Chemistry

An Overview about the Chemical Element Curium



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Curium

Symbol: Cm

Atomic Number: 96

Atomic Mass: 247.0 amu (atomic mass units)

Melting Point: 1345 C (1618 K, 2444.0 F)

Boiling Point: approx 3100 C (3400K, 5600F)

Number of Protons: 96

Number of Electrons: 96

Number of Neutrons: 151

Classification: Rare Earth (Man-made)

Crystal Structure: Unknown

Density @ 293 K: 13.51 grams per cubic centimeter

Color: Silver

The highly radioactive element curium was first made in 1944 by Glenn T. Seaborg, Ralph A. James and Albert Ghiorso at the Berkeley Campus of the University of California. They used the 60 inch cyclotron base at Berkeley to bombard plutonium-239 with alpha particles. This produced an atom of curium-242 and a neutron. Curium-242 has a half life of approximately 163 days and decays by alpha emission to form plutonium-238 or by spontaneous fission.

Curium was named after the Nobel Prize winning scientists Pierre and Marie Curie. It is part of the actinide or actinoid series of rare earth elements.

In 1947 the first visible amounts of curium were produced in the form of curium hydroxide. The first visible quantity of the pure element was produced in 1951. A number of compounds of curium have been produced including curium trioxide, curium dioxide and curium chloride. Most of the compounds made by this element have a yellow color.

Numerous isotopes have since been produced of curium, mainly within nuclear reactors, by neutron capture by different isotopes of americium and plutonium. Curium-247 has the longest half life at 15.6 million years. This isotope decays to form plutonium-243 by alpha decay. The shortest half life belongs to the isotope curium-242m at 40 picoseconds before decaying by spontaneous fission.

Curium presents a very real biological threat as it can accumulate within the bones of the body where it adversely affects the production of red blood cells. The maximum allowed body burden of curium-244 is 0.3 microcurie. Extreme caution must be taken when handling any of the isotopes of this element.

Although curium has never been found in nature small amounts of the element are thought to be present in uranium ores where it is formed by a series of neutron captures and beta decays.

Curium and its compounds are mainly used in scientific research. However NASA used curium-244 as an alpha particle source within the Alpha Proton X-Ray Spectrometer used on the Mars Rover.

The use of curium as a thermoelectric power source is being considered. Curium-242 will generate three watts of thermal energy per gram this is far greater than the half a watt per gram generated by plutonium-238.

Los Alamos Chemical Laboratory - http://periodic.lanl.gov/elements/96.html

NASA Mars Rover - http://marsrover.nasa.gov/technology/si_in_situ_instrumentation.html

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