STUDY OF INDOOR RADON, THORON AND THEIR PROGENY IN SOUTH WEST KHASI HILLS DISTRICT OF MEGHALAYA, INDIA

Assessment of Threshold Dose of Thoron Inhalation and Its Biological Effects by Mimicking the Radiation Doses in Monazite Placer Deposits Corresponding to the Normal, Medium and Very High Natural Background Radiation Areas

The dose contributed from thoron (²²⁰Rn) and its progeny has been neglected in the dose assessment because of its short half-life (t_1/2 = 55.6 s) and generally low concentrations. Recently, concentrations of ²²⁰Rn gas and its progeny were found to be pronounced in the traditional residential dwellings in China, on beaches of India and in other countries. Accordingly, we investigated the biological effects of thoron (²²⁰Rn) decay products in various mouse organs, succeeding inhalation of thoron gas in BALB/c mouse. We investigated the biological effects upon thoron inhalation on mouse organs with a focus on oxidative stress. These mice were divided into (4 random groups): sham inhalation, thoron inhalation for 1, 4 and 10 days. Various tissues (lung, liver and kidney) were then collected after the time points and subjected to various biochemical analyses. Immediately after inhalation, mouse tissues were excised for gamma spectrometry and 72 h post inhalation for biochemical assays. The gamma spectrometry counts and its subsequent calculation of the equivalent dose showed varied distribution in the lung, liver and kidney. Our results suggest that acute thoron inhalation showed a differential effect on the antioxidant function and exerted pathophysiological alterations via oxidative stress in organs at a higher dose. These findings suggested that thoron inhalation could alter the redox state in organs; however, its characteristics were dependent on the total redox system of the organs as well as the thoron concentration and inhalation time.

Radon mapping, correlation study of radium, seasonal indoor radon and radon exhalation levels in communities around Ghana atomic energy commission

Radon mapping and seasonal radon studies have been carried out within the communities around the Ghana Atomic Energy Commission (GAEC), using ArcMap geostatistical interpolation tool. The correlation analysis was done using Pearson's correlation tools. Average seasonal indoor radon variations for CR (rainy) and CD (dry) with mean values ranging from 28.9 to 177.2 Bq/m3 (78.1 ± 38.7 Bq/m3) and 24.4-125.5 Bq/m3 (69.9 ± 24.2 Bq/m3). Average seasonal soil radon exhalation for ER (rainy) and ED (dry) with mean values ranging from 39.6 to 100.3 (68.9 ± 24.2 μBq/m2 h) and 55.2 to 111.9 (77.1 ± 18.7 μBq/m2 h). Radium concentrations ranged from 8.1 to 42.2 Bq/kg (21.3 ± 9.9 Bq/kg). Annual effective dose and resultant effective dose to lungs were found to be 0.9 to 2.9 (1.9 ± 0.8 mSv/yr), 2.1 to 9.2 (4.6 mSv/yr). The study recorded the highest and lowest positive correlation coefficient was found in the study with higher and lower coefficient values of 0.81 and 0.47 recorded in radium concentration with radon exhalation and indoor radon concentration within the dry season respectively. Pearson correlation result recorded values 0.81 and 0.47 as the highest and lowest positive coefficient values for the radium concentration correlation between radon exhalation and indoor radon concentration. One directional principal component was observed in radium concentration, seasonal radon exhalation, and indoor radon concentration. Two clusters originated from radium and seasonal radon concentrations present in dwellings as well as soils. Pearson's correlation results were in agreed with the principal component and cluster factor analysis. The study obtained the highest and lowest indoor radon concentrations with radon exhalation in rainy and dry seasons. Radium concentration was found to have a considerable effect on indoor radon and radon exhalation in dwellings and soils.

A case study on seasonal and annual average indoor radon, thoron, and their progeny level in Kohima district, Nagaland, India

Indoor radon and thoron survey has been carried out in 50 dwellings under Kohima district, Nagaland, India, using the latest measurement technology. The survey has been carried out for a one-year period in 3 different seasons, and the dwellings were selected according to the building materials used for construction. Indoor radon and thoron concentrations, as well as their progeny, followed a predictable pattern with greater levels in the winter and lower levels in the summer. Concrete housing had greater radon and thoron concentrations than bamboo and semi-wood/bamboo homes. The equilibrium factor (E.F.) and inhalation dose due to radon, thoron, and their corresponding progeny were also studied in the present study.

