Synopsis
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Radon - (from radium; called niton at first, L. nitens,
shining), Rn; at. wt. (222); at, no. 86; m.p. -71 deg C; b.p. -61.7 deg
C; density of gas 9.73 g/l; sp. gr. liquid 4.4 at -62 deg C, solid 4; valence
usually 0. The element was discovered in 1900 by Dorn, who called it radium
emanation. In 1908 Ramsay and Gray, who named it niton, isolated the element
and determined its density, finding it to be the heaviest known gas. It
is essentially inert and occupies the last place in the zero group of gases
in the Periodic Table. Since 1923, it has been called radon. Thirty nine
isotopes and isomers are known. Radon-222, coming from radium, has a half-life
of 3.823 days and is an alpha emitter; Radon-220, emanating naturally from
thorium and called thoron, has a half-life of 55.6 s and is also an alpha
emitter. Radon-219 emanates from actinium and is called actinon. It has
a half-life of 3.96 s and is also on alpha emitter. It is estimated that
every square mile of soil to a depth of 6 inch contains about 1 g of radium,
which releases radon in tiny amounts to the atmosphere. Radon is present
in some spring waters, such as those at Hot Springs, Arkansas. On the average,
one part of radon is present to 1 x 10^21 part of air. At ordinary temperatures
radon is a colorless gas; when cooled below the freezing point, radon exhibits
a brilliant phosphorescence which becomes yellow as the temperature is
lowered and orange-red at the temperature of liquid air. It has been reported
that fluorine reacts with radon, forming radon fluoride. Radon clathrates
have also been reported. Radon is still produced for therapeutic use by
a few hospitals by pumping it from a radium source and sealing it in minute
tubes, called seeds or needles, for application to patients. This practice
has now been largely discontinued as hospitals can order the seeds directly
from suppliers, who make up the seeds with the desired activity for the
day of use. Radon is available at a cost of about $4/m Ci. Care must be
taken in handling radon, as with other radioactive materials. The main
hazard is from inhalation of the element and its solid daughters, which
are collected on dust in the air. Good ventilation should be provided where
radium, thorium, or actinium is stored to prevent build-up of this element.
Radon build-up is a health consideration in uranium mines. Recently radon
build-up in homes has been a concern. Many deaths from lung cancer are
caused by radon exposure. In the U.S. it is recommended that remedial action
be taken if the air in homes exceeds 4 pCi/l. |
