Assessment of Activity Concentrations of Radionuclide with Depth in Wasteland Soils in Abeokuta, Southwest Nigeria

A survey of natural radionuclide level with depth in wasteland soils in some locations in Abeokuta was carried out in February 2013. Samples were collected at 10 cm depth interval from each of the locations visited. They were collected into containers with length 9 cm and width 7 cm and then room dried. The different soil samples picked from different locations were not mixed together in order to avoid cross contamination of the soil samples. Analysis was carried out on each of the soil samples and the specific activity concentration of the radionuclides 40K, 238U and 234Th was measured using the model 802 series thallium activated sodium iodide detector NaI (Tl). The average specific activity values obtained for the 0 cm depth (surface) were 428.91±15.05 Bq/kg for 40K, 2.09±0.84 Bq/kg for 238U and 54.60±2.00 Bq/kg for 234Th. The gamma absorbed dose rate and effective dose equivalent were also calculated and an average of 55.5 nGy hr-1 and 0.136 mSv yr-1 were obtained. These obtained values were found to be below the recommended standard values by UNSCEAR which are 55.9 nGy hr-1 and 0.7 mSv yr-1. The results indicate that the radiation level within the dumpsites pose no significant health risk on the people living close to the dumpsite. Also, it was observed that as radionuclides are leached down, activity concentration reduces but may be altered again by factors such as the type of radionuclide, composition of subsurface materials, rate of ground water movement and the soil particles with which the radionuclides are connected.