Radioactivity Concentration and Assessment of Gamma-Radiation Exposure from the Soil of Different Type in Territory of Tbilisi City

There are given results of radioactivity research in different types of soil within the territory of some districts of Tbilisi. Twenty samples of brown and alluvial types have been selected from 20 locations. Up to 22 radionuclides were identified. Concentration of radionuclides of Th-232 family was in limits from 16.8 to 41.4 Bq/kg (average value of 22.6 Bq/kg), U-238 family – from 17.7 to 67.8 Bq/kg (average value of 29.3 Bq/kg), U-235 family - from 1.09 to 3.76 Bq/kg (average value of 1.77 Bq/kg). Also individual radionuclides have been identified: K-40 – from 365 to 618 Bq/kg (average value of 465 Bq/kg), Cs-137 – from 1.5 to 118 Bq/kg (average value of 19.9 Bq/kg); trace amounts of Be-7 were determined in several samples. Radium equivalent activity varied from 71.5 to 148 Bq/kg (average value of 95.8 Bq/kg. Annual effective dose varied from 0.042 to 0.088 mSv/y (average value of 0.058 mSv/y). There were marked some features of radionuclides distribution, in particular, depending on the type of soil and sampling locations. Several activity ratios of radionuclides were considered, in particular, U-238/U-235, U-238/Th-232, Ra-226/U-238 and Pb210/Ra-226.