Natural Radioactivity of Topsoil in Two Granite Areas of Guangzhou, South China

The natural radionuclide (238U, 226Ra, 232Th and 40K) concentrations in 152 soil samples were determined from two major granite areas in Guangzhou, using high resolution γ-ray spectroscopic system based on the characteristic spectral peaks. The mean activity values for 238U, 226Ra, 232Th and 40K were found to be 156.6±98.8, 160.9±96.5, 184.8±101.5 and 832.5±493.1 Bq kg–1 dry mass, respectively. The absorbed dose rate (D) calculated from activity concentration of 226Ra, 232Th and 40K ranged from 53.2 to 497.1 nGy h–1 with a mean of 220.7 nGy h–1. The Radium equivalent activity (Raeq), the outdoor annual effective dose and the external hazard index (Ir), which resulted from the natural radionuclides in soil, were also calculated and found to vary from 119.7 to 1117.2 Bq kg–1, from 0.07 to 0.61 mSv and from 0.33 to 3.07, respectively. The radium equivalent activities and the external hazard index in all the soil samples were same as 64.5% higher than the limit of 370 Bq kg–1 and 1.0, respectively. The outdoor annual effective dose was higher than the worldwide mean value of 0.07 mSv.