CdTe buffer layers which were grown on (211)B GaAs by molecular beam epitaxy were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The optical properties and thicknesses of the samples were obtained by ex situ spectroscopic ellipsometry. The surface morphologies of the CdTe epilayers were analyzed by atomic force microscopy, scanning electron microscopy, and Nomarski microscopy before and after chemical etching. We compare the triangle-and trapezoid-shaped etch pits due to the Everson and Nakagawa etch solutions, respectively. Measured etch pit density (EPD) values of triangle etch pits were found in the 8 9 10 7 cm À2 to 2 9 10 8 cm À2 range, and trapezoid-shaped etch pits were found in the 1 9 10 7 cm À2 to 7 9 10 7 cm À2 range for samples with thicknesses <2 lm.

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The Chernobyl accident caused artificial radioactive contamination, especially artificial 137 Cs radionuclide contamination. Due to having long half-life, 137 Cs still continues to remain in soils. In the present study, the surface soil samples were collected from various locations in Bulgaria-Turkey border. The activity concentrations of 137 Cs in collected soil samples were determined. In order to investigate the radiological hazard; the dose rates and the annual effective dose rates were estimated. The activity concentrations of artificial 137 Cs radionuclide in soils were found to range from 1.71±0.18 Bq kg −1 to 6.99±0.66 Bq kg −1 . The mean values of absorbed dose rates, outdoor and indoor annual effective dose rates were found to be 0.10, 4.19, and 16.77 µSv y −1 , respectively. The dose rates and the annual effective dose rates were below the worldwide limit values reported by UNSCEAR and ICRP. In addition, statistical data were estimated, frequency distribution and Q-Q plot were used to assess 137 Cs distribution.