Curium

Among the transuranium elements discovered during the Manhattan Project era, curium occupies a special place — a silvery, intensely radioactive metal synthesized in 1944 by Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso at the University of Chicago's Metallurgical Laboratory. Curium glows faintly in the dark due to its own radioactive decay, and it generates considerable heat, a property that has sent it far beyond Earth's atmosphere aboard interplanetary spacecraft.

Curium's most notable application leverages its alpha-particle emission. The Alpha Particle X-Ray Spectrometer (APXS) aboard NASA's Mars Pathfinder, Spirit, and Opportunity rovers used curium-244 sources to bombard Martian rocks and soils, allowing scientists to determine elemental composition at a distance. Curium-244 also serves as a heat source in radioisotope thermoelectric generators. In research laboratories, curium isotopes are studied to deepen understanding of actinide chemistry and nuclear structure.

On July 4, 1944, Seaborg, James, Morgan, and Ghiorso bombarded plutonium-239 with alpha particles in the 60-inch cyclotron at the University of Chicago, producing curium-242. The discovery was kept classified during World War II and not announced publicly until November 1945, when Seaborg revealed it — along with americium — on a children's radio quiz show. The element was named in honor of Marie and Pierre Curie, pioneers of radioactivity research, making it one of only two elements named after a married couple. Its chemical isolation was first accomplished in 1947.

Curium does not occur naturally on Earth. All known curium is produced artificially by bombarding lighter actinides — typically plutonium or americium — with neutrons or alpha particles in nuclear reactors and particle accelerators. Trace amounts may exist transiently in reactors that contain americium fuel.

Curium forms a limited range of compounds, primarily in the +3 oxidation state, consistent with its actinide neighbors. Known compounds include curium(III) oxide (Cm2O3), curium(III) fluoride (CmF3), and curium(III) chloride (CmCl3). A +4 state has been observed in curium dioxide (CmO2) and in solution under strongly oxidizing conditions. Because curium samples are scarce and highly radioactive, its chemistry has been studied only in small quantities, and much of its compound behavior is inferred from neighboring actinides.

• Curium was the fifth transuranium element discovered, but it was actually synthesized before americium — the announcement was just made in reverse order.
• Curium-244 has a half-life of about 18.1 years, making it an ideal long-lived but not excessively persistent alpha source for space instruments.
• A visible amount of curium would glow in the dark due to the ionization of surrounding air molecules caused by its intense radioactive decay.
• Curium-247 has a half-life of approximately 15.6 million years — long enough that it would theoretically occur in nature if produced in sufficient quantities by stellar processes.
• The element was named to honor both Marie and Pierre Curie simultaneously, much as curium's discovery itself was a collaborative achievement between four scientists.