Richard Renneboog, Radon, A Rare Element


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Radon, A Rare Element

Richard M. J. Renneboog
Information Technology Developer / Webmaster
Renaissance Aeronautics Associates Incorporated

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To the best of our knowledge, the entire universe is constructed from just over a hundred different types of building blocks called atoms. Each has its own characteristic properties, and while there are dangers associated with each and every one of them, it seems that the rarer the element, the more serious are its effects. Such is the case with the element we know as radon.

The eighty-sixth element in the periodic table, radon is a member of the group of elements known as the 'noble gases'. Those elements - helium, neon, argon, xenon, krypton, and radon - are all found in nature as monatomic ('single atom') species. They are never found bonded to other atoms in compounds, hence the notion of their 'nobility'; hobnobbing with the common elements is below their station in the Universe. The last three, however, have been induced to form compounds under controlled laboratory conditions.

The atomic weight of radon is 222 atomic mass units (amu, or Daltons), making it the heaviest gas known. A volume of 22.4 litres (or just under half of a cubic foot) of this gas at room temperature and normal pressure weighs 222 grams (or half a pound). That may not sound like much, but to put it into context, the same volume of hydrogen (H2) would weigh just 2 grams (barely noticeable) while that of water vapour (steam) would weigh only 18 grams. Radon is a readily compressible gas, becoming liquid at -62(C, and then a glowing solid at -71(C.

Why does solid radon glow? Radon is a radioactive element formed by the decay of the element radium. The glow is 'Cerenkov radiation', light produced as charged subatomic particles with fairly high energies pass through and interact with their immediate environment.

Therein lies the inherent danger associated with radon gas, and other radioactive elements. We tend to think of elements like radium and uranium as only found in mineral ores. The truth is that they are found throughout the world at very low levels. The mineral ores from which they are refined for industrial uses represent only very minor pockets in which nature has somehow concentrated those elements. Because radium is thus found everywhere, radon gas is similarly widespread. Radioactive decay is a continuous process, so new radon is always being produced to add to the environment. The vast majority of the radon that is produced remains securely trapped below ground in the soil and rock in which it was formed, where it poses little or no threat. What radon gas does escape from the soil is usually safely dispersed through the action of wind and rain.

There are regions of the Earth, though, in which the wind does not blow and the rain does not fall, and where underground water sources provide a path for radon gas to come to the surface and collect in higher-than-normal concentrations. These are the basements and cellars of the houses and other buildings in which we live, work, and play. Concrete, clay bricks, and other mineral-based building materials have the effect of concentrating or increasing the amount of radon gas produced in these areas. Normally, buildings with good air exchange, especially in the portions below ground level, do not have a problem with the build-up of radon gas. The flow of air removes the radon gas as it is produced. Where air flow is a problem, however, radon gas can accumulate in basements, crawl spaces, and other such locations.

In 1991, a national residential survey conducted in the United States found an average indoor level of radon gas of 1.3 picoCuries per litre. This was more than three times the average outdoor level observed in the same survey. This was an average value, so some residences contained much less, and some residences contained much more. Radon gas is powerful stuff. Exposure to between 3 and 4 picoCuries per litre is considered a health hazard. A picoCurie corresponds to the formation of 2.2 atoms of radon per minute. At that rate it would take about 5 X 1017 years - some 7,000,000,000,000,000 or seven quadrillion lifetimes - to accumulate that half pound of pure radon gas. In one year, then, an average residence could accumulate just over 1.15 million atoms of radioactive radon gas, a total of about 5 million picoCuries, requiring the exchange of at least 5 million litres of fresh air in order to be safely dispersed.

Exposure to radon gas in any quantity carries a risk of serious health consequences, particularly as a cause of lung cancer. There are no immediate symptoms that result from exposure to radon gas, and lung cancer is the only health effect that has been definitely linked to radon exposure. Other respiratory diseases have not been linked to radon exposure, but they can not at this time be precluded. It is estimated that exposure to radon gas accounts for approximately 20,000 deaths due to lung cancer annually in the United States. There is no evidence indicating greater risk to children than to adults, but people who smoke are at significantly greater risk than are non-smokers. When radon gas exposure is the cause, lung cancer generally appears from 5 to 25 years after exposure has occurred. This has made it very difficult to determine reliable figures for the risks associated with radon gas.

It should go without saying, then, that where radon gas is concerned, an ounce of prevention is invaluable. Routine test sampling of the air in any particular building can be carried out to monitor for the presence of radon gas in higher-than-normal concentrations. Simply ensuring that all areas of the building achieve an adequate exchange of fresh air removes any radon gas that may collect, as well as the risk associated with exposure.

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