Samarium Sm

Discovery

By the mid-nineteenth century chemists suspected that "didymium", then treated as an element, was really a mixture. In 1879 the French chemist Paul-Émile Lecoq de Boisbaudran examined didymium extracted from the Russian mineral samarskite and found new spectral absorption lines, which he attributed to a new element.

Samarium itself turned out to be impure: in 1901 Eugène-Anatole Demarçay separated europium from it. Reasonably pure samarium metal was not produced until the twentieth century, when better separation methods for the rare earths became available.

Origin of the name

Samarium is named after the mineral samarskite, which in turn honours Vasili Samarsky-Bykhovets, a Russian mining official who allowed samples to be studied. That makes samarium, indirectly, the first chemical element named after a real person.

Main uses

• Permanent magnets: samarium-cobalt magnets (SmCo5 and Sm2Co17) are slightly weaker than neodymium magnets but tolerate much higher temperatures and resist corrosion, so they appear in aerospace hardware, precision motors and sensors.
• Reactors: samarium-149, a fission product, absorbs thermal neutrons strongly and must be accounted for as a reactor "poison".
• Medicine: samarium-153 bound to a bone-seeking molecule delivers radiation to bone metastases to ease pain.
• Chemistry: samarium(II) iodide is a popular mild reducing agent in organic synthesis.

Isotopes

Natural samarium contains seven isotopes. Samarium-147 decays by alpha emission to neodymium-143 with a half-life of roughly 106 billion years, and the samarium-neodymium method built on this decay is a standard tool for dating meteorites and ancient rocks. Samarium-148 is also radioactive, with an even longer half-life. Medical samarium-153 has a half-life of about 46 hours.

In everyday life

Most people meet samarium only inside magnets: some headphones, electric-guitar pickups and high-temperature sensors rely on samarium-cobalt. The metal and its compounds are generally regarded as having low toxicity, but fine samarium powder can ignite in air and should be handled carefully. Despite the "rare earth" label, samarium makes up several parts per million of the crust, more than tin. It is mined together with other lanthanides from monazite and bastnäsite and then separated by solvent extraction.