Symbol Sm. A soft silvery metallic element belonging to the lanthanoids; a.n. 62; r.a.m. 150.35; r.d. 7.52 (20°C); m.p. 1077°C; b.p. 1791°C. It occurs in monazite and bastnatite. There are seven naturally occurring isotopes, all of which are stable except samarium–147, which is weakly radioactive (half-life 2.5 × 1011 years). The metal is used in special alloys for making nuclear-reactor parts as it is a neutron absorber. Samarium oxide (Sm2O3) is used in small quantities in special optical glasses. The largest use of the element is in the ferromagnetic alloy SmCo5, which produces permanent magnets five times stronger than any other material. The element was discovered by François Lecoq de Boisbaudran in 1879.
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