Gamma ray spectrometric analysis of sediment deposits at the shores of lake nakuru, kenya

Abstract

Natural activities like volcanic eruptions and anthropogenic activities such as excavation of rocks for buildings and road constructions expose originally concealed radioactive elements in the rocks within the earth crust. Poor agricultural practices such as excessive use of fertilizers lead to accumulation of radioactive elements in the environment. Transport agents like run-off water and rivers accumulate these radionuclides in lakes and other water bodies. Lake Nakuru is situated close to a fast growing Nakuru town and is fed by five rivers but does not have surface outlets. This makes the lake to be a possible sink for the accumulation of radionuclides and other pollutants. The accumulation of radionuclides in the environment can be hazardous if they are above the acceptable level. This study determined the concentration levels of radionuclides in Lake Nakuru. Samples of sediments from the shores of Lake Nakuru were collected, prepared and analysed using NaI(Tl) gamma ray spectrometer for the activity concentrations of the primordial 238U, 232Th and 40K. The results obtained showed average activity concentrations of 36.9±9.1 (11.2-92.5), 43.5±3.8 (35.4-74.6) and 708.3±33.2 (543.3-837.4) in Bqkg-1 for 238U, 232Th and 40K respectively. A total dose rate of 71.97 nGyh-1 and annual effective dose rate (outdoor) of 0.088±0.007 mSv were obtained which is less than safety limit to public exposure of 1 mSvy-1. The findings from all sampling sites showed that radiation hazard from terrestrial naturally occurring radionuclides is insignificant. Spatial difference in the activity concentration between the northern and southern sectors of Lake Nakuru was observed. The average dose rate for the northern sector was found to be 96.22±5.39 nGy/h while the southern sector has 26.69±0.69 nGy/h showing enhanced pollution at the northern sector.