Establishment of natural radioactivity baseline, mapping, and radiological hazard assessment in soils of Al-Qassim, Al-Ghat, Al-Zulfi, and Al-Majmaah

Abstract

Radionuclide species comprising the primordial radioactive decay chains lead by ²³²Th and ²³⁸U, along with their associated daughter and granddaughter decay series, constitute a major fraction of the naturally occurring radioactive material (NORM). Gamma-ray radiation emitted by the decay of these NORMs, along with the ⁴⁰K in the soil, is mainly responsible for the human exposure to external gamma-rays. The radioactivity concentrations in soil samples collected from 138 sites have been determined as part of a survey to produce a radiological map of AL-Qassim, Al-Ghat, Al-Majmaah, and Al-Zulfi regions in the Kingdom of Saudi Arabia. The estimated mean values of ²³⁸U, ²³²Th, ⁴⁰K, ²²⁶Ra, and gross α and β activities in the samples were 23.8 ± 11.61, 24.33 ± 17.63, 790 ± 398, 22.83 ± 11.70, 375 ± 205, and 734 ± 344 Bq kg⁻¹, respectively. The radiological risk indices related to the natural radioactivity in the soil samples, i.e., the absorbed dose rate in air, radium equivalent activity, and annual effective dose rate, were estimated to be 58.88 ± 29.21 nGy h⁻¹, 117.1 ± 59.65 Bq kg⁻¹, and 0.07 ± 0.04 mSv year⁻¹, respectively. The determined internal hazard index of the samples ranged from 0.07 to 1.45, with an estimated mean value of 0.4 ± 0.2. The radon concentration in the soil gas ranged from 39 to 508 Bq m⁻³, with a mean value of 145.0 ± 52.9 Bq m⁻³.