Synopsis
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Radium - (L. radius, ray), Ra; at. wt. (226); at. no.
88; m.p. 700 deg C; b.p. 1140 deg C; sp. gr. 5; valence 2. Radium was discovered
in 1898 by M. and 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. 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 the Republic of 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. Large uranium deposits are located in Ontario, New Mexico,
Utah, Australia, and elsewhere. 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 produce
neutrons. One gram of 226Ra undergoes 3.7 x 10^10 disintegrations per s.
The curie (Ci) is defined as that amount of radioactivity which has the
same disintegration rate as 1 g of 226Ra. Twenty nine isotopes and one
isomer are now known; radium 226, the common isotope, has a half-life of
1599 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 4186 kJ per year. Radium is used in producing
self-luminous paints, neutron sources, and in medicine for the treatment
of disease. Some of the more recently discovered radioisotopes, such as
6OCo, 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 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 226Ra is 7400 becquerel. |
