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europium eu·ro·pi·um (yu-rō'pē-əm)
A rare-earth element used as a neutron absorber in nuclear research. Atomic number 63; atomic weight 151.96; melting point 822°C; boiling point 1,596°C; specific gravity 5.244; valence 2, 3.
A very rare, silvery-white metallic element that is the softest member of the lanthanide series. It is used in making color television tubes and lasers and as a neutron absorber in nuclear research. Atomic number 63; atomic weight 151.96; melting point 826°C; boiling point 1,439°C; specific gravity 5.259; valence 2, 3. See Periodic Table.
(Eu), chemical element, rare-earth metal of the lanthanoid series of the periodic table; it is the least dense, softest, and most volatile member of the lanthanoid series. The element was discovered (1896) by Eugene-Anatole Demarcay and named for Europe. One of the least abundant rare earths, it occurs in minute amounts in many rare-earth minerals such as monazite and also in the products of nuclear fission. Europium is usually separated by reducing it to the +2 oxidation state and precipitating it with sulfate ions. The primary use of europium has been for research purposes. Because it readily absorbs thermal neutrons, it may prove to be of use in nuclear-reactor control rods. It has been used as a phosphor activator, as a component of certain electronic materials, and as an agent in the manufacture of fluorescent glass. The metal has been prepared by electrolysis of the fused halides and by reduction of its oxide by lanthanum metal followed by distillation of the europium metal. It quickly reacts in air, oxygen, and water. Both of its naturally occurring isotopes are stable: europium-151 (47.8 percent) and europium-153 (52.2 percent).