Overview

Radon is an important radioactive gas, responsible for environmental exposures and subsequent impact on human health. It is a Noble gas and under most circumstances is not chemically reactive. Its physical properties and resultant behavior, however, may not be simple in all cases, especially where barriers to free diffusion are present, or when encountering materials with special properties. The importance of radon comes from its radioactivity, by imparting energy in material after decay, with resulting damage to living tissue. Transport in the environment is controlled by its physical properties, since it is chemically inert. Aerogels made of silica glass are a relatively new material with the unique property of having a very large surface area, on the order of hundreds of m2 per gram, compared to the exterior surface of the bulk volume of typical solid materials. Insight may be gained into the behavior of both radon and unique materials by observing how radon interacts with such materials. Silica aerogel monoliths with bulk densities of approximately 0.25 g cm-3 were manufactured and exposed to radon gas diffusing freely into the gel using a closed chamber. Measurements were taken while allowing the gas to diffuse out of the gel. Radon is found to diffuse out of the sample chamber at about the same rate when a gel material is present as from an empty chamber. Long-term measurements show radioactivity (from progeny) remains present leading to the conclusion that, the radon may have penetrated some distance into the gel. This leaves open the possibility of applying aerogels as a radon detector. The aerogel manufactured in this study did not preferentially absorb radon. Some evidence suggests that radon may have penetrated the surface however, based on increased long-term radioactivity. Doping the gel with cerium salts, known to cause glass produced by melting processes to scintillate when exposed to ionizing radiation did not produce observable light signal distinguishable from Cerenkov radiation, thereby excluding the hypothesis that the cerium will scintillate in the current arrangement.

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