Relevance of radon progeny measurements for the assessment of inhalation doses in groundwater utilities.

The high radon concentrations measured in the indoor air of groundwater facilities and the prevalence of the problem have been known for several years. Unlike in other workplaces, in groundwater plants, radon is released into the air from the water treatment processes. During the measurements of this study, the average radon concentrations varied from 500 to 8800 Bq m-3. In addition, the indoor air of the treatment plants is filtered and there are no significant internal aerosol sources. However, only a few published studies on groundwater plants have investigated the properties of the radon progeny aerosol, such as the equilibrium factor (F) or the size distribution of the aerosol, which are important for assessing the dose received by workers. Moreover, the International Commission on Radiological Protection has not provided generic aerosol parameter values for dose assessment in groundwater treatment facilities. In this study, radon and radon progeny measurements were carried out at three groundwater plants. The results indicate surprisingly high unattached fractions (fp= 0.27-0.58), suggesting a low aerosol concentration in indoor air. The correspondingFvalues were 0.09-0.42, well below those measured in previous studies. Based on a comparison of the effective dose rate calculations, either the determination of thefpor, with certain limitations, the measurement of radon is recommended. Dose rate calculation based on the potential alpha energy concentration alone proved unreliable.

The causes of the abrupt enhancement of the natural gamma radiation in the thunderous atmosphere on the mountain tops.

The study presented the relationship between sudden Natural Gamma Radiation (NGR) increases related to enhanced atmospheric electric fields. We pinpoint Thunderstorm Ground Enhancements (TGEs) as the primary source of abrupt and significant NGR spikes. These TGEs, which are transient, several-minute-long increases in elementary particle fluxes, originate from natural electron accelerators within thunderclouds. The more prolonged, yet less pronounced, increases in NGR, persisting for several hours, are attributed to the gamma radiation from radon progeny and enhanced positron fluxes. This radon, emanating from terrestrial materials, is carried aloft by the Near-Surface Electric Field (NSEF). To measure NGR at Aragats Mountain, we use an ORTEC detector and custom-built large NaI (Tl) spectrometers, employing lead filters to discriminate between cosmic ray fluxes and radon progeny radiation. Our analysis differentiates between radiation enhancements during positive and negative NSEF episodes. The resultant data provide a comprehensive measurement of the intensities of principal isotopes and positron flux during thunderstorms compared to fair weather conditions.

Computational analysis of radon progeny deposition patterns in the human respiratory system.

In the last year, the use of computational fluid dynamics (CFD) techniques has gained prominence as a powerful tool for modeling biological phenomena and influencing the design of biomedical devices. In this study, we utilized a computational fluid dynamics (CFD) model to simulate airflow and the deposition of aerosol particles within the human respiratory tract. To achieve this, we meticulously constructed a 3D model of the human tracheobronchial airways using SolidWorks software. Our computational analyses encompassed a range of breathing conditions, ranging from 15 to 60 (L/min). Through the application of discrete phase modeling (DPM), we investigate the behavior of two-phase flow dynamics. Our focus lies in the examination of aerosol particles, with diameters ranging from 1 to 10 (µm), in order to evaluate the influence of aerosol particle size on deposition rates. Our findings encompass velocity contour maps, deposition rates of aerosol particles, and insights into the process of aerosol particle entrapment at various locations within the respiratory tract. Our study reveals a direct correlation between higher inhalation rates and larger aerosol particle sizes, resulting in increased deposition rates. Additionally, we observe a heightened deposition of aerosol-particles at bronchi region. These computational results hold significant value in estimating the distribution of doses resulting from radon progeny exposure in distinct anatomical regions of the respiratory tract.

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.

Simultaneous measurements of radon, thoron and thoron progeny and induced cancer risk assessment in Djeno, Pointe-Noire, Republic of Congo.

