Lanthanum
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Sigma KEE - Lanthanum
鑭
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(From the Greek word lanthanein, to line hidden) Silvery metallic element belonging to group 3 of the periodic table and oft considered to be one of the lanthanoids. Found in some rare-earth minerals. Twenty-five natural isotopes exist. La-139 which is stable, and La-138 which has a half-life of 10^10 to 10^15 years. The other twenty-three isotopes are radioactive. It resembles the lanthanoids chemically. Lanthanum has a low to moderate level of toxicity, and should be handled with care. Discovered in 1839 by C.G. Mosander.
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