Curium is a synthetic chemical element, represented by the symbol Cm and atomic number 96, that is not found naturally on Earth in significant quantities. This element is intensely radioactive, giving off a considerable amount of heat and even causing its compounds to glow a purple-pink color in the dark. Curium is classified as a transuranic element, meaning its atomic number is greater than that of uranium (92). It was named in honor of the pioneering scientists Marie and Pierre Curie, who were famous for their foundational research into radioactivity.
Curium’s Place on the Periodic Table
Curium occupies a specific location on the periodic table as a member of the actinide series, which is usually displayed below the main body of the table. Elements in this series are characterized by the filling of the inner 5f electron shell. Its atomic number of 96 places it between americium (95) and berkelium (97).
As a synthetic element, virtually all curium on Earth is produced in nuclear reactors. Trace amounts are found only in spent nuclear fuel or areas affected by nuclear testing. Curium’s chemical behavior is similar to the lanthanide element gadolinium, making it a silvery-white, dense metal.
How Curium Was Created
Curium was first intentionally synthesized in 1944 by a team of scientists led by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso. This work took place at the Metallurgical Laboratory at the University of Chicago during the Manhattan Project. The creation of curium marked it as the third transuranic element to be discovered.
The synthesis was achieved by using a 60-inch cyclotron to bombard plutonium-239 with alpha particles. This nuclear reaction resulted in the creation of curium-242 and the release of a free neutron. The discovery was initially classified due to its connection to the wartime project and was not officially announced to the public until after World War II concluded.
Key Characteristics of Curium Isotopes
Curium has approximately 20 known radioisotopes, none of which are stable. These isotopes range in mass number from 233 to 252, with their distinct properties determined primarily by their half-lives.
The longest-lived isotope is curium-247, which has a half-life of about 15.6 million years. This half-life is short compared to the age of the Earth, confirming that any primordial curium has long since decayed away. The isotopes most frequently produced in quantity for research and practical applications are curium-244 (half-life of 18.1 years) and curium-242 (half-life of 163 days).
All curium isotopes are highly radioactive and predominantly decay by emitting alpha particles. While this radiation is easily stopped by a sheet of paper or the outer layer of human skin, it is damaging if the source is ingested or inhaled. The intense alpha decay generates a significant amount of heat, with curium-244 producing approximately three watts of thermal energy per gram. This self-heating effect makes the element difficult to handle and study.
Why Curium is Used Today
Curium is utilized extensively in scientific research, particularly for creating even heavier, short-lived transuranic elements. The high energy density of certain curium isotopes is valued in specialized power systems.
The element’s isotopes are used in Radioisotope Thermoelectric Generators (RTGs) as a heat source to generate electricity. These power sources are deployed on deep space probes and planetary surface rovers where solar power is not feasible. Curium-244 has been studied for use in RTGs, though the shorter-lived curium-242 generates a higher thermal output per gram. Curium is also used as an alpha source in Alpha Particle X-ray Spectrometers (APXS) carried by space missions to analyze the elemental composition of rocks and soil.