Radon (Rn) is a radioactive chemical element with an atomic number of 86, generated by the decay of uranium and thorium. In its natural state on Earth, it exists as a colorless, odorless noble gas that can accumulate in homes, buildings, and basements, remaining undetectable without specialized equipment. The decay products of radon (also known as radon daughters or radon progeny) are the primary source of ionizing radiation exposure in humans. Since radon and its progeny are radioactive, no level of human exposure is considered safe.
Specialized equipment for detecting and measuring radon can be expensive. Before investing in a radon detector, it may be helpful to determine whether such an investment is necessary. This article explains how to screen for the presence of radon without using a dedicated radon detector.
Detecting Radon Decay Products
Radon has four key decay products: Po-214, Po-218, Pb-214, and Bi-214. All of these have half-lives of less than 30 minutes. By observing their presence and confirming their decay over time, we can infer the presence of radon. These radon daughters primarily decay via alpha decay, with some beta and gamma emissions.
To detect these decay products, you will need a Geiger-Mueller counter capable of detecting alpha, beta, and gamma radiation. Suitable devices include:
● A pancake tube detector (e.g., GQ-GMC-600+)
● A mica end-window device (e.g., SEI Monitor 4)
● Standard glass Geiger-Mueller tubes (e.g., M4011) will not detect alpha particles and are unsuitable for this procedure.
Procedure
1. Measure Background Radiation
● Use a Geiger counter that detects alpha particles.
● Measure and document the background counts per minute (CPM) at the location of concern.
2. Collect a Sample
● Remove an HVAC filter or another air filter that has been actively filtering air for at least two hours.
3. Measure Filter Radiation
● Take the measurement at the same location as the background reading.
Place the Geiger counter’s pancake tube or probe directly over the used filter.
Record the maximum stable CPM.
4. Measure After 48 Hours
● Wait 48 hours, then take and document another measurement of the filter.
Interpretation of Results
No Increased Radiation
If the freshly removed filter’s reading is similar to the background level, no radon progeny have been detected, meaning there is no evidence of radon presence.
Temporary Increase in Radiation
If the initial filter measurement is higher than the background, check the 48-hour measurement. If the 48-hour measurement returns to background levels, you have confirmed that the initial radiation was from radon decay products, which have since decayed.
Persistent Radiation Beyond 48 Hours
If the 48-hour measurement remains the same as the previous measurement, you may have radioactive dust or particulates trapped in your air filter. This scenario is unlikely but should be taken seriously. Contact your county health department as soon as possible for further evaluation.
By following this method, you can perform an initial screening to determine if purchasing a radon detector is necessary. However, for precise measurements and long-term monitoring, a dedicated radon detector is recommended.