Radon
Radon is a noble gas element denoted by the atomic symbol, Rn. It has an atomic number of 86 and the atomic weight of its most stable isotope is 222. It is a colorless, odorless gas that emits radioactivity.
Radon is the heaviest element in the family of inert, or noble, gases. The term radon refers loosely to the gas itself, which is emitted from the decay of the element radium, and to its twenty-five isotopes, all of which are also highly radioactive. Normally a colorless gas, radon can be condensed into a fluorescent liquid. Although radon's parent radium is extremely rare (it decays very rapidly), radon and its natural isotopes are also produced from uranium and thorium, which are much more prevalent in minerals, ores, and rocks. Uranium miners must take special precautions to avoid radioactive poisoning by radon. The gas can also migrate upward into the soil--the mechanism by which it leaks into buildings. Radon can seep into groundwater; it is not unusual to find it in public drinking supplies. (The danger here is not from drinking the water, but from breathing the radon that evaporates during bathing, cooking, etc.) Eventually radon decays into other products called "daughters," which can also be hazardous.
The discovery of radon is credited to Friedrich Dorn (1848-1916), a German physics professor. Marie Curie's experiments stimulated Dorn to begin studying the phenomenon of radioactivity. In 1900, he showed that radium emitted a radioactive gas that was called radium emanation for several years. (To this day, some scientists designate radon and its isotopes with the symbol Em instead of Rn.) Dorn's discovery represented the first clear proof that one element could be transmuted into another element during the radioactive decay process. A few years later, Sir William Ramsay, working with Robert Whytlaw-Gray (1877-1958) and other scientists, was able to map radon's characteristic spectral lines and determine its density and atomic weight. In 1918, radon was given its modern name by scientist C. Schmidt.
During the 1960s, Chinese scientists learned that radon levels in groundwater rise dramatically just before earthquakes. They have therefore predicted several quakes by monitoring radon concentrations in well water, and today researchers from other countries are studying this phenomenon. Radon is also used to detect leaks, measure flow rates, and inspect metal welds.
Until the late 1980s, the radioactive gas radon was well-known to scientists, but most people had no idea it existed. Then the threat of exposure to radioactivity from the gas brought it widespread public attention. It was found that many lung cancer deaths could be directly related to radon exposure. In fact, it is estimated that radon causes thousands of preventable cancer deaths each year. In 1988, the United States Environmental Protection Agency (EPA) estimated that ten million American homes could have harmfully high radon levels. Sales of radon detectors boomed, and the government advised people to seal their basements and ventilate their houses if radon exceeded certain levels. Since then, some scientists have disputed the government's findings, but a few regions of the United States are still generally acknowledged to be at higher than normal risk. In 1996, the EPA issued regulations aimed at controlling the amount of radon in drinking water.
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