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{{infobox americium}}
'''Americium''' is a [[synthetic element|synthetic chemical element]]; it has [[Chemical symbol|symbol]] '''Am''' and [[atomic number]] 95. It is [[radioactive]] and a [[transuranic]] member of the [[actinide]] series in the [[periodic table]], located under the [[lanthanide]] element [[europium]] and was thus named after the [[Americas]] by analogy.<ref>{{cite journal|title = The Transuranium Elements|first = Glenn T.|last = Seaborg|journal = Science|volume = 104|issue = 2704|date = 1946|pages = 379–386|doi = 10.1126/science.104.2704.379|pmid = 17842184|jstor = 1675046|bibcode = 1946Sci...104..379S }}</ref><ref>{{cite journal |url=http://acshist.scs.illinois.edu/bulletin_open_access/v33-2/v33-2%20p89-93.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://acshist.scs.illinois.edu/bulletin_open_access/v33-2/v33-2%20p89-93.pdf |archive-date=2022-10-09 |url-status=live |title=Americium – From Discovery to the Smoke Detector and Beyond |journal=Bull. Hist. Chem. |volume=33 |number=2 |date=2008 |last=Kostecka |first=Keith |pages=89–93}}</ref><ref>{{Cite web|url=http://pubsapp.acs.org/cen/80th/print/americiumprint.html?|title = C&En: It's Elemental: The Periodic Table - Americium}}</ref>
Americium was first produced in 1944 by the group of [[Glenn T. Seaborg]] from [[Berkeley, California]], at the [[Metallurgical Laboratory]] of the [[University of Chicago]], as part of the [[Manhattan Project]]. Although it is the third element in the transuranic series, it was discovered fourth, after the heavier [[curium]]. The discovery was kept secret and only released to the public in November 1945. Most americium is produced by [[uranium]] or [[plutonium]] being bombarded with [[neutron]]s in [[nuclear reactor]]s – one [[tonne]] of [[spent nuclear fuel]] contains about 100 grams of americium. It is widely used in commercial [[ionization chamber]] [[smoke detector]]s, as well as in [[neutron source]]s and industrial gauges. Several unusual applications, such as [[nuclear battery|nuclear batteries]] or fuel for space ships with nuclear [[propulsion]], have been proposed for the [[isotope]] <sup>242m</sup>Am, but they are as yet hindered by the scarcity and high price of this [[nuclear isomer]].
Americium is a relatively soft [[radioactive]] metal with a silvery appearance. Its most common [[Isotopes of americium|isotopes]] are [[americium-241|<sup>241</sup>Am]] and <sup>243</sup>Am. In chemical compounds, americium usually assumes the [[oxidation state]] +3, especially in solutions. Several other oxidation states are known, ranging from +2 to +7, and can be identified by their characteristic [[optical absorption]] spectra. The crystal lattices of solid americium and its compounds contain small intrinsic radiogenic defects, due to [[metamictization]] induced by self-irradiation with alpha particles, which accumulates with time; this can cause a drift of some material properties over time, more noticeable in older samples.
==History==
[[File:Berkeley 60-inch cyclotron.jpg|thumb|left|The 60-inch cyclotron at the Lawrence Radiation Laboratory, [[University of California, Berkeley]], in August 1939]]
Although americium was likely produced in previous nuclear experiments, it was [[discoveries of the chemical elements|first intentionally synthesized]], isolated and identified in late autumn 1944, at the [[University of California, Berkeley]], by [[Glenn T. Seaborg]], Leon O. Morgan, [[Ralph A. James]], and [[Albert Ghiorso]]. They used a 60-inch [[cyclotron]] at the University of California, Berkeley.<ref>[http://www.utexas.edu/faculty/council/2002-2003/memorials/Morgan/morgan.html Obituary of Dr. Leon Owen (Tom) Morgan (1919–2002)], Retrieved 28 November 2010</ref> The element was chemically identified at the Metallurgical Laboratory (now [[Argonne National Laboratory]]) of the [[University of Chicago]]. Following the lighter [[neptunium]], [[plutonium]], and heavier [[curium]], americium was the fourth [[transuranium element]] to be discovered. At the time, the [[periodic table]] had been restructured by Seaborg to its present layout, containing the actinide row below the [[lanthanide]] one. This led to americium being located right below its twin lanthanide element europium; it was thus by analogy named after the [[Americas]]: "The name americium (after the Americas) and the symbol Am are suggested for the element on the basis of its position as the sixth member of the actinide rare-earth series, analogous to europium, Eu, of the lanthanide series."<ref>Seaborg, G. T.; James, R.A. and Morgan, L. O.: "The New Element Americium (Atomic Number 95)", THIN PPR ''(National Nuclear Energy Series, Plutonium Project Record)'', ''Vol 14 B The Transuranium Elements: Research Papers'', Paper No. 22.1, McGraw-Hill Book Co., Inc., New York, 1949. [http://www.osti.gov/cgi-bin/rd_accomplishments/display_biblio.cgi?id=ACC0046&numPages=43&fp=N Abstract]; [http://www.osti.gov/accomplishments/documents/fullText/ACC0046.pdf Full text] (January 1948), Retrieved 28 November 2010</ref><ref>{{cite journal|last1=Street|first1=K.|last2=Ghiorso|first2=A.|last3=Seaborg|first3=G.|title=The Isotopes of Americium|doi=10.1103/PhysRev.79.530|date=1950|page=530|volume=79|journal=Physical Review|url=http://repositories.cdlib.org/cgi/viewcontent.cgi?article=7073&context=lbnl|issue=3|bibcode = 1950PhRv...79..530S }}</ref><ref name="g1252">Greenwood, p. 1252</ref>
The new element was isolated from its [[oxide]]s in a complex, multi-step process. First [[plutonium]]-239 nitrate (<sup>239</sup>PuNO<sub>3</sub>) solution was coated on a [[platinum]] foil of about 0.5&nbsp;cm<sup>2</sup> area, the solution was evaporated and the residue was converted into plutonium dioxide (PuO<sub>2</sub>) by [[calcining]]. After cyclotron irradiation, 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]]. Further separation was carried out by [[ion exchange]], yielding a certain isotope of curium. The separation of curium and americium was so painstaking that those elements were initially called by the Berkeley group as ''[[wikt:pandemonium|pandemonium]]''<ref>{{Cite web |title=Americium (Am) {{!}} AMERICAN ELEMENTS ® |url=https://www.americanelements.com/am.html |access-date=2024-05-09 |website=American Elements: The Materials Science Company |language=en}}</ref> (from Greek for ''all demons'' or ''hell'') and ''[[wikt:delirium|delirium]]'' (from Latin for ''madness'').<ref name="radio" /><ref>{{cite book| author = Robert E. Krebs| title = The History and Use of Our Earth's Chemical Elements: A Reference Guide| edition = Second| url = https://books.google.com/books?id=yb9xTj72vNAC&pg=PA322| date = 2006| publisher = Greenwood Publishing Group| isbn = 978-0-313-33438-2| page = 322 }}</ref>
Initial experiments yielded four americium isotopes: <sup>241</sup>Am, <sup>242</sup>Am, <sup>239</sup>Am and <sup>238</sup>Am. [[Americium-241]] was directly obtained from plutonium upon absorption of two neutrons. It decays by emission of a [[α-particle]] to <sup>237</sup>Np; the [[half-life]] of this decay was first determined as {{val|510|20}} years but then corrected to 432.2 years.<ref name="nubase">{{NUBASE 1997}}</ref>
:<math chem>\ce{^{239}_{94}Pu ->[\ce{(n,\gamma)}] ^{240}_{94}Pu ->[\ce{(n,\gamma)}] ^{241}_{94}Pu ->[\beta^-][14.35\ \ce{yr}] ^{241}_{95}Am}\ \left( \ce{->[\alpha][432.2\ \ce{yr}] ^{237}_{93}Np} \right)</math>
: <small> The times are [[half-lives]]</small>
The second isotope <sup>242</sup>Am was produced upon neutron bombardment of the already-created <sup>241</sup>Am. Upon rapid [[β-decay]], <sup>242</sup>Am converts into the isotope of curium <sup>242</sup>Cm (which had been discovered previously). The half-life of this decay was initially determined at 17 hours, which was close to the presently accepted value of 16.02 h.<ref name="nubase" />
: <math chem>\ce{^{241}_{95}Am ->[\ce{(n,\gamma)}] ^{242}_{95}Am}\ \left(\ce{->[\beta^-][16.02\ \ce{h}] ^{242}_{96}Cm} \right)</math>
The discovery of americium and curium in 1944 was closely related to the [[Manhattan Project]]; 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 ''[[Quiz Kids]]'' five days before the official presentation at an [[American Chemical Society]] meeting on 11 November 1945, when one of the listeners asked whether any new transuranium element besides plutonium and neptunium had been discovered during the war.<ref name="radio">{{cite web|url = http://pubs.acs.org/cen/80th/americium.html|title = Chemical & Engineering News: It's Elemental: The Periodic Table – Americium|access-date =7 July 2010| first = Rachel Sheremeta|last = Pepling|date = 2003}}</ref> After the discovery of americium isotopes <sup>241</sup>Am and <sup>242</sup>Am, their production and compounds were patented listing only Seaborg as the inventor.<ref>Seaborg, Glenn T. {{US patent|3156523}} "Element", Filing date: 23 August 1946, Issue date: 10 November 1964</ref> The initial americium samples weighed a few micrograms; they were barely visible and were identified by their radioactivity. The first substantial amounts of metallic americium weighing 40–200 micrograms were not prepared until 1951 by reduction of [[americium(III) fluoride]] with [[barium]] metal in high vacuum at 1100&nbsp;°C.<ref name="AM_METALL1">{{cite journal|title=The Preparation and Some Properties of Americium Metal|last1=Westrum|first1=Edgar F.|last2=Eyring|first2=Leroy|journal=Journal of the American Chemical Society|volume=73|page=3396|date=1951|doi=10.1021/ja01151a116|issue=7|hdl=2027/mdp.39015086480962|hdl-access=free}}</ref>
==Occurrence==
{{See also|Nuclear reprocessing}}
[[File:Ivy Mike - mushroom cloud.jpg|thumb|Americium was detected in the fallout from the ''[[Ivy Mike]]'' nuclear test.]]
