Editing Americium (section)

===Isotope nucleosynthesis===
[[File:Elutionskurven Tb Gd Eu und Bk Cm Am.png|thumb|[[Chromatography|Chromatographic]] [[elution]] curves revealing the similarity between the lanthanides Tb, Gd, and Eu and the corresponding actinides Bk, Cm, and Am]]

Americium has been produced in small quantities in [[nuclear reactor]]s for decades, and kilograms of its <sup>241</sup>Am and <sup>243</sup>Am isotopes have been accumulated by now.<ref name="g1262">Greenwood, p. 1262</ref> Nevertheless, since it was first offered for sale in 1962, its price, about {{Convert|1,500|$/g|$/oz|$=US$}} of <sup>241</sup>Am, remains almost unchanged owing to the very complex separation procedure.<ref name="smoke">[http://www.world-nuclear.org/info/inf57.html Smoke detectors and americium] {{webarchive|url=https://web.archive.org/web/20101112082137/http://www.world-nuclear.org/info/inf57.html |date=12 November 2010 }}, World Nuclear Association, January 2009, Retrieved 28 November 2010</ref> The heavier isotope <sup>243</sup>Am is produced in much smaller amounts; it is thus more difficult to separate, resulting in a higher cost of the order {{convert|100,000–160,000|$/g|$/oz|$=US$}}.<ref name="CRC">Hammond C. R. "The elements" in {{RubberBible86th}}</ref><ref>{{cite book| author = Emeleus, H. J. |author2= Sharpe, A. G. | title = Advances in Inorganic Chemistry | url = https://books.google.com/books?id=K5_LSQqeZ_IC&pg=PA2| date = 1987| publisher = Academic Press| isbn = 978-0-08-057880-4| page = 2 }}</ref>

Americium is not synthesized directly from uranium – the most common reactor material – but from the plutonium isotope <sup>239</sup>Pu. The latter needs to be produced first, according to the following nuclear process:

: <chem>^{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</chem>

The capture of two neutrons by <sup>239</sup>Pu (a so-called (n,γ) reaction), followed by a β-decay, results in <sup>241</sup>Am:

: <chem>^{239}_{94}Pu ->[\ce{2(n,\gamma)}] ^{241}_{94}Pu ->[\beta^-][14.35 \ \ce{yr}] ^{241}_{95}Am</chem>

The plutonium present in spent nuclear fuel contains about 12% of <sup>241</sup>Pu. Because it [[beta-decay]]s to <sup>241</sup>Am, <sup>241</sup>Pu can be extracted and may be used to generate further <sup>241</sup>Am.<ref name="smoke" /> However, this process is rather slow: half of the original amount of <sup>241</sup>Pu decays to <sup>241</sup>Am after about 15 years, and the <sup>241</sup>Am amount reaches a maximum after 70 years.<ref>[http://www.bredl.org/sapc/Pu_ReportI.htm BREDL Southern Anti-Plutonium Campaign], Blue Ridge Environmental Defense League, Retrieved 28 November 2010</ref>

The obtained <sup>241</sup>Am can be used for generating heavier americium isotopes by further neutron capture inside a nuclear reactor. In a [[light water reactor]] (LWR), 79% of <sup>241</sup>Am converts to <sup>242</sup>Am and 10% to its [[nuclear isomer]] <sup>242m</sup>Am:<ref group=note>The "metastable" state is marked by the letter m.</ref><ref>{{cite journal |doi=10.3327/jnst.41.448 |author=Sasahara, A. |title=Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO<sub>2</sub> and MOX Spent Fuels |journal=Journal of Nuclear Science and Technology |date=2004 |volume=41 |issue=4 |pages=448–456 |display-authors=etal |doi-access=free }} [http://sciencelinks.jp/j-east/ article/200410/000020041004A0333355.php Abstract] {{webarchive|url=https://web.archive.org/web/20101124010256/http://sciencelinks.jp/j-east/ |date=24 November 2010 }}</ref>
:<math chem>\begin{cases}
79\%: & \ce{^{241}_{95}Am ->[\ce{(n,\gamma)}] ^{242}_{95}Am}
\\
10\%: & \ce{^{241}_{95}Am ->[\ce{(n,\gamma)}] ^{242 m}_{95}Am}
\end{cases}</math>
[[Americium-242]] has a half-life of only 16 hours, which makes its further conversion to <sup>243</sup>Am extremely inefficient. The latter isotope is produced instead in a process where <sup>239</sup>Pu captures four neutrons under high [[neutron flux]]:

: <chem>^{239}_{94}Pu ->[\ce{4(n,\gamma)}] \ ^{243}_{94}Pu ->[\beta^-][4.956 \ \ce{h}] ^{243}_{95}Am</chem>