Radon

Radon is a chemical element in the periodic table that has the symbol Rn and atomic number 86. A radioactive noble gas that is formed by the disintegration of radium, radon is one of the heaviest gases and is considered to be a health hazard. The most stable isotope is Rn-222 which has a half-life of 3.8 days and is used in radiotherapy.

Table of contents

1 Notable characteristics

2 Applications

Notable characteristics

Essentially inert, radon is the heaviest noble gas and one of the heaviest gases at room temperature. (The heaviest is tungsten hexafluoride, WF₆.) At standard temperature and pressure radon is a colorless gas but when it is cooled below its freezing point is has a brilliant phosphorescence which turns yellow as the temperature is lowered and orange-red at the temperature air liquefies. Some experiments indicate that fluorine can react with radon and form radon fluoride. Radon clathrates have also been reported.

Natural radon concentrations in Earth's atmosphere are so low that natural waters in contact with the atmosphere will continually lose radon by volatilization. Hence, ground water has a higher concentration of Rn-222 than surface water. Likewise, the saturated zone of a soil frequently has a higher radon content than the unsaturated zone due to diffusional losses to the atmosphere.

Applications

Radon is sometimes produced by a few hospitals for therapeutic use by pumping its gas from a radium source and storing it in very small tubes which are called seeds or needles. This practice is being phased-out as hospitals get seeds from suppliers who make them with the desired activity levels.

Because of its rapid loss to air, radon is used in hydrologic research that studies the interaction between ground water, streams and rivers. Any significant concentration of radon in a stream or river is a good indicator that there are local inputs of ground water.

History

Radon (named for radium) was discovered in 1900 by Friedrich Ernst Dorn, who called it radium emanation. In 1908 William Ramsay and Robert Whytlaw-Gray, who named it niton (Latin nitens meaning "shining"), isolated it, determined its density and that it was the heaviest known gas. It has been called radon since 1923.

Occurrence

On average, one molecule of radon is in 1 x 10²¹ molecules of air. Every square mile of soil down to depth of 6 inches has about 1 gram of radium, which decays to radon and release tiny amounts of this deadly gas into the atmosphere. Radon can be found in some spring waters and hot springs.

Isotopes

There are twenty known isotopes of radon. The most stable isotope is radon-222 which is a decay product (daughter isotope) of radium-226, has a half-life of 3.823 days and emits radioactive alpha particles. Radon-220 is a natural decay product of thorium and is called thoron. It has a half-life of 55.6 seconds and also emits alpha rays. Radon-219 is derived from actinium, is called actinon, is an alpha emitter and has a half-life of 3.96 seconds.

Precautions

Radon is a carcinogenic gas. Radon is a radioactive material and must be handled with care at all times. It is hazardous to inhale this element since it emits alpha particles.

Also, its solid decay products, and their respective products, tend to form a fine dust which can easily enter the airways and become permanently stuck in lung tissue, producing heavy localized exposure. Rooms where radium, actinium, or thorium are stored should be well-ventilated in order to prevent build-up in the air. The build-up of radon is a potential health hazard in uranium and some lead mines. Build-up of radon in homes has also been a more recent health concern and many lung cancer cases are attributed to radon exposure each year.

Reference

Los Alamos National Laboratory - Radon