{{Elementbox_header | number=95 | symbol=Am | name=americium | left=[[plutonium]] | right=[[curium]] | above=[[europium|Eu]] | below=(Uqp) | color1=#ff99cc | color2=black }}
{{Elementbox_series | [[actinide]]s }}
{{Elementbox_periodblock | period=7 | block=f }}
{{Elementbox_appearance | silvery white sometimes yellow }}
{{Elementbox_atomicmass_gpm | [[1 E-25 kg|(243)]] }}
{{Elementbox_econfig | [[[radon|Rn]]] 5f⁷ 7s² }}
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{{Elementbox_phase | [[solid]] }}
{{Elementbox_density_gpcm3nrt | 12 }}
{{Elementbox_meltingpoint | k=1449 | c=1176 | f=2149 }}
{{Elementbox_boilingpoint | k=2880 | c=2607 | f=4725 }}
{{Elementbox_heatfusion_kjpmol | 14.39 }}
{{Elementbox_heatcapacity_jpmolkat25 | 62.7 }}
{{Elementbox_vaporpressure_katpa | 1239 | 1356 |   |   |   |   | comment= }}
{{Elementbox_section_atomicprop | color1=#ff99cc | color2=black }}
{{Elementbox_crystalstruct | hexagonal }}
{{Elementbox_oxistates | 6, 5, 4, '''3'''<br />([[amphoteric]] oxide) }}
{{Elementbox_electroneg_pauling | 1.3 }}
{{Elementbox_ionizationenergies1 | 578 }}
{{Elementbox_atomicradius_pm | [[1 E-10 m|175]] }}
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{{Elementbox_magnetic | no data }}
{{Elementbox_thermalcond_wpmkat300k | 10 }}
{{Elementbox_cas_number | 7440-35-9 }}
{{Elementbox_isotopes_begin | color1=#ff99cc | color2=black }}
{{Elementbox_isotopes_decay2 | mn=241 | sym=Am
| na=[[synthetic radioisotope|syn]] | hl=[[1 E10 s|432.2 y]]
| dm1=[[spontaneous fission|SF]] | de1=- | pn1= | ps1=-
| dm2=[[alpha decay|α]] | de2=5.638 | pn2=237 | ps2=[[neptunium|Np]] }}
{{Elementbox_isotopes_decay3 | mn=242[[nuclear isomer|m]] | sym=Am
| na=[[synthetic radioisotope|syn]] | hl=141 [[year|y]]
| dm1=[[Isomeric transition|IT]] | de1=0.049 | pn1= | ps1=-
| dm2=α | de2=5.637 | pn2=238 | ps2=[[neptunium|Np]]
| dm3=SF | de3=- | pn3= | ps3=- }}
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| na=[[synthetic radioisotope|syn]] | hl=[[1 E11 s|7370 y]]
| dm1=SF | de1=- | pn1= | ps1=-
| dm2=α | de2=5.438 | pn2=239 | ps2=[[neptunium|Np]] }}
{{Elementbox_isotopes_end}}
{{Elementbox_footer | color1=#ff99cc | color2=black }}

'''Americium''' ({{pronEng|ˌæməˈrɪsiəm}}) is a [[synthetic element]] that has the symbol '''Am''' and [[atomic number]] 95. A [[radioactive decay|radioactive]] [[metal]]lic element, americium is an [[actinide]] that was obtained in 1944 by bombarding [[plutonium]] with [[neutron]]s and was the fourth [[transuranic element]] to be discovered. It was named for the [[Americas]], by analogy with [[europium]].

== Properties ==
{{main|Actinides in the environment}}
Pure americium has a silvery and white [[Lustre (mineralogy)|lustre]]. At [[room temperature]]s it slowly tarnishes in dry air. It is more silvery than [[plutonium]] or [[neptunium]] and apparently more malleable than neptunium or [[uranium]]. [[Alpha emission]] from ²⁴¹Am is approximately three times that of [[radium]]. [[Gram]] quantities of ²⁴¹Am emit intense [[gamma ray]]s which creates a serious exposure problem for anyone handling the element.

