Assessment of natural radioactivity and radiation hazard in volcanic tuff stones used as building and decoration materials in the Cappadocia region, Turkey

The concentrations of natural radionuclides in 6 different colors of volcanic tuff stones which are derived from the Cappadocia region in Turkey were determined using gamma-ray spectroscopy with a HPGe detector, and the mineralogical composition and formula of stones were determined by an X-ray powder diffractometer. The average activity concentrations of U-238, Th-232 and K-40 are 50.7, 58.6 and 717.6 Bq.kg(-1), which are higher than the world averages of 35, 30 and 400 Bq.kg(-1), respectively. The radium equivalent activities (Ra-eq), external hazard index (H-ex), and internal hazard (H-in) associated with the natural radionuclides, alpha (I-alpha) and gamma indices (I-gamma) were calculated to assess the radiation hazard of the natural radioactivity in the volcanic tuff stones. The average indoor annual effective dose equivalent is 0.1 mSv. All values of the indoor effective dose are lower than the exemption dose value of 0.3 mSv. The calculated radium equivalent activity values vary from 60.31 Bq.kg(-1) to 281.32 Bq.kg(-1) with a mean of 189.78 Bq.kg(-1). All values of radium equivalent activity are lower than the world average. The average indoor absorbed dose rate (D-in) for volcanic tuff stones, calculated to be 21.18 nGy.h(-1), is lower than the world average of 84 nGy.h(-1).