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Synopsis from the
CRC Handbook of Chemistry and Physics
92nd Edition 2011-2013
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Radium — (L. radius, ray), Ra; at. wt. (226); at. no. 88; m.p. 696 °C;
sp. gr. 5; valence 2. Radium was discovered in 1898 by M. and
Mme. Curie in the pitchblende or uraninite of North Bohemia
(Czech Republic), 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 Congo-Kinshasa 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 × 1010 disintegrations per s. The curie (Ci) is defined
as that amount of radioactivity which has the same disintegration
rate as 1 g of 226Ra. Thirty-six isotopes 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
cancer. Some of the more recently discovered 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 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. |
