Americium
Americium is a synthetic element in the periodic table that has the symbol Am and atomic number 95. A
radioactive metallic element, americium is an
actinide that was obtained by bombarding
plutonium with
neutrons and was the fourth
transuranic element to be discovered. It was named for the
Americas, by analogy with europium.
Encyclopedia
Americium is a synthetic element in the periodic table that has the symbol
Am and atomic number 95. A
radioactive metallic element, americium is an
actinide that was obtained by bombarding
plutonium with
neutrons and was the fourth
transuranic element to be discovered. It was named for the
Americas, by analogy with europium.
Notable characteristics
Freshly prepared americium
metal has a white and silvery 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.
Please see Actinides in the environment for details of the environmental aspects of this element.Applications
This element can be produced in
kilogram amounts and has some uses . Americium has found its way into the household, where one type of
smoke detector contains a tiny amount 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. However this isotope is extremely expensive to produce in usable quantities.
History
Americium was first synthesized 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 . 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
patent 3,156,523 for "Element 95 and Method of Producing Said Element". The discovery of americium and curium was first announced informally on a children's quiz show in 1945.
Isotopes
18
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 . The isotopes of americium range in atomic weight from 231.046 amu to 249.078 amu .
Chemistry
In aqueous systems the most common oxidation state is +3, it is very much harder to oxidise Am to Am than it is to do the same oxidation for Pu.
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 unlike uranium does not readily form a dioxide americyl core , this is because americium is very hard to oxidise about the +3 oxidation state when it is in an aqeuous solution. In the environment, this americyl core could complex with carbonate as well as other oxygen moeities to form charged complexes which tend to be readily mobile with low affinities to soil.
- AmO2+1
- AmO22+2
- AmO21+1
- AmO22-1
- AmO23-3
References
- Guide to the Elements - Revised Edition, Albert Stwertka, ISBN 0-19-508083-1
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External links
