This article outlines a method for inferring and confirming the presence of radon gas with the Radiacode 103. This approach allows for qualitative detection without a dedicated radon detector by analyzing an exposed air filter in a low-background environment over a few hours. As radon in the air decays, its daughter products can become trapped in the air filter, making it a temporarily contaminated source for testing.
Since radon progeny may undergo alpha, beta, and/or gamma decay, we will use the Radiacode 103 to demonstrate the decay of the gamma-emitting progeny, Pb-214, and Bi-214. Both of these have half-lives of less than 30 minutes, necessitating a few hours to complete this series of automated measurements.
A steady logarithmic decrease in the count rate over time can indicate the presence of radon daughter decay. Furthermore, we can confirm the presence of radon daughters by identifying the characteristic gamma emissions of Pb-214 (at 295 keV and 352 keV) and Bi-214 (at 609 keV) from the Radiacode spectrum measurement.
Please note: These instructions are intended to demonstrate the general method of detecting and confirming the presence of radon gas progeny with the Radiacode 103 via its mobile app (available for Android and Apple). This procedure was used to successfully confirm the presence of radon progeny when a fiberglass air filter was exposed to a known concentration of 3 pCi/L for three hours, as shown in the following images.
Required Materials
- Radiacode 103
- One new fiberglass air filter
- Air filtering device (e.g., a fan with a filter)
- Lead Shielding (if necessary)
Procedure
1) Expose the Air Filter
• Place the new air filter into your air filtering device. It is not necessary to perform this testing with a dirty air filter as using a clean one will produce sufficient results.
• Run the air filter fan for at least three hours to circulate the air in the environment you want to test and filter out potential radon progeny.
?? Safety Warning: During this procedure, the air filter may accumulate radon progeny, short-lived radioactive isotopes such as Po-214, Po-218, Pb-214 and Bi-214. While their half-lives are less than 30 minutes, care should still be taken when handling the exposed filter. Use gloves to avoid direct contact, and avoid inhaling any dust or fibers released when cutting or moving the filter material. Perform the procedure in a well-ventilated area and keep the sample away from children and pets. Once testing is complete, the filter may be safely discarded in regular household trash, as the radioactive daughters will decay to background levels in a matter of hours.
2) Measure Background Radiation
- While the air filter is being exposed, we will measure the normal background gamma radiation count rate for the same location where the exposed air filter will be measured.
- Power on the Radiacode 103 and connect it to the mobile app.
- In the spectrum tab, tap the three-dot menu and select Restart Accumulation. This will reset the average count rate displayed near the top of the spectrum tab.
- After approximately five minutes, note the new average count rate.
- If the average background count rate is above 100 CPM (counts per minute), lead shielding may be required to better demonstrate the logarithmic decay and enhance the spectrum peaks.
- In our example, the average background was 288 CPM, so 3/8” thick lead shielding (in the form of two lead pigs) was used to mitigate the background below 30CPM for the final measurement.
- If using lead shielding, repeat this background measurement step with the shielding in place and record the shielded background count rate.
3) Measure the Filter
- After the air filter has been exposed for the required time, carefully remove it.
- Cut out a strip of the filter measuring approximately 2×10 inches.
- Wrap the exposed filter material sample around the detecting end of the Radiacode 103.
- Stuff the filter wrapped device as far as possible into one of the lead pigs (if using shielding), ensuring the filter sample remains positioned at the detecting end of the Radiacode 103.
- Fully enclose the filter-wrapped Radiacode 103 by placing the second lead pig over the remainder of the device (if using shielding).
- With the Radiacode 103 connected to the mobile app, select Restart Accumulation to reset the spectrum and average count rate.
- Observe the starting count rate. Keep the spectrum running until the instantaneous count rate is observed to be close to the background count rate. This can take 8 to 10 hours, starting with an instantaneous count rate around 700 CPM in our example.
- To read the instantaneous count rate, switch to the Charts tab; it’s displayed on the top chart.
- Once the spectrum measurement is complete, select Save Spectrum to Library from the three-dot menu in the spectrum tab.
- Save the spectrum and switch to the Charts tab. Adjust the visible time frame so that the entire testing period is visible in the chart.
- Take a screenshot at this point to save the chart for easy future reference.
Interpretation of Results
Radon (Progeny) Not Detected:
If the starting count rate is similar to the background count rate, it suggests that no significant amount of radon progeny was detected on the filter.
Radon (Progeny) Inferred:
If the starting count rate is substantially higher than the background count rate, and you observe a steady decrease in the count rate over time in the chart, radon progeny decay can be inferred. This strongly suggests that radon gas was present in the air being filtered.
Test Invalid:
If neither of the above situations applies, there might be an issue interfering with the analysis. Repeat the procedure, paying close attention to the background measurement and ensuring proper setup.
Radon (Progeny) Confirmed:
If you observe distinguishable peaks at approximately 295 keV, 352 keV, and 609 keV in the saved spectrum, and radon progeny has been inferred by a decreasing count rate, you can confidently say that radon (progeny) has been detected. However, the concentration remains unknown. A dedicated radon detector should be used to quantitatively determine the radon gas concentration.
Conclusion
This method provides a practical and accessible way to qualitatively infer and confirm the presence of radon gas by detecting its short-lived progeny using the Radiacode 103. While it is not a substitute for quantitative radon testing with a calibrated detector, this process effectively demonstrates the principles of radioactive decay, particularly for gamma-emitting daughters like Pb-214 and Bi-214. By minimizing background radiation and observing both spectral peaks and count rate decay, users can gain meaningful insights into potential radon exposure in their environment and provide solid evidence to justify future investment.