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Radon & Radioactivity Measurement Safety Guide

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Measuring radioactivity from radon is potentially very confusing for the lay person for several reasons. One of which is that there are several different units of measurement depending on the application, era of standards and preference based on world regionalisms. Applications include activity, (which radon measurement falls under) absorbed dose, which is the measure of radioactive energy absorbed by tissue per unit mass and dose equivalent which is the measure of absorbed doses from DIFFERENT types of radioactivity such as alpha, beta, and gamma radiation. Many scintillation meters still measure this in the older measurement unit rem (Roentgen Equivalent Man) or microrems for gamma radiation.

For instance, when measuring radon, North America prefers to use the picoCuries per liter (pCi/L) designation as opposed to Becquerels  or Bq / meter^3 which is typically used in Europe and the UK. These both measure a specific number of atomic disintegrations per volume of space.

In the case of the Becquerel, this is 1 atomic disintegration per second or 60 events per minute. For a picoCurie, this is translated as 2.2 radioactive disintegrations per minute. A convenient conversion chart is shown below.

Just as a quick conversion from the picoCurie/liter to the Becquerel / m^3:

1 picoCurie / liter = ~ 37.1 Bq/m^3     EPA action limit 4 pCi/L = ~ 148.4 Bq/m^3

Units of Measurement for Radioactivity and Dose

Units of Measurement for Radioactivity and Dose

As an added note, a little known unit of radon is what is known as a Working Level (WL) which is the quantity of radon that will produce 1.3 X 10^5 MeV (Mega Electron Volts) of potential alpha particle energy per liter of air. A single WL of radon is equal to the RDP’s (Radon Decay Products) in equilibrium with 100 pCi/L of radon. Because the equilibrium value for RDP’s for indoor environments is typically 0.5, radon concentrations of 1 WL would be around 200 pCi/L.

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Radon Gas Mitigation Solutions in Brief

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While I do not personally perform radon mitigation, I wanted to share in brief what is generally entailed. The cost in the Dallas area for reducing radon below the EPA action limit of 4.0 pCi/l varies depending on the construction / size of the house and how high the levels are. In general, you can expect an estimate of anywhere from $2000 – $5000.

It is suggested that the solution follow the ASTM E-2121 standard for lowering radon and that information can be found in detail here:

http://www.astm.org/Standards/E2121.htm

While homes that contain excessive radon can be found in every state in the nation, many people (such as in Texas) are not aware that it is a problem, nor is testing / mitigation required by Texas law as of this writing. However it is not unusual for some relocation companies to require testing for radon gas first as a condition of a real estate purchase.

Bear in mind that radon levels do fluctuate with weather conditions and home ventilation, so before investing in a mitigation expense, it may be worth testing more than once.

The main idea behind mitigation is to ventilate the excess radon (which is heavier than air) to the outside so as to minimize impact to occupants. The method by which this is done depends on whether you have a basement (rare in the Dallas/Ft. Worth area) have a pier and beam or slab on grade foundation.

For slab foundations, sealing the interior spaces from the ground is generally not enough, and often a soil suction system is required to actively draw the radon out via a vent pipe and specialized fan. These systems are generally referred to as active soil depressurization, sub-slab depressurization or just simply soil suction.

In some cases, a heat exchanger or ERV (Energy Recovery Ventilator) can recover some of the energy lost in the process of exchanging the vented radon to the outside with fresh air.

For pier and beam foundations (houses with crawlspaces) you can cover over the base soil with a special heavy duty plastic sheet whose underside connects to a ventilation system similar to the one described above in a method known as sub-membrane suction.

Sub-membrane Suction Radon Mitigation

Sub-membrane Suction Radon Mitigation