Editing Curium (section)

==Characteristics==

===Physical===
[[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)]]
[[File:Cm(HDPA)3·H2O_PL_420_nm.jpg|220x124px|thumb|right|[[Photoluminescence]] of the Cm(HDPA)<sub>3</sub>·H<sub>2</sub>O crystal upon [[irradiation]] with 420&nbsp;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&nbsp;°C is significantly higher than that of the previous elements neptunium (637&nbsp;°C), plutonium (639&nbsp;°C) and americium (1176&nbsp;°C). In comparison, gadolinium melts at 1312&nbsp;°C. Curium boils at 3556&nbsp;°C. With a density of 13.52&nbsp;g/cm<sup>3</sup>, curium is lighter than neptunium (20.45&nbsp;g/cm<sup>3</sup>) and plutonium (19.8&nbsp;g/cm<sup>3</sup>), 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]] P6<sub>3</sub>/mmc, lattice parameters ''a''&nbsp;=&nbsp;365&nbsp;[[picometer|pm]] and ''c''&nbsp;=&nbsp;1182&nbsp;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|date=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 double-[[Close-packing of equal spheres|hexagonal close packing]] with the layer sequence ABAC and so is isotypic with α-lanthanum. At pressure >23&nbsp;[[Pascal (unit)|GPa]], at room temperature, α-Cm becomes β-Cm, which has [[Cubic crystal system|face-centered cubic]] symmetry, space group Fm{{overline|3}}m and lattice constant ''a''&nbsp;=&nbsp;493&nbsp;pm.<ref name = "Milman" /> On further compression to 43&nbsp;GPa, curium becomes an [[Orthorhombic crystal system|orthorhombic]] γ-Cm structure similar to α-uranium, with no further transitions observed up to 52&nbsp;GPa. These three curium phases are also called Cm I, II and III.<ref>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</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|date=1985|doi=10.1016/0022-5088(85)90108-0}}</ref>

Curium has peculiar magnetic properties. Its neighbor element americium shows no deviation from [[Curie–Weiss law|Curie-Weiss]] [[paramagnetism]] in the entire temperature range, but α-Cm transforms to an [[Antiferromagnetism|antiferromagnetic]] state upon cooling to 65–52&nbsp;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|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. }}</ref><ref>{{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. }}</ref> and β-Cm exhibits a [[Ferrimagnetism|ferrimagnetic]] transition at ~205&nbsp;K. Curium pnictides show [[Ferromagnetism|ferromagnetic]] transitions upon cooling: <sup>244</sup>CmN and <sup>244</sup>CmAs at 109&nbsp;K, <sup>248</sup>CmP at 73&nbsp;K and <sup>248</sup>CmSb at 162&nbsp;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.<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>

In accordance with magnetic data, electrical resistivity of curium increases with temperature – about twice between 4 and 60&nbsp;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]].<ref name="res" />

Under ultraviolet illumination, curium(III) ions show strong and stable yellow-orange [[fluorescence]] with a maximum in the range of 590–640&nbsp;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|date=2005|pmid=16270980|doi=10.1021/ic0511726|pages=8418–8425}}</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>

===Chemical===
[[File:Curium-248.png|thumb|A solution of curium|right|150px]]
Curium ion in solution almost always has a +3 [[oxidation state]], the most stable oxidation state for curium.<ref>Penneman, p. 24</ref> A +4 oxidation state is seen 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.|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 }}</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 itself.<ref name="Lumetta" /> Chemical behavior of curium is different from the actinides thorium and uranium, and is similar to americium and many [[lanthanide]]s. In aqueous solution, the Cm<sup>3+</sup> ion is colorless to pale green;<ref name="g1265">Greenwood, p. 1265</ref> Cm<sup>4+</sup> ion is pale yellow.<ref name="HOWI_1956">Holleman, p. 1956</ref> The optical absorption of Cm<sup>3+</sup> ion contains three sharp peaks at 375.4, 381.2 and 396.5&nbsp;nm 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 [[beta decay]] of [[americium-242]] in the americium(V) ion {{chem|242|AmO|2|+}}.<ref name="CmO3" /> Failure to get 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 energy|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|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}}</ref>

