [http://www.kernenergie-wissen.de/pu-batterien.html Plutonium-Batterien] {{Webarchive|url=https://web.archive.org/web/20131226011403/http://www.kernenergie-wissen.de/pu-batterien.html |date=2013-12-26 }} (in German)

{{Cite web |url=http://www.kronenberg.kernchemie.de/ |title=Archived copy |access-date=April 28, 2011 |archive-url=https://web.archive.org/web/20110221040021/http://www.kronenberg.kernchemie.de/ |archive-date=February 21, 2011 |url-status=bot: unknown |df=mdy-all }} Curium is a common starting material for making higher transuranic and superheavy elements. Thus, bombarding ²⁴⁸Cm with neon (²²Ne), magnesium (²⁶Mg), or calcium (⁴⁸Ca) yields isotopes of seaborgium (²⁶⁵Sg), hassium (²⁶⁹Hs and ²⁷⁰Hs), and livermorium (²⁹²Lv, ²⁹³Lv, and possibly ²⁹⁴Lv).Holleman, pp. 1980–1981. Californium was discovered when a microgram-sized target of curium-242 was irradiated with 35 MeV alpha particles using the {{convert|60|in|cm|adj=on}} cyclotron at Berkeley:

:{{nuclide|curium|242}} + {{nuclide|helium|4}} → {{nuclide|californium|245}} + {{nuclide|neutronium|1}}

Only about 5,000 atoms of californium were produced in this experiment.{{cite book|title=One Hundred Years after the Discovery of Radioactivity|editor=Adloff, J. P.|last=Seaborg|first=Glenn T.|page=82|date=1996|publisher=Oldenbourg Wissenschaftsverlag|isbn=978-3-486-64252-0}}

The odd-mass curium isotopes ²⁴³Cm, ²⁴⁵Cm, and ²⁴⁷Cm are all highly fissile and can release additional energy in a thermal spectrum nuclear reactor. All curium isotopes are fissionable in fast-neutron reactors. This is one of the motives for minor actinide separation and transmutation in the nuclear fuel cycle, helping to reduce the long-term radiotoxicity of used, or spent nuclear fuel.{{Citation needed|date=April 2025}}

File:MER APXS PIA05113.jpg

The most practical application of ²⁴⁴Cm—though rather limited in total volume—is as α-particle source in alpha particle X-ray spectrometers (APXS). These instruments were installed on the Sojourner, Mars, Mars 96, Mars Exploration Rovers and Philae comet lander,{{cite web|url=http://www.bernd-leitenberger.de/philae.shtml |title=Der Rosetta Lander Philae |publisher=Bernd-leitenberger.de |date=2003-07-01 |access-date=2011-03-25}} as well as the Mars Science Laboratory to analyze the composition and structure of the rocks on the surface of planet Mars.{{cite journal|bibcode=1996DPS....28.0221R|title=An Alpha Proton X-Ray Spectrometer for Mars-96 and Mars Pathfinder|author=Rieder, R.|author2=Wanke, H.|author3=Economou, T.|journal=Bulletin of the American Astronomical Society|volume=28|page=1062|date=September 1996}} APXS was also used in the Surveyor 5–7 moon probes but with a ²⁴²Cm source.[http://www.ead.anl.gov/pub/doc/curium.pdf Human Health Fact Sheet on Curium] {{Webarchive|url=https://web.archive.org/web/20060218162709/http://www.ead.anl.gov/pub/doc/curium.pdf |date=2006-02-18 }}, Los Alamos National LaboratoryLeitenberger, Bernd [http://www.bernd-leitenberger.de/surveyor.shtml Die Surveyor Raumsonden] (in German){{cite book|chapter-url=https://history.nasa.gov/SP-480/ch9.htm |author=Nicks, Oran |

chapter=Ch. 9. Essentials for Surveyor|publisher=NASA|date=1985|title=SP-480 Far Travelers: The Exploring Machines}}

An elaborate APXS setup has a sensor head containing six curium sources with a total decay rate of several tens of millicuries (roughly one gigabecquerel). The sources are collimated on a sample, and the energy spectra of the alpha particles and protons scattered from the sample are analyzed (proton analysis is done only in some spectrometers). These spectra contain quantitative information on all major elements in the sample except for hydrogen, helium and lithium.[https://web.archive.org/web/20060302040531/http://athena.cornell.edu/pdf/tb_apxs.pdf Alpha Particle X-Ray Spectrometer (APXS)], Cornell University

Due to its radioactivity, curium and its compounds must be handled in appropriate labs under special arrangements. While 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 rays, which require a more elaborate protection. If consumed, curium is excreted within a few days and only 0.05% is absorbed in the blood. From there, ~45% goes to the liver, 45% to the bones, and the remaining 10% is excreted. In 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. Curium is absorbed in the body much more strongly via inhalation, and the allowed total dose of ²⁴⁴Cm in soluble form is 0.3 μCi. Intravenous injection of ²⁴²Cm- and ²⁴⁴Cm-containing solutions to rats increased the incidence of bone tumor, and inhalation promoted lung and liver cancer.

Curium isotopes are inevitably present in spent nuclear fuel (about 20 g/tonne).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 The isotopes ²⁴⁵Cm–²⁴⁸Cm have decay times of thousands of years and must be removed to neutralize the fuel for disposal.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] {{Webarchive|url=https://web.archive.org/web/20050426092418/http://www.ictp.trieste.it/~pub_off/lectures/lns012/Baetsle.pdf |date=2005-04-26 }}, Nuclear Research Centre of Belgium Sck/Cen, Mol, Belgium, September 2001. Such a 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.

{{Reflist|30em}}

• {{Greenwood&Earnshaw2nd}}
• Holleman, Arnold F. and Wiberg, Nils Lehrbuch der Anorganischen Chemie, 102 Edition, de Gruyter, Berlin 2007, {{ISBN|978-3-11-017770-1}}.
• 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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{{wiktionary|curium}}

• [http://www.periodicvideos.com/videos/096.htm Curium] at The Periodic Table of Videos (University of Nottingham)
• [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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