Dose estimation derived from the exposure to radon, thoron and their progeny in the indoor environment

Indoor concentrations of radioactive aerosols from nuclear accidents

In previous studies, some of the important factors that affect the spread of radioactive aerosols into indoors were considered. The studies were based on a new CFD approach and provided good descriptions for the deposition of aerosol particles inside small spaces and the penetration of aerosols into buildings through wall cracks. In this article, an application of those studies is implemented, where all the graphical relations that are required to estimate the indoor concentrations of radioactive aerosols from nuclear accidents are provided. This includes the deposition velocities, deposition rate, and the penetration factor. Particular interest is in the Fukushima-Daiichi nuclear power plant accident that took place in Japan in 2011. The aerosols carrying the radioiodine iodine-131 and the radiocesium cesium-134 and cesium-137 are studied. Based on the model's assumptions, and assuming steady-state air concentrations, the radioactive aerosols' concentrations in indoor air are about 97% of the concentrations in outdoor air. The applications demonstrate the model to be convenient and practical.

Assessment of radiological risk associated with thoron gas at primary schools in Al-Najaf city, Iraq

Children spend considerable time at home and school, so school is likely to be a second source of natural radionuclide exposure after home. This study evaluates the radiological risk associated with thoron gas in the air within the building of one hundred primary schools in Al-Najaf City, Iraq, using a CR-39 detector. The results of the average value of thoron concentration detector, the annual effective dose (AED), Excessive Lifetime Cancer Risk (ELCR) × 10-3, and Lung Cancer Case (LCC) × 10-9 measured in the building of the schools were 7.47 ± 2.85 Bq/m3, 0.03 ± 0.01 mSv/y, 0.11 ± 0.04, and 0.54 ± 0.20, respectively. All the results of indoor thoron were below the global average limit. The results of the radiological survey due to thoron concentrations for studied primary schools suggest that the radionuclides and their radiological hazard indexes in all studied schools in AL Najaf city, Iraq, do not impose a health hazard.

Application of CFD modeling for indoor radon and thoron dispersion study: A review

This paper provides an in-depth discussion of the CFD implications to the design/study of interior environments and an overview of the most widely used CFD model for indoor radon and thoron dispersion study. For the design and analysis of indoor environments, CFD is a powerful tool that enables simulation and measurement-based validation. Simulating an indoor environment involves deliberate thought and skilful management of complicated boundary conditions. User and CFD programs can develop results through gradual effort that can be relied upon and applied to the design and study of indoor environments. Radon and thoron are natural radioactive gases and play a crucial role in accurately assessing the radioactive hazard within an indoor environment. This review comprise the work related to measurement and CFD modeling on these radioactive pollutant for indoors.Highlighting the current state of environmental radioactive pollutants and potentially identified areas that require further attention or research regarding investigating factors affecting indoor radioactive pollutants.

Characteristics of 222Rn and 220Rn equilibrium factors in the indoor environments

Humans receive a significant portion (˃50%) of the total dose attributed to all the natural radiation sources from indoor radon (222Rn), thoron (220Rn), and their progeny. While progeny contributes an overwhelming part to the dose, in most surveys, only radon gas is measured because of the simplicity of measurement. Progeny concentration is usually estimated by multiplying gas concentration with an assumed factor, called the equilibrium factor, and taken from literature. Recently, results of the measurements of equilibrium factors for 222Rn and 220Rn were reported from various parts of the globe. In India, many such studies have been conducted in the current decade. The studies show a wide variation of equilibrium factors which suggests that they depend on environmental factors and measurement conditions. Therefore, they should be determined site specifically if accurate site-specific dose estimation is targeted. This paper summarizes concepts, definitions, and methods to determine equilibrium factors and reviews literature about reported equilibrium factors worldwide, focusing on data reported from India.

Characterization of environmental radiological parameters on dose coefficient - Realistic dosimetry compared with epidemiological dosimetry models

Radiation exposure due to all-natural sources amounts to about 2.4 mSv per year. However, this amount might be changed to over 3 mSv y-1 according to the recently introduced ICRP radon dose coefficient factor. Previously, the radon contribution to the total dose from natural sources was about 1.2 mSv y-1. However, after the latest introduced dose conversion factor by ICRP, this value could technically be increased to around 2 mSv y-1. This paper attempts to address the following questions: (i) whether reducing radon concentration to the recommended level could address concerns about radiation exposure in underground workplaces, and (ii) the effects of the difference between the epidemiological dosimetry models and realistic dose estimation. The actual dose conversion factor (DCF) was calculated using measured annual average unattached and equilibrium factors, ranging from 16 ± 9 to 25 ± 10 mSv·WLM-1. Then, the estimated inhalation dose, both from self-calculated DCF and the value reported by ICRP-137, was compared: 5.6 ± 0.7-7.6 ± 0.9 mSv y-1 and 3.3 ± 0.4-3.6 ± 0.5 mSv y-1, respectively. It can be observed that exposure to a radon concentration lower than the recommended level does not guarantee a lower dose than the recommended value. The estimated dose was at least two times greater than the dose using pre-estimated values from epidemiological dosimetry models, specifically in this case study. Further experiments in different underground working environments, excluding caves, are needed for more precise observations. It might also be time to update the data regarding the dose contribution from natural radiation sources, as the radon contribution increased according to ICRP.

