Over half the background radiation that we receive comes from radon gas, a naturally occurring daughter product of Uranium decay. It is present in granite -some granite buildings have radon monitors installed; Cornwall in the UK is a prime location – giving people a scare some years ago. Concentration is higher indoors due to lack of ventilation and U based building products. Cosmic radiation sources are galactic cosmic rays, geomagnetically trapped particles and solar cosmic rays. The amount of cosmic radiation varies with atmospheric thickness, i.e. altitude and latitude, so taking a plane ride increases our exposure to background radiation. On the ground, fortunately, the atmosphere provides an effective shield. The gamma and x-ray radiation from the soil is due to uranium and thorium decay chains and naturally occurring Potassium-40 and varies with geographical location. A man of mass 80kg probably has 160g of K in his body of which radioactive 40 K comprises 0.01% of the total so we ourselves contribute to our own background dose. Rich sources of potassium in our foods are ready to eat apricots and tomato puree – thus in baked beans also, so it really is true – eating baked beans irradiates you. Here’s the whole nine yards, but percentages vary geographically. The chart includes consumer products such as tobacco products which contain 210 Po, a compelling reason for giving up smoking, domestic water containing 226 Ra and 220 Rn, combustible fuels, ophthalmic glass containing thorium for rose tinting, luminous dials and signs containing 3 H and 147 Pm and smoke detectors containing 241 Am amongst many others. It’s worth pointing out that nuclear warfare, nuclear accidents and controlled detonations add very little to global body irradiation per person, although the Chernobyl disaster of 1986 released 1.4 EBq (exabecquerels) of radiation and caused significant local damage.