1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰f¹⁴ 5s²p⁶d¹⁰f⁷ 6s²p⁶d¹ 7s²

History Characteristics Compounds Isotopes Precautions Nuclear Fuel Cycle

Curium Data Atomic Structure Chemical Properties Physical Properties Miscellaneous Interactive Periodic Table

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.  They performed a careful chemical fractionation on a sample of plutonium-239, an isotope of plutonium, which had been irradiated with 32 MeV helium ions(alpha particles) at the University of California.  A new radioactive isotope was found, which emitted 4.7 MeV alpha particles and was chemically separable from neptunium and plutonium.  Both nuclear and chemical evidence indicated that the activity could be ascribed to an isotope of a new element with atomic number 96.  It was actually the third transuranium element to be discovered even though it is the second in the series.  This produced atoms of curium-242 and one free neutron.  Curium-242 has a half-life of about 163 days and decays into plutonium-238 through alpha decay or decays through spontaneous fission.

Marie & Pierre Curie

Visible amounts (30Mg) of ²⁴²Cm, in the form of the hydroxide [Cm(OH)₃], were first isolated by  Louis Werner and  Isadore Perlman of the University of California in 1947 by bombarding americium-241 with neutrons.  In 1950, Crane, Wallmann, and Cunningham found that the magnetic susceptibility of microgram samples of CmF₃ was of the same magnitude as that of GdF₃.  This provided direct experimental evidence for assigning an electronic configuration to Cm⁺³.   In 1951, the same workers prepared curium in its elemental form for the first time.

The crystal structure and melting point of curium metal were determined in 1964 by B.B. Cunningham and J.C. Wallmann.

Characteristics

Minute amounts of curium probably exist in natural deposits of uranium, as a result of a sequence of neutron captures and beta decays sustained by the very low flux of neutrons naturally present in uranium ores. The presence of natural curium, however, has never been detected. ²⁴²Cm and ²⁴⁴Cm are available in multigram quantities. ²⁴⁸Cm has been produced only in milligram amounts.   ²⁴²Cm generates about three watts of thermal energy per gram. This compares to one-half watt per gram of ²³⁸pU. This suggests use for curium as a power source. ²⁴⁴Cm is now offered for sale at $160/mg plus packing charces. ²⁴⁸Cm is available at a cost of $160/mg, plus packing charges, from the O.R.N.L. Curium absorbed into the body accumulates in the bones, and is therefore very toxic as its radiation destroys the red-cell forming mechanism.  The maximum permissible total body burden of ²⁴⁴Cm (soluble) in a human being is 0.3 uCi (microcurie).  

Electron Shell Configuration

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

Curium has been studied greatly as a potential fuel for Radioisotope Thermoelectric Generators (RTGs).  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

Since only milligram amounts of curium have ever been produced, there are currently no commercial applications for it, although it might be used in radioisotope thermoelectric generators in the future.  Curium is primarily used for basic scientific research.   Curium-242 and curium-244 are used in the space program as a heat source for compact thermionic and thermoelectric power generation. Being an alfa-emitter, its radiation can be easily shielded against.

Isotopes

21 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. Cm-247 decays into plutonium-243 through alpha decay.  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).

Precautions

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.