The bedrock under our neighbourhood contains small amounts of uranium. It’s an unstable chemical element that is subject to radioactive decay. The amounts are small and it wouldn’t be a problem but for the fact that one of the decay products is a gas at room temperature – a radioactive gas, radon. It seeps up through cracks in the rock and disperses into the atmosphere, unless it happens upon an enclosed space, such as a building, where it will accumulate. When radon decays it produces solid particles of radioactive polonium, bismuth and lead. These tend to cling to particles of dust and smoke in the air, and when you breathe these in, the heavy metals lodge in your lungs. There they decay, send out alpha radiation, and increase your risk of lung cancer. (The more smoke you breathe, the higher the radiation dose.)
The Swedish authorities recommend a highest level of radioactivity in indoors air of 200 Becquerels per cubic metre. My wife saw to it that during the winter we had two little particle collectors hanging from the ceiling for four months, with bits of sticky tape inside grabbing a sample of the ambient dust. When they were analysed, it turned out that the radioactivity in our winter air was 270 Bq/m3. This needs to be fixed.
The first thing to rule out was an unfortunate building material, blåbetong, “blue concrete”, which is a type of aerated autoclaved concrete. It was made from limestone and a carbon-rich slate and used up until about 1980, when it was realised that the slate contained enough uranium that the concrete blocks exude considerable amounts of radon. There’s no blue concrete in our house.
Then we called in a radon consultant. He came over with a fast measuring instrument that can give you a radon reading in ten minutes and proceeded to take four measurements.
Outdoors: 20 Bq/m3
Bedroom: 140 Bq/m3
Living room: 210 Bq/m3
Crawl space: 1570 Bq/m3
In the summers we open doors and windows a lot more, which explains why much of our house is currently below the recommended max radioactivity level. But our crawl space is not a healthy place to be, at eight times the max value. The radon collects down there and seeps up into the house. Luckily the problem is easily fixed: we just need to put a small fan in one of the crawl space’s air vents to suck the radon out of the enclosed space and into the atmosphere, and fresh air in. The municipality pays.