|Name, Symbol, Number||curium, Cm, 96|
|Group, Period, Block||n/a, 7, f|
|Atomic mass||(247) g/mol|
|Electron configuration||[Rn] 5f7 6d1 7s2|
|Electrons per shell||2, 8, 18, 32, 25, 9, 2|
|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|
|Crystal structure||hexagonal close-packed|
|Electronegativity||1.3 (Pauling scale)|
|Ionization energies||1st: 581 kJ/mol|
|Magnetic ordering||no data|
|CAS registry number||7440-51-9|
Curium (chemical symbol Cm, atomic number 96) is a radioactive, metallic, transuranic element 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.
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.
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).
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).
Known compounds of curium include the following:
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.
If MOX nuclear fuel 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.
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