AskDefine | Define americium

Dictionary Definition

americium n : a radioactive transuranic metallic element; discovered by bombarding uranium with helium atoms [syn: Am, atomic number 95]

User Contributed Dictionary

see Americium

English

Etymology

From America + -ium, by analogy with europium.

Noun

  1. The chemical element (symbol Am) with an atomic number of 95.

Related terms

Translations

chemical element with atomic number 95

External links

For etymology and more information refer to: http://elements.vanderkrogt.net/elem/am.html (A lot of the translations were taken from that site with permission from the author)

Extensive Definition

Americium () is a synthetic element that has the symbol Am and atomic number 95. A radioactive metallic element, americium is an actinide that was obtained in 1944 by bombarding plutonium with neutrons and was the fourth transuranic element to be discovered. It was named for the Americas, by analogy with europium.

Properties

Pure americium has a silvery and white lustre. At room temperatures 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 rays 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.

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 is the only synthetic element to have 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 as well as a neutron emitting radioactive source used in well logging applications (Am241Be). It has also been cited for use as an advanced nuclear rocket propulsion fuel. This isotope is, however, extremely expensive to produce in usable quantities.

History

Americium was 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 239Pu 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." The discovery of americium and curium was first announced informally on a children's quiz show in 1945.

Isotopes

left|150px|thumb|Sample of Americium18 radioisotopes 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 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 states, with the most stable being 242mAm (t½ 141 years). The isotopes of americium range in atomic weight from 231.046 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 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.
Americium, unlike uranium, does not readily form a dioxide americyl core (AmO2). 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.

Further reading

  • Nuclides and Isotopes - 14th Edition, GE Nuclear Energy, 1989.
  • Patent

External links

americium in Afrikaans: Amerikium
americium in Arabic: أمريكيوم
americium in Bengali: অ্যামেরিসিয়াম
americium in Belarusian: Амерыцый
americium in Bosnian: Americijum
americium in Catalan: Americi
americium in Czech: Americium
americium in Corsican: Americiu
americium in Danish: Americium
americium in German: Americium
americium in Estonian: Ameriitsium
americium in Modern Greek (1453-): Αμερίκιο
americium in Spanish: Americio
americium in Esperanto: Americio
americium in Basque: Amerizio
americium in Persian: امریسیوم
americium in French: Américium
americium in Friulian: Americi
americium in Manx: Americium
americium in Galician: Americio
americium in Korean: 아메리슘
americium in Armenian: Ամերիցիում
americium in Croatian: Americij
americium in Ido: Americio
americium in Italian: Americio
americium in Hebrew: אמריציום
americium in Javanese: Amerisium
americium in Haitian: Amerisyòm
americium in Latin: Americium
americium in Latvian: Amerīcijs
americium in Luxembourgish: Americium
americium in Lithuanian: Americis
americium in Lojban: merjinme
americium in Hungarian: Amerícium
americium in Malayalam: അമെരിസിയം
americium in Mongolian: Америци
americium in Dutch: Americium
americium in Japanese: アメリシウム
americium in Norwegian: Americium
americium in Norwegian Nynorsk: Americium
americium in Polish: Ameryk
americium in Portuguese: Amerício
americium in Romanian: Americiu
americium in Russian: Америций
americium in Sicilian: Americiu
americium in Simple English: Americium
americium in Slovak: Amerícium
americium in Slovenian: Americij
americium in Serbian: Америцијум
americium in Serbo-Croatian: Americijum
americium in Saterfriesisch: Americium
americium in Finnish: Amerikium
americium in Swedish: Americium
americium in Thai: อะเมริเซียม
americium in Turkish: Amerikyum
americium in Ukrainian: Америцій
americium in Chinese: 镅
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