Pedantically, we could say that your house is literally bathed in radiation day and night, since visible light is radiation, and so are the infrared wavelengths coming from your radiators and the 2.4GHz frequency radio waves from your home Wi-Fi and mobile phone.
But what you’re probably referring to is ionising radiation – the kind powerful enough to knock electrons out of atoms and thereby cause cancer and, at very high doses, radiation poisoning and burns.
Old-fashioned cathode-ray tube monitors used to be a low-level source of ionising X-rays, but these have virtually all been replaced with flat-screen monitors, which don’t emit X-rays. So the remaining domestic sources of radiation are mostly things that contain small amounts of radioactive elements. Bananas, for example, contain enough of the isotope potassium-40 that eating one gives you 0.0001 millisieverts (mSv) – roughly the same radiation dose as living within 80km (50 miles) of a nuclear power plant (in other words, virtually none).
Brazil nuts are about five times more radioactive as a result of the very deep roots of Brazil nut trees that concentrate radioactive radium in the soil. But eating two or three Brazil nuts a day is still perfectly safe.
Smoking is already very bad for your health of course, but it’s made slightly worse by the fact that the fertilisers used on tobacco plants contain radioactive radium, lead and polonium, making a single cigarette as radioactive as seven bananas.
Smoke detectors contain tiny amounts of the isotope americium-241. Americium emits radiation by alpha decay, which can be completely blocked by as little as a sheet of paper so it never escapes the smoke detector case and would only be a health hazard if you ate it.
Speaking of eating, some ceramic plates and cups made between the 1930s and 1970s used uranium oxide glazes. Eating or drinking from these was roughly equivalent to eating one banana an hour.
But if you mean how radioactive is your house, specifically (as in the building in which you reside), well that depends on where you live. If you live in the Southwest of England, then the largest source of the radiation in your home by far is the granite beneath it.
Granite naturally contains some uranium, and this undergoes radioactive decay to form radium and then radon gas. This gas seeps slowly into the air and, because it emits alpha radiation, can increase the risk of lung cancer if the concentration is allowed to rise.
In parts of the UK with lots of granite, such as Cornwall, the background dose can be 7.8mSv per year (78,000 bananas). The health risks of radon in the home can be greatly reduced by improving ventilation, particularly in basements, to prevent the radon gas concentration from building up.
Radiation dose also increases with altitude, because there’s less atmosphere between you and the cosmic rays bombarding Earth from space. Each day you spend in Denver, Colorado (altitude 1,600m/5,200ft) gives you an extra 12 bananas worth of radiation, while a single transatlantic plane flight will give you about 0.04mSv of radiation (400 bananas).
If you’re lucky enough to be one of the astronauts that calls the International Space Station home, a six-month stay up there would add another 80mSv. Which is quite a lot, but still better for your health than eating 800,000 bananas!
Read more:
- Top 10: Which are the most radioactive foods?
- How many bananas would I need to eat to become radioactive?
- Can life survive in a radioactive environment?
- Why are there still radioactive elements after billions of years?
Asked by: Albie Hewitt, Ripon
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