Investigation of Gebze-Darica metro line (Kocaeli Province/Turkey) in terms of radon and gamma radiation levels

Abstract

In this study, 222Rn and gamma radiation levels were measured in soil and rock samples taken from Gebze Darica Metro Line, which is under construction, within the borders of Kocaeli province (Turkey), which is an important industrial city. Measurements were made in the summer of 2021 and are interpreted by environmental factors such as depth, humidity, temperature, air pressure and geological formations (granite and non-granite) that may affect radiation levels. It was observed that radon concentrations were in the range of 145-3696 Bqm- 3 in measurements made on soil samples. The highest radon values in rocks were measured in granodiorite (3242.8 Bq m-3) and granite (2253.4 Bqm- 3) samples. The amount of radionuclide and radon in soils is higher than in rocks. In the measurements made at 48 selected points, the World Health Organization (WHO) limit value was exceeded at 27 points in total (%56 of all samples). There are six measurement points exceeding the limit values for both public and employees, with the highest annual average effective dose (H) for radon concentration of 2.94-23.55 mSv y-1 at S11. The highest surface radon exhalation rate was calculated as 508.02 Bq m-2 h-1 at station S11. Indoor measurements at 20 cm below the soil surface range from 81 to 252 nSvh-1, and all but S5 exceed the indoor gamma dose rate level of 84 nGy h-1 worldwide. Effective dose level caused by the gamma radiation originating from the Earth's surface, specified in the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (2000) report, is exceeded 0.5 mSv y-1 at all stations. In the statistical analyzes based on X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) results, positive strong and moderate correlations were found between the average 222Rn concentration and weight percentage (Wt %) of K2O, Na2O, ThO2, ZrO2 oxides and Quartz, Montmorillonite, Albite minerals, respectively. Gamma radiation is correlated with Na2O Wt% content (R2 = 0.7056). A moderately negative correlation was found between the mean 222Rn concentration and temperature, a weak negative correlation with pressure, a weak positive correlation with humidity, and a moderately significant correlation with the presence of granite.