Evaluation des paramètres radiologiques d’exposition et du risque radiologique pour les habitants de la zone bauxitique de Fongo-Tongo

Abstract

The present study aims at the evaluation of the radiological risk related to the external exposure to the natural radioactivity of the soil in the bauxite site of Fongo-Tongo in the Department of Menoua, West Cameroon Region. Fourteen (14) soil samples collected in the localities of Ndifonda et Apouh were analyzed on a gamma-ray spectrometry system equipped with a Hyper Pure Germanium (GeHP) detector to evaluate the radiological exposure parameters and the radiological risk based on the concentrations of 226Ra;232 Th and 40K. The average activity concentrations of 226Ra;232 Th and 40Kmeasured in the soil samples collected are respectively 121 _ 4 Bq/kg, 117 _ 5 Bq/kg and 142 _ 12 Bq/kg in Ndifonda, 166_ 22 Bq/kg, 177 _29 Bq/kg, 98 _ 16 Bq/kg in Apouh,. The average activity concentrations of 226Ra;232 Th are comparatively higher than the respective world average values of 33 Bq/kg et 45 Bq/kg reported by UNSCEAR. These measurements are within the range of activity concentrations given by the IAEA for bauxite deposits.. The average radium equivalent activity values are 300 Bq/kg in Ndifonda and 426 Bq/kg in Apouh. The value obtained at Apouh is higher than the ICRP recommended limit value of 370 Bq/kg for soil to be used as a safe building material The average absorbed dose rate values in air at one meter above ground level are 133 nGy/h at Ndifonda and 187 nGy/h at Apouh. The corresponding total annual effective doses are 0.81 mSv/yr and 1.15 mSv/yr respectively. At Apouh, the annual effective dose is higher than the limit of 1 mSv/year specified in the national radiation protection regulations. The average probabilities ELCR (« Excess Lifetime Cancer Risk ») are respectively 2; 41 _10􀀀3 and 3; 40_10􀀀3 in Ndifonda and Apouh. These values are higher than the world average of 1:45_10􀀀3 reported by UNSCEAR. The radiological risk for external exposure due to natural radioactivity in soil is high in our study areas. It is recommended that studies of internal exposures be considered in these locations.