The effect of geological formations on natural radioactivity and radiological hazards in the Northern Zamfara State, Nigeria

Measurement of activity concentration of natural radionuclides and the associated health hazards are very important to health physicists in setting national average permissible dose for public. The knowledge of effect of natural radioactivity and the associated radiological hazards with respect to geological formation is essential in radiation monitoring. This study investigates the effect of geological formation on the activity concentrations of 238 U, 232 Th and 40 K and the associated health hazards in Northern Zamfara State (Nigeria). HPGe (high purity germanium) gamma ray spectrometer was used for the laboratory analyses to measure the activity concentrations in the soil samples collected based on the geological formations of the studied area. The activity concentrations of 238 U, 232 Th and 40 K in the soil samples varied from 8.82 ± 0.95 to 44.22 ± 5.78 Bq kg-1 , 11.02 ± 1.03 to 43.96 ± 2.15 Bq kg-1 and 57.45 ± 2.88 to 527.36 ± 12.38 Bq kg-1 respectively. The highest activity concentrations of 238 U, 232 Th and 40 K were recorded in a place underlain by Older Granite formation, which are enriched with high radioactive minerals. The radiological hazards to the public in the studied area were also assessed by calculating the values of radium equivalent activity, external hazard index, activity utilization index, absorbed gamma dose rates, annual outdoors effective dose rates, and excess lifetime cancer risk in the soil samples. Moreover, Older Granite formation recorded highest calculated values of the hazards; 131 Bq kg-1 , 0.35, 0.85, 60.79 nGyh-1 , 0.075 mSvy-1 , and 262 x10-6 respectively. Therefore, activity concentrations of the primordial radionuclides depend on the geological formations, and the radiological hazards also depend on the activity concentrations. Hence, the exposure level of terrestrial radionuclides in the soils of any region depends mainly on the geological formations of that region