Assessment of radon, thoron, and their progeny concentrations in the dwellings of Shivalik hills of Jammu and Kashmir, India

The present work determines the contents of active and passive indoor 222Rn, 220Rn, and their daughter in the 32 houses of the Reasi district of J&K, India. The passive 222Rn and 220Rn concentration was measured by dosimeters, whereas the active content was measured by active radon monitor. Progeny sensors and integrated samplers were operated for the evaluation of passive and active daughter contents of 222Rn and 220Rn. The measured averaged values of indoor 220Rn and 222Rn were 73 ± 40 and 22 ± 8 Bqm-3, respectively. The radon and thoron equilibrium factor has varied from 0.3 to 1.7 and from 0.006 to 0.6. The fine fraction of the above-mentioned gases was also calculated. The results of Mann-Whitney test statistically demonstrated significant differences between the content of indoor 222Rn, 220Rn, and their daughter for different seasons. The values of 222Rn, 220Rn, and their daughter content were appeared to be elevated in set of mud houses among all sets of houses. The values of all daughter concentration and indoor 222Rn were appeared to lie within the limit proposed by various agencies. The total doses were detected less than range commended by ICRP that suggested the district is safe as a health hazard point of view.

Age-dependent potential health risk assessment due to radioactive radon-222 in the environs of highly populated Durgapur industrial zone and nearby Bakreswar hot spring, India

It is well known that exposure to a high concentration of radon-222 causes severe health effects, including cancer. The present article includes a survey on radon-222 in the water bodies of the city Durgapur [non-geothermal area] and nearby Bakreswar hot spring [geothermal province], India. The possible sources of radon from natural radionuclides and industries have been discussed in the article. Durgapur is a densely populated [~ 3680 persons/km2] industrial city with a population of 0.57 million. On the other hand, many tourists and pilgrims usually visit Bakreswar throughout the year. Age-dependent potential health risk assessments of the dwellers at Durgapur and Bakreswar due to radon exposure were performed for the first time. The present work is the first attempt to estimate the mean ingestion /and inhalation dose per annum, total effective dose [TED] per annum and the health risk assessment for cancer in adults, children and infants due to radon exposure at Durgapur and Bakreswar. In some cases, the values of TED exceed the permissible limit of 100 micro Sievert per year [µSv/y] as recommended by EUC and WHO. The radiation profile maps relating to radon concentration and associated contour maps of health risk factors [HRF] for the adults, children and infants were also prepared for the first time. Some areas were identified as high-risk zones, and the dwellers are prone to a high risk of cancer. The article also proposed several techniques to reduce radon in water and buildings. The authors also recommended banning some water sources to protect people from radon risk. This study will help scientists, policymakers, industrialists, farmers, government agencies and public health departments.

Radon and thoron concentrations in the southwest region of Angola: dose assessment and implications for risk mapping

Indoor radon (²²²Rn) and thoron (²²⁰Rn) are the most important natural sources of ionizing radiation to the public. Radiological studies that assess simultaneously ²²²Rn and ²²⁰Rn, and their controlling factors are particularly scarce in African countries. Hence, we conducted a survey of indoor ²²²Rn and ²²⁰Rn in buildings located in the SW region of Angola. Bedrock samples were also collected, and a borehole was executed to assess ²²⁶Ra and ²²⁴Ra activity concentration, ²²²Rn and ²²⁰Rn exhalation and emanation potential in the surface and at depth. The aim of this study was to determine the factors (geological and anthropogenic) that may influence the annual inhalation dose (AID) received by the population. Overall, the sum of indoor radon and indoor thoron concentrations, labelled the total indoor radon concentration (TIRC), was higher than 300 Bq/m³ in only 5% of the buildings studied. The contribution of ²²⁰Rn to the TIRC averaged 35% but may reach 95%, demonstrating the relevance of discriminating radon and thoron in indoor radon surveys. Indoor ²²²Rn and ²²⁰Rn were not correlated, indicating both must be estimated to properly assess the AID. Indoor ²²⁰Rn concentrations were statistically different according to the building materials and type of usage. Higher ²²²Rn and ²²⁰Rn concentrations were observed in dwellings compared to workplaces. The median AID estimated for dwellings was 1.50 mSv/y compared to 0.26 mSv/y for workplaces, which are lower than the estimated average radiation exposure due to natural sources of 2.4 mSv/y. AID values higher than 1 mSv/y effective dose threshold established in the Council Directive 2013/59/EURATOM for the purpose of radiation protection in workplaces were observed in 12% of the workplaces studied suggesting the need for mitigation measures in those buildings. The analysis of bedrock samples revealed statistically significant correlations between ²²⁴ and ²²⁶Ra activity concentration, and ²²⁰Rn and ²²²Rn exhalation and emanation potential. The borehole samples indicated a strong influence of weathering processes in the distribution of radioisotopes. The highest ²²⁶Ra and ²²⁴Ra activity concentration, and ²²²Rn and ²²⁰Rn exhaled per unit mass, TIRC and AID were observed in association with A-type red granites and porphyries. We conclude that both geological and anthropic factors, such as the type of building usage and building materials, must be considered in dose assessment studies and for the development of risk maps.

