What Is Samarium?

Samarium is a chemical element with symbol Sm and atomic number 62, one of the fifteen lanthanide rare-earth elements in the periodic table. It is a moderately hard silvery metal with a density of about 7.52 grams per cubic centimeter, an atomic weight of 150.36, and a melting point near 1,072 degrees Celsius. Discovered in 1879 by the French chemist Paul-Emile Lecoq de Boisbaudran in the mineral samarskite, samarium is notable for its stable divalent and trivalent ionic states, a distinctive set of absorption bands in the visible and near-infrared, and the unusually high thermal neutron cross-section of the isotope samarium-149.

Naturally occurring samarium is a mixture of seven isotopes, three of which are radioactive with half-lives so long that the element is treated as effectively stable for engineering purposes. The primary commercial ores are bastnasite and monazite, and production is dominated by separation from mixed rare-earth concentrates using solvent extraction and ion-exchange chemistry.

Physical and Chemical Properties

Samarium crystallizes in a rhombohedral structure at room temperature and transforms to body-centered cubic above 922 degrees Celsius. It tarnishes slowly in air, reacts with water to liberate hydrogen, and burns readily above 150 degrees Celsius to form the sesquioxide Sm2O3. The element shows paramagnetic behavior at room temperature and orders antiferromagnetically below about 14 kelvin. The USGS Rare Earth Elements fact sheet classifies samarium among the light rare earths and documents its occurrence alongside neodymium, praseodymium, and europium in carbonatite and placer deposits.

Nuclear and Spectroscopic Behavior

Samarium-149 has a thermal neutron absorption cross-section of roughly 41,000 barns, second only to gadolinium-157 among naturally abundant nuclides, making samarium relevant to nuclear reactor control and neutron shielding. The samarium-147 to neodymium-143 alpha decay, with a half-life of about 1.06 x 10^11 years, underpins the Sm-Nd radiometric dating method used in geochronology of mantle and early solar system materials, as described in resources from the Jet Propulsion Laboratory. Optical transitions of the trivalent Sm3+ ion generate narrow emission lines in the orange-red region, which are exploited in laser and phosphor applications.

Production and Supply

World samarium production tracks the broader rare-earth supply chain and is concentrated in China, with additional output from Australia, the United States, Myanmar, and India. Separation from the other lanthanides relies on sequential solvent extraction and, for high-purity grades, ion-exchange chromatography or metallothermic reduction of the fluoride. According to USGS Mineral Commodity Summaries, rare-earth demand continues to grow with the expansion of permanent-magnet motors, clean-energy generators, and military electronics, and samarium is classified as a critical mineral in both the United States and the European Union.

Applications

Samarium has applications across a wide range of technical disciplines, including:

• Samarium-cobalt permanent magnets used in motors, generators, actuators, and traveling-wave tubes
• Nuclear reactor control rods and neutron shielding that exploit the high absorption cross-section of samarium-149
• Solid-state and fiber lasers doped with Sm3+ for emission in the orange-red visible band
• Phosphors for fluorescent lighting and display panels, including red-emitting cathode-ray-tube coatings
• Sm-Nd radiometric dating of igneous and meteoritic samples in cosmochemistry and geology
• Catalysts for ethanol dehydration and other organic transformations
• Specialty optical glass and infrared-absorbing glass that uses samarium oxide as a dopant