Granite, cancer, and windows

A few months ago I moved back to Spain to work at the Geography department of the University of Santiago de Compostela, at the NW of the Iberian Peninsula. The geological basement in this area is dominated by variscian granites containing Uranium.

The decay chain of Uranium produces Radon-222, a radioactive noble gas that escapes the bedrock and accumulates inside the buildings producing lung cancer.

The department of Geography is located in a historic building in the old town of Santiago with high levels of Radon accumulation.

Motivated by a desire not to die of lung cancer and a certain scientific curiosity, my office mate and I decided to buy a device that would measure the radon concentration in the office, and any other places. We finally got an Airthings Wave Plus, a relatively inexpensive device that detects radon gas through alpha spectrometry.

According to Airthings, the radon sensor consists of a passive diffusion chamber, which allows air samples to flow into it. There is a photodiode located inside this chamber, which essentially counts the amount of “daughter” radon particles in the air sample.

The device produces a 24-h rolling average of the radon concentration every hour, but this was not answering the questions we were asking:

  • Are the Rn levels below 300 Bq/m³ now?
  • How often do we need to open the window to keep a safe Rn concentration?

So we developed a methodology to use this device and our experimental data (open/close window times) to answer these questions:

The RadonSim tool can be downloaded from GitHub. It fits a simple model of radon accumulation/loss (thin blue line) according to the recorded ventilation pattern (top blue) to the data provided by the detector (thick black line):

9-day data and the fitted model.

The results show that the radon is eliminated by ventilation much faster than the accumulation rate. This means that, although radon accumulates in our office well above safe levels, it is possible to maintain a safe concentration by opening the window for one hour every 12 hours. So we just need to air the room one hour in the morning and work safely the rest of the day.

Lung cancer mitigation measures.

If you are also playing with a domestic radon detector that yields 24-h averages and just want to have a look at how the short-term data looks like, you can download Airthings plotter from my GitHub too.

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