RISK ASSESSMENT OF BASELINE OUTDOOR GAMMA DOSE　RATE LEVELS STUDY OF NATURAL RADIATION SOURCES　IN BURSA, TURKEY

摘要

Within the scope of this study, gamma radiation dose rate measurements have been carried out in the province of Bursa. The mean outdoor (terrestrial and cosmic) gamma dose rate in this area was 90 nGy h~(-1). The cosmic gamma dose rate was measured to be 16 nGy h~(-1) at the Iznik lake in the region. The mean annual effective dose due to outdoor gamma radiations was determined to be 110.4 μSv. The collective effective dose equivalent was calculated to be 3.21 × 10~2 man Sv per year. The average relative excess lifetime risk of fatal cancer was calculated at 4.50×10~4 for the people living in the city. The activity concentrations of natural radionuclides such as ~(237)U series, ~(232)Th series, ~(40)K and fission products like ~(137)Cs in surface soil samples were measured by using an HPGe-based gamma spectrometry system. The mean activity concentration of ~(238)U series, ~(232)Th series, ~(40)K and ~(137)Cs were found to be 55.9 Bq kg~(-1) for ~(226)Ra, 23.6 Bq kg~(-1) for ~(214)Pb, 22.5 Bq kg~(-1) for ~(214)Bi, 31.3 Bq kg~(-1) for ~(208)Tl, 32.9 Bq kg~(-1) for ~(228)Ac, 430 Bq kg~(-1) for ~(40)K and 5.4 Bq kg~(-1) for ~(137)Cs. The radiation hazards associated with the radionuclides were estimated at an average of 136 Bq kg~(-1) by calculating the radium equivalent activity (Ra_(eq). The mean calculated value of the external hazard index (H_(ex)) for the soil was found to be 0.37.