Simultaneous measurements of radon and thoron, and their progeny levels in dwellings on anticlinal structures of Assam, India

Abstract

Radon and thoron, and their progeny concentrations along with equilibrium factors for gas progeny and radiological risks to the residents have been measured in dwellings of Digboi and Mashimpur areas located on anticlines during the winter season. In this present investigation, twin-cup dosemeters fitted with LR-115 (II) nuclear detectors have been employed. The present work has shown that there exist considerable house-to-house variations in values with maximum values in mud houses and minimum values in assam type (AT) houses. It has been found that mean (and geometric standard deviations (GSD)) radon concentrations are 83.8 (1.3), 113.5 (1.1) and 157.2 (1.2) Bq m(-3) in AT, reinforced cement concrete (RCC) and mud houses in Digboi area and 63.0 (1.1), 87.1 (1.4) and 182.1 (1.2) Bq m(-3) in AT, RCC and mud houses in Mashimpur area, respectively. The overall mean radon concentrations in Digboi and Mashimpur are estimated to be 114.4 (1.4) and 100.0 (1.7) Bq m(-3). The mean radon concentrations are found to be less than the lower reference level of 200 Bq m(-3) of the International Commission on Radiological Protection (ICRP 2007). The thoron concentrations in Digboi area are estimated to be 31.1 (1.3), 50.8 (1.4) and 67.0 (1.6) Bq m(-3) in AT, RCC and mud houses, respectively, whereas in Mashimpur area, the thoron concentrations are estimated to be 26.4 (1.3), 44.4 (1.3) and 77.7 (1.3) Bq m(-3) in AT, RCC and mud houses, respectively. The mean annual effective doses in Digboi area are found to be 1.9 (1.3), 2.7 (1.2) and 4.1 (1.4) mSv y(-1) in AT, RCC and mud houses, respectively, while in the case of Mashimpur area, the mean annual effective doses are found to be 1.5 (1.4), 2.2 (1.2) and 4.9 (1.3) mSv y(-1) in AT, RCC and mud houses, respectively. Nevertheless, the obtained results are much lower than the upper reference level of 10 mSv (ICRP 2007).

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

“…The detector used in this investigation was LR-115 (II) manufactured by Kodak Pâthé Company, France and has a 12 μm thick nitrocellulose (C 6 H 8 O 7 N 2 ) layer laminated on a strippable 100 μm thick transparent non-etchable polyester sheet. The LR-115 (II) detector does not exhibit the 'self-plate-out effect,' which means that tracks formed by alpha particles emitted from its progenies deposited on the detector films are not recorded [Barooah et al 2014]. Radon ( 222 Rn), thoron ( 220 Rn) and actinon ( 219 Rn) decay out to their solid progeny 218 Po, 216 Po, and 215 Po respectively, by the alpha emission of energy of 5.49 MeV, 6.29 MeV and 6.94 MeV respectively.…”

“…Radon ( 222 Rn), thoron ( 220 Rn) and actinon ( 219 Rn) decay out to their solid progeny 218 Po, 216 Po, and 215 Po respectively, by the alpha emission of energy of 5.49 MeV, 6.29 MeV and 6.94 MeV respectively. An LR-115 (II) detector detects only alpha particles with energies between 1.9 and 4.2 MeV [Barooah et al 2013, Barooah et al 2014. As a result, alpha emissions from progeny with energy more than 5 MeV deposited on the detector films are unlikely to contribute to track registration.…”

“…After one month of exposure, the detector films were retrieved and chemical etching was performed in a constant temperature bath in 2.5 N NaOH solution maintained at 60 °C for 110 min with a bulk etch rate (V B ) of 4 μm h −1 [Mayya et al 1998, Eappen and Mayya 2004, Mehta et al 2015. This process of chemical etching lowers the thickness of the detectors to roughly 5 μm [Somogyi 1986], helping to visualise the latent tracks as 'thorough etched holes' [Barooah et al 2014]. Then the detectors were rinsed and dried before the cellulose nitrate layers were pulled away from the polyester sheet.…”

“…Radon ( 222 Rn) is a chemically inert gas, radioactive in nature and is found in the natural decay series of uranium. The half-life of radon is 3.82 days and disintegrates into the radioactive isotope of polonium ( 218 Po) that emits an alpha particle with an energy of 5.49 MeV [Barooah et al 2014, Barooah and Phukan 2012, Fleischer 1997, Kaliprasad et al 2017.…”

Assessment of Active Ground Subsidence in the Dibrugarh and Digboi Areas of Assam, Northeast India, Using the PSInSAR Technique

“…Large fields were later found in the Assam-Arakan foreland basin and along the Brahmaputra arch after the use of numerous seismic investigation methods. According to Barooah et al [48], the middle Miocene Tipam series of rocks make up the extended anticlinal trap known as the Digboi anticline, which is where the Digboi oil field is located. The lower Tipam and upper Girujan formations (Table 1) are stratigraphically well-exposed in the Digboi anticline.…”