Radiological risk estimation from indoor radon, thoron, and their progeny concentrations using nuclear track detectors

In this paper, we report the results of seasonal variations of indoor radon and thoron concentrations, equilibrium factors for gas progeny, and radiological risks to dwellers in the hilly area of Guwahati City, Assam, India. Twin-cup dosemeters with LR-115 (II) nuclear track detectors were used in this study. The findings show that values vary significantly, with winter having the highest values and summer having the lowest, with spring and autumn having moderate values. In winter, radon concentrations range from 61.6 ± 11.2 Bq m^-3 (Mud) to 115.3 ± 34.3 Bq m^-3 (AT), with geometric mean values of 69.2 ± 13.8 Bq m^-3 and 109.4 ± 27.9 Bq m^-3, and in summer, they range from 21.1 ± 5.9 Bq m^-3 (Mud) to 28.4 ± 8.3 Bq m^-3 (AT), with geometric mean values of 22.7 ± 6.3 Bq m^-3 and 26.1 ± 7.1 Bq m^-3, whereas thoron concentrations range from 13.1 ± 5.1 Bq m^-3 (Mud) to 58.8 ± 12.6 Bq m^-3 (AT), with geometric mean values of 27.6 ± 7.0 Bq m^-3 and 52.9 ± 10.1 Bq m^-3 in winter, respectively, and in summer, from 8.8 ± 2.3 Bq m^-3 (Mud) to 13.0 ± 5.5 Bq m^-3 (Mud), with a geometric mean value of 1.87 ± 1.29 Bq m^-3. Radon and thoron progeny levels are reported to vary from 4.1 ± 0.3 mWL (Mud) to 15.1 ± 4.3 mWL (AT) and 2.6 ± 0.9 mWL (Mud) to 14.3 ± 4.2 mWL (AT) in winter and from 1.5 ± 0.7 mWL (AT) to 3.0 ± 2.5 mWL (Mud) and 0.9 ± 0.3 mWL (AT) to 2.7 ± 0.5 mWL (Mud) in summer, respectively. The equilibrium factors for radon and its progeny have been reported to range from 0.23 ± 0.1 (Mud) to 0.51 ± 0.3 (AT) in winter, whereas from 0.23 ± 0.1 (AT) to 0.48 ± 0.4 (Mud) in summer, respectively. The equilibrium factors for thoron and its progeny have been estimated in the range of 0.02 ± 0.01 (Mud) to 0.09 ± 0.06 (AT) in winter, whereas 0.02 ± 0.02 (AT) to 0.07 ± 0.05 (Mud) in summer, respectively. The inhalation dose rates differed from house to house, having values in the range of 1.2 ± 0.2 mSv year^-1 (Mud) to 4.6 ± 1.3 mSv year^-1 (AT) in winter, whereas 0.5 ± 0.3 mSv year^-1 (AT) to 0.9 ± 0.5 mSv year^-1 (Mud) in summer, respectively. The effective doses (EDs) due to the exposure of radon and thoron in the study area have been found to range from 2.5 ± 0.3 mSv (Mud) to 9.1 ± 2.7 mSv (AT) in winter and 0.9 ± 0.4 mSv (AT) to 1.8 ± 1.3 mSv (Mud) in summer, respectively. The levels of radon and thoron in similar types of construction were found to be significantly different from one house to another. The estimated radon and thoron concentrations in the houses of that region during winter are found to be substantially higher than the global averages as reported by UNSCEAR.

INTERNAL EXPOSURE FROM INDOOR RADON, THORON AND THEIR PROGENY IN RESIDENCE AROUND HIGH BACKGROUND RADIATION AREA, PHANG NGA PROVINCE, THAILAND

A passive integrating discriminative radon-thoron monitor (Raduet) and a radon-thoron progeny monitor with a solid-state nuclear tracking detector were used for estimating indoor radon, thoron and their progeny concentrations in residential areas around the old mines of southern Thailand. Exposure to high background radiation levels from natural 238U and 232Th in the tin mine areas or active fault areas may increase the risk of lung cancer in the respiratory system when considering the health effects of the surrounding inhabitants. In this study, radon thoron and their progeny concentrations from inhalation in the study site have been assessed in dose at volunteer houses to confirm radiation effects. The annual effective doses due to inhalation of radon-thoron, radon progeny and thoron progeny using the ICRP latest dose conversion factors were estimated to be 3.0-4.6, 2.5-3.7 and 0.4-1.0 mSv, respectively, and as 5.9-9.0 mSv in total.

