Gamma activity concentrations (²²⁶Ra, ²³²Th, ⁴⁰K) of mineralized Homret Akarem composite granitic pluton, Egyptian Nubian Shield: environmental hazards assessment

Homret Akarem composite granitic pluton (HAGP) occupies an area of approximately 13 km², and is in the southern part of the Egyptian Nubian Shield. This pluton displays a composite makeup, incorporating alkali feldspar granite, albite granite, and muscovite granite. These diverse granite varieties intrude the surrounding country rocks, including metasediments and granodiorite. Greisens and mineralized vein types are erratically distributed in the granitic pluton and metasediments. Twenty samples, collected from along and/or shear zones of the granitic pluton, underwent radiometric analysis to measure the activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K using an N-type HPGe detector. This analysis aimed to determine the radiological hazard factors associated with the samples. In addition to the chemical analysis of these samples, the concentrations of U, Th, and K in ppm are examined to ascertain the origin of these radioactive isotopes. The average value of activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K is 125.16 ± 0.54 Bq/kg, 112.48 ± 0.60 Bq/kg, and 3909.4 ± 37.56 Bq/kg, respectively. Based on the radiological hazards risk assessment, the average annual effective dose indoors (AEDE_in) was estimated to be approximately 2.58 mSv on average. Both the external (H_ex) and internal (H_in) hazard indices were found to exceed > 1. Additionally, other radiological hazard factors were considered, including the average radium equivalent content of 563.35 Bq/kg. The dose rate in the air (D) measured 269.02 nGy/h, with a gamma radiation index (Iγ) averaging 4.32. Furthermore, the annual effective dose outdoors (AEDE_out) was approximately 0.33 mSv, with an estimated excess lifetime cancer risk (indoor and outdoor) approximately 0.09–0.01. On the other hand, the geochemical characteristics of U, Th, and K versus some chemical parameters, major, trace, and REEs, indicated magmatic origin in the early phase, followed by later alkali metasomatism. The D-factor calculated for U clearly demonstrates the disequilibrium state in the composite granite pluton, suggesting old uranium leaching. A comparison was made between granite samples from the study area and other surroundings in Egyptian Nubian Shield, focusing on radioactive element concentrations and radiation factor risks. Our results show that Homret Akarem granite has the highest concentrations of ⁴⁰K Bq/kg, D (nGy/h) and AEDE (mSv/year) among those examined. These studies have confirmed that the examined granites have been deemed unsuitable for applications in construction and infrastructure. It is crucial to exercise caution and implement necessary safety measures in this potentially hazardous environment.