A Study on Radon (222Rn) Exhalation Rate in the Rocks Used as Building Materials in Tiruchirappalli District, TN, India

Tiruchirappalli district is naturally endowed with rich building material resources, like stone, granite, sand, brick, cement etc. which are also used in the neighbouring districts. Hence, measurement of radon level in these building materials is important, because radon, a radioactive gas, is one of the major causative factors for human lung cancer and it is important to assess its impact on human health. The present study was undertaken to measure the activity concentrations of radon in 14 sedimentary rock (sand stone) quarries and 9 igneous rock (granite) quarries spread over Tiruchirappalli district. The Sealed Can Technique using Solid State Nuclear Track Detector (SSNTD) was employed for the measurement of radon emanation. The activity concentrations of radon in sedimentary rocks analyzed ranged from 13.2±0.7 Bq m-3 to 218.0± 10.6 Bq m-3 with the geometric mean activity level of 46.3 Bq m-3. However, radon concentrations in igneous rocks are distinctly higher than those of sedimentary rocks and ranged from 95.6 ± 8.0 Bq m-3 to 1140±95.0 Bq m-3 with the geometric mean activity concentration of 392.6±2.1 Bq m-3. The geometric mean radium concentration (CRa) recorded in both sedimentary (3.4±2.3 Bq kg-1) and igneous rocks (50.2±2.1 Bq kg-1) were well within the limit prescribed for dwellings (370 Bq kg-1). The mass and surface exhalation rates were also calculated in all the rock samples. The study concludes that the sedimentary rocks and the igneous rocks analyzed were radiologically safe (less than the permissible limit of 600 Bq m-3) when used as building materials except the granite rocks from Narthamalai (682±57.3 Bq m-3) and Vilathupatti (1140.0 ±121 Bq m-3).