Curium Cm

Discovery

Curium was first produced in the summer of 1944 by Glenn Seaborg, Ralph James and Albert Ghiorso. They used Berkeley's 60-inch cyclotron to bombard plutonium-239 with alpha particles (helium nuclei) and analysed the product at the University of Chicago's Metallurgical Laboratory, identifying a new isotope, curium-242, with a half-life of about five months. It was actually discovered slightly before element 95, americium.

Like americium, it remained secret during the war and was first mentioned publicly by Seaborg on a children's radio quiz programme in November 1945, shortly before the formal announcement. Early samples were invisibly small. By around 1947 researchers had produced a visible quantity of curium hydroxide by irradiating americium with neutrons in a reactor, and curium metal was isolated in 1951.

Origin of the name

The lanthanide directly above curium is gadolinium, named after the Finnish chemist Johan Gadolin. Seaborg's team followed that parallel by naming element 96 after Marie and Pierre Curie, pioneers of radioactivity. The symbol is Cm. It was one of the first elements named after scientists.

Main uses

• Planetary science: Curium-244 has served as the radiation source in alpha particle X-ray spectrometers (APXS). Pressed against a rock, the instrument bombards it with alpha particles and X-rays and reads the returning X-rays to determine which elements the rock contains. Several Mars rovers have carried such instruments.
• Making heavier elements: Curium-248 targets were used to create element 116, livermorium, among other superheavy nuclei.
• Possible heat source: Curium-242 and curium-244 produce a lot of decay heat and were studied for radioisotope power, although plutonium-238 is the usual choice.
• Otherwise curium is used mainly in basic research.

Isotopes

Curium has no stable isotopes. The longest-lived is curium-247, with a half-life of about 15.6 million years. The first isotope found, curium-242, has a half-life of about 163 days, and curium-244, used in space instruments, about 18 years. Curium-242 and curium-244 also build up in spent reactor fuel, where their heat output and neutron emission make them significant for waste handling.

In everyday life

Curium does not appear in everyday life; nearly all of it on Earth was made in reactors and weapons tests. It is a strong alpha emitter, and when taken into the body it concentrates in bone and liver and stays for a long time, so it is classed as a highly hazardous radioactive material. Laboratories often handle it remotely inside sealed enclosures. The metal is silvery-white but oxidises readily in air.