“…For some geological situations, radon migrates long distances from its place of origin and can be detected by alpha particle recorders at the earth surface [2,3]. This rate of migration is affected by many factors, such as distribution of 226 Ra in the soil and bedrock, soil porosity, micro-cracks of bedrock, rainfall, air temperature, barometric pressure and surface winds [4,5]. The fraction of radon atoms released into a rock or soil pore space from a 226 Ra bearing grain is expressed in terms of 'radon emanation coefficient', which is mainly affected by the size of soil grain and soil moisture condition [6].…”