NATURE → Radon
Radon is a colourless, odourless radioactive gas that is emitted from the ground and which can cause lung cancer. It is formed by the radioactive decay of small amounts of uranium which occur naturally in all rocks and soils worldwide.
Different rocks (and their overlying weathered soils) have diffent concentrations of uranium so the amount of emmitted radon gas will vary depending on the nature of the underlying geology. Granite bedrock for example will contain higher levels of uranium so will produce higher levels of surface radon gas.
Measurement of Radon Levels
Radon concentrations in the UK are measured in becquerels per cubic metre of air (Bq m-3). The annual average level in UK homes is around 20 Bq m-3 which is low, and presents no cause for concern (average outdoor levels are around 4 Bq m-3). However, should annual indoor measured levels exceed 200 Bq m-3 you are at increased risk and action needs to be taken to mitigate radon ingress into your house.
Note, most countries use Bq m-3 to quantify radon levels but, in the USA, radon levels are measured in units of picocuries per liter (pCi/L) of air.
Radon action levels UK and Canada
Note the UK and Canada operate the same action levels
Source: http://radontech.ca/radon-gas/
Risk Profile
As mentioned earlier contamination by radon gas is not constant across the UK and radon levels within any particular property will also vary depending on the individual structure of that property and also relative to external local weather conditions. The British Geological Survey in conjunction with the UK Health Security Agency has produced an indicative atlas of radon concentration across the UK showing the likelyhood of any particular property being at or above the UK action level ie., 200 Bq m-3. I would recommend that you launch the Atlas (available online and free) and enter your postcode to check your risk of potential radon contamination.
BGS Indicative Atlas of Radon for the UK
Source British Geological Survey