Measurement of gamma radiation from rocks used as building material in Tiruchirappalli district,Tamil Nadu,India

Tiruchirappalli district is naturally endowed with rich building material resources which are also used in neighboring districts. Hence, measurements of activity concentrations and absorbed dose rate of primordial radionuclides (²³⁸U, ²³²Th and ⁴⁰K) in the rock samples collected from 14 sedimentary rocks and 9 igneous rocks were carried out employing gamma ray spectrometry. In sedimentary rocks the geometric mean activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K were found to be 7.4, 29.5 and 233.6 Bq kg^?1, respectively. On the other hand in igneous rocks geometric mean activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K were distinctly higher and found to be 13.1, 105.7 and 888.8 Bq kg^?1, respectively. The mean radium equivalent activity (Ra_eq) recorded in both sedimentary (20.8 Bq kg^?1) and igneous rocks (245.4 Bq kg^?1) were well within the limit prescribed for dwellings (370 Bq kg^?1) except Vilathupatti (689.3 Bq kg^?1) and Narthamalai (371.6 Bq kg^?1). The mean absorbed dose rate from igneous rock (115 nGy h^?1) exceeded the prescribed limit of 55 nGy h^?1. The mean indoor annual effective dose from the sedimentary rock (0.056 mSv y^?1) and igneous rock (0.580 mSv y^?1) did not exceed the prescribed limit (1 mSv y^?1) except the igneous rock from Vilathupatti (1.51 mSv y^?1). The study concludes that sedimentary and igneous rocks analyzed were radiologically safe when used as building materials except igneous rock from Vilathupatti and Narthamalai.