Radiation occurs from two sources. Natural radiation exists due to materials present in the earth and particles arriving from outer space. Artificial radiation is caused by man made processes. There is no difference in the effects of the radiation regarding it's source.
An average person in the UK will receive approximately 10% of their annual dose of radiation from the suns cosmic rays, whilst another 50% is due to Radon (Rn) a gas generated from naturally occurring uranium present in the earth. Artificial radiation sources included medical treatments (approximately 15%) and fall out from nuclear tests and accidents (approximately 1%).
For more information see Radon in Ribble Valley.