Environmental radiation in high exposure building materials

ABSTRACT: In this thesis, we investigated the specific radioactivity concentrations of Ra, Th and K in different types of commonly used granite stone samples collected from the Tehran city of Iran by means of a high-resolution HPGe gamma-spectroscopy system. The result of Th, Ra and K are ranged from 18 to 178, 6 to 160 and 556 to1539 Bq kg- , respectively. The radium equivalent activities ( ) are lower than the limit of 370 Bq kg- set by NEA (Nuclear Energy Agency, OECD 1979) except in two samples. The internal hazard indexes have been found well below the acceptable limit in most of the samples. Five samples of investigated commercial granite stones do not satisfy the safety criterion illustrated by UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation, 1993). Applying dose criteria recently recommended by the EC [European Commission (1999)] for superficial materials, all investigated samples meet the exemption dose limit of 0.3 mSv y- . Also in this thesis, health hazards from gamma radiation doses due to granite and radon concentration have been calculated. The dose rate of exposure from granite building materials on humans is obtained as a result of an external exposure from gamma-emitting radionuclides in the granites. Another mode of exposure is from the inhalation of the decay products of Rn and Rn. The radon exhalation rates have also been studied and values were in the range of 0.32±0.01 to 7.86±1.65 Bq m- h- . For two models of standard living rooms (5.0 m×4.0 m area; 2.8 m), the radon concentration ( and the absorbed dose ( ) rates were calculated and the results were found to be 10.64–29.32 Bq m- , 3.84–68.02 nGy h- and 0.02–0.33 mSv y- for Model 1, 10.07–15.38 Bq m- and 2.29–39.99 nGy h- for Model 2, respectively. According to our estimations, mechanical ventilation systems ( ) in a room all granite samples would produce radon concentration of <100 Bq m- . Finally, radon exhalation rates and radon concentrations in selected granite stones were measured by means of a gamma-spectroscopy system (passive method) and an AlphaGUARD (active method). The radon exhalation rates measured by the passive and active methods were compared and the results of this study were similar, with the active method being 22 % higher than the passive method. Keywords: Radioactivity, Internal Hazard, Radiation Dose, Radon Exhalation, Passive Method, Active Method. …………………………………………………………………………………………………………………………………………………………………………………………………………