The specific activities of natural radionuclides in twenty seven samples
collected from the eastern Dahomey basin in southwestern Nigeria were
evaluated. Experimental results were obtained by using a 3" x 3" sodium
iodide NaI(Tl) detector. A major trace element assessment of the samples was
made by Inductively Coupled Plasma Mass Spectrometry techniques. Gamma ray
radioactive standard sources, 137Cs and 60Co, were used to calibrate the
measurement system and the International Atomic Energy Agency SOIL-375
radioactive standard source was also used to analyze and compute the specific
activities of desired natural radionuclides. Three radioelements, viz. 238U,
232Th and 40K, were identified in the samples with the following specific
activities of 238U ranging from 9.88 ? 4.70 Bq/kg to 69.15 ? 12.37 Bq/kg with
an average of 26.50 ? 7.18 Bq/kg; 232Th from 12.78 ? 5.16 Bq/kg to 36.86 ?
13.35 Bq/kg with an average of 22.77 ? 4.28 Bq/kg; 40K ranging from 189.82 ?
79.51 Bq/kg to 518.77 ? ? 119.54 Bq/kg with an average of 297.69 ? 16.21
Bq/kg. The result was compared with the world mean values of 35, 30 and 400
Bq/kg, respectively, specified by the United Nations Scientific Committee on
the Effects of Atomic Radiation. The mean result obtained for the radium
equivalent, total absorbed dose rate, external hazard index, internal hazard
index, and the annual effective dose equivalent, were 79.90 Bq/kg, 38.50
?Sv/h, 0.22 Bq/kg, 0.29 Bq/kg, and 47.22 ?Sv, respectively. With respect to
radiological risk to human health, the absorbed gamma dose rate in air was
estimated to be in the range of 21.7 ? 0.4 to 155.7 ? 2.2 ?Sv/h; the outdoor
annual effective dose equivalent was evaluated to vary from 26.6 ? 0.4 to
190.9 ? ? 2.7 ?Sv with the arithmetic mean value of 79.06 ? 33.23 ?Sv and
compared to the world-wide effective dose of 70 ?Sv. Also, the values of the
radium equivalent and the external hazard index for all samples in the study
area were found to be lower than the accepted safety limit value of 370 Bq/kg
and equally below the limit of unity, respectively. The results indicate
that, at present, the radiation hazard from radionuclides in all samples
analyzed is within permissible limits.