Radiation exposure due to 222Rn, 220Rn and their progenies in three metropolises in China and Japan with different air quality levels

Radiation exposure due to radon contributes most of the ionizing radiation exposure to people among natural radiation sources. This research measured the ²²²Rn, ²²⁰Rn by the RADUET and their progeny concentrations by the improved deposition based ²²²Rn and ²²⁰Rn progeny monitor, and the contribution of outdoor PM_2.5 concentrations to indoors by a modified steady-state mass balance model in Beijing, Changchun, China and Aomori, Japan. Based on these results, we preliminarily explored the relevance between the city level outdoor PM_2.5 exposure and indoor ²²²Rn, ²²⁰Rn inhalation exposure in these three metropolises with different air quality levels. The average equilibrium equivalent radon concentration (EERC) and equilibirum equivalent thoron concentration (EETC) indoor were 17.2 and 1.1 Bq m^-3 in Beijing, 19.4 and 1.3 Bq m^-3 in Changchun, and 10.8 and 0.9 Bq m^-3 in Aomori, respectively. The indoor EERC and EETC in Beijing showed 1.4 and 2.2 times as high as that measured in 2006. The indoor radiation dose due to inhalation presented in a descending order as Changchun, Beijing and Aomori, which were in accordance with their outdoor ²²²Rn concentrations. The indoor radiation doses due to ²²⁰Rn contributed 30% of the total dose in the three cities, indicating that ²²⁰Rn cannot be neglected when evaluating indoor radiation dose. It should be noted that, the indoor PM_2.5 concentrations of outdoor origin presented strong correlation (r = 0.772) with indoor EETC and moderate correlation (r = 0.663) with indoor EERC, indicating that the PM_2.5 of outdoor origin can break the concentration balance of the indoor PM_2.5, then affect the indoor ²²²Rn and ²²⁰Rn behaviors, and further affect the inhalation exposure of radon.

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.

Dosimetry of indoor alpha flux belonging to seasonal radon, thoron and their EECs

Radon (²²²Rn) and thoron (²²⁰Rn) are ubiquitous radioactive noble gases present in the earth's crust. The source term for these gases includes soil and building materials as well. The radiological impact of radon/thoron gases and their decay products on human life is a matter of concern and has been given due attention in research and policy. The present study aims to measure and quantify residential radon/thoron gas and the decay product's concentration and to discuss the associated interpretations for Ludhiana district of Punjab, India. Passive measurement techniques employing a single-entry pinhole dosimeter for gases and direct progeny sensors for the decay product's concentration have been used in this work. The obtained data from these measurements have been analysed using appropriate statistical techniques. The variations have been linked with the changes in the ventilation conditions, building material, room type and altitude. A higher concentration of radon and thoron gas was observed in the winter season for the study region. It was estimated that the contribution of radon and thoron decay products towards the annual average inhalation dose is 75% and 25%, respectively.

Predictors of indoor radon levels in the Midwest United States

Radon (Rn) is a natural and toxic radioactive gas that accumulates indoors, mainly in low-ventilated underground floors and basements. Several factors make prediction of indoor Rn exposure in enclosed spaces challenging. In this study, we investigated the influence of soil, geology, topography, atmospheric variables, radiation, urbanization, community economic well-being, and monthly and yearly variations on indoor Rn concentrations. We analyzed 7,515 monthly indoor Rn measurements in 623 zip codes from two U.S. States (Michigan and Minnesota) during 2005-2018 using a random forest model. Using Shapley Additive exPlanations (SHAP) values we investigated the contribution of each factor using variable importance and partial dependence plots. Factors that predict indoor Rn differed between states, with topographical, geological and soil composition being most influential. Cross-validated Pearson correlation between predictions and measurements was 0.68 (RMSE = 47.8 Bq/m³) in Minnesota, and 0.67 (RMSE = 52.5 Bq/m³) in Michigan. Our results underline the importance of soil structure for radon exposure, presumably due to strapped Rn in soil. The differences across states also suggest that Rn studies performing model development should consider geographical variables, along with other factors. As indoor Rn levels are multifactorial, an understanding of the factors that influence its emanation and build up indoors will help better assess spatial and temporal variations, which will be useful to improve prevention and mitigation control strategies.Implications: Radon exposure has become a year-round problem as people spend most of their time indoors. In North America, radon exposure is increasing over time and awareness related to its health effects remains low in the general population. Several factors make prediction of indoor radon exposure in enclosed spaces challenging. In this study, we used random forest to investigate the influence of factors on indoor radon in the Midwest United States. We found that topography, geology, and soil composition were the most influential factors on indoor radon levels. These results will help better assess spatial and temporal variations, which will further help better prevention and mitigation control strategies.