The longest-lived and most common isotopes of americium, <sup>241</sup>Am and <sup>243</sup>Am, have half-lives of 432.2 and 7,370 years, respectively. Therefore, any [[Primordial nuclide|primordial]] americium (americium that was present on Earth during its formation) should have decayed by now. Trace amounts of americium probably occur naturally in uranium minerals as a result of neutron capture and beta decay (<sup>238</sup>U → <sup>239</sup>Pu → <sup>240</sup>Pu → <sup>241</sup>Am), though the quantities would be tiny and this has not been confirmed.<ref>{{Cite web|url=https://www.livescience.com/39874-facts-about-americium.html|title=Facts About Americium|last=Earth|first=Rachel Ross 2017-05-23T02:31:00Z Planet|website=livescience.com|date=23 May 2017|language=en|access-date=2019-08-10}}</ref><ref>{{Cite web|url=http://www.rsc.org/periodic-table/element/95/americium|title=Americium - Element information, properties and uses {{!}} Periodic Table|website=www.rsc.org|access-date=2019-08-10}}</ref><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> Extraterrestrial long-lived <sup>247</sup>Cm is probably also deposited on Earth and has <sup>243</sup>Am as one of its intermediate decay products, but again this has not been confirmed.<ref name=ThorntonBurdette/>
Existing americium is concentrated in the areas used for the atmospheric [[nuclear weapons tests]] conducted between 1945 and 1980, as well as at the sites of nuclear incidents, such as the [[Chernobyl disaster]]. For example, the analysis of the debris at the testing site of the first U.S. [[hydrogen bomb]], [[Ivy Mike]], (1 November 1952, [[Enewetak Atoll]]), revealed high concentrations of various actinides including americium; but due to military secrecy, this result was not published until later, in 1956.<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=G. 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> [[Trinitite]], the glassy residue left on the desert floor near [[Alamogordo, New Mexico]], after the [[plutonium]]-based [[Trinity test|Trinity]] [[nuclear testing|nuclear bomb test]] on 16 July 1945, contains traces of americium-241. Elevated levels of americium were also detected at the [[1968 Thule Air Base B-52 crash|crash site]] of a US [[Boeing B-52]] bomber aircraft, which carried four hydrogen bombs, in 1968 in [[Greenland]].<ref>{{cite book|author=Eriksson, Mats |title=On Weapons Plutonium in the Arctic Environment |publisher=[[Lund University]] |date=April 2002 |location=Risø National Laboratory, Roskilde, Denmark |access-date=15 November 2008 |url=http://www.risoe.dk/rispubl/NUK/nukpdf/ris-r-1321.pdf |page=28 |archive-url=https://web.archive.org/web/20081218233551/http://www.risoe.dk/rispubl/NUK/nukpdf/ris-r-1321.pdf |archive-date=18 December 2008 |url-status=dead }}</ref>
In other regions, the average radioactivity of surface soil due to residual americium is only about 0.01&nbsp;[[picocuries]] per gram (0.37&nbsp;[[mBq]]/g). Atmospheric americium compounds are poorly soluble in common solvents and mostly adhere to soil particles. Soil analysis revealed about 1,900 times higher concentration of americium inside sandy soil particles than in the water present in the soil pores; an even higher ratio was measured in [[loam]] soils.<ref name="am">[http://www.ead.anl.gov/pub/doc/americium.pdf Human Health Fact Sheet on Americium] {{webarchive|url=https://web.archive.org/web/20110716164652/http://www.ead.anl.gov/pub/doc/americium.pdf |date=16 July 2011 }}, Los Alamos National Laboratory, Retrieved 28 November 2010</ref>
Americium is produced mostly artificially in small quantities, for research purposes. A tonne of spent nuclear fuel contains about 100&nbsp;grams of various americium isotopes, mostly <sup>241</sup>Am and <sup>243</sup>Am.<ref>Hoffmann, Klaus ''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</ref> Their prolonged radioactivity is undesirable for the disposal, and therefore americium, together with other long-lived actinides, must be neutralized. The associated procedure may involve several steps, where americium is first separated and then converted by neutron bombardment in special reactors to short-lived nuclides. This procedure is well known as [[nuclear transmutation]], but it is still being developed for americium.<ref>Baetslé, L. [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=26 April 2005 }}, Nuclear Research Centre of Belgium Sck/Cen, Mol, Belgium, September 2001, Retrieved 28 November 2010</ref><ref>Fioni, Gabriele; Cribier, Michel and Marie, Frédéric [http://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_30.html Can the minor actinide, americium-241, be transmuted by thermal neutrons?] {{webarchive|url=https://web.archive.org/web/20071111175005/http://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_30.html |date=11 November 2007 }}, Department of Astrophysics, CEA/Saclay, Retrieved 28 November 2010</ref> The [[transuranic element]]s from americium to [[fermium]] 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>
Americium is also one of the elements that have theoretically been detected in [[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>
==Synthesis and extraction==
===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>
=== Metal generation ===
Most synthesis routines yield a mixture of different actinide isotopes in oxide forms, from which isotopes of americium can be separated. In a typical procedure, the spent reactor fuel (e.g. [[MOX fuel]]) is dissolved in [[nitric acid]], and the bulk of uranium and plutonium is removed using a [[PUREX]]-type extraction ('''P'''lutonium–'''UR'''anium '''EX'''traction) with [[tributyl phosphate]] in a [[hydrocarbon]]. The lanthanides and 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. Americium compounds are then selectively extracted using multi-step [[chromatographic]] and centrifugation techniques<ref>Penneman, pp. 34–48</ref> with an appropriate reagent. A large amount of work has been done on the [[solvent extraction]] of americium. For example, a 2003 [[EU]]-funded project codenamed "EUROPART" studied [[triazine]]s and other compounds as potential extraction agents.<ref>{{cite journal|journal = [[Dalton Trans.]]|date = 2003|pages = 1675–1685|doi = 10.1039/b301178j|title = The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanide(III) elements – implications for the partitioning of americium(III)|author = Hudson, M. J.|issue = 9|display-authors=etal}}</ref><ref>{{cite web|author = Geist, A.|title = Actinide(III)/Lanthanide(III) Partitioning Using n-Pr-BTP as Extractant: Extraction Kinetics and Extraction Test in a Hollow Fiber Module|work = 6th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation|publisher = [[OECD Nuclear Energy Agency]]|date = 11–13 December 2000|url = https://www.oecd-nea.org/pt/docs/iem/madrid00/Proceedings/Paper14.pdf|display-authors = etal|access-date = 26 May 2014|archive-date = 24 September 2015|archive-url = https://web.archive.org/web/20150924055355/http://www.oecd-nea.org/pt/docs/iem/madrid00/Proceedings/Paper14.pdf|url-status = dead}}</ref><ref>{{cite web|url = http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-26.pdf|title = Sanex-BTP Process Development Studies|work = Atalante 2000: Scientific Research on the Back-end of the Fuel Cycle for the 21st Century|publisher = Commissariat à l'énergie atomique|date = 24–26 October 2000|author = Hill, C.|author2 = Guillaneux, D.|author3 = Hérès, X.|author4 = Boubals, N.|author5 = Ramain, L.|name-list-style = amp|url-status = dead|archive-url = https://web.archive.org/web/20121115151847/http://www-atalante2004.cea.fr/home/liblocal/docs/atalante2000/P3-26.pdf|archive-date = 15 November 2012}}</ref><ref>{{cite web|title = Effective Actinide(III)-Lanthanide(III) Separation in Miniature Hollow Fibre Modules|author = Geist, A.