(Pierre and Marie Curie) Although curium follows americium in the periodic system, itwas actually known before americium and was the third transuranium element to bediscovered. It was identified by Seaborg, James, and Ghiorso in 1944 at the wartimeMetallurgical Laboratory in Chicago as a result of helium-ion bombardment of 239Pu in theBerkeley, California, 60-inch cyclotron. Visible amounts (30Mg) of 242Cm, in the form ofthe hydroxide, were first isolated by Werner and Perlman of the University of Californiain 1947. In 1950, Crane, Wallmann, and Cunningham found that the magnetic susceptibilityof microgram samples of CmF3 was of the same magnitude as that of GdF3. This provideddirect experimental evidence for assigning an electronic configuration to Cm+3.  In 1951, the same workers preparedcurium in its elemental form for the first time. Fourteen isotopes of curium are nowknown. The most stable, 247Cm, with a half-life of 16 million years, is so short comparedto the earth's age that any primordial curium must have disappeared long ago from thenatural scene. Minute amounts of curium probably exist in natural deposits of uranium, asa result of a sequence of neutron captures and beta decays sustained by the very low fluxof 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 hasbeen 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 incolor, is chemically reactive, and is more electropositive than aluminum. Most compoundsof trivalent curium are faintly yellow in color. 242 Cm generates about three watts ofthermal energy per gram. This compares to one-half watt per gram of 238Pu. This suggestsuse for curium as a power source. 244Cm is now offered for sale at $100/mg. Curiumabsorbed into the body accumulates in the bones, and is therefore very toxic as itsradiation destroys the red-cell forming mechanism. The maximum permissible total bodyburden of 244Cm (soluble) in a human being is 0.3 microcurie.