Assessment of radon exhalation rates, effective radium content and radiological exposure dose, of coal and rocks in Tiru Valley Coal Field, India using track etched technique

Abstract

In this study, the outcomes of assessments of radon exhalation rates for both mass and surface, radium content and annual effective dose from 45 numbers of geological samples in Tiru Valley Coal Field area are presented. The nuclear track detector LR-115 (II) of bulk etch rate, VB = 4 µm h-1 with a spark counter to archive alpha track density of radon was used to measure radon exhalation rate from the samples and to assess radiological exposure in the coalfield area, which has significant geological characteristics. In this work, the surface exhalation rates for coal, carbonaceous shale and sandstone samples have been estimated to be in the range of 217.4-659.9 mBq m-2 h-1, 234.0-381.1 mBq m-2 h-1 and 337.1-741.4 mBq m-2 h-1, respectively. The mass exhalation rates for coal, carbonaceous shale and sandstone samples varied in the range of 6.5-19.8 mBq kg–1 h-1, 7.0-11.4 mBq kg–1 h-1, and 10.1-22.2 mBq kg–1 h-1, respectively. The radium contents have been found to vary in the range of 6.7-20.3 Bq kg-1, 7.2-11.8 Bq kg-1 and 10.4-22.9 Bq kg-1 for coal, carbonaceous shale and sandstone respectively. The annual effective doses related to the inhalation of radon from the exposure to the samples have been estimated to be in the range of 15.8-47.9 µSv y-1, 17.0-27.7 µSv y-1 and 24.5-53.8 µSv y-1 for coal, carbonaceous shale and sandstone respectively. In this investigation, the lifetime fatality-risks have also been assessed. The values were generally higher in rock samples than in coal. However, the findings have shown that the obtained values are within the internationally accepted recommended values.