Hi Scorpio. Radon 222 is the particular radon gas you're refering to and is the product of decaying U238. Under normal conditions radon is found as a colorless gas. However, when radon is cooled below freezing point, it emits magnificent phosphorescence. If the temperature is lowered the color starts turning yellow and orange-red at the temperature of liquid air. Chemically it is not a hazard, but the gas is a poison. When radon or its decay products are inhaled, it becomes a hazard. Traces of radon are usually found in basements of certain areas around the world. It is the heaviest known gas and so is found in some spring waters.

High levels of radon have been discovered in homes in every state, and found in more than 70,000 schools in use today across the country. A nationwide survey of radon levels indicates that nearly one in five schools has at least one classroom with high radon levels (EPA, 1994). Studies of radon's behavior in the geological environment suggest that a direct relationship exist between indoor levels of radon and the concentration of the gas in soil.

Investigations throughout the world over the past 15 years provide evidence, which indicates that significant variations of radon concentration may occur in association with major geophysical events such as earthquakes and volcanic eruptions

Higher then normal levels have been found in the Mammoth Lakes area along with He-3, which is helium and is rare at the surface, but can be found in deep magma. Radon 222 was found to be at very high levels in water wells before the Kobe earthquake. A couple of weeks (not sure of the time period as my Japanese is not as good as it use to be) before the quake it supposedly return to near normal levels

The problem with using Radon 222 as a precursor to earthquakes or volcanic eruptions is that it may not always be present. Take Care…Don in creepy town