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.