Investigation of the radioactivity of soils collected from Shumen Plateau Nature Park, Bulgaria

The aim of the present study was to evaluate the levels of radioactivity, radiological doses and the increased lifetime risk of cancer of radionuclides contained in soils collected from the territory of Shumen Plateau Nature Park, (North-Eastern Bulgaria). A gamma spectrometric system was used to estimate the natural radionuclides. The average values for the specific activities for 238U, 232Th, 40K measured in soils were 28.65 ± 4.30 Bq/kg, 18.86 ± 2.83 Bq/kg and 609.09 ± 91.36 Bq/kg, respectively. Only the average value for 40K was higher than the documented worldwide values of, respectively 35 Bq/kg, 30 Bq/kg and 400 Bq/kg. We calculated the average values for assessing radiological hazards: radium equivalent activity 102.52 Bq/kg, external hazard index 0.28 Bq/kg, internal hazard index 0.35 Bq/kg, absorbed gamma dose rate in air 52.04 nGy/h, annual effective dose rate 0.32 mSv/y, total excess lifetime cancer risk 1.95 × 10-3 and radioactivity level index 0.79 mSv. The average values we obtained for radiological indices and specific activities are lower than the global average values quoted in UNSCEAR 2000.