europium [key] [from Europe], metallic chemical element; symbol Eu; at. no. 63; at. wt. 151.964; m.p. about 820℃; b.p. about 1,600℃; sp. gr. 5.25 at 25℃; valence +2 or +3. Europium is a ductile silvery-white metal; it is both rare and expensive. It is a member of Group 3 of the periodic table. Its oxides are found in minerals with the other rare earths. Europium has been identified in the sun and some stars by spectroscopy. Its physical properties are like those of the other members of the lanthanide series, but many of its chemical properties are more like those of calcium. The most reactive of the rare-earth metals, it tarnishes quickly in air at room temperature and ignites and burns above 150℃. It reacts readily with water. Twenty-one isotopes of europium are known, most of them unstable. Since it is a good neutron absorber, europium metal is used in nuclear reactor control rods. Europium oxide, a pinkish powder, is used to activate red phosphors in the manufacture of color television picture tubes. The discovery of europium is credited to Eugène Demarcay, who isolated fairly pure europium oxide in 1901.
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