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Radon gas

Radon is a naturally occurring gas that comes from the decay of uranium. It has a high density, about 7.8 times that of air, and is formed as part of the decay series of uranium 238 from the decay of radium 226. Its short half-life makes it something we should be concerned about if it occurs in large quantities.

(See: Decay series)

Isotope Decay type Half life
Radium 226 alpha 1620 years
Radon 222 alpha 3.8 days
Polonium 218 alpha 3.1 minutes

Radon is responsible for almost 50% of the background radiation that we receive and just how much depends on the sort of houses we live in and where in the country (UK) those houses are. It is especially dangerous because it is a gas and so can be breathed in. This means the alpha particles that it emits will irradiate your lungs.

In Britain the region most affected by radon is the South West with areas like Dartmoor and Exmoor having a particularly high emission. Concentrations of the gas build up in underground caves and a small tunnel carrying a stream running under a hill on Dartmoor has its entrance closed by an iron grill with a 'danger radioactivity' sign fixed to it. A pub in the nearby village is supposed to have the most radioactive toilet in the whole country!

Modern houses are at risk more than older ones because they can act like sealed boxes. (See Figure1) Radon from the ground seeps up through the hardcore and concrete floor through minute cracks and then gets trapped in the house. Double-glazing, solid walls and well fitting ceilings and roofs all help to keep it in. The slightly lower air pressure inside a house compared with the outside is also a problem. The concentration of gas can build up overnight and then get less as people get up and open doors and windows.

Windy days help as soon as a door is opened the wind will disperse the gas.

A solution is to make a cavity in the hardcore and fit low energy pump that will pass the radon to the outside.

The danger is not great but it is something that people should be aware of.

The 'action level' for radioactivity from radon in the UK is 200 Bq/cubic metre but it is hoped to reduce this to 20 Bq/cubic metre which is the average level in the UK.

More excellent information on radon and other radiation issues may be found on the Health Protection Authority website.
Packs to test your own houses can also be bought from them.

© Keith Gibbs 2020