Radon

Radon is a colorless, odorless gas (one of the “noble gases”) in its natural form, and is a chemical element in the periodic table which uses the symbol “Rn” and has an atomic number 86. Being 7.5 times heavier than air and 100 times heavier than oxygen, it liquefies at minus 61.8 degrees C (minus 80 degrees F) and freezes at minus 71 degrees C (minus 96 degrees F). Radon is generated by the radioactive decay of radium, from which it gets its name. It is very rare in nature because of the short life of its isotopes, and because radium itself is rare. It occurs naturally in the Earth's atmosphere but at extremely low levels, and occurs near the ground as a result of seepage from rocks and soils. It can often be found in radon-rich water, and some health spas such as those at Misasa, Tottori, Japan, where the water is rich in radium, exuding radon and believed to have special powers.

Overall, radon atoms have an extremely stable electronic configuration which consists of eight electrons in their outer shell. These account for the characteristic chemical inactivity of the element, making the radon gas regarded as one of the “noble gases.” However, chemically, radon is not completely inert. In 1962, scientists found the existence of a compound, radon difluoride, which is, apparently, far more stable chemically than compounds formed from krypton and xenon, the other reactive “noble gases.” However, the short life of radon and the energy of its radioactivity have combined to make it difficult to investigate the properties of these radon compounds.

Natural radon consists of three isotopes, with each one coming from the three natural radioactive-disin-tegration series: the uranium, thorium, and actinium series. The longest-lived isotope, radon-222 (which has a half-life of 3.823 days), was discovered in 1900 by the German chemist Friedrich Ernst Dorn, arises in the uranium series. He called it “radium emanation,” and some scientists reserve the name radon for this isotope to differentiate it from the two natural isotopes, which they call thoron and actinon as they originate in the thorium and the actinium series, respectively. Eight years later, William Ramsay and Robert Whytlaw-Gray named it “niton” from the Latin nitens (“shining”), and determined that it was the heaviest known gas. It has also been called “radon” since 1923, taking the name from “radium.”

The radon-220 (thoron; with a half-life of 51.5 seconds) was first observed in 1899 by the British scientists R. B. Owens and Ernest Rutherford (later Lord Rutherford), who, during experiments, both noticed that some of the radioactivity of thorium compounds could actually be blown away. In 1904, the radon-219 (actinon; with a half life of 3.92 seconds) was found independently by the scientists Friedrich O. Giesel and André-Louis Debierne to be associated with actinium. Since then, more than a dozen artificial radioactive isotopes of radon have been isolated.

It was not until the 1980s that the naturally occurring radon gas was recognized as being a potentially serious health hazard. Prolonged use of radon-rich spas are now regarded as unhealthy, and it is also dangerous to live in buildings in areas where radon occurs naturally, especially over geological formations where there are significant deposits of uranium minerals. Because of its weight, radon gas generally tends to collect in the foundations of buildings or basements and sometimes makes its way into the piping of building which can affect places that are poorly ventilated.

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