Comprehensive exposure assessments from the viewpoint of health in a unique high natural background radiation area, Mamuju, Indonesia

Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study.

Study of Surface Emissions of 220Rn (Thoron) at Two Sites in the Campi Flegrei Caldera (Italy) during Volcanic Unrest in the Period 2011–2017

The study concerns the analysis of 220Rn (thoron) recorded in the surface soil in two sites of the Campi Flegrei caldera (Naples, Southern Italy) characterized by phases of volcanic unrest in the seven-year period 1 July 2011–31 December 2017. Thoron comes only from the most surface layer, so the characteristics of its time series are strictly connected to the shallow phenomena, which can also act at a distance from the measuring point in these particular areas. Since we measured 220Rn in parallel with 222Rn (radon), we found that by using the same analysis applied to radon, we obtained interesting information. While knowing the limits of this radioisotope well, we highlight only the particular characteristics of the emissions of thoron in the surface soil. Here, we show that it also shows some clear features found in the radon signal, such as anomalies and signal trends. Consequently, we provide good evidence that, in spite of the very short life of 220Rn compared to 222Rn, both are related to the carrier effect of CO2, which has significantly increased in the last few years within the caldera. The hydrothermal alterations, induced by the increase in temperature and pressure of the caldera system, occur in the surface soils and significantly influence thoron’s power of exhalation from the surface layer. The effects on the surface thoron are reflected in both sites, but with less intensity, the same behavior of 222Rn following the increasing movements and fluctuations of the geophysical and geochemical parameters (CO2 flux, fumarolic tremor, background seismicity, soil deformation). An overall linear correlation was found between the 222−220Rn signals, indicating the effect of the CO2 vector. The overall results represent a significant step forward in the use and interpretation of the thoron signal.

Wire mesh capped DRPS based bronchial dosimeter for personal inhalation dosimetry due to radon progeny

A study has been carried out to experimentally determine the calibration factor (CF) of the passive bronchial dosimeter, which consists of a direct radon progeny sensor capped with a 100-wire mesh. First, the CF was determined in controlled environmental conditions simulated in a calibration chamber. With aerosol concentrations varying from 10⁴p cm^-3to 10⁵p cm^-3and relative humidity varying from 60% to 80% in the chamber, CF was observed to be nearly constant with an average value of (3.8 ± 0.5) × 10^-3mSv tracks^-1cm². Then, the CF was determined in real indoor environments in which it was again observed to be almost constant and the mean value was found to be (5.6 ± 0.1) × 10^-3mSv tracks^-1cm². Pooling all the data on CFs obtained under controlled conditions and in real indoor environments, a lognormal distribution of the CF was observed with a geometric mean and geometric standard deviation of 0.0052 mSv tracks^-1cm²and 1.28 respectively. The experimentally determined value of CF was found to be in close agreement with the theoretically estimated value, taking into consideration the unattached fraction of radon progeny. This dosimeter is passive, cheap, lightweight and, moreover, the CF being stable against environmental variations, will be useful in monitoring inhalation doses due to radon progeny for occupational workers.

A novel method based on 220Rn (thoron) exhalation rate of indoor surfaces for robust estimates of 220Rn concentration and equilibrium factor to compute inhalation dose

The research into ²²⁰Rn (thoron) has generated an increasing interest in recent times due to the realisation of its radiological importance in many indoor environments. Though it is assumed that the contribution of ²²⁰Rn, per se, to the inhalation dose is negligible in comparison with that of its decay products, this may not be always true. Correct estimation of inhalation dose due to thoron requires a reliable method to measure the concentration of both ²²⁰Rn and its decay products in indoor air. However, due to its very short half-life (55.6 s) ²²⁰Rn shows large variation in its indoor activity concentration. This makes it difficult to have a robust value of ²²⁰Rn concentration which can be considered representative of a house, thus making the dose estimation unreliable. This issue has been addressed in the present study by developing a novel method that utilises the ²²⁰Rn exhalation rate from indoor surfaces as the basis for estimation of average ²²⁰Rn concentration in indoor air. The ²²⁰Rn concentration estimated in this manner can be converted to decay products concentration using a suitable equilibrium factor and finally the inhalation dose using appropriate dose conversion factors. A wall mounting accumulator setup has been developed for easy in-situ measurement of ²²⁰Rn exhalation from room surfaces. The method has been validated through comprehensive measurements in 25 dwellings in two different regions of India. The developed method is very good for large scale field surveys because of fast and easy applicability.

