Radon Surveys and Mapping of ²²²Rn Prone Areas. Annex I (French Edition)

Measures to control the public health risk from radon must be determined on the basis of knowledge of concentrations of radon indoors in a State. A number of international authorities have pointed to the need to understand concentrations of radon and their variations from place to place in determining the exposure due to radon of a population. This implies the need for radon surveys and ²²²Rn mapping. WHO has carried out a radon survey of a number of States. High concentrations of ²²²Rn indoors almost always derive ultimately from uranium in the ground. In some cases, building materials may give rise to high concentrations of radon indoors, but this is not the usual situation. Relatively high concentrations of ²²²Rn are associated with particular types of bedrock and unconsolidated deposits, for example, certain granites, phosphatic rocks and shales rich in organic materials. The uranium content is not the only determinant of the rate of ²²²Rn emission from rocks: permeability, the extent of fracturing and faulting, and weathering are also important factors. The impact of human activities such as mining also needs to be considered. Once ²²²Rn gas is released, its migration to the surface is governed by a number of complex processes. The movement of ²²²Rn from soil gas to indoor air is dependent on a number of factors which may vary greatly from building to building and with time