Americium is also [[fissile]]; the critical mass for an unreflected sphere of ²⁴¹Am is approximately 60 kilograms. It is unlikely that Americium would be used as a weapons material, as its minimum critical mass is considerably larger than more readily obtained [[plutonium]] or [[uranium]] isotopes.<ref>{{cite web | publisher = International Panel on Fissile Materials | title = Fissile Materials & Nuclear Weapons: Introduction | url = http://www.fissilematerials.org/ipfm/pages_us_en/fissile/fissile/fissile.php | accessdate = 2007-11-22}}</ref>

== Applications ==
This element can be produced in [[kilogram]] amounts and has some uses (mostly ²⁴¹Am since it is easier to produce relatively pure samples of this isotope). Americium has found its way into the household, where one type of [[smoke detector]] contains a tiny amount (about 0.2 [[microgram]]) of ²⁴¹Am as a source of [[ionizing radiation]]. ²⁴¹Am has been used as a portable gamma ray source for use in [[radiography]]. The element has also been employed to gauge [[glass]] thickness to help create flat glass. ²⁴²Am is a neutron emitter and has found uses in [[neutron radiography]]. It has also been cited for use as an advanced nuclear rocket propulsion fuel.<ref>{{cite news | title = Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks | publisher = [[ScienceDaily]] | date = 3 Jan 2001 | url = http://www.sciencedaily.com/releases/2001/01/010103073253.htm | accessdate = 2007-11-22}}</ref> This isotope is, however, extremely expensive to produce in usable quantities.

== History ==
Americium was [[discovery of the chemical elements|first isolated]] by [[Glenn T. Seaborg]], Leon O. Morgan, Ralph A. James, and [[Albert Ghiorso]] in late [[1944]] at the wartime Metallurgical Laboratory at the [[University of Chicago]] (now known as [[Argonne National Laboratory]]). The team created the [[isotope]] ²⁴¹Am by subjecting ²³⁹[[plutonium|Pu]] to successive [[neutron capture]] reactions in a [[nuclear reactor]]. This created ²⁴⁰Pu and then ²⁴¹Pu which in turn decayed into ²⁴¹Am via [[beta decay]]. Seaborg was granted a patent for "Element 95 and Method of Producing Said Element," whose unusually terse claim number 1 reads simply, "Element 95."<ref>{{US patent|3156523}}</ref> The discovery of americium and [[curium]] was first announced informally on a children's quiz show in 1945.<ref>{{cite web | title = It's Elemental: The Periodic Table: Americium | author = Rachel Sheremeta Pepling | publisher = [[Chemical & Engineering News]] | url = http://pubs.acs.org/cen/80th/print/americiumprint.html}}</ref>

== Isotopes ==<!-- This section is linked from [[Alpha decay]] -->
{{main|isotopes of americium}}
[[Image:Americium.jpg|left|150px|thumb|Sample of Americium]]18 [[radioisotope]]s of americium have been characterized, with the most stable being ²⁴³Am with a [[half-life]] of 7370 years, and ²⁴¹Am with a half-life of 432.2 years. All of the remaining [[radioactive decay|radioactive]] isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 [[meta state]]s, with the most stable being ^242mAm (t_½ 141 years). The isotopes of americium range in [[atomic weight]] from 231.046 [[atomic mass unit|u]] (²³¹Am) to 249.078 u (²⁴⁹Am).

== Chemistry ==

In aqueous systems the most common oxidation state is +3. It is very much harder to oxidize Am(III) to Am(IV) than it is to oxidise Pu(III) to Pu(IV).

Currently the [[solvent extraction]] chemistry of americium is important as in several areas of the world [[scientists]] are working on reducing the medium term [[Ionizing radiation|radiotoxicity]] of the waste from the reprocessing of used [[nuclear fuel]].

See [[liquid-liquid extraction]] for some examples of the solvent extraction of americium.