|url = http://www.nea.fr/html/pt/docs/iem/jeju02/session2/SessionII-15.pdf|work = 7th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation|date = 14–16 October 2002|publisher = OECD Nuclear Energy Agency|display-authors = etal|access-date = 17 March 2007|archive-date = 29 September 2009|archive-url = https://web.archive.org/web/20090929023456/http://www.nea.fr/html/pt/docs/iem/jeju02/session2/SessionII-15.pdf|url-status = dead}}</ref><ref>{{cite web|title = Separation Studies of ''f''-Elements|author = Ensor, D.D.|publisher = [[Tennessee Tech University]]|url = http://www.tntech.edu/WRC/pdfs/Projects04_05/Ens_Elem.pdf|url-status = dead|archive-url = https://web.archive.org/web/20060922113030/http://www.tntech.edu/wrc/pdfs/Projects04_05/Ens_Elem.pdf|archive-date = 22 September 2006}}</ref> A [[BTBP|''bis''-triazinyl bipyridine]] complex was proposed in 2009 as such a reagent is highly selective to americium (and curium).<ref>{{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|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|issue = 2|title-link = centrifugal extractor|s2cid = 94720457}}</ref> Separation of americium from the highly similar curium can be achieved by treating a slurry of their hydroxides in aqueous [[sodium bicarbonate]] with [[ozone]], at elevated temperatures. Both Am and Cm are mostly present in solutions in the +3 valence state; whereas curium remains unchanged, americium oxidizes to soluble Am(IV) complexes which can be washed away.<ref>Penneman, p. 25</ref>
Metallic americium is obtained by [[Redox|reduction]] from its compounds. [[Americium(III) fluoride]] was first used for this purpose. The reaction was conducted using elemental [[barium]] as reducing agent in a water- and oxygen-free environment inside an apparatus made of [[tantalum]] and [[tungsten]].<ref name="AM_METALL1" /><ref name = "Gmelin">''Gmelin Handbook of Inorganic Chemistry'', System No. 71, transuranics, Part B 1, pp. 57–67.</ref><ref name="p3">Penneman, p. 3</ref>
: <math>\mathrm{2\ AmF_3\ +\ 3\ Ba\ \longrightarrow \ 2\ Am\ +\ 3\ BaF_2}</math>
An alternative is the reduction of [[americium dioxide]] by metallic [[lanthanum]] or [[thorium]]:<ref name="p3" /><ref name="AM_METALL2" />
: <math>\mathrm{3\ AmO_2\ +\ 4\ La\ \longrightarrow \ 3\ Am\ +\ 2\ La_2O_3}</math>
==Physical properties==
[[File:Closest packing ABAC.png|thumb|Double-hexagonal close packing with the layer sequence ABAC in the crystal structure of α-americium (A: green, B: blue, C: red)]]
In the [[periodic table]], americium is located to the right of plutonium, to the left of curium, and below the lanthanide [[europium]], with which it shares many physical and chemical properties. Americium is a highly radioactive element. When freshly prepared, it has a silvery-white metallic lustre, but then slowly tarnishes in air. With a density of 12&nbsp;g/cm<sup>3</sup>, americium is less dense than both curium (13.52&nbsp;g/cm<sup>3</sup>) and plutonium (19.8&nbsp;g/cm<sup>3</sup>); but has a higher density than europium (5.264&nbsp;g/cm<sup>3</sup>)—mostly because of its higher atomic mass. Americium is relatively soft and easily deformable and has a significantly lower [[bulk modulus]] than the actinides before it: Th, Pa, U, Np and Pu.<ref name="pressure" /> Its melting point of 1173&nbsp;°C is significantly higher than that of plutonium (639&nbsp;°C) and europium (826&nbsp;°C), but lower than for curium (1340&nbsp;°C).<ref name="AM_METALL2">{{cite journal|last1=Wade|first1=W.|title=Preparation and some properties of americium metal|journal=Journal of Inorganic and Nuclear Chemistry|volume=29|page=2577|date=1967|doi=10.1016/0022-1902(67)80183-0|issue=10|last2=Wolf|first2=T.|s2cid=98370243 }}</ref><ref name="AM_METALL4" />
At ambient conditions, americium is present in its most stable α form which has a [[Hexagonal crystal system|hexagonal crystal symmetry]], and a [[space group]] P6<sub>3</sub>/mmc with cell parameters ''a''&nbsp;= 346.8&nbsp;[[picometer|pm]] and ''c''&nbsp;= 1124&nbsp;pm, and four atoms per [[unit cell]]. The crystal consists of a double-[[hexagonal close packing]] with the layer sequence ABAC and so is isotypic with α-lanthanum and several actinides such as α-curium.<ref name="Gmelin" /><ref name = "AM_METALL4">{{cite journal|last1=McWhan|first1=D. B.|last2=Cunningham|first2=B. B.|last3=Wallmann|first3=J. C.|title=Crystal structure, thermal expansion and melting point of americium metal|journal=Journal of Inorganic and Nuclear Chemistry|volume=24|page=1025|date=1962|doi=10.1016/0022-1902(62)80246-2|issue=9}}</ref> The crystal structure of americium changes with pressure and temperature. When compressed at room temperature to 5 GPa, α-Am transforms to the β modification, which has a [[face-centered cubic]] (''fcc'') symmetry, space group Fm{{overline|3}}m and lattice constant ''a''&nbsp;= 489&nbsp;pm. This ''fcc'' structure is equivalent to the closest packing with the sequence ABC.<ref name="Gmelin" /><ref name = "AM_METALL4" /> Upon further compression to 23 GPa, americium transforms to an [[orthorhombic]] γ-Am structure similar to that of α-uranium. There are no further transitions observed up to 52 GPa, except for an appearance of a monoclinic phase at pressures between 10 and 15 GPa.<ref name="pressure">{{cite journal|last1=Benedict|first1=U.|title=Study of actinide metals and actinide compounds under high pressures|journal=Journal of the Less Common Metals|volume=100|page=153|date=1984|doi=10.1016/0022-5088(84)90061-4}}</ref> There is no consistency on the status of this phase in the literature, which also sometimes lists the α, β and γ phases as I, II and III. The β-γ transition is accompanied by a 6% decrease in the crystal volume; although theory also predicts a significant volume change for the α-β transition, it is not observed experimentally. The pressure of the α-β transition decreases with increasing temperature, and when α-americium is heated at ambient pressure, at 770&nbsp;°C it changes into an ''fcc'' phase which is different from β-Am, and at 1075&nbsp;°C it converts to a [[body-centered cubic]] structure. The pressure-temperature phase diagram of americium is thus rather similar to those of lanthanum, [[praseodymium]] and [[neodymium]].<ref>{{cite book| last1= Young |first1= D. A. | title = Phase diagrams of the elements| url = https://books.google.com/books?id=F2HVYh6wLBcC&pg=PA226| date = 1991| publisher = University of California Press| isbn = 978-0-520-91148-2| page = 226 }}</ref>
As with many other actinides, self-damage of the crystal structure due to alpha-particle irradiation is intrinsic to americium. It is especially noticeable at low temperatures, where the mobility of the produced [[Interstitial defect|structure defects]] is relatively low, by broadening of [[X-ray diffraction]] peaks. This effect makes somewhat uncertain the temperature of americium and some of its properties, such as electrical [[resistivity]].<ref>{{cite journal|last1=Benedict|first1=U.|last2=Dufour|first2=C.|title=Low temperature lattice expansion of americium dioxide|journal=Physica B+C|volume=102|issue=1|page=303|date=1980|doi=10.1016/0378-4363(80)90178-3|bibcode = 1980PhyBC.102..303B }}</ref> So for americium-241, the resistivity at 4.2 K increases with time from about 2&nbsp;μOhm·cm to 10&nbsp;μOhm·cm after 40 hours, and saturates at about 16&nbsp;μOhm·cm after 140 hours. This effect is less pronounced at room temperature, due to annihilation of radiation defects; also heating to room temperature the sample which was kept for hours at low temperatures restores its resistivity. In fresh samples, the resistivity gradually increases with temperature from about 2 μOhm·cm at [[liquid helium]] to 69&nbsp;μOhm·cm at room temperature; this behavior is similar to that of neptunium, uranium, thorium and [[protactinium]], but is different from plutonium and curium which show a rapid rise up to 60&nbsp;K followed by saturation. The room temperature value for americium is lower than that of neptunium, plutonium and curium, but higher than for uranium, thorium and protactinium.<ref name="res" />
