Evaluation of NORM and Dose Assessment in an Aluminium Industry in Nigeria

Abstract

The activity concentrations of natural radionuclides 226 Ra, 232 Th and 40 K in bauxite ore, alumina, dross tailing, alumin-ium scraps and soil samples collected from an aluminium industry in Nigeria were determined by gamma ray spectros-copy method. The mean values of 226 Ra, 232 Th and 40 K content of the samples ranged from 16 ± 6 (alumina) to 31 ± 10 (scrap), 41 ± 0.12 (scrap) to 134 ± 21 (bauxite) and 47 ± 14 (bauxite) to 354 ± 8 (scrap) Bq·kg −1 , respectively. The mean activity concentrations of 226 Ra and 40 K in all the samples are lower than the world average for soil while 232 Th is higher with the exception of alumina and scrap. As a measure of radiation hazard to the occupational workers and the members of the public, the radium equivalent activities and external gamma dose rates due to the radionuclides at 1 m above ground surface were calculated. The radium equivalent activities which varied between 88 ± 10 (alumina) and 222 ± 34 (bauxite) Bq·kg −1 are within the safety recommended limit of 370 Bq·kg −1 . The mean annual effective doses calculated from the absorbed dose rates in air were between 54 ± 6 (alumina) and 134 ± 20 (bauxite) µSv·y −1 , which is lower than the 1 mSv·y −1 recommended for the general public. The annual gonadal dose equivalent of all the samples with the ex-ception of alumina was higher than the world average for soil.