Afolabi OM *,Aboluwoye CO ,Ajayi IR
Twelve soil samples were collected near Bitumen intrusions in Agbabu and its adjoining environments and were analyzed with HPGe detector Gamma ray spectrometer and counted with comparative method. It was found that K-40, U-238, Th-232 concentrations in the soil range from 370.46 ± 4.5-887.18 ± 6.91, x8.14 ± 5.49-71.35 ± 21.92 and 17.48 ± 2.18-124.36 ± 30.44 Bq/kg respectively. The highest radioactivity in this research work is higher than former value of 165.64 ± 2.91. The highest concentration of K-40 in all the samples occurring close to the Oluwa river is 887.18 ± 6.91 Bq/kg, which location also coincide with the place of highest sample concentration of Th-232 124.36 ± 30.44 Bq/kg. The area of large concentration of K-40 and Th-232 does not coincide with that of U-238, The average concentration of 40K in all the analyzed samples is 640.72 ± 5.42 Bq/kg very high compared to the undetectable level formally reported and generally the radionuclide concentration values obtained have increased than the data in the former analysis done in the area. The highest U-238 concentration value of 71.35 Bq/kg is higher than worldwide 40 Bq/ kg average and it occurs around 1.2 km after Agbabu town close to the road 50 m from a bitumen outcrop. The absorbed dose rates 1 m in air have the highest value of 134.77 nG/h. This is more than 3 times the worldwide average value 43 nG/h for the soil sample collected close to the Oluwa River. The calculated absorbed dose rate in air range from 38.24- 134.77 nG/h. while the Annual effective absorbed dose is also highest with a value 165.39 μSv/y close to river Oluwa (at GPS location N6035I24.7 E4050I10.5) 9 times lower than the effective annual dose value of 1mSv/y permitted for public exposure. The maximum external hazardous index value of 0.81 is less than the unity (1) permitted in ICRP 2000. Mining locations are suggested at other areas of bitumen outcrop with near surface soil that has lower than worldwide average concentration of radioisotopes and away from dwelling places and rivers where transport of mining tailings can increase accumulation of radionuclides in aquatic animals and local inhabitants.
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