Curium

Author: Robert Husted, Mollie Boorman

History

(Pierre and Marie Curie) Although curium follows americium in the periodic system, it was actually the third transuranium element to be discovered. It was identified by Seaborg, James, and Ghiorso in 1944 at the wartime metallurgical laboratory at the University of Chicago as a result of helium-ion bombardment of ²³⁹Pu in the Berkeley, California, 60-inch cyclotron. Visible amounts (30Mg) of ²⁴²Cm, in the form of the hydroxide, were first isolated by Werner and Perlman of the University of California in 1947. 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. Fourteen isotopes of curium are now known. The most stable, ²⁴⁷Cm, with a half-life of 16 million years, is so short compared to the earth's age that any primordial curium must have disappeared long ago from the natural scene.

Properties

 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. Curium is similar in some regards to gadolinium, its rare earth homolog, but it has a more complex crystal structure. Curium is silver in color, is chemically reactive, and is more electropositive than aluminum. Most compounds of trivalent curium are faintly yellow in color. ²⁴²Cm generates about three watts of thermal energy per gram. This compares to one-half watt per gram of ²³⁸Pu, suggesting that curium can be used for as a power source. ²⁴⁴Cm is now offered for sale at $100/mg. 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 microcurie.