What Is Radon and How Do You Detect and Measure It?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. Because it is a gas, it can seep into buildings through floors, foundations, and gaps, where it can accumulate to levels that matter for health. The practical way to know whether a building has a problem is to measure it: short-term detectors give a quick indication, while long-term detectors (commonly passive track-etch plastics such as CR-39/PADC) give the reliable average needed to decide on mitigation. This article explains the mechanism, the main measurement options, how a test is run, and how to read the result.
What radon is and why it is measured
Radon forms as uranium and radium in soil and rock decay. It is chemically inert as a gas, so it moves through the ground and into the air rather than binding to surfaces. Indoors, it can concentrate when ventilation is low and the building sits over radon-producing ground.
The health concern is long-term exposure. Radon decay produces radioactive particles that can be inhaled; prolonged exposure raises the risk of lung cancer, and the risk is greater for smokers. This is why measurement, not guesswork, drives decisions: two similar houses on the same street can differ substantially because of soil, construction, and how the building is used.
How radon is detected and measured
Different methods trade speed against accuracy.
| Method | How it works | Typical use |
|---|---|---|
| Passive track-etch detectors (CR-39/PADC) | Alpha particles from radon decay leave damage tracks in the plastic; etching and counting reveal track density, which corresponds to radon exposure | Long-term average measurement, the basis for deciding on mitigation |
| Charcoal canisters | Charcoal adsorbs radon over a short period, then the canister is analysed | Quick screening |
| Electronic monitors | Continuous sensing with immediate readout | Short-term checks, tracking how levels vary over time |
Track-etch detectors are widely used because they are passive (no power needed), integrate exposure over months, and are analysed in a laboratory. TASL, a Bristol-based company, manufactures dosimetry-grade TASTRAK PADC (CR-39) plastic and supplies TASL Image systems for reading such detectors, alongside radon measurement services. Its detectors are used in radon measurements, neutron dosimetry, and nuclear technology, and the company states ISO-accredited laboratories in Europe, HSE accreditation in the UK, and NVLAP accreditation in the USA.
How a radon test is carried out
A typical long-term test follows this sequence:
- Placement. Detectors are set in occupied rooms, typically the lowest lived-in level, away from drafts, direct heat, and exterior walls where practical. Placement matters because radon concentration varies within a building.
- Exposure period. The detector is left in place for the measurement period — long-term tests run for several months to average out daily and seasonal variation.
- Retrieval and analysis. The detector is returned to a laboratory, where track-etch plastic is etched and the tracks are counted, or the analysis method appropriate to the detector is applied.
- Reporting. The result is expressed as a radon concentration, allowing comparison against the relevant reference level.
The key point is that the exposure period and placement determine what the number means. A short test tells you about that window; a long test tells you about the average you are actually living with.
Interpreting results and deciding what to do
Compare the reported concentration against the action level that applies where you are — these are set by national authorities and differ by country, so check the current local figure rather than assuming one. If the reading is at or above the applicable level, the next step is mitigation: sealing entry routes, improving sub-floor ventilation or installing a radon sump, and increasing general ventilation. Because radon varies over time and between rooms, a single borderline result may warrant a confirmatory long-term measurement before committing to structural work.
Where to go next
If you need detectors or analysis, look for a laboratory with relevant accreditation and a documented measurement protocol, and confirm the exposure period and reporting format before you start. TASL's site provides information on TASTRAK PADC plastic, TASL Image systems, radon detectors and services, plus publications and downloads, and lists authorised agents for different regions.