A Study on Radioactivity Levels in Sedimentary and Igneous Rocks Used as Building Materials in and Around Tiruchirappalli District, Tamil Nadu, India

The paper presents the results of the study on the activity concentrations of primordial radionuclides (238 U, 232 Th and 40 K) in the rock samples collected from eight sedimentary rocks and six igneous rocks which supply stones for construction of buildings in Tiruchirappalli district. In sedimentary rocks, the mean activity concentrations of 238 U, 232 Th and 40 K were found to be 5.4, 12.4, and 372.8 Bq kg⁻¹, respectively. On the other hand, in igneous rocks the mean activity concentrations of 238 U, 232 Th and 40 K were distinctly higher and found to be 15.5, 135 and 859.4 Bq kg⁻¹, respectively. The mean radium equivalent activity (Raeq) recorded in both sedimentary (32.8 Bq kg⁻¹) and igneous rocks (278 Bq kg⁻¹) was well within the limit prescribed for dwellings (370 Bq kg⁻¹) except Narthamalai (S13) (689.3 Bq kg⁻¹). The mean absorbed dose rate from igneous rock (124.5 nGy h ⁻¹) exceeded the prescribed limit of 55 nGy h ⁻¹. The mean annual effective dose from the sedimentary (0.089 mSv y-1) and igneous rocks (0.63 mSv y−1) did not exceed the prescribed limit (1 mSv y ⁻¹) except the igneous rock from Narthamalai (S13) (1.48 mSv y ⁻¹). The study concludes that the sedimentary and the igneous rocks analysed were radiologically safe when used as building materials except igneous rock from Narthamalai (S13).