Determination of natural radioactivity levels in some construction materials used in the Gebze region, SEM/EDS analyses, and measurement of radon gas in soil and water

The fact that individuals spend a significant portion of their daily lives indoors highlights the impact of radiation energy emitted from building materials on public health. Natural radioactivity is directly associated with the presence of uranium, thorium, potassium, and their decay products within the composition of materials commonly used in the construction sector. Uranium and thorium contained in these materials, through their decay processes, generate radioactive gases that carry a potential risk of accumulation in indoor environments. Prolonged exposure to such radioactive substances may leave detrimental effects on human health over time. The primary objective of this study is to conduct a comprehensive analysis of methods for determining the levels of natural radioactivity in construction materials, and to assess the potential health impacts associated with this exposure. Recognizing the significance of natural radionuclides in contributing to indoor radiation levels, this research aims to provide a multidimensional evaluation of both material properties and their implications for human health. Within the scope of the study, the geological and industrial characteristics of the Kocaeli-Gebze region (including central Gebze, Köseler Village, Tavşanlı Village, Pelitli Village, Çayırova, Dilovası, and Hereke) were taken into account. Various building material samples collected from these areas were analyzed for natural radionuclide concentrations, specifically focusing on potassium-40 (⁴⁰K), thorium-232 (²³²Th), and uranium-238 (²³⁸U). These concentrations were determined using a 3×3 inch NaI(Tl) scintillation detector coupled with a gamma spectrometry system. In total, 32 samples were obtained from 9 different locations within the Gebze district, comprising 17 distinct types of construction materials, such as bricks, fire bricks, insulation bricks, roof tiles, calcite, plaster (satin and gypsum board types), ceramics, dolomite, granite, cement, limestone, plaster coating, autoclaved aerated concrete (gas concrete), marble, travertine, and tile joint materials. The activity concentrations were measured at characteristic gamma energies of 1460 keV for ⁴⁰K, 2610 keV for ²³²Th (via ²⁰⁸Tl decay), and 1760 keV for ²³⁸U (via ²¹⁴Bi decay), using laboratory facilities at Sakarya University. The measured activity concentrations in the building materials were found to vary within the ranges of 32–199 Bq/kg for ⁴⁰K, 10.6–39 Bq/kg for ²³⁸U, and 9.8–152.3 Bq/kg for ²³²Th. Furthermore, in order to evaluate the implications of these radioactivity levels on public health, several radiological hazard indices were calculated, including the absorbed dose rate indoors (Din) and outdoors (Dout), the annual effective dose equivalent (AED), the radium equivalent activity (Raeq), the gamma activity index (Iγ), the alpha activity index (Iα), and the internal and external hazard indices (Hin and Hex). Furthermore, in order to determine the surface morphology and elemental composition of certain building materials, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses were conducted. Through SEM imaging, the pore structures, surface roughness, and microstructural characteristics of the materials were examined, whereas the EDS technique was employed to identify their elemental compositions. The results enabled a comprehensive evaluation of the mineral phases and structural properties associated with radioactive constituents within the materials. In addition to the determination of natural radioactivity levels, the radiation attenuation properties of selected building materials — including granite, marble, autoclaved aerated concrete, ceramic, fire brick, regular brick, insulation brick, and roof tile — were also assessed. Measurements were conducted using gamma rays of energies 1173 keV and 1332 keV, and the total linear attenuation coefficients (μ, cm⁻¹) were calculated. The attenuation coefficients were found to range from 0.08 to 0.135 cm⁻¹ for 1173 keV and from 0.013 to 0.156 cm⁻¹ for 1332 keV gamma energies. Compared to standard concrete, the building materials examined in this study demonstrated lower attenuation capabilities, indicating a relatively limited ability to absorb gamma radiation. Understanding the natural radioactivity levels of construction materials is of critical importance, as these materials constitute the primary sources of indoor exposure to gamma radiation. The accumulation of radioactive gases, particularly radon, within enclosed environments elevates the background radiation dose received by occupants, thereby emphasizing the necessity for comprehensive assessments of construction-related radiological parameters. Moreover, the evaluation of radiological indices provides essential insights into the potential risks posed by building materials. The radium equivalent activity (Raeq) serves as a consolidated parameter representing the combined activities of ⁴⁰K, ²³⁸U, and ²³²Th, and facilitates a direct comparison with internationally recommended safety thresholds. Similarly, the internal (Hin) and external (Hex) hazard indices offer a quantitative measure of the possible radiological hazards associated with prolonged exposure to materials containing natural radionuclides. The gamma activity index (Iγ) and alpha index (Iα) further contribute to the radiological risk assessment by specifically addressing the contributions of high-energy gamma emitters and alpha particle-emitting isotopes, respectively. In accordance with UNSCEAR (2000) and European Commission guidelines, all calculated indices for the analyzed samples in this study remained well within the permissible limits, corroborating the finding that the investigated building materials, soil, and water samples pose no significant radiological threat under typical usage scenarios. Although the primary focus of the research centered on building materials, complementary measurements were conducted on soil and water samples. Soil samples collected from areas in close proximity to mining activities were analyzed for radon gas concentrations, while water samples gathered from central Gebze and surrounding villages were similarly evaluated for radon levels. These additional assessments provided a broader understanding of the natural radiation burden within the region. In conclusion, this research highlights the importance of systematic radiological evaluations for construction materials, particularly in regions with diverse geological and industrial characteristics such as Gebze. The findings contribute to a growing body of knowledge that supports the safe use of building materials in residential and commercial infrastructure, while simultaneously addressing public health concerns related to natural radiation exposure. Furthermore, the inclusion of soil and water analyses enriches the regional radiation profile, providing a more holistic understanding of environmental radioactivity levels in the study area.