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|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}}</ref> The bonding is mostly ionic, with a small covalent component.<ref>{{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 }}</ref> Curium in its complexes commonly exhibits a 9-fold coordination environment, with a [[tricapped trigonal prismatic molecular geometry]].<ref>Greenwood, p. 1267</ref>

===Isotopes===
{{see also|Isotopes of curium}}
About 19 [[radioisotope]]s and 7 [[nuclear isomer]]s, <sup>233</sup>Cm to <sup>251</sup>Cm, are known; none are [[stable isotope|stable]]. The longest half-lives are 15.6 million years (<sup>247</sup>Cm) and 348,000 years (<sup>248</sup>Cm). Other long-lived ones are <sup>245</sup>Cm (8500 years), <sup>250</sup>Cm (8300 years) and <sup>246</sup>Cm (4760 years). Curium-250 is unusual: it mostly (~86%) decays by [[spontaneous fission]]. The most commonly used isotopes are <sup>242</sup>Cm and <sup>244</sup>Cm with the half-lives 162.8 days and 18.11 years, respectively.{{NUBASE2020|name}}
<div style="float:right; margin:0.5em; font-size:85%;">
{| class="wikitable"
!colspan="7"| [[Neutron temperature#Thermal|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>
|-
| ||<sup>242</sup>Cm||<sup>243</sup>Cm||<sup>244</sup>Cm||<sup>245</sup>Cm||<sup>246</sup>Cm||<sup>247</sup>Cm
|-
|Fission||5||617||1.04||2145||0.14||81.90
|-
|Capture||16||130||15.20||369||1.22||57
|-
|C/F ratio||3.20||0.21||14.62||0.17||8.71||0.70
|-
!colspan="7"| [[Enriched uranium#Low-enriched uranium (LEU)|LEU]] [[spent nuclear fuel]] 20 years after 53 MWd/kg [[burnup]]<ref>{{cite journal|doi=10.1080/08929880500357682|last1=Kang|date=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 |archive-url=https://web.archive.org/web/20111128070246/http://www.princeton.edu/sgs/publications/sgs/pdf/13_3%20Kang%20vonhippel.pdf |archive-date=2011-11-28 |url-status=live|first1=Jungmin|last2=Von Hippel|first2=Frank|title=Limited Proliferation-Resistance Benefits from Recycling Unseparated Transuranics and Lanthanides from Light-Water Reactor Spent Fuel|bibcode=2005S&GS...13..169K|s2cid=123552796}}</ref>
|-
|colspan="2" |3 common isotopes ||51||3700||390|| ||
|-
!colspan="7"| [[Fast-neutron reactor]] [[MOX fuel]] (avg 5 samples, [[burnup]] 66–120 GWd/t)<ref>{{cite journal|doi=10.3327/jnst.38.912 |title=Analysis of Curium Isotopes in Mixed Oxide Fuel Irradiated in Fast Reactor |journal=Journal of Nuclear Science and Technology |volume=38 |date=2001 |issue=10 |pages=912–914 |author=Osaka, M. |display-authors=etal |doi-access=free }}</ref>
|-
|colspan="2" |Total curium 3.09{{e|-3}}% ||27.64%||70.16%||2.166%||0.0376%||0.000928%
|}
{| Class = "wikitable"
|-
| 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
|-
|[[Critical mass]], kg|| 25|| 7.5||33||6.8||39||7||40.4||23.5
|}
</div>

All isotopes ranging from <sup>242</sup>Cm to <sup>248</sup>Cm, as well as <sup>250</sup>Cm, 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 <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 [[Breeder reactor#Fast breeder reactor|fast breeder reactors]] 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"] {{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</ref> The mixed-oxide (MOX) fuel, which is to be used in power reactors, should contain little or no curium because [[neutron activation]] of <sup>248</sup>Cm 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 actinide]]s 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=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–}}</ref>

