Editing Americium (section)

==Fission==
The isotope <sup>242m</sup>Am (half-life 141 years) has the largest cross sections for absorption of thermal neutrons (5,700 [[Barn (unit)|barns]]),<ref name = "Karlsruhe">Pfennig, G.; Klewe-Nebenius, H and Seelmann Eggebert, W. (Eds.): Karlsruhe [[nuclide]], 7 Edition 2006.</ref> that results in a small [[critical mass]] for a sustained [[nuclear chain reaction]]. The critical mass for a bare <sup>242m</sup>Am sphere is about 9–14&nbsp;kg (the uncertainty results from insufficient knowledge of its material properties). It can be lowered to 3–5&nbsp;kg with a metal reflector and should become even smaller with a water reflector.<ref>{{cite journal |author=Dias, H. |author2=Tancock, N. |author3=Clayton, A. |name-list-style=amp |title=Critical Mass Calculations for <sup>241</sup>Am, <sup>242m</sup>Am and <sup>243</sup>Am |journal=Nippon Genshiryoku Kenkyujo JAERI |date=2003 |pages=618–623 |url=http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |archive-url=https://web.archive.org/web/20110722105207/http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |url-status=dead |archive-date=2011-07-22 }} [http://sciencelinks.jp/j-east/article/200403/000020040303A0828431.php Abstract] {{webarchive|url=https://web.archive.org/web/20120313120209/http://sciencelinks.jp/j-east/article/200403/000020040303A0828431.php |date=13 March 2012 }}</ref> Such small critical mass is favorable for portable [[nuclear weapon]]s, but those based on <sup>242m</sup>Am are not known yet, probably because of its scarcity and high price. The critical masses of the two readily available isotopes, <sup>241</sup>Am and <sup>243</sup>Am, are relatively high – 57.6 to 75.6&nbsp;kg for <sup>241</sup>Am and 209&nbsp;kg for <sup>243</sup>Am.<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> Scarcity and high price yet hinder application of americium as a [[nuclear fuel]] in [[nuclear reactor]]s.<ref>{{cite journal|author= Ronen, Y.|author2= Aboudy, M.|author3= Regev, D.|name-list-style= amp|title=A novel method for energy production using <sup>242m</sup>Am as a nuclear fuel|journal=Nuclear Technology |date=2000|volume=129|issue=3|pages=407–417|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=1337515|doi=10.13182/nt00-a3071|bibcode= 2000NucTe.129..407R|s2cid= 91916073}}</ref>

There are proposals of very compact 10-kW high-flux reactors using as little as 20&nbsp;grams of <sup>242m</sup>Am. Such low-power reactors would be relatively safe to use as [[neutron source]]s for [[Nuclear medicine|radiation therapy]] in hospitals.<ref>{{cite journal|author=Ronen, Y.|author2=Aboudy, M.|author3=Regev, D.|name-list-style=amp|title=Homogeneous <sup>242m</sup>Am-Fueled Reactor for Neutron Capture Therapy|journal=Nuclear Science and Engineering|date=2001|volume=138|issue=3|pages=295–304|osti=20804726|doi=10.13182/nse01-a2215|bibcode=2001NSE...138..295R |s2cid=118801999}}</ref>