The outdoor ? radiation exposure dose rates due to the radioactivity concentration of 40K, 238U and 232Th in the soil across different environments in Nigeria have been carried out using the low-cost method of in situ ? ray spectrometry. Measurements were made in 18 cities, spread across the three major zones of the country. The radioactivity concentrations of these radionuclides in the soil were used to determine their ? radiation absorbed dose rates in the air. The range of average total dose rate due to the three radionuclides in the Eastern zone is between 0.025 and 0.081 µGy.h-1 with an average of 0.040 ± 0.006 µGy.h-1, 0.041 and 0.214 µGy.h-1 with a mean of 0.089 ± 0.014 µGy.h-1 for the Western zone and between 0.066 and 0.222 µGy.h-1 with a mean of 0.102 ± 0.032 µGy.h-1 for the Northern zone. The average annual outdoor effective dose equivalents of 51 ± 8 µSv.y-1, 114 ± 18 µSv.y-1 and 130 ± 41 µSv.y-1 have been estimated for the Eastern, Western and Northern zones, respectively. The average annual effective dose equivalent for the country has been estimated to be 98 ± 15 µSv.y-1 and the collective effective dose equivalent as 9.7 x 103 man.Sv.y-1. Measurements have been taken as representing the baseline values of natural radioactivity as no artificial radionuclide was detected at any of the sites surveyed.
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Farai et al. (2000) studied this question.