[[File:Sasahara.svg|thumb|upright=1.5|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 |archive-url=https://web.archive.org/web/20150903170300/http://nuclear.ee.duth.gr/upload/A11%20%20%20200401.pdf |archive-date=2015-09-03 |url-status=live|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|date=2004|doi=10.3327/jnst.41.448|author=Sasahara, Akihiro|last2=Matsumura|first2=Tetsuo|last3=Nicolaou|first3=Giorgos|last4=Papaioannou|first4=Dimitri|doi-access=free}}</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.]]
The adjacent table lists the [[critical mass]]es for curium isotopes for a sphere, without moderator or reflector. With a metal reflector (30&nbsp;cm of steel), the critical masses of the odd isotopes are about 3–4&nbsp;kg. When using water (thickness ~20–30&nbsp;cm) as the reflector, the critical mass can be as small as 59&nbsp;grams for <sup>245</sup>Cm, 155&nbsp;grams for <sup>243</sup>Cm and 1550&nbsp;grams for <sup>247</sup>Cm. There is significant uncertainty in these critical mass values. While it is usually on the order of 20%, the values for <sup>242</sup>Cm and <sup>246</sup>Cm were listed as large as 371&nbsp;kg and 70.1&nbsp;kg, respectively, by some research groups.<ref name="irsn" /><ref>{{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}}</ref>

Curium is not currently used as nuclear fuel due 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 very small critical mass and so could be used in [[tactical nuclear weapon]]s, 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.<ref>{{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–}}</ref> 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 weapon]]s).

===Occurrence===
[[File:Ivy Mike - mushroom cloud.jpg|thumb|Several isotopes of curium were detected in the fallout from the ''[[Ivy Mike]]'' nuclear test.]]
The longest-lived isotope, <sup>247</sup>Cm, has half-life 15.6&nbsp;million years; so any [[primordial nuclide|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 <sup>235</sup>U.<ref>{{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}}</ref> Traces of <sup>242</sup>Cm may occur naturally in uranium minerals due to neutron capture and beta decay (<sup>238</sup>U → <sup>239</sup>Pu → <sup>240</sup>Pu → <sup>241</sup>Am → <sup>242</sup>Cm), though the quantities would be tiny and this has not been confirmed: even with "extremely generous" estimates for neutron absorption possibilities, the quantity of <sup>242</sup>Cm present in 1&nbsp;×&nbsp;10<sup>8</sup>&nbsp;kg of 18% uranium pitchblende would not even be one atom.<ref name=ThorntonBurdette/><ref>{{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}}</ref><ref>{{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}}</ref> Traces of <sup>247</sup>Cm are also probably brought to Earth in [[cosmic ray]]s, but this also has not been confirmed.<ref name=ThorntonBurdette>{{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}}</ref> There is also the possibility of <sup>244</sup>Cm being produced as the [[double beta decay]] daughter of natural <sup>244</sup>Pu.<ref name=ThorntonBurdette/><ref name="Tretyak2002">{{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
 |doi=10.1006/adnd.2001.0873
|bibcode=2002ADNDT..80...83T }}</ref>

Curium is made artificially in small amounts for research purposes. It also occurs as one of the waste products in [[spent nuclear fuel]].<ref>{{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 }}</ref><ref>{{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}}</ref> Curium is present in nature in some areas used for [[nuclear weapons testing]].<ref name="lenntech">[http://www.lenntech.de/pse/pse.htm Curium] (in German)</ref> 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 <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.<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=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}}</ref>

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" />

The [[transuranium element]]s from americium to fermium, including curium, occurred naturally in the [[natural nuclear fission reactor]] at [[Oklo]], but no longer do so.<ref name="emsley">{{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}}</ref>

Curium, and other non-primordial actinides, have also been suspected to exist in the spectrum of [[Przybylski's Star]].<ref name=gopka08>{{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 }}</ref>