Natural radioactivity and environmental risk assessment of Sokoto phosphate rock, Northwest Nigeria

Phosphate rock samples collected from the phosphate bearing formations of Sokoto State, Northwest Nigeria were assessed for their radiological contents by gamma spectrometric technique (sodium iodide (NaI (Tl) detector). The mean activity concentrations of 226Ra, 232Th and 40K in all the studied samples were 720.1±4.2 Bqkg-1, 33.5±1.4 Bqkg-1, and 315.3±6.7 Bqkg-1 respectively. Contributions from radium contents to the overall radionuclide activity concentrations were quite significant. The calculated mean value of the absorbed dose rate was found to be 3.6 times the maximum value for the world background level, which shows the severity of radiation risk the public is exposed to in the study areas. The computed values for radiation hazard indices were above the world’s proposed safety limits by UNSCEAR, which place the study areas among high background radiation zones. Some restrictive measures and precautionary actions are therefore obligatory for the local farmers and the general public from the view point of radiation protection.   Key words: Natural radioactivity, Sokoto, phosphate rock, radiation hazard, NaI (Tl) detector, radiation dose.