   #copyright

Curium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


              96               americium ← curium → berkelium
              Gd
             ↑
             Cm
             ↓
             (Uqh)

                                  Periodic Table - Extended Periodic Table

                                                                   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] 5f^7 6d^1 7s^2
                                Electrons per shell 2, 8, 18, 32, 25, 9, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 13.51 g·cm^−3
                                                     Melting point 1613  K
                                                    (1340 ° C, 2444 ° F)
                                                      Boiling point 3383 K
                                                    (3110 ° C, 5630 ° F)
                                         Heat of fusion  ? 15 kJ·mol^−1

   CAPTION: 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
                                                         Selected isotopes

                  CAPTION: 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 1.56×10^7 y α   5.353     ^243Pu
                               ^248Cm syn 3.40×10^5 y α   5.162     ^244Pu
                                                      SF  -         -
                               ^250Cm syn 9000 y      SF  -         -
                                                      α   5.169     ^246Pu
                                                      β^- 0.037     ^250Bk

                                                                References

   Curium ( IPA: /ˈkjuːriəm/) is a synthetic element in the periodic table
   that has the symbol Cm and atomic number 96. A radioactive metallic
   transuranic element of the actinide series, curium is produced by
   bombarding plutonium with alpha particles (helium ions) and was named
   for Marie Curie and her husband Pierre.

Notable characteristics

   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. Curium does not occur in nature. There are few
   commercial applications for curium but it may one day be useful in
   radioisotope thermoelectric generators. Curium bio-accumulates in bone
   tissue where its radiation destroys bone marrow and thus stops red
   blood cell creation.

   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 colour and the element is more
   electropositive than aluminium (most trivalent curium compounds are
   slightly yellow).

   Curium has been studied greatly as a potential fuel for Radioisotope
   thermoelectric generators. Curium-242 can generate up to 120 watts of
   thermal energy per gram (W/g); its very short half-life though makes it
   undesirable 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 ~3 W/g, but produces a large amount of neutron
   radiation from spontaneous fission. Curium-243 with a ~30 year
   half-life and good energy density of ~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.

   Compounds include:
     * curium dioxide (CmO[2])
     * curium trioxide (Cm[2]O[3])
     * curium bromide (CmBr[3])
     * curium chloride (CmCl[3])
     * curium tetrafluoride (CmF[4])
     * curium iodide (CmI[3])

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 discovering radium and for their work in radioactivity.
   It was chemically identified at the Metallurgical Laboratory (now
   Argonne National Laboratory) at the University of Chicago. It was
   actually the third transuranium element to be discovered even though it
   is the second in the series. Curium-242 ( half-life 163 days) and one
   free neutron were made by bombarding alpha particles onto a
   plutonium-239 target in the 60-inch cyclotron at Berkeley. 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. Curium was made in its elemental form in 1951 for the first
   time.

Isotopes

   19 radioisotopes of curium have been characterized, with the most
   stable being Cm-247 with a half-life of 1.56 × 10^7 years, Cm-248 with
   a half-life of 3.40 × 10^5 years, Cm-250 with a half-life of 9000
   years, and Cm-245 with a half-life of 8500 years. All of the remaining
   radioactive isotopes have half-lifes that are less than 30 years, and
   the majority of these have half lifes that are less than 33 days. This
   element also has 4 meta states, with the most stable being Cm-244m
   (t[½]34 ms). The isotopes of curium range in atomic weight from 233.051
   u (Cm-233) to 252.085 u (Cm-252).

Nuclear fuel cycle

   The MOX which is to be used in power reactors should contain little or
   no curium as the neutron activation of this element will create
   californium which is a strong neutron emitter. The californium would
   pollute the back end of the fuel cycle and increase the dose to
   workers. Hence if the Minor actinides are to be used as fuel in a
   thermal neutron reactor the curium should be excluded from the fuel or
   placed in special fuel rods where it is the only actinide present.
   Retrieved from " http://en.wikipedia.org/wiki/Curium"
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