Americium is [[paramagnetic]] in a wide temperature range, from that of [[liquid helium]], to room temperature and above. This behavior is markedly different from that of its neighbor curium which exhibits antiferromagnetic transition at 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|page=713|date=1975|doi=10.1016/0038-1098(75)90392-0|issue=6|bibcode = 1975SSCom..17..713K|last2=Blaise|first2=A.|last3=Fournier|first3=J. M.|last4=Müller|first4=W. }}</ref> The [[thermal expansion]] coefficient of americium is slightly anisotropic and amounts to {{val|7.5e-6|0.2|u=/°C}} along the shorter ''a'' axis and {{val|6.2e-6|0.4|u=/°C}} for the longer ''c'' hexagonal axis.<ref name = "AM_METALL4" /> The [[enthalpy of dissolution]] of americium metal in [[hydrochloric acid]] at standard conditions is {{val|−620.6|1.3|u=kJ/mol}}, from which the [[standard enthalpy change of formation]] (Δ<sub>f</sub>''H''°) of aqueous Am<sup>3+</sup> ion is {{val|−621.2|2.0|u=kJ/mol}}. The [[standard potential]] Am<sup>3+</sup>/Am<sup>0</sup> is {{val|−2.08|0.01|u=V}}.<ref>{{cite journal|last1=Mondal|first1=J. U.|last2=Raschella|first2=D. L.|last3=Haire|first3=R. G.|last4=Petereson|first4=J. R.|title=The enthalpy of solution of 243Am metal and the standard enthalpy of formation of Am3+(aq)|journal=Thermochimica Acta|volume=116|page=235|date=1987|doi=10.1016/0040-6031(87)88183-2}}</ref>
==Chemical properties==
Americium metal readily reacts with oxygen and dissolves in aqueous [[acid]]s. The most stable [[oxidation state]] for americium is +3.<ref name="p4">Penneman, p. 4</ref> The chemistry of americium(III) has many similarities to the chemistry of [[lanthanide]](III) compounds. For example, trivalent americium forms insoluble [[fluoride]], [[oxalate]], [[iodate]], [[hydroxide]], [[phosphate]] and other salts.<ref name="p4" /> Compounds of americium in oxidation states +2, +4, +5, +6 and +7 have also been studied. This is the widest range that has been observed with actinide elements. The color of americium compounds in aqueous solution is as follows: Am<sup>3+</sup> (yellow-reddish), Am<sup>4+</sup> (yellow-reddish), {{chem2|Am^{V}O2+}}; (yellow), {{chem2|Am^{VI}O2(2+)}} (brown) and {{chem2|Am^{VII}O6(5-)}} (dark green).<ref>[http://www.chemie-master.de/FrameHandler.php?loc=http://www.chemie-master.de/pse/pse.php?modul=Am Americium] {{Webarchive|url=https://web.archive.org/web/20190609181845/http://www.chemie-master.de/FrameHandler.php?loc=http%3A%2F%2Fwww.chemie-master.de%2Fpse%2Fpse.php%3Fmodul%3DAm |date=9 June 2019 }}, Das Periodensystem der Elemente für den Schulgebrauch (The periodic table of elements for schools) chemie-master.de (in German), Retrieved 28 November 2010</ref><ref name="g1265">Greenwood, p. 1265</ref> The absorption spectra have sharp peaks, due to ''f''-''f'' transitions' in the visible and near-infrared regions. Typically, Am(III) has absorption maxima at ca. 504 and 811&nbsp;nm, Am(V) at ca. 514 and 715&nbsp;nm, and Am(VI) at ca. 666 and 992&nbsp;nm.<ref>Penneman, pp. 10–14</ref><ref name="amoh4" /><ref name="carbonate" /><ref name="haxav" />
Americium compounds with oxidation state +4 and higher are strong oxidizing agents, comparable in strength to the [[permanganate]] ion ({{chem2|MnO4-}}) in acidic solutions.<ref name = "HOWI_1956">Wiberg, p. 1956</ref> Whereas the Am<sup>4+</sup> ions are unstable in solutions and readily convert to Am<sup>3+</sup>, compounds such as [[americium dioxide]] (AmO<sub>2</sub>) and [[americium(IV) fluoride]] (AmF<sub>4</sub>) are stable in the solid state.
The pentavalent oxidation state of americium was first observed in 1951.<ref>{{cite journal|title=The Pentavalent State of Americium|last1=Werner|first1=L. B.|last2=Perlman|first2=I.|journal=Journal of the American Chemical Society|volume=73|page=495|date=1951|doi=10.1021/ja01145a540|hdl=2027/mdp.39015086479774|hdl-access=free}}</ref> In acidic aqueous solution the {{chem2|AmO2+}} ion is unstable with respect to [[disproportionation]].<ref>{{cite journal|last1=Hall|first1=G.|title=The self-reduction of americium(V) and (VI) and the disproportionation of americium(V) in aqueous solution|journal=Journal of Inorganic and Nuclear Chemistry|volume=4|page=296|date=1957|doi=10.1016/0022-1902(57)80011-6|issue=5–6|last2=Markin|first2=T. L.}}</ref><ref>{{cite journal|last1=Coleman|first1=James S.|title=The Kinetics of the Disproportionation of Americium(V)|journal=Inorganic Chemistry|volume=2|page=53|date=1963|doi=10.1021/ic50005a016}}</ref><ref name="g1275">Greenwood, p. 1275</ref> The reaction
: {{chem2|3[AmO2]+ + 4H+ -> 2[AmO2](2+) + Am(3+) + 2H2O}}
is typical. The chemistry of Am(V) and Am(VI) is comparable to the chemistry of [[uranium]] in those oxidation states. In particular, compounds like {{chem2|Li3AmO4}} and {{chem2|Li6AmO6}} are comparable to [[uranate]]s and the ion {{chem2|AmO2(2+)}} is comparable to the [[uranyl]] ion, {{chem2|UO2(2+)}}. Such compounds can be prepared by oxidation of Am(III) in dilute nitric acid with [[ammonium persulfate]].<ref>{{cite journal|last1=Asprey|first1=L. B.|title=A New Valence State of Americium, Am(Vi)1|last2=Stephanou|first2=S. E.|last3=Penneman|first3=R. A.|journal=Journal of the American Chemical Society |volume=72|page=1425| date=1950|doi=10.1021/ja01159a528|issue=3| url=https://digital.library.unt.edu/ark:/67531/metadc1020623/}}</ref> Other oxidising agents that have been used include [[silver(I) oxide]],<ref name="haxav">{{cite journal|last1=Asprey|first1=L. B.|last2=Stephanou|first2=S. E.|last3=Penneman|first3=R. A.|title=Hexavalent Americium|journal=Journal of the American Chemical Society|volume=73|page=5715|date=1951|doi=10.1021/ja01156a065|issue=12}}</ref> [[ozone]] and [[sodium persulfate]].<ref name="carbonate">{{cite journal|last1=Coleman|first1=J. S.|last2=Keenan|first2=T. K.|last3=Jones|first3=L. H.|last4=Carnall|first4=W. T.|last5=Penneman|first5=R. A.|title=Preparation and Properties of Americium(VI) in Aqueous Carbonate Solutions|journal=Inorganic Chemistry|volume=2|page=58|date=1963|doi=10.1021/ic50005a017}}</ref>
==Chemical compounds==
{{Main|Americium compounds}}
===Oxygen compounds===
Three americium oxides are known, with the oxidation states +2 (AmO), +3 (Am<sub>2</sub>O<sub>3</sub>) and +4 (AmO<sub>2</sub>). [[Americium(II) oxide]] was prepared in minute amounts and has not been characterized in detail.<ref>{{Cite journal| doi = 10.1016/0022-1902(67)80191-X| title = A note on AmN and AmO| journal = Journal of Inorganic and Nuclear Chemistry| volume = 29| issue = 10| pages = 2650–2652| year = 1967| last1 = Akimoto | first1 = Y.}}</ref> [[Americium(III) oxide]] is a red-brown solid with a melting point of 2205&nbsp;°C.<ref name = "HOWI_1972">Wiberg, p. 1972</ref> [[Americium(IV) oxide]] is the main form of solid americium which is used in nearly all its applications. As most other actinide dioxides, it is a black solid with a cubic ([[fluorite]]) crystal structure.<ref name="g1267">Greenwood, p. 1267</ref>
The oxalate of americium(III), vacuum dried at room temperature, has the chemical formula Am<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>·7H<sub>2</sub>O. Upon heating in vacuum, it loses water at 240&nbsp;°C and starts decomposing into AmO<sub>2</sub> at 300&nbsp;°C, the decomposition completes at about 470&nbsp;°C.<ref name="p4" /> The initial oxalate dissolves in nitric acid with the maximum solubility of 0.25&nbsp;g/L.<ref name="p5">Penneman, p. 5</ref>
===Halides===
[[Halide]]s of americium are known for the oxidation states +2, +3 and +4,<ref name="HOWI_1969">Wiberg, p. 1969</ref> where the +3 is most stable, especially in solutions.<ref name="hal1">{{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|page=985|date=1965|doi=10.1021/ic50029a013|issue=7|s2cid=96551460 |url=https://digital.library.unt.edu/ark:/67531/metadc1035960/}}</ref>
{| Class ="wikitable" style ="text-align:center;"
|-
! Oxidation state
! F
! Cl
! Br
! I
|-
! +4
