Alpha Track Detector

The CR-39 Plastic Technology

Alpha track detectors contain a small piece of CR-39 plastic, a special polymer that records the path of charged particles. When radon decays, it releases alpha particles (helium nuclei) that travel through the air and strike the plastic surface. Each alpha particle creates a microscopic track—a tiny path of damage—in the plastic material. These tracks accumulate throughout the testing period. The number of visible tracks corresponds directly to the amount of radon exposure, allowing laboratory analysis to calculate the average radon concentration over the entire test duration.

Long-Term Testing: 90+ Days

Alpha track detectors are designed for extended monitoring periods, typically 90 days (approximately 3 months) or longer. The EPA recommends minimum testing periods of 90 days for establishing reliable baseline radon levels. Some homeowners extend testing to 6-12 months to account for seasonal variations in radon levels. The longer testing period captures the typical range of radon concentrations throughout different seasons and weather conditions, providing a much more representative average than short-term tests.

Advantages Over Short-Term Testing

Short-term tests (2-7 days) can be significantly affected by temporary conditions—weather patterns, door/window openings, heating and cooling system operation. Radon levels fluctuate daily and seasonally, meaning a short test might capture an unusually high or low reading that doesn't represent typical exposure. Alpha track detectors eliminate this variability by averaging radon levels over months, providing results that reflect true long-term radon conditions. This makes alpha track results far more reliable for deciding whether radon mitigation is necessary. For critical decisions like home purchases or legal determinations, alpha track detectors provide the credible evidence that short-term devices cannot match.

Laboratory Analysis Process

After the exposure period, the alpha track detector is sealed and mailed to a certified laboratory. The lab uses specialized equipment to chemically etch the CR-39 plastic, enlarging the microscopic alpha tracks so they become visible under a microscope. A technician counts the visible tracks to quantify radon exposure. The number of tracks, divided by the exposure time, equals the average radon concentration in pCi/L (picocuries per liter). Results are returned to the homeowner with a detailed report showing the calculated radon level and measurement uncertainty.

Accuracy and Measurement Uncertainty

Alpha track detectors have excellent accuracy when used properly, typically with a measurement uncertainty of ±25-30%, particularly for longer testing periods. This uncertainty accounts for variations in radon distribution within the home and inherent limitations in counting alpha particle tracks. For context, this level of accuracy is significantly better than short-term electronic devices (±50% uncertainty or higher). The uncertainty decreases with longer testing periods and higher radon levels. A 90-day test result of 3.5 pCi/L with 25% uncertainty means the true level is likely between 2.6-4.4 pCi/L—precise enough for making mitigation decisions.

Cost and Practical Considerations

Alpha track detectors are among the most affordable radon testing options, typically costing $15-$30 per device. Many hardware stores, health departments, and online retailers sell these devices. The low cost makes it practical to test multiple locations in a home—basement, main living level, and bedrooms—simultaneously. Being passive devices, alpha track detectors require no electricity, no setup, and no monitoring during the test. Simply open the detector, place it in the test location, and leave it undisturbed for 90+ days. The simplicity and affordability make alpha track detectors the recommended first choice for homeowners evaluating radon risk.

Proper Placement for Accurate Results

For accurate results, alpha track detectors must be placed in living areas (not crawl spaces or attics) at least 20 inches above the floor. Placement in basements where families spend time is typical for initial testing. The detector should be in areas with average air circulation—not directly above heating vents, not in extremely drafty locations, and away from exterior walls. Avoid kitchens and bathrooms where ventilation affects radon distribution. The detector must remain undisturbed throughout the testing period—don't move it, seal it, or expose it to moisture. These placement guidelines ensure results represent actual radon exposure.

When to Use Alpha Track Detectors

Alpha track detectors are the ideal choice for initial baseline radon testing in any Ohio home, particularly for:

• • Initial screening to determine if mitigation is needed
• • Real estate transactions requiring defensible test results
• • Multi-room testing to identify radon hotspots
• • Seasonal variations assessment (spring/fall testing)
• • Legal proceedings or insurance claims
• • Post-mitigation verification after system installation