Concentration of natural radionuclides in soil and assessment of external exposure to the public in Tehran

ABSTRACT

Natural radionuclides in soil constitute a significant component of the background exposure sources of the population. A meaningful contribution to the total dose from natural sources comes from terrestrial radionuclides such as 238U, 232Th and 40K. The concentrations of natural radionuclides of 238U, 232Th and 40K in surface soil [5 cm depth] of Tehran have been measured by gamma spectrometry. The samples were dried and homogenized and measured for 60k seconds after radionuclides secular equilibrium, using a high purity germanium [HPGe] gamma-ray spectrometer. The high energy resolution of this type of detector is particularly useful for activity measurements of uranium and thorium chain members due to their complex spectras. The absorbed dose rates in air were also measured by using ionization-chamber at the point where soil samples were collected which includes terrestrial and cosmic rays. The natural gamma emitting terrestrial radionuclides in soils are directly relevant to outdoor exposure. The average activity concentrations of 238U, 232Th and 40K in different districts of Tehran were found to be 24, 28 and 635 Bq kg-1, respectively. The average outdoor gamma absorbed dose rate in air at 1 meter above ground was calculated as 102 nGy h-1. By using the data obtained in this study the average annual effective dose equivalent for a person living in Tehran Sv. According to data of 66 soil samples was found to be about 125 measurement covering 22 districts in Tehran, the average outdoor gamma dose rate in air due to terrestrial and cosmic radiation was found to be about 102 nGy h-1 and the average annual effective dose equivalent for a person living in Tehran Svmicrois about 125