   #copyright

Americium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


              95               plutonium ← americium → curium
              Eu
             ↑
             Am
             ↓
             (Uqp)

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number americium, Am, 95
                                                 Chemical series actinides
                                            Group, Period, Block n/a, 7, f
                                                  Appearance silvery white
                                                   Atomic mass (243) g/mol
                                     Electron configuration [Rn] 5f^7 7s^2
                                Electrons per shell 2, 8, 18, 32, 25, 8, 2
                                                       Physical properties
                                                               Phase solid
                                         Density (near r.t.) 12 g·cm^−3
                                                     Melting point 1449  K
                                                    (1176 ° C, 2149 ° F)
                                                      Boiling point 2880 K
                                                    (2607 ° C, 4725 ° F)
                                         Heat of fusion 14.39 kJ·mol^−1
                           Heat capacity (25 °C) 62.7 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                        P/Pa   1    10  100 1 k 10 k 100 k
                                       at T/K 1239 1356

                                                         Atomic properties
                                               Crystal structure hexagonal
                                               Oxidation states 6, 5, 4, 3
                                                       ( 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

                CAPTION: Main article: Isotopes of americium

                                  iso    NA  half-life DM DE ( MeV)   DP
                                ^241Am   syn 432.2 y   SF -         -
                                                       α  5.638     ^237Np
                                ^242 mAm syn 141 y     IT 0.049     -
                                                       α  5.637     ^238Np
                                                       SF -         -
                                ^243Am   syn 7370 y    SF -         -
                                                       α  5.438     ^239Np

                                                                References

   Americium ( IPA: /ˌaməˈrɪsiəm/) 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 poop poop 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.

   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.

   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
   (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.
   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 (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 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

   Sample of Americium
   Enlarge
   Sample of Americium

   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 (t[½] 141 years). The
   isotopes of americium range in atomic weight from 231.046 amu (^231Am)
   to 249.078 amu (^249Am).

Chemistry

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

   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
   (AmO[2]) , this is because americium is very hard to oxidise above 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 moieties (OH^-, NO[2]^-, NO[3]^-, and SO[4]^-2) to form
   charged complexes which tend to be readily mobile with low affinities
   to soil.
     * AmO[2](OH)^+1
     * AmO[2](OH)[2]^+2
     * AmO[2](CO[3])[1]^+1
     * AmO[2](CO[3])[2]^-1
     * AmO[2](CO[3])[3]^-3

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