Radon Exposure-Therapeutic Effect and Cancer Risk

Largely unnoticed, all life on earth is constantly exposed to low levels of ionizing radiation. Radon, an imperceptible natural occurring radioactive noble gas, contributes as the largest single fraction to radiation exposure from natural sources. For that reason, radon represents a major issue for radiation protection. Nevertheless, radon is also applied for the therapy of inflammatory and degenerative diseases in galleries and spas to many thousand patients a year. In either case, chronic environmental exposure or therapy, the effect of radon on the organism exposed is still under investigation at all levels of interaction. This includes the physical stage of diffusion and energy deposition by radioactive decay of radon and its progeny and the biological stage of initiating and propagating a physiologic response or inducing cancer after chronic exposure. The purpose of this manuscript is to comprehensively review the current knowledge of radon and its progeny on physical background, associated cancer risk and potential therapeutic effects.

Significance of thoron measurements in indoor environment

Radon, ²²²Rn, is the major contributor to natural radiation in human environment. The exposure of high radon is known as one of the causative factors of lung cancer. Though thoron, ²²⁰Rn, has been a matter of study in atmospheric science, but it was often neglected compared to radon. It was considered that the amount of thoron in the environment is less than that of radon. However, recent studies show that thoron and its progeny sometime contribute significantly to the radiation dose in residential buildings. A review of methodologies, measurement protocols and concepts used in various thoron measurement surveys performed in India is presented in this paper. The results of measurements of thoron and its progeny, carried out in the Himalayan region and in the high background radiation area of the south-eastern coast of Odisha, India are also presented. The results obtained using various thoron measurements techniques and the resulting doses to the general public are discussed in details.

Statistical inferences from measured data on concentrations of naturally occurring radon, thoron, and decay products in Kumaun Himalayan belt

Regional averages of radon, thoron, and associated decay product concentration are reported to be higher than their respective global averages in recent studies conducted in Indian Himalayan belt. The present study explores another region in Indian Himalayan belt by conducting measurements of radon, thoron, and decay product's activity concentration in 92 dwellings of Bageshwar district. The year-long measurements were performed in all 3 seasons distinguishing dwellings as per their construction material. The average radon and thoron concentration for the study region was measured as 57 Bq/m³ and 66 Bq/m³, respectively. Analysis of the measured data in terms of seasonal effects and construction material led to well established inferences, i.e., higher concentration for mud houses and for winter season. In addition, the present study focuses on lesser probed statistical inferences. One of them is related to the appropriateness of frequency distribution function for the measured data and other dwells upon the correlation analysis of inter-related factors for high concentration cases. Three distribution functions (Lognormal, Weibull, and Gamma) were found to be following the trend of frequency distribution curve of the measured data. For mud houses in winter season, variations of radon/thoron concentration were attempted to correlate with mass/surface exhalation rate, emanation rate, and source term content. More than 80% of the dwellings of the study region were found to have gas and decay product's concentration levels, higher than the respective global average values. However, these values were mostly within the reference levels for residential environments. Nevertheless, this region requires further studies to pinpoint the causes for elevated levels and suggest simple remedial modifications if required.

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

A survey of indoor radon/thoron and their progeny concentrations was carried out in dwellings in the South West Khasi Hills district of Meghalaya, India. The survey was carried out using solid-state nuclear track detectors based on single-entry pinhole dosimeter and direct radon/thoron progeny sensors. The results are subjected to statistical analysis and discussed in the manuscript. The mean value of annual effective dose of the study region is estimated at 1.8 mSv.y -1. Seasonal variability and role of different indoor parameters are also discussed.

ASSESSMENT OF DOSE DUE TO AMBIENT Rn222/Rn220 PROGENY IN DIFFERENT DWELLINGS OF JAMMU AND KASHMIR STATE, INDIA

The un-attached part of radon (222Rn) progeny is one of the imperative variables for the definitive evaluation of the effective dose from the radon exposure perspective, and it might fluctuate enormously in various ecological conditions. Therefore, estimate dispersion of 222Rn/220Rn progeny, un-attached part and aerosol concentration was estimated in an indoor domain of Jammu and Kashmir State, India utilizing progeny deposition based sensors. Distinctive sorts of residence were picked up for this exploratory examination and maximum 222Rn and thoron (220Rn) descendants concentration was found in working environments or workplaces when contrasted from other abodes because of low ventilation rate. The average evaluated portions of an unattached for 222Rn and 220Rn are 0.29 and 0.26 and in addition, observed to be most extreme in work environments. The age-dependent dose has furthermore been determined utilizing attached and un-attached 222Rn/220Rn progeny concentrations. The dose to trachea-bronchial region and aerosol concentrations has additionally been estimated.

