The natural radioactive element Uranium is present everywhere in rocks and soil.
The radioactive decay of Uranium produces Radium, which in turn decays to Radon, a radioactive colourless, tasteless and odourless inert gas.
As it is a gas, it can move easily through bedrock and soil and escape into the outdoor air or seep into a home or building.
All soil contain varying amounts of Uranium, so Radon is present in all types of soil. Radon that moves from the ground into the outdoor air is rapidly diluted to low concentrations and is not a health concern.
Homes and buildings usually create some sort of stack effect which simply put, is air rising. This draws in soil gases, including Radon, through openings in the foundation where it is in contact with the ground. This includes construction joints, gaps around service pipes and support posts, floor drains and sumps, cracks in foundation walls and in floor slabs, and openings in concrete block walls.
Once inside the house, Radon can accumulate to high levels and become a long-term health concern.
In some areas, Radon in the water supply can also contribute to the indoor air concentration in the building. In such cases, Radon dissolves in the water as it travels through rocks and soils. This situation is generally associated with ground water and thus is more likely to affect well water sources rather than surface waters used for most municipal water supplies. The health risk associated with Radon dissolved in water is not from drinking the water, but from breathing the air into which Radon has been released. Considerable amounts of Radon in water are required to contribute to airborne levels within a home or building. As a rule of thumb it can take 10,000 pCi/L of Radon in water to contribute just 1 pCi/L to airborne Radon levels.
Radon is very site specific and testing has shown neighbouring homes in some cases to vary drastically. The only way to know if a home or building has a high Radon concentration is to test for it.
Radon in Air
The E-PERM® is a patented passive radon monitor listed as approved by the C-NRPP and the NRPP certifying agencies. These devices are widely used in more than 30 countries and are listed as the most used devices in the USA for both long and short term radon measurement. Only radon gas, not radon decay products, diffuses through the filtered inlet into the chamber volume until the concentration of radon inside the chamber is the same as that in the room. Radiation emitted by the decay of the radon and the decay products formed inside the chamber ionizes the air. The positively charged electret attracts the negative ions generated by the radiation in the chamber resulting in a net decrease of the electret voltage. Positive ions go to the wall of the chamber and get dissipated. This voltage decrease of the electret is proportional to the radon concentration and the time of the exposure. The drop in voltage of the electret is a measure of the product of the radon concentration and the exposure time given in; (pCi/L)-days or Bq/m3 –days. Different combination of volumes and electrets covers virtually all the ranges of interest in scientific and professional fields.
These devices are not affected by varying concentration, temperatures or humidity and are therefore excellent for use in a variety of applications which include basic research, health related measurements, indoor and outdoor radon measurements, and uranium exploration projects.
Short term Testing
This is usually done as follow up testing after mitigation. However, short term tests can be deployed to identify your radon potential in a Real Estate transaction or if you have a suspicion that your radon levels would be high and you don’t want to go through with long term testing and have yourself exposed unnecessarily to high radon levels. With the E-perm system we have the ability to place test chambers side by side (duplicate measurements) which helps ensure accuracy of the radon value and complies with quality control protocols.
Long term testing
This is the best testing of a building and is recommended by Health Canada. As the reason being is during a short term period we will not experience many of the dynamics that could influence your indoor radon levels as we would over the long term. Long term is anywhere from 91 days up to a period of 365 days. Health Canada also recommends that a test period of no less than 30 days should be used to determine your need for mitigation.
Radon in Water
A small water sample is placed in the bottom of a glass jar. An E-PERM® radon monitor is suspended in the air phase above the water. The lid of the flask is closed and sealed to make it radon-tight. Radon reaches equilibrium between the water and air phase. At the end of the desired exposure period, the flask is opened and the E-PERM® removed. The average radon concentration in the air phase is calculated using the standard E-PERM® procedure. A calculation using this air concentration in conjunction with the other parameters gives the radon concentration of the water.
Radium Concentration in Soil
The procedure for measuring radium in soil is similar to that used for measuring radon in water.
A soil sample, weighing about 30 grams, is dried and humidified with 30% moisture. It is placed in a Petri dish and lowered to the bottom of the analysis bottle. An E-PERM® is suspended from the top of the lid. Radon emanated from the sample accumulates for a period from 5 to 15 days. At the end of the exposure period, the E-PERM® is taken out and the average radon concentration is calculated.
Using this information it is possible to calculate the radium concentration by assuming an emanation coefficient of 0.25. This coefficient is usually valid for most soils.
Radon Flux from Ground, Soils, Surfaces and from Building Materials
There are several applications for procedure. These include:
- Measuring radon flux from the uranium mill tailings
- Estimating indoor radon potential of building sites
- Uranium prospecting
- Radon emanation from objects and building materials
The E-PERM® H chamber is modified to feature a large, carbon coated Tyvek® diffusion window. The chamber is vented by filtered outlets so that it will not accumulate radon. When the E-PERM® flux monitor is placed on radon emanating surface, the radon enters through the Tyvek® barrier and exits through the vents. The semi-equilibrium radon concentration established inside the chamber is representative of dynamic flux from the surface. Because of the equilibrium between the ground and outside environment through vents, the flux emanation from the ground is not disturbed. The electret discharge rate of the electret is a measure of the radon flux. E-PERM® flux monitors are calibrated on the well-characterized radon flux beds at CANMET (Canada). These flux beds consist of 226Ra bearing material (well-characterized uranium tailings) 5.5 cm thick and 5 meter in diameter. The bed is precisely characterized by CANMET to provide a radon flux of 7.7 ± 1.1 pCi m2 sec-1 ( 7.7 flux units).
To measure Radon emanation rates from objects and building materials), the object is enclosed in an accumulator along with the E-PERM® radon monitor.