| [[Americium(IV) fluoride]] <br /> AmF<sub>4</sub><br /> pale pink
|
|
|
|-
! +3
| [[Americium(III) fluoride]] <br /> AmF<sub>3</sub><br /> pink
| [[Americium(III) chloride]] <br /> AmCl<sub>3</sub><br /> pink
| [[Americium(III) bromide]] <br /> AmBr<sub>3</sub><br /> light yellow
| [[Americium(III) iodide]] <br /> AmI<sub>3</sub><br /> light yellow
|-
! +2
|
| [[Americium(II) chloride]] <br /> AmCl<sub>2</sub><br /> black <!-- (CAS: 16601-54-0) --->
| [[Americium(II) bromide]] <br /> AmBr<sub>2</sub><br /> black <!-- (CAS: 39705-49-2) -->
| [[Americium(II) iodide]] <br /> AmI<sub>2</sub><br /> black <!-- (CAS: 38150-40-2) -->
|}
Reduction of Am(III) compounds with sodium [[Amalgam (chemistry)|amalgam]] yields Am(II) salts – the black halides AmCl<sub>2</sub>, AmBr<sub>2</sub> and AmI<sub>2</sub>. They are very sensitive to oxygen and oxidize in water, releasing hydrogen and converting back to the Am(III) state. Specific lattice constants are:
* [[Orthorhombic]] AmCl<sub>2</sub>: ''a'' = {{val|896.3|0.8|u=pm}}, ''b'' = {{val|757.3|0.8|u=pm}} and ''c'' = {{val|453.2|0.6|u=pm}}
* [[Tetragonal]] AmBr<sub>2</sub>: ''a'' = {{val|1159.2|0.4|u=pm}} and ''c'' = {{val|712.1|0.3|u=pm}}.<ref>{{cite journal|last1=Baybarz|first1=R. D.|title=The preparation and crystal structures of americium dichloride and dibromide|journal=Journal of Inorganic and Nuclear Chemistry|volume=35|page=483|date=1973|doi=10.1016/0022-1902(73)80560-3|issue=2}}</ref> They can also be prepared by reacting metallic americium with an appropriate mercury halide HgX<sub>2</sub>, where X = Cl, Br or I:<ref name="g1272">Greenwood, p. 1272</ref>
: <chem>{Am} + \underset{mercury\ halide}{HgX2} ->[{} \atop 400 - 500 ^\circ \ce C] {AmX2} + {Hg}</chem>
Americium(III) fluoride (AmF<sub>3</sub>) is poorly soluble and precipitates upon reaction of Am<sup>3+</sup> and fluoride ions in weak acidic solutions:
: <chem>Am^3+ + 3F^- -> AmF3(v)</chem>
The tetravalent americium(IV) fluoride (AmF<sub>4</sub>) is obtained by reacting solid americium(III) fluoride with molecular [[fluorine]]:<ref name="f4">{{cite journal|title=New Compounds of Quadrivalent Americium, AmF<sub>4</sub>, KAmF<sub>5</sub>|last1=Asprey|first1=L. B.|journal=Journal of the American Chemical Society|volume=76|page=2019|date=1954|doi=10.1021/ja01636a094|issue=7}}</ref><ref name="g1271">Greenwood, p. 1271</ref>
: <chem>2AmF3 + F2 -> 2AmF4</chem>
Another known form of solid tetravalent americium fluoride is KAmF<sub>5</sub>.<ref name="f4" /><ref name="p6">Penneman, p. 6</ref> Tetravalent americium has also been observed in the aqueous phase. For this purpose, black Am(OH)<sub>4</sub> was dissolved in 15-[[Mole (unit)|M]] NH<sub>4</sub>F with the americium concentration of 0.01 M. The resulting reddish solution had a characteristic optical absorption spectrum which is similar to that of AmF<sub>4</sub> but differed from other oxidation states of americium. Heating the Am(IV) solution to 90&nbsp;°C did not result in its disproportionation or reduction, however a slow reduction was observed to Am(III) and assigned to self-irradiation of americium by alpha particles.<ref name="amoh4">{{cite journal|last1=Asprey|first1=L. B.|title=First Observation of Aqueous Tetravalent Americium1|last2=Penneman|first2=R. A.|journal=Journal of the American Chemical Society|volume=83|page=2200|date=1961|doi=10.1021/ja01470a040|issue=9}}</ref>
Most americium(III) halides form hexagonal crystals with slight variation of the color and exact structure between the halogens. So, chloride (AmCl<sub>3</sub>) is reddish and has a structure isotypic to [[uranium(III) chloride]] (space group P6<sub>3</sub>/m) and the melting point of 715&nbsp;°C.<ref name="HOWI_1969" /> The fluoride is isotypic to LaF<sub>3</sub> (space group P6<sub>3</sub>/mmc) and the iodide to BiI<sub>3</sub> (space group R{{overline|3}}). The bromide is an exception with the orthorhombic PuBr<sub>3</sub>-type structure and space group Cmcm.<ref name="hal1" /> Crystals of americium(III) chloride hexahydrate (AmCl<sub>3</sub>·6H<sub>2</sub>O) can be prepared by dissolving americium dioxide in hydrochloric acid and evaporating the liquid. Those crystals are hygroscopic and have yellow-reddish color and a [[monoclinic]] crystal structure.<ref>{{cite journal|last1=Burns|first1=John H.|last2=Peterson|first2=Joseph Richard|title=Crystal structures of americium trichloride hexahydrate and berkelium trichloride hexahydrate|journal=Inorganic Chemistry|volume=10|page=147|date=1971|doi=10.1021/ic50095a029}}</ref>
Oxyhalides of americium in the form Am<sup>VI</sup>O<sub>2</sub>X<sub>2</sub>, Am<sup>V</sup>O<sub>2</sub>X, Am<sup>IV</sup>OX<sub>2</sub> and Am<sup>III</sup>OX can be obtained by reacting the corresponding americium halide with oxygen or Sb<sub>2</sub>O<sub>3</sub>, and AmOCl can also be produced by vapor phase [[hydrolysis]]:<ref name="g1272" />
: AmCl<sub>3</sub> + H<sub>2</sub>O -> AmOCl + 2HCl
===Chalcogenides and pnictides===
The known [[chalcogenide]]s of americium include the [[sulfide]] AmS<sub>2</sub>,<ref name="AM_S_SE">{{cite journal|last1=Damien|first1=D.|title=Americium disulfide and diselenide|journal=Inorganic and Nuclear Chemistry Letters|volume=7|page=685|date=1971|doi=10.1016/0020-1650(71)80055-7|issue=7|last2=Jove|first2=J.}}</ref> [[selenide]]s AmSe<sub>2</sub> and Am<sub>3</sub>Se<sub>4</sub>,<ref name = "AM_S_SE " /><ref name="AM_METALLIDE">{{cite journal|last1=Roddy|first1=J.|title=Americium metallides: AmAs, AmSb, AmBi, Am3Se4, and AmSe2|journal=Journal of Inorganic and Nuclear Chemistry|volume=36|page=2531|date=1974|doi=10.1016/0022-1902(74)80466-5|issue=11}}</ref> and [[tellurides]] Am<sub>2</sub>Te<sub>3</sub> and AmTe<sub>2</sub>.<ref>{{cite journal|last1=Damien|first1=D.|title=Americium tritelluride and ditelluride|journal=Inorganic and Nuclear Chemistry Letters|volume=8|page=501|date=1972|doi=10.1016/0020-1650(72)80262-9|issue=5}}</ref> The [[pnictides]] of americium (<sup>243</sup>Am) of the AmX type are known for the elements [[phosphorus]], [[arsenic]],<ref>{{cite journal|last1=Charvillat|first1=J.|title=Americium monoarsenide|journal=Inorganic and Nuclear Chemistry Letters|volume=9|page=559|date=1973|doi=10.1016/0020-1650(73)80191-6|issue=5|last2=Damien|first2=D.}}</ref> [[antimony]] and [[bismuth]]. They crystallize in the [[Cubic crystal system|rock-salt]] lattice.<ref name="AM_METALLIDE" />
===Silicides and borides===
Americium [[silicide|monosilicide]] (AmSi) and "disilicide" (nominally AmSi<sub>x</sub> with: 1.87 < x < 2.0) were obtained by reduction of americium(III) fluoride with elementary [[silicon]] in vacuum at 1050&nbsp;°C (AmSi) and 1150−1200&nbsp;°C (AmSi<sub>x</sub>). AmSi is a black solid isomorphic with LaSi, it has an orthorhombic crystal symmetry. AmSi<sub>x</sub> has a bright silvery lustre and a tetragonal crystal lattice (space group ''I''4<sub>1</sub>/amd), it is isomorphic with PuSi<sub>2</sub> and ThSi<sub>2</sub>.<ref>{{cite journal|last1=Weigel|first1=F.|last2=Wittmann|first2=F.|last3=Marquart|first3=R.|title=Americium monosilicide and "disilicide"|journal=Journal of the Less Common Metals|volume=56|page=47|date=1977|doi=10.1016/0022-5088(77)90217-X}}</ref> [[Boride]]s of americium include AmB<sub>4</sub> and AmB<sub>6</sub>. The tetraboride can be obtained by heating an oxide or halide of americium with [[magnesium diboride]] in vacuum or inert atmosphere.<ref>Lupinetti, A. J. ''et al''. {{US patent|6830738}} "Low-temperature synthesis of actinide tetraborides by solid-state metathesis reactions", Filed 4 Apr 2002, Issued 14 December 2004</ref><ref>{{cite journal|last1=Eick|first1=Harry A.|last2=Mulford|first2=R. N. R.|title=Americium and neptunium borides|journal=Journal of Inorganic and Nuclear Chemistry|volume=31|page=371|date=1969|doi=10.1016/0022-1902(69)80480-X|issue=2}}</ref>
===Organoamericium compounds===
[[File:Uranocene-3D-balls.png|thumb|upright=0.55|Predicted structure of amerocene [(η<sup>8</sup>-C<sub>8</sub>H<sub>8</sub>)<sub>2</sub><nowiki>Am]</nowiki>]]