Investigation of 220Rn emanation and exhalation from soil samples of Larsemann Hills region, Antarctica

In the present study, thoron exhalation flux density were measured in the soil samples collected around the Indian station namely Bharati (69° 24.41' S, 76° 11.72' E) and its nearby islands in the Larsemann hills region of Antarctica. Further, dependency of thoron mass emanation rate and emanation coefficient on the soil grain size was studied by segregating the soil samples into four different grain size groups: 50-100 μm, 100-200 μm, 200-500 μm and 500-1000 μm which showed that both of them follow a decreasing trend with increase in grain size. A comparison of measured mass emanation rate between different soil samples showed that it had a larger variation for the smaller grain size which eventually decreased as grain size increased while emanation coefficient was observed to be nearly constant for all the grain size groups. The variation in emanation coefficient with respect to mean grain size has been investigated and an empirical exponential model has been proposed for predicting emanation coefficient for different grain sizes.

Numerical analysis and modeling of two-loop experimental setup for measurements of radon diffusion rate through building and insulation materials

Radon is a natural radioactive gas present in the environment, which is considered as the second most important lung cancer cause worldwide. Currently, radon gas is under focus and was classified as contaminant of emerging concern, which is responsible for serious biological/health effects in human. In presented work we propose the numerical model and analysis method for radon diffusion rate measurements and radon transport parameters determination. The experimental setup for radon diffusion was built in a classical, two chamber configuration, in which the radon source and outlet reservoirs are separated by the sample being tested. The main difference with previously known systems is utilization of only one radon detector, what was achieved by a careful characterization of the Rn-222 source and development of a numerical model, which allows for exact determination of radon transport parameters by fitting simulated radon concentration profile in the outlet reservoir to experimental data. For verification of the developed system, several insulation materials commonly used in building industry and civil engineering, as well as, common building materials (gypsum, hardened cement paste, concrete) were tested for radon diffusion rate through these barriers. The results of radon transmittance, permeability and diffusion coefficients for investigated materials are in compliance with values known previously from the literature. The analysis method is fast and efficient, and requires measurement period varying from a dozen or so hours up to 2-3 days depending on material properties. The described method is entirely based on a numerical analysis of the proposed differential equation model using freely available SCILAB software and experimental data obtained during sample measurements.

A WALK-IN TYPE CALIBRATION CHAMBER FACILITY FOR 222Rn MEASURING DEVICES AND INTER-COMPARISON EXERCISES

A walk-in type 222Rn calibration chamber of volume 22.7 m3, which has traceability to international standards, is established at the Centre for Advanced Research in Environmental Radioactivity, Mangalore University, India. It has a human-machine interface communication system, a programmable logic controller and sensor feedback circuit for controlling and data acquisition of relative humidity (RH) and temperature (T). An innovative method for the generation of desired 222Rn concentration (a few hundred Bq m-3 up to about 36 kBq m-3) using soil gas as a source was adopted. Leak rates of 222Rn from the chamber for the mixing fan ON and OFF conditions were determined to be 0.0011 and 0.00018 h-1 respectively. With the exhaust system fully turned on, the maximum clearance rate of the chamber was 0.58 ± 0.07 h-1. Excellent spatial uniformity in 222Rn concentration in the chamber was confirmed (with a mean value of relative standard deviation < 12%) through measurements at 23 locations using CR-39 film-based passive devices. Demonstration of calibration applications was performed using charcoal canister and PicoRad vials as the 222Rn adsorption devices. The study shows that gamma spectrometry is a convenient alternative approach to liquid scintillation analysis of PicoRad vials for 222Rn measurement.

Simultaneous measurements of indoor radon and thoron and inhalation dose assessment in Douala City, Cameroon

Radon, thoron and associated progeny measurements have been carried out in 71 dwellings of Douala city, Cameroon. The radon-thoron discriminative detectors (RADUET) were used to estimate the radon and thoron concentration, while thoron progeny monitors measured equilibrium equivalent thoron concentration (EETC). Radon, thoron and thoron progeny concentrations vary from 31 ± 1 to 436 ± 12 Bq m^-3, 4 ± 7 to 246 ± 5 Bq m^-3, and 1.5 ± 0.9 to 13.1 ± 9.4 Bq m^-3. The mean value of the equilibrium factor for thoron is estimated at 0.11 ± 0.16. The annual effective dose due to exposure to indoor radon and progeny ranges from 0.6 to 9 mSv a^-1 with an average value of 2.6 ± 0.1 mSv a^-1. The effective dose due to the exposure to thoron and progeny vary from 0.3 to 2.9 mSv a^-1 with an average value of 1.0 ± 0.4 mSv a^-1. The contribution of thoron and its progeny to the total inhalation dose ranges from 7 to 60 % with an average value of 26 %; thus their contributions should not be neglected in the inhalation dose assessment.