Americium dioxide is used in smoke detectors.<ref>[http://www.uic.com.au/nip35.htm]</ref>

Americium, unlike uranium, does not readily form a dioxide americyl core (AmO₂).<ref>{{cite journal | journal = Los Alamos Science | format = Reprinted at fas.org | title = The Chemical Complexities of Plutonium | author = David L. Clark | issue = 26 | year = 2000 | url = http://fas.org/sgp/othergov/doe/lanl/pubs/00818038.pdf}}</ref> This is because americium is very hard to oxidise above the +3 oxidation state when it is in an aqueous solution. In the environment, this americyl core could complex with carbonate as well as other oxygen moieties (OH^-, NO₂^-, NO₃^-, and SO₄^-2) to form charged complexes which tend to be readily mobile with low affinities to soil.

*AmO₂(OH)⁺¹
*AmO₂(OH)₂⁺²
*AmO₂CO₃⁺¹
*AmO₂(CO₃)₂^-1
*AmO₂(CO₃)₃^-3

A large amount of work has been done on the [[solvent extraction]] of americium, as it is the case that americium and the other transplutonium elements are responsible for the majority of the long lived radiotoxicity of [[spent nuclear fuel]]. It is thought that by removal of the americium and [[curium]] that the used fuel will only need to be isolated from man and his environment for a shorter time than that required for the isolation of untreated used fuel. One recent [[EU]] funded project on this topic was known by the codename "EUROPART". Within this project [[triazines]] and other compounds were studied as potential extraction agents.<ref>{{cite journal | journal = [[Dalton Trans.]] | year = 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 = Michael J. Hudson, Michael G. B. Drew, Mark R. StJ. Foreman, Clément Hill, Nathalie Huet, Charles Madic and Tristan G. A. Youngs}}
</ref><ref>{{cite web | author = Andreas Geist, Michael Weigl, Udo Müllich, Klaus Gompper |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 Dec 2000 | url = http://www.nea.fr/html/pt/docs/iem/madrid00/Paper14.pdf}}</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 Oct 2000
author = C. Hill, D. Guillaneux, X. Hérès, N. Boubals and L. Ramain}}</ref><ref>{{cite web | title = Effective Actinide(III)-Lanthanide(III) Separation in Miniature Hollow Fibre Modules | author =
Andreas Geist, Michael Weigl and Klaus Gompper | 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 Oct 2002 | publisher = [[OECD Nuclear Energy Agency]]}}</ref><ref>{{cite web | title = Separation Studies of ''f''-Elements | author = D.D. Ensor | publisher = [[Tennessee Tech University]] | url = http://www.tntech.edu/WRC/pdfs/Projects04_05/Ens_Elem.pdf}}</ref>

==References==
* [http://www.webelements.com/webelements/elements/text/Am/index.html WebElements.com - Americium]
<references/>

==Further reading==
*''Nuclides and Isotopes - 14th Edition'', GE Nuclear Energy, 1989.
*Patent {{US patent reference
| number = 3156523
| y = 1964
| m = 11
| d = 10
| inventor = Glenn T. Seaborg
| title = Element 95 and Method of Producing Said Element
}}
* {{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 = Gabriele Fioni, Michel Cribier and Frédéric Marie | publisher = [[Commissariat à l'énergie atomique]]}}
* {{cite conference | title = An americium-fueled gas core nuclear rocket | booktitle = AIP Conf. Proc. | date = January 10, 1993 | volume = 271 | pages = 585-589 | conference = Tenth symposium on space nuclear power and propulsion | author = Terry Kammash, David L. Galbraith, and Ta-Rong Jan | doi = 10.1063/1.43073}}

==External links==
*[http://periodic.lanl.gov/elements/95.html Los Alamos National Laboratory - Americium]
*''Guide to the Elements - Revised Edition'', Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
* [http://education.jlab.org/itselemental/ele095.html It's Elemental - Americium]
*[http://www.atsdr.cdc.gov/toxprofiles/phs156.html ATSDR - Public Health Statement: Americium]

{{Commons|Americium}}
{{wiktionary|americium}}


[[Category:Actinides]]
[[Category:Americium]]
[[Category:Carcinogens]]

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