Editing Curium (section)

===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).