Results of Yangjiang study in China and an experience of Ramsar survey in Iran

While we attempted to assess the annual effective doses of inhabitants living in high levels of natural radiation areas (HLNRAs) in Yangjiang, China, the number of subjects was too large to determine directly each dose of all inhabitants with personal dosimeters. Individual dose rates were therefore estimated from ambient radiation dose rates and occupancy factors, based on the result of preliminary examination, which had indicated a good correlation between dose values obtained through this estimation and personal dosimetry. In Ramsar, Iran, studding was observed around springs with a high level of natural radiation, and outdoor dose rates varied largely and irregularly, even within a narrow area. Owing to the uneven distribution of natural radiation sources in building materials, indoor dose rates were so grossly different, even among rooms, that it appeared difficult to accurately estimate individual dose rates of inhabitants in these areas by the abovementioned indirect method. Consequently, it would be reasonable that direct and indirect methods are applied properly according to objects of study and some conditions, such as level of individual doses and number of inhabitants.