Research Paper : Radiometric Survey to Determine the Terrestrial Gamma Radiation Levels: A Case Study of Sagamu and Abeokuta, South Western Nigeria

J.O. Coker... [et.all];

Gamma ray radiation alert monitoring 4 was used to determine the variation of terrestrial gamma radiation levels in some parts of Ogun state, South Western Nigeria. The study revealed that there is variation in the value of absorbed dose on ground surface and a metre above the ground surface. The value recorded on the ground for sedimentary terrain, basement complex and suspected transition zone across the study area are higher than the values recorded above the ground surface. On compares of the absorbed dose recoded, the ranges of values for both on ground and above the ground for basement complex are (between 32.79 and 42.58) and (between 26.71 and 38.25) higher than in sedimentary terrain (between 23.79 and 23.83) and (between 20.37 and 21.32) respectively. The suspected transition
zone in the study area was delineated through the average values obtained on ground surface (32.83) and 1metre above the surface (28.18) which lies between the values recorded for both sedimentary terrain and basement complex. Based on the
major peak and troughs of the radioactivity graph, the different formations in the study area were clearly delineated and these correspond approximately to the geological boundaries in the area, lithological characterization of the formations revealed the concentration of radioactive elements in rock varies. The uranium and thorium content of rocks generally increases with acidity, with the highest concentrations found in pegmatite’s and granites (basement complex) and lowest concentrations found in shale and clay (sedimentary terrain). Because terrestrial
gamma rays emanate from the ground surface and not from a height, hence, radiometric survey, unlike aeromagnetic method measure what lies on the ground surface rather than above the surface.