ANNUAL EFFECTIVE DOSE ASSESSMENT DUE TO RADON AND THORON PROGENIES IN DWELLINGS OF KILIMAMBOGO, KENYA

Human beings are continuously exposed to ionising radiation originating from natural or artificial sources. Uranium-238 and Thorium-232 found in building materials are important sources of radon and thoron in the indoor environment. The concentration levels of radon, thoron and thoron progeny were measured in mud-walled, metallic or iron sheet-walled and stone-walled modern houses in Kilimambogo region, Kenya for 3 months. Radon and thoron concentration levels were measured using passive radon-thoron discriminative monitors (RADUET), while thoron progeny concentrations as the equilibrium equivalent thoron concentration (EETC) were measured using thoron progeny monitors. The mean radon concentration levels in mud, metallic and stone-walled dwellings were 67 ± 11, 60 ± 10 and 75 ± 10 Bq m-3, respectively. The mean thoron concentration levels in the corresponding dwellings were 195 ± 36, 71 ± 24 and 161 ± 31 Bq m-3, respectively, while EETCs were 12 ± 2, 3 ± 1 and 7 ± 1 Bq m-3, respectively. The annual effective doses for radon were 1.3 ± 0.2, 1.1 ± 0.1 and 1.4 ± 0.2 mSv y-1 in mud, metallic and stone-walled houses while those from thoron estimated from EETC were 2.4 ± 0.4, 0.5 ± 0.1 and 1.5 ± 0.2 mSv y-1 in the corresponding houses, respectively.

Indoor and Outdoor Exposure to Radon, Thoron and Thoron Decay Products in a NORM Area with Highly Elevated Bedrock Thorium and Legacy Mines

Radon (²²²Rn) and thoron (²²⁰Rn), and especially their short-lived decay products, are major contributors to dose received by the public from naturally occurring radioactive material (NORM), particularly in areas with elevated levels of naturally occurring radionuclides. Mining in such areas can involve ventilation of high amounts of these gases, which may influence outdoor levels. In this work, we assessed indoor and outdoor levels of ²²²Rn, ²²⁰Rn and ²²⁰Rn decay products (TnDP) in close proximity to an area with elevated bedrock levels of thorium (²³²Th) and a NORM legacy mining site with high natural ventilation. We assess municipal buildings at distances from a few hundred meters to 2 km from the NORM legacy mines. In some buildings, high indoor levels of ²²²Rn were observed in winter, as expected for temperate areas. In summer, high indoor levels of ²²²Rn and ²²⁰Rn were observed in some buildings, and very low associated levels of TnDP in actively ventilated buildings may suggest entry by ventilation and an outdoor source. Outdoor levels of TnDP increased with decreased distance from the legacy mines, suggesting dispersal from these during both summer and winter.

Modelling of the temporal indoor radon variation in Bulgaria

In this study, temporal variations of indoor radon concentrations in Bulgaria were investigated. The radon concentrations were measured by nuclear track detectors as part of the Bulgarian National Survey, performed in the dwellings of 28 regional districts. The detectors were exposed through a year in two consecutive time periods of different lengths. For 2433 dwellings, measurements could be completed for both time periods, while for 345 dwellings they could only be completed for one of the periods. To estimate any missing radon concentrations, a temporal correction procedure was developed. This procedure, which included development of a linear correlation between the ln-transformed radon concentrations from the 9-month period [CRn(L)] and from the 3-month period [CRn(S)]. A normal distribution of the data, which is a condition for linear regression, was achieved when the ln-transformed radon concentrations were grouped by climate zone, then by regional districts, and finally by the presence/absence of a basement in the investigated building. The linear models obtained for each group showed reasonable coefficients of determination (R² ≈ 0.50) and root mean square errors (RMSEs) of about 0.50. When these correlations were used to reconstruct radon concentrations in missing measurement periods, it turned out that the reconstructed data (for 345 dwellings) were within the 95% confidence interval of the measured data (for 2433 dwellings). The geometric means of CRn(L) and CRn(S) were 76 Bq/m³ and 100 Bq/m³, respectively, for 2433 dwellings, which are almost equal to those of 75 Bq/m³ and 98 Bq/m³, which represent the measured and reconstructed data together (for 2778 dwellings).

A combined experimental and theoretical study of radon solubility in fat and water

Radon is a radioactive noble gas that can enter the human body, thus increasing the risk of lung cancer. But it is also used for treatment of various ailments, most notably rheumatoid arthritis. The accumulation of radon differs between tissues, with particularly high concentrations in fat tissue. To understand the underlying mechanisms, a combination of γ-spectroscopy and molecular dynamics simulations were performed, to study the accumulation of radon gas in contact with several liquids (water, fatty acids). The solubilities, specific for a defined radon activity concentration, are in good agreement and differ by two orders of magnitude between water and fat, caused by radon disrupting the hydrogen bond network of water. In contrast, the energy cost of introducing radon atoms into fat is low due to the dispersive interaction between radon and fat, which is a non-polar solvent. This correlation was also explicitly demonstrated in our simulations by changing the polarization of the solvent.