Synopsis from the
CRC Handbook of Chemistry and Physics
92nd Edition 2011-2013
|Radon — (from radium; called niton at first, L. nitens, shining),
Rn; at. wt. (222); at. no. 86; m.p. –71 °C; b.p. –61.7 °C;
tc 104 °C; density of gas 9.73 g/L; sp. gr. liquid 4.4 at –62 °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-seven 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 3.9 s and is also an
alpha emitter. It is estimated that every square mile of soil
to a depth of 6 inches 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
× 1021 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.
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 from radon in homes exceeds 4 pCi/L.