|
|
Atomic Number: |
88 |
Melting Point: | 700 șC | |
| Atomic Symbol: | Ra | Boiling Point: | 1140 șC | ||
| Atomic Weight: | 226.0254 amu | Density: | 5000
kg/m 3 |
||
| Atomic Radius: |
223 pm |
Oxidation States: | 2 | ||
| Covalent Radius: | -- | Electron Configuration: | [Rn]7s2 | ||
| van der Waals Radius: |
-- |
State of Matter: | solid (nonmagnetic) |
(L. radius: ray) Radium was discovered in 1898 by Mme. Curie in the pitchblende or uraninite of North Bohemia, where 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.
Radium is obtained commercially as bromide and 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 slats; 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 produce neutrons. One gram of 226Ra undergoes 3.7 x 1010 disintegrations per second. The curie is defined as that amount of radioactivity which has the same disintegration rate as 1 g of 226Ra. Twenty five isotopes are now known; radium 226, the common isotope, has a half-life of 1600 years.
Its compounds color flames crimson carmine and give a characteristic spectrum. Due to its very short half life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.
Originally, radium was obtained from the rich pitchblende ore found in Joachimsthal, Bohemia. The carnotite sands of Colorado furnish some radium, but richer ores are found in the Republic of Zaire and the Great Lake region of Canada. Radium is present in all uranium minerals, and could be extracted, if desired, from the extensive wastes of uranium processing. Large uranium deposits are located in Ontario, New Mexico, Utah, Australia, and elsewhere.
One gram of radium produces about 0.0001 ml (stp) of emanation, or radon gas, per day. This is purged from the radium and sealed in minute tubes, which are used in the treatment of cancer and other diseases. Radium was used in the producing of self-luminous paints, neutron sources, and in medicine for the treatment of disease. Other radioisotopes, such as 60Co, are now being 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. Stored radium and radium-containing products or minerals should be ventilated to prevent build-up of radon.
Radium has 25 different isotopes, four of which are found in nature, with radium-226 being the most common and stable. Ra-223, Ra-224, Ra-226 and Ra-228 are all generated in the decay of either Uranium or Thorium.
Radium is extremely radioactive and its decay product, radon is a radioactive gas. Since Ra is closely related to calcium, it has the potential to cause great harm by substituting it in bone. Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. Stored radium should be ventilated to prevent build-up of radon.
Emitted energy from the decay of radium ionizes gases, affects photographic plates, causes sores on the skin, and produces many other dramatic effects. The maximum permissible border in the total body for 226Ra is 7400 becquerel.
