5. Sources and levels of exposure

Figure 6 shows the levels of exposure to which we are subjected according to the nature of the sources and their origin. These figures represent averages, as exposure levels vary widely from region to region, depending on the natural environment, lifestyle or medical practices.

In terms of natural radiation, cosmic rays are homogeneous throughout mainland France, varying essentially with altitude and only slightly with latitude (at sea level, they are identical in Dunkirk and Marseille). On the other hand, radiation from land-based sources varies according to soil type: for example, exposure levels can vary by a factor of 3 between Landes (sandy soils) and Morbihan or Cantal (granitic soils).