Area and time distribution of external and internal doses from Chernobyl fallout: the lack of correlation in Norway.

Population doses from external radiation and internal food-based radioactivity were calculated each month for each municipality for 3 y immediately following the Chernobyl contamination in Norway. The main polluted regions are sparsely populated but comprise important food production areas. The external dose data base was calculated based on fallout deposition and measurements in dwellings, whereas the totally independent internal dose data base was calculated on a large number of food measurements and knowledge of both the food distribution system and the countermeasures taken. The internal dose in the densely populated municipalities was comparably higher than expected from local deposition, despite the fact that countermeasures had some effect. Thus, the correlation between internal and external dose for individual municipalities is rather weak. This study shows that a traditional deposition/transfer factor approach may be inappropriate if used in countries with large variation in population density and agricultural ecosystems and in combination with effective countermeasures.