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(From radium; called niton at first, L. nitens, shining) 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.
Twenty isotopes are known. Radon-22, 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 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 into 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 ot 1 x 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 a
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
patient. This practice has been largely discontinued as hospitals can get the seeds
directly from suppliers, who make up the seeds with the desired activity for the day of
Radon is available at a cost of about $4/m.
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 the 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.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.