Analogous to [[uranocene]], americium is predicted to form the organometallic compound amerocene with two [[cyclooctatetraene]] ligands, with the chemical formula (η<sup>8</sup>-C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>Am.<ref>{{cite book| last = Elschenbroich| first = Christoph| title = Organometallchemie| date = 2008| publisher = Vieweg+teubner Verlag| isbn = 978-3-8351-0167-8| page = 589 }}</ref> A [[cyclopentadienyl complex]] is also known that is likely to be stoichiometrically AmCp<sub>3</sub>.<ref>{{cite book|author-link=Thomas Albrecht-Schönzart | author = Albrecht-Schmitt, Thomas E. | title = Organometallic and Coordination Chemistry of the Actinides| url = https://books.google.com/books?id=rgmnVSzFzXMC&pg=PA8| date = 2008| publisher = Springer| isbn = 978-3-540-77836-3| page = 8 }}</ref><ref>{{cite journal |last1=Dutkiewicz |first1=Michał S. |last2=Apostolidis |first2=Christos |last3=Walter |first3=Olaf |last4=Arnold |first4=Polly L. |date=30 January 2017 |title=Reduction chemistry of neptunium cyclopentadienide complexes: from structure to understanding |journal=Chemical Science |volume=2017 |issue=8 |pages=2553–61 |doi= 10.1039/C7SC00034K |pmid=28553487 |pmc=5431675 }}</ref>
Formation of the complexes of the type Am(n-C<sub>3</sub>H<sub>7</sub>-BTP)<sub>3</sub>, where BTP stands for 2,6-di(1,2,4-triazin-3-yl)pyridine, in solutions containing n-C<sub>3</sub>H<sub>7</sub>-BTP and Am<sup>3+</sup> ions has been confirmed by [[EXAFS]]. Some of these BTP-type complexes selectively interact with americium and therefore are useful in its selective separation from lanthanides and another actinides.<ref>{{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.|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|pages=9627–35|date=2010|pmid=20849125|doi=10.1021/ic101309j|url=https://www.escholar.manchester.ac.uk/api/datastream?publicationPid=uk-ac-man-scw:209191&datastreamId=POST-PEER-REVIEW-PUBLISHERS.PDF}}</ref>
==Biological aspects==
Americium is an artificial element of recent origin, and thus does not have a [[dietary element|biological requirement]].<ref>Toeniskoetter, Steve; Dommer, Jennifer and Dodge, Tony [http://umbbd.ethz.ch/periodic/elements/am.html The Biochemical Periodic Tables – Americium], University of Minnesota, Retrieved 28 November 2010</ref><ref>{{cite journal|url=http://www.osti.gov/bridge/product.biblio.jsp?osti_id=2439|author=Dodge, C.J.|title=Role of Microbes as Biocolloids in the Transport of Actinides from a Deep Underground Radioactive Waste Repository|journal=Radiochim. Acta |date=1998|volume=82|pages=347–354|doi=10.1524/ract.1998.82.special-issue.347|s2cid=99777562|display-authors=etal}}</ref> It is harmful to [[life]]. It has been proposed to use bacteria for removal of americium and other [[heavy metals]] from rivers and streams. Thus, [[Enterobacteriaceae]] of the genus ''[[Citrobacter]]'' precipitate americium ions from aqueous solutions, binding them into a metal-phosphate complex at their cell walls.<ref>{{cite journal|doi=10.1111/j.1574-6976.1994.tb00109.x|last1=MacAskie|first1=L. E.|last2=Jeong|first2=B. C.|last3=Tolley|first3=M. R. |title=Enzymically accelerated biomineralization of heavy metals: application to the removal of americium and plutonium from aqueous flows|journal=FEMS Microbiology Reviews|volume=14|issue=4|pages=351–67|date=1994|pmid=7917422|doi-access=free}}</ref> Several studies have been reported on the [[biosorption]] and [[bioaccumulation]] of americium by bacteria<ref>{{cite journal|doi=10.1097/00004032-198601000-00007|last1=Wurtz|first1=E. A.|last2=Sibley|first2=T. H.|last3=Schell|first3=W. R.|title=Interactions of Escherichia coli and marine bacteria with 241Am in laboratory cultures|journal=Health Physics|volume=50|issue=1|pages=79–88|date=1986|pmid=3511007}}</ref><ref>{{cite journal|author=Francis, A.J.|title=Role of Bacteria as Biocolloids in the Transport of Actinides from a Deep Underground Radioactive Waste Repository|journal= Radiochimica Acta|date=1998|volume=82|pages= 347–354|osti=2439|display-authors=etal|doi=10.1524/ract.1998.82.special-issue.347|s2cid=99777562}}</ref> and fungi.<ref>{{cite journal|last1=Liu|first1=N.|last2=Yang|first2=Y.|last3=Luo|first3=S.|last4=Zhang|first4=T.|last5=Jin|first5=J.|last6=Liao|first6=J.|last7=Hua|first7=X.|title=Biosorption of 241Am by Rhizopus arrihizus: preliminary investigation and evaluation|journal=Applied Radiation and Isotopes|volume=57|issue=2|pages=139–43|date=2002|pmid=12150270|doi=10.1016/s0969-8043(02)00076-3}}</ref> In the laboratory, both americium and curium were found to support the growth of [[methylotroph]]s.<ref>{{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}}</ref>
==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>
==Isotopes==
{{See also|Isotopes of americium}}
About 18 [[isotope]]s and 11 [[nuclear isomer]]s are known for americium, having mass numbers 229, 230, and 232 through 247.<ref name="NUBASE2020"/> There are two long-lived alpha-emitters; <sup>243</sup>Am has a half-life of 7,370&nbsp;years and is the most stable isotope, and <sup>241</sup>Am has a half-life of 432.2&nbsp;years. The most stable nuclear isomer is <sup>242m1</sup>Am; it has a long half-life of 141&nbsp;years. The half-lives of other isotopes and isomers range from 0.64&nbsp;microseconds for <sup>245m1</sup>Am to 50.8&nbsp;hours for <sup>240</sup>Am. As with most other actinides, the isotopes of americium with odd number of neutrons have relatively high rate of nuclear fission and low critical mass.<ref name = "nubase" />
[[Americium-241]] decays to <sup>237</sup>Np emitting alpha particles of 5 different energies, mostly at 5.486&nbsp;MeV (85.2%) and 5.443&nbsp;MeV (12.8%). Because many of the resulting states are metastable, they also emit [[gamma ray]]s with the discrete energies between 26.3 and 158.5&nbsp;keV.<ref>{{cite web|url=http://87.139.25.178:81/eng/theory.htm|title=α-decay of <sup>241</sup>Am. Theory – A lecture course on radioactivity|author=Klinck, Christian|publisher=University of Technology Kaiserslautern|access-date=28 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20110706052757/http://87.139.25.178:81/eng/theory.htm|archive-date=6 July 2011}}</ref>
[[Americium-242]] is a short-lived isotope with a half-life of 16.02&nbsp;h.<ref name="nubase" /> It mostly (82.7%) converts by β-decay to <sup>242</sup>Cm, but also by [[electron capture]] to <sup>242</sup>Pu (17.3%). Both <sup>242</sup>Cm and <sup>242</sup>Pu transform via nearly the same decay chain through <sup>238</sup>Pu down to <sup>234</sup>U.
Nearly all (99.541%) of <sup>242m1</sup>Am decays by [[internal conversion]] to <sup>242</sup>Am and the remaining 0.459% by α-decay to <sup>238</sup>Np. The latter subsequently decays to <sup>238</sup>Pu and then to <sup>234</sup>U.<ref name="nubase" />
[[Americium-243]] transforms by α-emission into <sup>239</sup>Np, which converts by β-decay to <sup>239</sup>Pu, and the <sup>239</sup>Pu changes into <sup>235</sup>U by emitting an α-particle.
==Applications==
{{Multiple image|direction=vertical|align=right|image1=Residential smoke detector.jpg|image2=InsideSmokeDetector.jpg|width=200|caption2=Outside and inside view of an americium-based smoke detector}}
===Ionization-type smoke detector===
{{Main|Smoke detector#Ionization}}
Americium is used in the most common type of household [[smoke detector]], which uses <sup>241</sup>Am in the form of americium dioxide as its source of [[ionizing radiation]].<ref>{{citation |url=http://www.uic.com.au/nip35.htm |archive-url=http://webarchive.loc.gov/all/20020911070229/http%3A//www%2Euic%2Ecom%2Eau/nip35%2Ehtm |archive-date= 11 September 2002 |title=Smoke Detectors and Americium |work=Nuclear Issues Briefing Paper |volume=35 |date=May 2002 |access-date=2015-08-26}}</ref> This isotope is preferred over <sup>226</sup>[[radium|Ra]] because it emits 5 times more alpha particles and relatively little harmful gamma radiation.
