radium

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radium (symbol Ra) White, radioactive, metallic element of the alkaline-earth metals, first discovered (1898) in pitchblende by French physicists Pierre and Marie Curie; the metal is present in uranium ores. It is used in radiotherapy to treat tumours. Radium has 16 isotopes, which emit alpha, beta and gamma radiation, as well as heat. Radon gas is a decay product. Properties: at.no. 88; r.a.m. 226.025; r.d. 5.0; m.p. 700°C (1292°F); b.p. 1140°C (2084°F); most stable isotope Ra226 (half-life 1622 years).

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