Measurements of 222Rn exhalation rates, effective 226Ra contents, and radiological risks from geological samples of Kopili Fault Zone and gneissic complex of Shillong Plateau, India

Abstract

This report unveils the outcomes of measurements of 222Rn exhalation rates, effective 226Ra content, and the annual effective dose for rocks and soil collected in the vicinity and far from the seismically active Kopili Fault Zone, India. LR-115 (II) nuclear track detector has been used to investigate radiation exposure in the seismically active fault zone and gneissic complex of the Shillong Plateau, which have significant geological characteristics and frequently produce earthquakes. In this study, 222Rn mass exhalation rates for granite, gneiss, and soil samples collected near and far from the fault were calculated to be in the ranges of 73.2–83.0, 11.0–14.8, 21.1–70.7 and 34.3–65.5, 6.4–9.9, 19.1–28.9 mBq kg−1 h−1, respectively. Surface exhalation rates of 222Rn for granite, gneiss, and soil samples collected near and far from the fault varied between 2428.8–2751.7, 365.6–491.9, 698.3–2345.9, and 1138.6–2172.7, 211.9–328.2, 634.9–960.0 mBq m−2 h−1, respectively. The 226Ra contents of granite, gneiss, and soil collected in similar distributions were found to vary from 9.76–11.06, 1.47–1.98, 2.8–9.4, and 4.58–8.74, 0.85–1.32, 2.6–3.6 Bq kg−1, respectively. The annual effective doses attributed to 222Rn inhalation from exposure to the samples were calculated to be in the ranges of 176.3–199.8, 26.5–35.7, 50.7–170.3 and 82.7–157.7, 15.4–23.8, 46.1–69.7 μSv y−1, respectively, for granite, gneiss, and soil. The lifetime fatality-risks have also been analysed in this study. The samples that were collected in close proximity to the fault showed higher values than those that were collected farther away. However, the results reveal that the measured values are within the globally recognised permissible range.