eng Science and Education Publishing International Journal of Physics 2333-4576 2015-11-25 3 6 244 247 10.12691/ijp-3-6-4 IJP2015364 article OJO Taiwo John talk2ojotj@yahoo.com 1 GBADEGESIN Karonwi A. Joseph 1 Physics Unit, Department of Science Technology, The Federal Polytechnic, Ado-Ekiti Nigeria The activity concentrations of natural gamma-emitting radionuclides 238U, 232Th and 40K in soils from 7 sampling sites each in Ondo and Lagos States, southwestern Nigeria have been measured by using a well calibrated Hyper Pure Germanium Detector (HPGe). The mean activity concentration values of 39.24±1.12, 52.86±1.40 and 445.02±12.24 Bq kg-1 for 238U, 232Th and 40K respectively were obtained for . Activity concentration values of 23.21±0.92, 22.84 ± 0.78 and 204.02±7.00 Bq kg-1 were recorded for 238U, 232Th and 40K respectively for . The results obtained were used to estimate the absorbed dose rates in outdoor air which was found to be in the range of 12.35±179.59 nGy h-1 for Ondo State and 5.91±83.29 nGy h-1 for Lagos State with an overall mean values of 67.50±1.86 nGy h-1 and 33.83±1.17 nGy h-1 respectively for the two States. The corresponding outdoor annual effective dose rates were estimated to be between 22.7 and 330.6 μSv y-1 for and between 7.3 and 102.2 ̦Sv y-1 for assuming 30% and 20% occupancy factors for the two states respectively. The average outdoor annual effective dose rate for towns in Ondo State is 64.85 ̦Sv y-1 representing 92.64% of the world average value (70 ̦Sv y-1) given by UNSCEAR. However, the cities in have an average outdoor effective dose of 41.52 ̦Sv y-1 which is less than 60% of the world average value. The values of the collective effective dose as calculated from the outdoor annual effective dose rates were found to be 540858 and 273296 person-Sv for Ondo and Lagos States respectively. http://pubs.sciepub.com/ijp/3/6/4/ijp-3-6-4.pdf radionuclide activity concentration outdoor effective dose absorbed dose