The amount of americium in a typical new smoke detector is 1&nbsp;[[microcurie]] (37&nbsp;[[kBq]]) or 0.29 [[microgram]]. This amount declines slowly as the americium decays into [[neptunium]]-237, a different transuranic element with a much longer half-life (about 2.14 million years). With its half-life of 432.2 years, the americium in a smoke detector includes about 3% [[neptunium]] after 19 years, and about 5% after 32 years. The radiation passes through an [[ionization chamber]], an air-filled space between two [[electrode]]s, and permits a small, constant [[Electric current|current]] between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and affects this current, triggering the alarm. Compared to the alternative optical smoke detector, the ionization smoke detector is cheaper and can detect particles which are too small to produce significant light scattering; however, it is more prone to [[Type I and type II errors|false alarms]].<ref>Residential Smoke Alarm Performance, Thomas Cleary. Building and Fire Research Laboratory, National Institute of Standards and Technology; UL Smoke and Fire Dynamics Seminar. November 2007</ref><ref name="NIST">Bukowski, R. W. ''et al''. (2007) [http://www.fire.nist.gov/bfrlpubs/fire07/art063.html Performance of Home Smoke Alarms Analysis of the Response of Several Available Technologies in Residential Fire Settings] {{Webarchive|url=https://web.archive.org/web/20100822192559/http://www.fire.nist.gov/bfrlpubs/fire07/art063.html |date=22 August 2010 }}, NIST Technical Note 1455-1</ref><ref>{{cite web |url=http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf |archive-url=
https://web.archive.org/web/20160325003327/https://cns-snc.ca/media/uploads/teachers/smoke_am241.pdf|archive-date=2016-03-25|title = Smoke detectors and americium-241 fact sheet|publisher = Canadian Nuclear Society|access-date =31 August 2009}}</ref><ref>{{cite web|url=http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf|title=Toxicological Profile For Americium|author=Gerberding, Julie Louise |publisher=[[United States Department of Health and Human Services]]/[[Agency for Toxic Substances and Disease Registry]]|access-date=29 August 2009|date=2004| archive-url= https://web.archive.org/web/20090906112953/http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf| archive-date= 6 September 2009 | url-status= live}}</ref>
===Radionuclide===
As <sup>241</sup>Am has a roughly similar half-life to <sup>238</sup>Pu (432.2 years vs. 87 years), it has been proposed as an active element of [[radioisotope thermoelectric generator]]s, for example in spacecraft.<ref name="RTG">[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=15 February 2013 }}, G.L. Kulcinski, NEEP 602 Course Notes (Spring 2000), Nuclear Power in Space, University of Wisconsin Fusion Technology Institute (see last page)</ref> Although americium produces less heat and electricity – the power yield is 114.7&nbsp;mW/g for <sup>241</sup>Am and 6.31&nbsp;mW/g for <sup>243</sup>Am<ref name="res" /> (cf. 390&nbsp;mW/g for <sup>238</sup>Pu)<ref name="RTG" /> – and its radiation poses more threat to humans owing to neutron emission, the [[European Space Agency]] is considering using americium for its space probes.<ref>[http://www.spaceflightnow.com/news/n1007/09rtg/ Space agencies tackle waning plutonium stockpiles], Spaceflight now, 9 July 2010</ref>
Another proposed space-related application of americium is a fuel for space ships with nuclear propulsion. It relies on the very high rate of nuclear fission of <sup>242m</sup>Am, which can be maintained even in a micrometer-thick foil. Small thickness avoids the problem of self-absorption of emitted radiation. This problem is pertinent to uranium or plutonium rods, in which only surface layers provide alpha-particles.<ref name="rocket">{{cite web|title = Extremely Efficient Nuclear Fuel Could Take Man To Mars in Just Two Weeks|website = [[ScienceDaily]]|date = 3 January 2001|url = https://www.sciencedaily.com/releases/2001/01/010103073253.htm|access-date =22 November 2007| archive-url= https://web.archive.org/web/20071017120211/https://www.sciencedaily.com/releases/2001/01/010103073253.htm| archive-date= 17 October 2007 | url-status= live}}</ref><ref>{{cite conference|title = An americium-fueled gas core nuclear rocket|book-title = AIP Conf. Proc.|date = 10 January 1993|volume = 271|pages = 585–589|conference = Tenth symposium on space nuclear power and propulsion|author = Kammash, T. |doi = 10.1063/1.43073|display-authors=etal|url = https://deepblue.lib.umich.edu/bitstream/2027.42/87734/2/585_1.pdf|hdl = 2027.42/87734|hdl-access = free}}</ref> The fission products of <sup>242m</sup>Am can either directly propel the spaceship or they can heat a thrusting gas. They can also transfer their energy to a fluid and generate electricity through a [[magnetohydrodynamic generator]].<ref name="mprice">{{cite journal|last1=Ronen|first1=Y.|last2=Shwageraus|first2=E.|title=Ultra-thin 242mAm fuel elements in nuclear reactors|journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|volume=455|page=442|date=2000|doi=10.1016/S0168-9002(00)00506-4|issue=2|bibcode = 2000NIMPA.455..442R }}</ref>
One more proposal which utilizes the high nuclear fission rate of <sup>242m</sup>Am is a nuclear battery. Its design relies not on the energy of the emitted by americium alpha particles, but on their charge, that is the americium acts as the self-sustaining "cathode". A single 3.2&nbsp;kg <sup>242m</sup>Am charge of such battery could provide about 140&nbsp;kW of power over a period of 80 days.<ref>Genuth, Iddo [http://thefutureofthings.com/3015-americium-power-source/ Americium Power Source] {{webarchive|url=https://web.archive.org/web/20100507103250/http://thefutureofthings.com/articles.php?itemId=26%2F64%2F |date=7 May 2010 }}, The Future of Things, 3 October 2006, Retrieved 28 November 2010</ref> Even with all the potential benefits, the current applications of <sup>242m</sup>Am are as yet hindered by the scarcity and high price of this particular [[nuclear isomer]].<ref name="mprice" />
In 2019, researchers at the UK [[National Nuclear Laboratory]] and the [[University of Leicester]] demonstrated the use of heat generated by americium to illuminate a small light bulb. This technology could lead to systems to power missions with durations up to 400 years into [[interstellar space]], where solar panels do not function.<ref>{{cite web |title=UK scientists generate electricity from rare element to power future space missions |url=https://www.nnl.co.uk/2019/05/uk-scientists-generate-electricity-from-rare-element-to-power-future-space-missions/ |website=[[National Nuclear Laboratory]] |date=3 May 2019 |access-date=3 May 2019}}</ref><ref>{{cite magazine |author=<!--Staff writer(s); no by-line.--> |title=Rare element could power distant space missions |url=https://eandt.theiet.org/content/articles/2019/05/rare-element-could-power-far-flung-space-missions |magazine=E&T Engineering and Technology |publisher=[[Institution of Engineering and Technology]] |date=3 May 2019 |access-date=3 May 2019 }}</ref>
===Neutron source===
The oxide of <sup>241</sup>Am pressed with [[beryllium]] is an efficient [[neutron source]]. Here americium acts as the alpha source, and beryllium produces neutrons owing to its large cross-section for the (α,n) nuclear reaction:
: <chem>^{241}_{95}Am -> ^{237}_{93}Np + ^{4}_{2}He + \gamma</chem>
: <chem>^{9}_{4}Be + ^{4}_{2}He -> ^{12}_{6}C + ^{1}_{0}n + \gamma</chem>
The most widespread use of <sup>241</sup>AmBe neutron sources is a [[neutron probe]] – a device used to measure the quantity of water present in soil, as well as moisture/density for quality control in highway construction. <sup>241</sup>Am neutron sources are also used in well logging applications, as well as in [[neutron radiography]], tomography and other radiochemical investigations.<ref name="Binder" />
===Production of other elements===
Americium is a starting material for the production of other transuranic elements and [[transactinide]]s – for example, 82.7% of <sup>242</sup>Am decays to <sup>242</sup>Cm and 17.3% to <sup>242</sup>Pu. In the nuclear reactor, <sup>242</sup>Am is also up-converted by neutron capture to <sup>243</sup>Am and <sup>244</sup>Am, which transforms by β-decay to <sup>244</sup>Cm:
: <chem>^{243}_{95}Am ->[\ce{(n,\gamma)}] ^{244}_{95}Am ->[\beta^-][10.1 \ \ce{h}] ^{244}_{96}Cm</chem>
Irradiation of <sup>241</sup>Am by <sup>12</sup>C or <sup>22</sup>Ne ions yields the isotopes <sup>247</sup>Es ([[einsteinium]]) or <sup>260</sup>Db ([[dubnium]]), respectively.<ref name="Binder">{{cite book| author = Binder, Harry H. | title = Lexikon der chemischen Elemente: das Periodensystem in Fakten, Zahlen und Daten : mit 96 Abbildungen und vielen tabellarischen Zusammenstellungen| date = 1999| publisher = Hirzel| isbn = 978-3-7776-0736-8 }}</ref> Furthermore, the element [[berkelium]] (<sup>243</sup>Bk isotope) had been first intentionally produced and identified by bombarding <sup>241</sup>Am with alpha particles, in 1949, by the same Berkeley group, using the same 60-inch cyclotron. Similarly, [[nobelium]] was produced at the [[Joint Institute for Nuclear Research]], [[Dubna]], Russia, in 1965 in several reactions, one of which included irradiation of <sup>243</sup>Am with <sup>15</sup>N ions. Besides, one of the synthesis reactions for [[lawrencium]], discovered by scientists at Berkeley and Dubna, included bombardment of <sup>243</sup>Am with <sup>18</sup>O.<ref name="g1252" />
===Spectrometer===
Americium-241 has been used as a portable source of both gamma rays and alpha particles for a number of medical and industrial uses. The 59.5409&nbsp;keV gamma ray emissions from <sup>241</sup>Am in such sources can be used for indirect analysis of materials in [[radiography]] and [[X-ray fluorescence]] spectroscopy, as well as for quality control in fixed [[nuclear density gauge]]s and [[nuclear densometer]]s. For example, the element has been employed to gauge [[glass]] thickness to help create flat glass.<ref name="g1262" /> Americium-241 is also suitable for calibration of gamma-ray spectrometers in the low-energy range, since its spectrum consists of nearly a single peak and negligible Compton continuum (at least three orders of magnitude lower intensity).<ref>[http://www.nndc.bnl.gov/nudat2/indx_dec.jsp Nuclear Data Viewer 2.4] {{Webarchive|url=https://web.archive.org/web/20170601010723/http://www.nndc.bnl.gov/nudat2/indx_dec.jsp |date=1 June 2017 }}, NNDC</ref> Americium-241 gamma rays were also used to provide passive diagnosis of thyroid function. This medical application is however obsolete.
