By Alatise, O. O.; University of Agriculture, Abeokuta, Department of Physics (Nigeria). (Thesis available at the Ghana Atomic Energy Commission Library).
The radiation levels and radionuclide distribution of some naturally occurring radioactive materials (NORM) in the soils of some coastal states of Nigeria were investigated from their activity concentrations. This is to be used to identify areas with high values of natural background radiation. A total of 279 soil samples were collected from 81 different locations at distance of between 100 m and 500 m from the coast and at a depth of 0.15 m in Akwa-Iborn, Bayelsa, Delta, Ondo and Rivers States. The activities of these naturally occurring radionuclides (specifically 40K, 238U, 232Th) in the soil samples of these areas were analyzed using a high-resolution, low-background, hyper-pure coaxial gamma-ray detector (EG&G ORTEC HPGe) coupled to an amplifier and multi-channel analyzer.
The range of the mean radioactivity concentrations were obtained to be between 111.85 kBq kg-1 (in Ondo State) and 444.67 kBq kg-1 (in Bayelsa State) for 40K; between 23.24 kBq kg-1 (in Akwa-Ibom State) and 43.66 kBq kg-1 (in Delta State) for 238U; and between 6.45 kBq kg-1 (in Akwa-lbom State) and 12.79 kBq kg-1 (in Bayelsa State) for 232Th. From the analysis of variance (ANOVA) and the General Linear Models (GLM) procedure, the result obtained showed that there was a significant difference (P <0.05) in the occurrence of the three radionuclides in each State and across the States studied. The correlation analyses showed a positive relationship between the radionuclides in all the States except for Ondo State.
The resulting absorbed dose rates in air at a height of 1 m above the ground, for each of the locations were also calculated and expressed in nGy h-1. The mean absorbed dose rates in air due to the three radionuclides, and the annual human effective dose equivalents were calculated to be 24.26 ± 3.57 nGy h-1 and 29.71 ± 4.38 µSv y-1 respectively for Akwa-Iborn State; 44.96 ± 2.86 nGy h-1 and 55.14 ± 3.51 µSv y-1 for Bayelsa State; 39.86 ± 4.36 nGy h-1 and 48.89 ± 5.34 µSv y-1 for Delta State; 20.83 ± 2.31 nGy h-1 and 25.55 ± 2.83 µSv y-1 for Ondo State; and 38.37 ± 3.95 nGy h-1 and 47.05 ± 4.84 µSv y-1 for Rivers State. The ANOVA
results also showed a significant difference (P < 0.05) between the mean absorbed dose rates in air obtained for the States.
The results obtained imply a collective effective dose of between 43.95 Sv y-1 and 121.99 Sv y-1 which is found to be within the acceptable dose limit and therefore indicating a low probability of severe somatic or genetic health problems for the population. A high value of human effective dose of 78.19 ± 0.09 µSv y-1 was obtained at Ugbo in Delta State which is 11.703 % above the world average of 70.00 µSv y-1. Long exposure to this dose of ionizing radiation over the years could constitute serious health hazards to people living around Ugbo. This study has provided a baseline data that could be used for effective monitoring of unforeseeable radioactive fallout in the coastal areas.
Publ. Year: 2007