MEASUREMENT OF NATURAL RADIOACTIVITY IN ROCK AND SOIL-TO-PLANT TRANSFER FACTOR IN SELECTED AREAS IN ONDO STATE, NIGERIA

Abstract

The activity concentrations of naturally-occurring radionuclides in rocks, soils, and plants were measured in this work with the aim to determine their transfer factors from soil to plant. Samples of these materials were collected from selected areas in Ondo State. Activity concentration measurement was done using NaI(Tl) detector coupled to a multichannel analyzer. The average activity concentrations of 40K, 238U, and 232Th in rocks were 380.57  72.24, 20.09  7.87 and 11.41  3.68 Bq kg-1 respectively, soils had 332.53  60.02, 20.09  7.74 and 20.09  7.74 Bq kg-1 respectively and plants had 125.54  31.26, 11.14  3.26 and 9.61  2.99 Bq kg-1 respectively. Calculated soil-to-plant transfer factor (TF) for 40K, 238U and 232Th at the study areas were 0.396, 0.561 and 0.936 respectively. The TF for the plant species varies in order of 232Th > 238U > 40K. The absorbed dose rates in air were also calculated to be in the range of 27.42 and 36.87 nGy h–1 for rock and 24.43 to 36.25 nGy h-1for soils with overall mean values of 32.16 nGy h–1 for rock and 30.78 nGy h-1 for soil. The estim ated corresponding outdoor annual effective dose rates were between 33.53 and 45.22 μSv y-1 for rock and 29.96 to 44.46 μSv y-1 for soil. The average annual effective dose rate for rock and soil were found to be 39.44 μSv y-1 and 37.75 μSv y-1 respectively. The value of annual effective dose equivalent in this study is low compared to the world average of 70 μSv y-1specified by UNSCEAR for an outdoor effective dose, hence the chances of radiological hazards to the health of the populace are generally low.