Americium



95 curium
Eu
↑
Am
↓
(Uqp)
General
Number americium, Am, 95
actinides
Block f
Appearance silvery white sometimes yellow
Standard atomic weight (243)  g·mol−1
Rn] 5f7 7s2
shell 2, 8, 18, 32, 25, 8, 2
Physical properties
Phase solid
r.t.) 12  g·cm−3
F)
F)
kJ·mol−1
Heat capacity (25 °C) 62.7  J·mol−1·K−1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1239 1356        
Atomic properties
Crystal structure hexagonal
amphoteric oxide)
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 578 kJ/mol
Atomic radius 175  pm
Miscellaneous
Magnetic ordering no data
Thermal conductivity (300 K) 10  W·m−1·K−1
CAS registry number 7440-35-9
Selected isotopes
Main article: Isotopes of americium
iso NA half-life DM DE (MeV) DP
241Am syn 432.2 y SF - -
α 5.638 237Np
242mAm syn 141 y IT 0.049 -
α 5.637 238Np
SF - -
243Am syn 7370 y SF - -
α 5.438 239Np
References

Americium (europium.

Properties

Main article: Actinides in the environment

Pure americium has a silvery and white 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 uranium isotopes.[1]

Applications

This element can be produced 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.[2] This isotope is, however, extremely expensive to produce in usable quantities.

History

Americium was curium was first announced informally on a children's quiz show in 1945.[4]

Isotopes

Main article: isotopes of americium

 18 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 nuclear fuel.

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

Americium dioxide is used in smoke detectors.[5]

Americium, unlike uranium, does not readily form a dioxide americyl core (AmO2).[6] 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 triazines and other compounds were studied as potential extraction agents.[7][8][9][10][11]

References

  • WebElements.com - Americium
  1. ^ Fissile Materials & Nuclear Weapons: Introduction. International Panel on Fissile Materials. Retrieved on 2007-11-22.
  2. ^ "Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks", ScienceDaily, 3 Jan 2001. Retrieved on 2007-11-22. 
  3. ^ U.S. Patent 3,156,523 
  4. ^ Rachel Sheremeta Pepling. It's Elemental: The Periodic Table: Americium. Chemical & Engineering News.
  5. ^ [1]
  6. ^ David L. Clark (2000). "The Chemical Complexities of Plutonium" (Reprinted at fas.org). Los Alamos Science (26).
  7. ^ Michael J. Hudson, Michael G. B. Drew, Mark R. StJ. Foreman, Clément Hill, Nathalie Huet, Charles Madic and Tristan G. A. Youngs (2003). "The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanide(III) elements – implications for the partitioning of americium(III)". Dalton Trans.: 1675 - 1685. doi:10.1039/b301178j.
  8. ^ Andreas Geist, Michael Weigl, Udo Müllich, Klaus Gompper (11-13 Dec 2000). [http://www.nea.fr/html/pt/docs/iem/madrid00/Paper14.pdf Actinide(III)/Lanthanide(III) Partitioning Using n-Pr-BTP as Extractant: Extraction Kinetics and Extraction Test in a Hollow Fiber Module]. 6th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation. OECD Nuclear Energy Agency.
  9. ^ Sanex-BTP Process Development Studies. Atalante 2000: Scientific Research on the Back-end of the Fuel Cycle for the 21st Century. Commissariat à l'énergie atomique (24-26 Oct 2000 author = C. Hill, D. Guillaneux, X. Hérès, N. Boubals and L. Ramain).
  10. ^ Andreas Geist, Michael Weigl and Klaus Gompper (14-16 Oct 2002). Effective Actinide(III)-Lanthanide(III) Separation in Miniature Hollow Fibre Modules. 7th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation. OECD Nuclear Energy Agency.
  11. ^ D.D. Ensor. Separation Studies of f-Elements. Tennessee Tech University.

Further reading

  • Nuclides and Isotopes - 14th Edition, GE Nuclear Energy, 1989.
  • Patent US3,156,523 (PDF version) (1964-11-10) Glenn T. Seaborg Element 95 and Method of Producing Said Element 
  • Gabriele Fioni, Michel Cribier and Frédéric Marie. Can the minor actinide, americium-241, be transmuted by thermal neutrons?. Commissariat à l'énergie atomique.
  • Terry Kammash, David L. Galbraith, and Ta-Rong Jan (January 10, 1993). "An americium-fueled gas core nuclear rocket" in Tenth symposium on space nuclear power and propulsion. AIP Conf. Proc. 271: 585-589. DOI:10.1063/1.43073. 
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Americium". A list of authors is available in Wikipedia.