Radium

Radium, chemical element, symbol Ra; for physical constants see Periodic Table. Radium was discovered by Pierre and Marie Curie in 1898. It occurs in the minerals carnotite, uraninite, and pitchblende. Radium is produced by electrolysis of its chloride. Radium is a brilliant, white, radioactive, reactive metal. It is decomposed by water and turns black in air. It is a member of the alkaline-earth metals. Its salts color a flame carmine red. Radium is radioactive and emits alpha, beta, and gamma rays. The curie (Ci), a unit of radioactivity, is defined as the amount of radioactivity that has the same disintegration rate as 1 g of radium-226 (3.7 × 10¹⁰ disintegrations/second). Radium and its compounds are used in medicine, neutron sources, and self-luminous paints. Radium is a source of the element radon.