Radon exhalation from cement-based materials under accelerated carbonation

Cement-based materials manufactured from rocks and soils will release radon which is a carcinogen and affects indoor air quality. The alkaline cement-based material neutralizes with the acidic gas carbon dioxide in the air, reducing its pH value, known as carbonation. Carbonation of cement-based materials is an important environmental factor that can change the pore structure and effect radon release. In this study, test blocks of concrete, fly ash concrete, cement mortar, and cement paste were subjected to carbonation at 20 vol% CO₂, 70% relative humidity, and a temperature of 20 ± 2 ℃ for 28 days to explore the effect of material characteristics and carbonation age on the radon exhalation rate. Carbonation had a significant influence on the radon exhalation rate, but this effect showed positive (promoting/increasing) and negative (inhibiting/decreasing) fluctuations with carbonation age. Among the material characteristics, aggregate content had the most significant influence, followed by fly ash and cement variety. The radon exhalation rate was ordered as cement mortar > concrete > cement paste before carbonation, but was concrete > cement mortar > cement paste after carbonation. The radon exhalation rate of cement paste blocks without aggregate was ~ 1 mBq/(m²·s) lower than that of cement mortar. The inhibition of radon emission by concrete was mainly observed in the early carbonation period (< 7 days), while that by fly ash concrete was observed after 7 days. The content of fly ash did not have a significant influence on the radon exhalation rate of materials. Radon inhibition by composite Portland cement concrete was mainly observed in the middle stage of carbonation (~ 14 days), while inhibition by ordinary Portland cement concrete was mainly observed in the early (3-7 days) and late (i.e., ~ 28 days) stages. The water/binder ratio did not significantly affect the radon exhalation; concrete with a low water/binder ratio showed weak radon inhibition only when the carbonation age was long. These results will help to evaluate radon pollution in indoor or underground environments under long-term use.

A COMPREHENSIVE STUDY ON INDOOR RADON, THORON AND THEIR PROGENY LEVEL IN DIMAPUR DISTRICT OF NAGALAND, INDIA

Indoor radon (222Rn), thoron (220Rn) and their progeny concentrations were detected in several homes in Dimapur district, Nagaland, utilizing Direct Radon and Thoron progeny sensors based on solid-state Nuclear Track Detectors (Type-2 film) and pinhole type radon-thoron discriminating dosemeters. For three separate seasons, the annual inhalation dose has been determined in 80 residences in the research regions. The residences were chosen to have various types of housing, such as concrete, semi-wood/bamboo and bamboo, with varying levels of ventilation that contribute to indoor 222Rn, 220Rn and their progeny. The inhalation dose in the survey area lies between 0.33 and 3.04 mSvy-1 and is within the reference value as suggested by ICRP, 2018.

Seasonal variation of indoor radon, thoron and their progeny in Belagavi district of Karnataka, India

Systematic investigations on the seasonal variation of indoor radon, thoron and their progeny levels have been carried out in Belagavi district of Karnataka, India. The radon and thoron levels were measured using LR-115 type II dosimeter in cups with single-entry pinhole. The measurements were carried out in all the four season, viz, monsoon, autumn, winter and summer, in selected houses of the region. The higher indoor radon levels were observed during autumn with an average concentration of 56.45 Bq m^-3. The minimum in radon levels was observed in summer with an average concentration of 21.8 Bq m^-3. The indoor thoron concentration was also maximum during autumn with an average value of 36.44 Bq m^-3 and minimum in summer with an average value of 15.9 Bq m^-3. The radon and thoron levels were also found to depend on the nature of walls and floorings of dwellings. The lung dose rate to the population due to radon ranged from 1.195 to 9.557 mSv year^-1, with an average of 4.572 mSv year^-1. Risk levels were found to be significant during autumn and winter due to the inhalation of indoor radon and thoron. The study forms the first comprehensive report on the indoor radon and thoron levels and the resulting population dose in the Belagavi region. The studies reveal that the major contributor to the population is radon and its progeny. However, a sizable dose also comes from indoor thoron and its progeny. The study emphasises the need to provide better ventilation system to future dwellings to reduce the risk from indoor radon and thoron.