==Health concerns==
As a highly radioactive element, americium and its compounds must be handled only in an appropriate laboratory under special arrangements. Although most americium isotopes predominantly emit alpha particles which can be blocked by thin layers of common materials, many of the daughter products emit gamma-rays and neutrons which have a long penetration depth.<ref>[https://web.archive.org/web/20120315061533/http://www.atsdr.cdc.gov/phs/phs.asp?id=809&tid=158 Public Health Statement for Americium] Section 1.5., Agency for Toxic Substances and Disease Registry, April 2004, Retrieved 28 November 2010</ref>
If consumed, most of the americium is excreted within a few days, with only 0.05% absorbed in the blood, of which roughly 45% goes to the [[liver]] and 45% to the bones, and the remaining 10% is excreted. The uptake to the liver depends on the individual and increases with age. In the bones, americium is first deposited over [[Cortex (anatomy)|cortical]] and [[trabecula]]r surfaces and slowly redistributes over the bone with time. The biological half-life of <sup>241</sup>Am is 50 years in the bones and 20 years in the liver, whereas in the [[gonad]]s (testicles and ovaries) it remains permanently; in all these organs, americium promotes formation of cancer cells as a result of its radioactivity.<ref name="am" /><ref>{{cite web|url=http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-pdf/fs23am241.pdf|author=Division of Environmental Health, Office of Radiation Protection|title=Fact Sheet # 23. Americium-241|date=November 2002|access-date=28 November 2010|archive-url=https://web.archive.org/web/20101111125906/http://www.doh.wa.gov/ehp/rp/factsheets/factsheets-pdf/fs23am241.pdf|archive-date=11 November 2010|url-status=dead}}</ref><ref>Frisch, Franz ''Crystal Clear, 100 x energy'', Bibliographisches Institut AG, Mannheim 1977, {{ISBN|3-411-01704-X}}, p. 184</ref>
Americium often enters landfills from discarded [[smoke detector]]s. The rules associated with the disposal of smoke detectors are relaxed in most jurisdictions. In 1994, 17-year-old [[David Hahn]] extracted the americium from about 100 smoke detectors in an attempt to build a breeder nuclear reactor.<ref name="Silverstein2005">[[Ken Silverstein]], [https://harpers.org/archive/1998/11/the-radioactive-boy-scout/ The Radioactive Boy Scout: When a teenager attempts to build a breeder reactor]. ''[[Harper's Magazine]]'', November 1998</ref><ref>{{cite news |publisher=[[Fox News]] |url=http://www.foxnews.com/story/0,2933,292111,00.html |title='Radioactive Boy Scout' Charged in Smoke Detector Theft |date=4 August 2007 |access-date=28 November 2007 |archive-url=https://web.archive.org/web/20071208062559/http://www.foxnews.com/story/0%2C2933%2C292111%2C00.html |archive-date=8 December 2007 |url-status=dead}}</ref><ref>{{cite news|work=Detroit Free Press |url=http://www.freep.com/apps/pbcs.dll/article?AID=/20070827/BUSINESS05/70827091 |title=Man dubbed 'Radioactive Boy Scout' pleads guilty |date=27 August 2007 |agency=Associated Press |access-date=27 August 2007 |archive-url=https://web.archive.org/web/20070929095926/http://www.freep.com/apps/pbcs.dll/article?AID=%2F20070827%2FBUSINESS05%2F70827091 |archive-date=29 September 2007 |url-status=dead }}</ref><ref>{{cite news |publisher=[[Fox News]] |url=https://www.foxnews.com/story/radioactive-boy-scout-sentenced-to-90-days-for-stealing-smoke-detectors |title='Radioactive Boy Scout' Sentenced to 90 Days for Stealing Smoke Detectors |date=4 October 2007 |access-date=28 November 2007 |archive-url=https://web.archive.org/web/20071113123408/http://www.foxnews.com/story/0%2C2933%2C299362%2C00.html |archive-date=13 November 2007 |url-status=live}}</ref> There have been a few cases of exposure to americium, the worst case being that of [[Chemical technologist|chemical operations technician]] [[Harold McCluskey]], who at the age of 64 was exposed to 500 times the occupational standard for americium-241 as a result of an explosion in his lab. McCluskey died at the age of 75 of unrelated pre-existing disease.<ref name="tristateherald">{{cite news|first=Annette |last=Cary |title=Doctor remembers Hanford's 'Atomic Man' |newspaper=Tri-City Herald |url=http://www.hanfordnews.com/news/2008/story/11403.html |date=25 April 2008 |access-date=17 June 2008 |url-status=dead |archive-url=https://web.archive.org/web/20100210232231/http://www.hanfordnews.com/news/2008/story/11403.html |archive-date=10 February 2010}}</ref><ref>{{cite news|author=AP wire |title=Hanford nuclear workers enter site of worst contamination accident |url=http://www.billingsgazette.com/index.php?id=1&display=rednews/2005/06/03/build/nation/94-contamination.inc |date=3 June 2005 |access-date=17 June 2007 |archive-url=https://web.archive.org/web/20071013185723/http://www.billingsgazette.com/newdex.php?display=rednews%2F2005%2F06%2F03%2Fbuild%2Fnation%2F94-contamination.inc |archive-date=13 October 2007 |url-status=dead }}</ref>
==See also==
* [[Actinides in the environment]]
* [[:Category:Americium compounds]]
==Notes==
{{Reflist|group=note}}
==References==
{{Reflist|30em}}
==Bibliography==
* {{Greenwood&Earnshaw2nd}}
* 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
* {{cite book| last = Wiberg| first = Nils| title = Lehrbuch Der Anorganischen Chemie| date = 2007| publisher = De Gruyter| isbn = 978-3-11-017770-1 }}
==Further reading==
* ''Nuclides and Isotopes – 14th Edition'', GE Nuclear Energy, 1989.
* {{cite web|url = http://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_30.html|title = Can the minor actinide, americium-241, be transmuted by thermal neutrons?|author = Fioni, Gabriele|author2 = Cribier, Michel|author3 = Marie, Frédéric|name-list-style = amp|publisher = [[Commissariat à l'énergie atomique]]|url-status = dead|archive-url = https://web.archive.org/web/20071111175005/http://www.cea.fr/var/cea/storage/static/gb/library/Clefs46/pagesg/clefs46_30.html|archive-date = 11 November 2007}}
* {{cite book| last = Stwertka| first = Albert| title = A Guide to the Elements| url = https://archive.org/details/guidetoelements00stwe| url-access = registration| date = 1999| publisher = Oxford University Press, USA| isbn = 978-0-19-508083-4 }}
==External links==
{{Commons}}
{{Wiktionary|americium}}
* [http://www.periodicvideos.com/videos/095.htm Americium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://web.archive.org/web/20060830050012/http://www.atsdr.cdc.gov/toxprofiles/phs156.html ATSDR – Public Health Statement: Americium]
* [https://web.archive.org/web/20081224123105/http://www.world-nuclear.org/info/inf57.html World Nuclear Association – Smoke Detectors and Americium ]
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{{Americium compounds}}
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[[Category:Americium| ]]
[[Category:Chemical elements]]
[[Category:Chemical elements with double hexagonal close-packed structure]]
[[Category:Actinides]]
[[Category:Carcinogens]]
[[Category:Synthetic elements]]