Curium

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96 americiumcuriumberkelium
Gd

Cm

(Uqh)
Cm-TableImage.png
General
Name, Symbol, Number curium, Cm, 96
Chemical series actinides
Group, Period, Block n/a, 7, f
Appearance silvery
Atomic mass (247) g/mol
Electron configuration [Rn] 5f7 6d1 7s2
Electrons per shell 2, 8, 18, 32, 25, 9, 2
Physical properties
Phase solid
Density (near r.t.) 13.51 g/cm³
Melting point 1613 K
(1340 °C, 2444 °F)
Boiling point 3383 K
(3110 °C, 5630 °F)
Heat of fusion  ? 15 kJ/mol
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1788 1982        
Atomic properties
Crystal structure hexagonal close-packed
Oxidation states 3
(amphoteric oxide)
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 581 kJ/mol
Miscellaneous
Magnetic ordering no data
CAS registry number 7440-51-9
Notable isotopes
Main article: Isotopes of curium
iso NA half-life DM DE (MeV) DP
242Cm syn 160 days SF - -
α 6.1 238Pu
243Cm syn 29.1 y α 6.169 239Pu
ε 0.009 243Am
SF - -
244Cm syn 18.1 y SF - -
α 5.902 240Pu
245Cm syn 8500 y SF - -
α 5.623 241Pu
246Cm syn 4730 y α 5.475 242Pu
SF - -
247Cm syn 1.56×107 y α 5.353 243Pu
248Cm syn 3.40×105 y α 5.162 244Pu
SF - -
250Cm syn 9000 y SF - -
α 5.169 246Pu
β- 0.037 250Bk

Curium (chemical symbol Cm, atomic number 96) is a radioactive, metallic, transuranic element[1] of the actinide series. It is produced synthetically by bombarding plutonium with alpha particles (helium ions). It was named after Marie Curie and her husband Pierre.

Two isotopes of curium (curium-242 and curium-244) can be produced in multigram amounts, making it feasible to study the element's chemical properties. The isotope curium-242 is the precursor to plutonium-238, the most common fuel for radioisotope thermoelectric generators (RTGs) that have been used to power certain space probes. Other curium isotopes (Cu-243, Cu-244) are also being investigated for their potential as fuels for RTGs.

Contents

History

Curium was first synthesized at the University of California, Berkeley by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944. The team named the new element after Marie Curie and her husband Pierre, who are famous for their work on radioactivity and the discovery of radium and polonium.

Curium was the third transuranic element to be discovered. The isotope curium-242 (half-life 163 days) was made by bombarding a plutonium-239 target with alpha particles in the 60-inch cyclotron at Berkeley. The element was chemically identified at the Metallurgical Laboratory (now Argonne National Laboratory) at the University of Chicago.

Louis Werner and Isadore Perlman created a visible sample of curium-242 hydroxide at the University of California in 1947 by bombarding americium-241 with neutrons. The elemental form of curium was prepared for the first time in 1951.

Notable characteristics

Curium is an inner transition metal of the actinide series, located in period seven of the periodic table, between americium and berkelium. It does not occur in nature.

The isotope curium-248 has been synthesized only in milligram quantities, but curium-242 and curium-244 are made in multigram amounts, which allows for the determination of some of the element's properties. Curium-244 can be made in quantity by subjecting plutonium to neutron bombardment.

A rare earth homolog, curium is somewhat chemically similar to gadolinium but with a more complex crystal structure. Chemically reactive, its metal is silvery-white in color and the element is more electropositive than aluminum (most trivalent curium compounds are slightly yellow).

Isotopes

Many radioisotopes of curium have been characterized, with the most stable being Cm-247, with a half-life of 1.56 × 107 years; Cm-248, with a half-life of 3.40 × 105 years; Cm-250, with a half-life of 9000 years; and Cm-245, with a half-life of 8500 years. All the remaining radioactive isotopes have half-lives of less than 30 years, and the majority of these have half-lives that are less than 33 days. This element also has four meta states, with the most stable being Cm-244m (t½ 34 ms). The isotopes of curium range in atomic weight from 233.051 amu (Cm-233) to 252.085 amu (Cm-252).

Compounds

Known compounds of curium include the following:

  • Oxides:
    • curium dioxide (CmO2)
    • curium trioxide (Cm2O3)
  • Halides:
    • curium tetrafluoride (CmF4)
    • curium chloride (CmCl3)
    • curium bromide (CmBr3)
    • curium iodide (CmI3)

Applications

Curium has been studied extensively as a potential fuel for Radioisotope thermoelectric generators that could be used to power space probes. Curium-242 can generate up to 120 watts of thermal energy per gram (W/g). Its very short half-life, however, makes it unsuitable as a power source for long-term use. Curium-242 is the precursor to plutonium-238, which is the most common fuel for RTGs. Curium-244 has also been studied as an energy source for RTGs having a maximum energy density about three W/g, but produces a large amount of neutron radiation from spontaneous fission. Curium-243, with a roughly 30-year half-life and good energy density (about 1.6 W/g), would seem to make an ideal fuel, but it produces significant amounts of gamma and beta radiation from radioactive decay products.

Nuclear fuel cycle

If MOX nuclear fuel[2] is to be used in nuclear power reactors, it should contain little or no curium, because neutron activation of this element will create californium, a strong neutron emitter. The californium would pollute the back end of the fuel cycle and increase the dose to workers.

Biological effects

Curium bio-accumulates in bone tissue where its radiation destroys bone marrow and thus stops the production of red blood cells.

See also

Notes

  1. "Transuranic elements" are the chemical elements with atomic numbers greater than that of uranium (atomic number 92).
  2. "MOX" (mixed oxide) nuclear fuel is a blend of plutonium with natural uranium, reprocessed uranium, or depleted uranium. Its behavior is similar to that of low enriched uranium (LEU) fuel, and it is an alternative to the LEU used in the light water reactors that predominate nuclear power generation.

References

  • Emsley, John. 2001. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford Univ. Press. ISBN 0198503407
  • Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann. ISBN 0750633654
  • Hampel, Clifford A. 1968. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp. ISBN 0442155980
  • Morss, Lester R., Norman M. Edelstein, and Jean Fuger, eds. 2006. The Chemistry of the Actinide and Transactinide Elements. 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer. ISBN 1402035551
  • Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford: Oxford University Press. ISBN 0-19-508083-1

External links

  • Chemistry Operations. 2003. Curium Los Alamos National Laboratory, Chemistry Division. Retrieved December 22, 2007.
  • Thomas Jefferson National Accelerator Facility, Office of Science Education. 2007. It's Elemental: Curium Jefferson Lab. Retrieved December 22, 2007.
  • Human Health Fact Sheet. 2005. Curium Argonne National Laboratory. Retrieved December 22, 2007.
  • Winter, Mark. 2007. Curium. The University of Sheffield and WebElements Ltd. Retrieved December 22, 2007.
  • Hazardous Substances Data Bank. 2007. Curium, Radioactive TOXNET, National Library of Medicine. Retrieved December 22, 2007.

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