Radium—(L. radius, ray), Ra; atomic weight 226.0254; atomic number 88; melting point 700°C; boiling point 1140°C; specific gravity 5; valence 2.
Radium was discovered in 1898 by M. and Mme. Curie in the pitchblende or uraninite of North Bohemia, in which it occurs. There is about 1 g of radium in 7 tons of pitchblende. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode; on distillation in an atmosphere of hydrogen this amalgam yielded the pure metal. Originally, radium was obtained from the rich pitchblende ore found at Joachimsthal, Bohemia. The carnotite sands of Colorado furnish some radium, but richer ores are found in Zaire and the Great Bear Lake region of Canada. Radium is present in all uranium minerals, and could be extracted, if desired, from the extensive wastes of uranium processing.
Radium is obtained commercially as the bromide or chloride; it is doubtful if any appreciable stock of the isolated element now exists. The pure metal is brilliant white when freshly prepared, but blackens on exposure to air, probably due to formation of the nitride. It exhibits luminescence, as do its salts; it decomposes in water and is somewhat more volatile than barium. It is a member of the alkaline-earth group of metals. Radium imparts a carmine red color to a flame.
Radium emits alpha, beta, and gamma rays and when mixed with beryllium produces neutrons. One gram of Ra226 undergoes 3.7 × 1010 disintegrations per sec. The curie (Ci) is defined as that amount of radioactivity which has the same disintegration rate as 1g of Ra226. Sixteen isotopes are now known; radium 226, the common isotope, has a hall-life of 1620 years. One gram of radium produces about 0.0001 ml(stp) of emanation, or radon gas, per day. This is pumped from the radium and sealed in minute tubes, which are used in the treatment of cancer and other diseases. One gram of radium yields about 1000 cal per year. Radium is used in producing self-luminous paints, neutron sources, and in medicine. Radioisotopes, such as Co60, are now used in place of radium. Some of these sources are much more powerful, and others are safer to use. Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight. Lead is a final product of disintegration. Radium is a radiological hazard. (Stored radium should be ventilated to prevent build-up of radon.) Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. The maximum permissible burden in the total body for Ra226 is 0.2 μCi (microcuries).