Radiological Risk Due to the Terrestrial Gamma Exposure in Soil Samples from Central Balkan National Park, Bulgaria

Radiological investigations have been performed in the Central Balkan National Park region which was declared a protected area and included in Nature 2000. The activity concentrations of the natural radionuclides U-238, Th-232 and K-40 as well as of the fission product Cs-137 have been determined by means of high-resolution gamma-ray spectrometry. The activity concentrations of U-238, Th-232 and K-40 vary in the ranges 31.0-60.3 Bq.kg(-1), 19.7-55.3 Bq.kg(-1) and 338.3-661.4 Bq.kg(-1), respectively. The activity concentrations of Cs-1(37) vary in the range 15.0-221.6 Bq.kg(-1). The absorbed gamma dose rate due to the radionuclides mentioned above, the external hazard index and the outdoor effective dose have been estimated after the inquiry which was carried out among the local population and tourists. The calculated values of the absorbed gamma dose rate, the annual outdoor effective dose and the external hazard index for the local population were 71.98 nGy.h(-1), 0.088 mSv.y(-1) and 0.399, respectively. These values are comparable to the averages values for Bulgaria.