Population dose distribution due to soil radioactivity concentration levels in 18 cities across Nigeria.

The natural radioactivity concentrations in soil samples collected from 186 locations across 18 cities in the six geo-political zones of Nigeria have been determined using gamma-ray spectrometry. Results show that the concentrations of (40)K, (238)U and (232)Th in the soil samples varied from below detection limits (BDL) to 1459.4 Bq kg(-1) with a mean of 73.3 +/- 18.5 Bq kg(-1) for (40)K, whereas for (238)U and (232)Th values varied from 9.2 to 113.7 Bq kg(-1) with a mean of 33.9 +/- 7.4 Bq kg(-1) and from BDL to 175.7 Bq kg(-1) with a mean of 12.4 +/- 3.1 Bq kg(-1), respectively. The average gamma absorbed dose rate in air across the cities ranged between 19 +/- 5 and 88 +/- 44 nGy h(-1) and the gross mean was 42.0 +/- 21.0 nGy h(-1). Using available population data in the study areas, about 2.84% of the population is exposed to a radiation dose rate of less than 20 nGy h(-1), 52.40% to a radiation dose rate between 20 and 30 nGy h(-1), 31% to a radiation dose rate between 30 and 60 nGy h(-1) and about 13.76% to dose rates greater than 60 nGy h(-1).