Several instruments may be used to determine the concentration of Radon in a dwelling. The most popular being the alpha-track detectors (ATDs), electret ion chambers (EICs), and activated charcoal detectors (ACDs), according to the WHO International Radon Project.
Table 1. Radon measurement devices are listed by their electricity needs, costs, and length of use, as determined by the World Health Organization.
Detector Electrical Source Length of Test Cost
Alpha-track Detector (ATD) Passive 1-12 Months Low
Activated Charcoal Detector (ACD) Passive 2 - 7 Days Low
Electret Ion Chamber (EIC) Passive 5 Days - 1 Year Medium
Electronic Integrating Device (EID) Active 2 Days - Year(s) Medium
Continuous Radon Monitor (CRM) Active 1 Hour - Year(s) High
Alpha-track Detectors (ATD) are a plastic substrate that is enclosed in a diffusion chamber which does not permit the entry of Radon decay products. When Alpha particles are produced close to the detector, a track is made in the detecting material causing a latent alpha track to be formed. The number of tracks on the surface is relative to the concentration of Radon gas.
Activated Charcoal Detectors (ACD) function on the principle of detection that Radon is absorbed on the active sites of the activated carbon. After collection occurs, the detector is sealed and the Radon decay will equilibrate with the collected Radon. The amount may then be counted using gamma counting or be prepared analytically for liquid scintillation techniques.
Electret Ion Chambers (EIC) are made from an electrostatically charged disk in a chamber into which Radon may diffuse. The decay products cause the voltage of the electret to decrease. A calibration factor is then used to calculate the amount of Radon present to the amount of decrease in the voltage.
The faster measurement methods involving continuous monitors require a trained operator and expensive equipment and will normally have prices starting at $200. Wolfville homeowners may request to have their houses tested for free. Please see the link on the left.