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Samarium (Sm)
Samarium (symbol Sm) is the chemical element with atomic number 62: a lanthanide (rare earth), solid at 0 °C, with an atomic mass of 150.36 u. Discovered in 1879 (Paul-Émile Lecoq de Boisbaudran).
Combined with cobalt, samarium forms magnets slightly weaker than neodymium ones but far more resistant to heat and corrosion. It is also used in medicine to ease the pain of bone cancers, and in geology to date the oldest rocks.
Key facts
- Atomic number
- 62
- Symbol
- Sm
- French name
- Samarium
- Atomic mass
- 150.36 u
- Molar mass
- 150.36 g/mol
- Family
- Lanthanides
- Position
- period 6, f-block
- State at 0 °C
- Solid
- Melting point
- 1,071.9 °C
- Boiling point
- 1,899.9 °C
- Density
- 7.52 g/cm³
- Electronegativity (Pauling)
- 1.17
- First ionization energy
- 545 kJ/mol
- Atomic radius
- 185 pm
- Electron configuration
- [Xe] 4f⁶ 6s²
- Abundance in Earth's crust
- 7.05 ppm (40th most abundant element)
- Indicative price
- 14 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1879, Paul-Émile Lecoq de Boisbaudran
Origin of the name
From samarskite, a mineral named after the Russian engineer Samarsky.
What does samarium look like?
A bright, fairly hard silvery metal that stays relatively stable in dry air before slowly tarnishing.
Where is samarium found?
About 7 ppm of Earth's crust, three times as much as tin. It is found in monazite, bastnäsite and samarskite.
Natural sources
- Monazite
- Bastnäsite
- Samarskite
How is samarium produced?
Separated from the other rare earths by solvent extraction or ion exchange. The metal is made by reducing its oxide with lanthanum, then distilling off the more volatile samarium.
Top producers
- China
- United States
- Myanmar
- Australia
What is samarium used for?
- Samarium-cobalt magnets for aerospace, military hardware and hot-running motors.
- Samarium-153, a drug for the pain of bone metastases.
- Neutron absorber in nuclear reactors.
- Samarium iodide, a reagent in organic synthesis.
- Samarium-neodymium dating of rocks and meteorites.
In everyday life
- High-end electric guitar pickups
- Small motors and sensors in aircraft
Role in living things
No known biological role.
Hazards of samarium
Low toxicity. Medical samarium-153 is radioactive and given in hospitals under strict control.
Cosmic origin
- Neutron stars: Created when two neutron stars collide — the “forge” of gold.
- Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
History of samarium
The Frenchman Paul-Émile Lecoq de Boisbaudran identified it in 1879 in samarskite, a mineral itself named after Vasili Samarsky-Bykhovets, a Russian mining engineer. That makes it the first element whose name honors, indirectly, a real person.
Did you know?
- Natural samarium-147 is radioactive, but so slow (half-life of 106 billion years) that it serves as a geological clock.
- SmCo magnets keep working above 300 °C, where neodymium magnets lose their strength.
- Samarium-149, produced in reactors, is a “poison” that slows the chain reaction.
Isotopes of samarium
Natural samarium has seven isotopes, two of them weakly radioactive. Samarium-149 is a notorious “poison” in nuclear reactors, so greedily does it swallow neutrons.
- samarium-144: 3.07% of natural samarium, stable
- samarium-146: radioactive, half-life 1.03 × 10⁸ years. Present in the early solar system and now extinct, it is used to date the formation of the planets.
- samarium-147: 14.99% of natural samarium, radioactive, half-life 1.06 × 10¹¹ years. Its slow transformation into neodymium-143 makes it possible to date rocks billions of years old.
- samarium-148: 11.24% of natural samarium, radioactive, half-life 6.3 × 10¹⁵ years
- samarium-149: 13.82% of natural samarium, stable. Captures neutrons very efficiently, slowing down the chain reaction in reactors.
- samarium-150: 7.38% of natural samarium, stable
- samarium-151: radioactive, half-life 94.6 years
- samarium-152: 26.75% of natural samarium, stable
- samarium-153: radioactive, half-life 1.93 days. Injected to relieve the pain of bone metastases.
- samarium-154: 22.75% of natural samarium, stable
Related elements
Same family (lanthanides): Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu).