Indoor and outdoor gamma radiation exposure levels in selected residential buildings across Ondo state, Nigeria

Indoor and outdoor gamma radiation exposure levels were measured in a total of 360 randomly selected dwellings categorized as local, semi-modern and modern buildings across Ondo State, Nigeria to determine the annual effective doses. All radiation measurements were taken using a calibrated Kindenoo PG-15 Geiger Muller detector and a GPS for geographical coordinates of sample points. Equal number (360) sample point measurements were carried out for indoor and outdoor measurements. Measurements at each location point were performed holding the survey meter at 1 m above ground surface or floor to avoid unwanted effects of radiation from soil or building floor. The detector was also held at least six to seven meters away from buildings nearby in order to avoid unwanted effects of the building materials on outdoor measurements. Each measurement was repeated six times and the average was taken to represent the value for a sample point. The average outdoor and indoor dose rates were determined as 263 ± 32 μSvh-1 and 213 ± 64 μSvh-1 respectively. The highest contribution to the total indoor dose was from the local buildings followed by semi modern buildings and the modern buildings contributed the least dose. The average annual effective dose was calculated as 1.56 ± 0.33 mSv, which is higher than the world average value (0.48 mSv). In view of the potential radiation resulting from building materials, comprehensive assessment of natural radiations in such materials is required.