In this study, the activity concentrations of radon (222Rn), thoron (220Rn) and thoron progeny were measured simultaneously in Djeno (Pointe-Noire, Republic of Congo) using RADUET detectors to evaluate the air quality and the radiological risks due to the inhalation of these radionuclides. Activity concentrations of radon progeny were calculated from those of radon. Indoor radon, thoron and progenies followed a lognormal distribution ranging between 20 and 40, 6 and 62, 8 and 17.6 and 0.4 and 19.6 Bq m-3 for radon, thoron, radon progeny and thoron progeny, respectively. Mean values for radon were lower than the worldwide values estimated by the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which are 40 Bq m-3 (arithmetic mean) and 45 Bq m-3 (geometric mean). Radon concentrations in the dwellings under study were below the World Health Organization and the International Commission on Radiological Protection recommended reference levels, which are, respectively, 100 and 300 Bq m-3. The mean concentration of thoron was twice the world average value of 10 Bq m-3 estimated by UNSCEAR. Thoron progeny mean concentration was sharply greater than the typical value (0.3 Bq m-3) for indoor atmosphere provided by UNSCEAR. Annual effective dose ranges were 0.40-0.87 mSv (arithmetic mean, 0.57 ± 0.11 mSv) for radon and 0.10-4.14 mSv (arithmetic mean, 0.55 ± 0.77 mSv) for thoron. The mean value for radon was lower than the value (1.15 mSv) estimated by UNSCEAR, while the mean value for thoron was five times higher than the UNSCEAR value (0.10 mSv). The study showed that the use of the typical equilibrium factor value given by UNSCEAR to compute effective dose led to an error above 80%. Finally, the results of this study showed that the excess relative risk of radon-induced cancer was low, below 2% for the population under 55 y. The results presented in the present study prove that the population of Djeno is exposed to a relatively low potential risk of radon- and thoron-induced cancer.

Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave.

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces - the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11-6653 by Bq m-3 and 10-89,020 Bq m-3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process - convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Radon activity concentration RnCA and workers lung cancer risks in SENA coal mines, Colombia.

The risk of lung cancer or pneumoconiosis mortality, increases with radioactive radon gas exposures. This article report health risk for underground workers exposed to radioactive gas and radon daughters carried by airborne dust at the coal mining in the Central Mountainous Region of Colombia. A set of 33 measurement points located in that mine galleries were selected to monitor radon gas concentration activity, by passive LR-115 detectors, during two months. Resulting values provided radon concentrations, absorbed dose, environmental equivalent dose and the effective dose; miners increased risk of contracting lung cancer is included. It is concluded that the mine ventilation system satisfies the conditions required by the current radiological protection of the miners. Our study point out that Colombia can effectively address the potential risks associated with radon exposure and ensure a safer living environment for its citizens.

Radon decay product particle radioactivity and oxidative stress biomarkers in patients with COPD.

Radon decay products include α-radiation emitting radionuclides that attach to airborne particles that have potential to promote oxidative tissue damage after inhalation. To assess associations between α-particle radioactivity (α-PR) with urinary biomarkers of oxidative tissue damage, 140 patients with chronic obstructive pulmonary disease (COPD) had up to four 1-week seasonal assessments (N = 413) of indoor (home) and ambient (central site) PM2.5 and black carbon (BC). Following environmental sampling, urine samples were analyzed for total and free malondialdehyde (MDA), biomarkers of lipid oxidation, and 8-hydroxyl-2'-deoxyguanosine (8-OHdG), a biomarker of DNA oxidative damage. Particle radioactivity was measured as α-activity on PM2.5 filter samples. Linear mixed-effects regression models adjusted for urinary creatinine and other personal characteristics were used to assess associations. Indoor α-PR was associated with an increase in 8-OhdG (8.53%; 95% CI: 3.12, 14.23); total MDA (5.59%; 95% CI: 0.20, 11.71); and free MDA (2.17%; 95% CI: 2.75, 7.35) per interquartile range (IQR) of α-PR [median 1.25 mBq/m3; IQR 0.64], similar adjusting for PM2.5 or BC. The ratio of indoor/ambient α-PR was positively associated with each biomarker and associations with ambient α-PR were positive but weaker than with indoor concentrations. These findings are consistent with a contribution of radon decay products as measured by α-PR to oxidative stress in patients with COPD, with a greater contribution of indoor radon decay products.

Estimation of radiation dose due to thoron and progeny inhalation in high background natural radiation area of Odisha, India.

Results of the preliminary measurements of indoor radon, thoron and progeny concentrations showed very high values of thoron concentrations in the eastern coastal region of Odisha, India. Therefore, measurements of thoron and its progeny concentrations were extended to a larger number of houses in this area for the assessment of the radiation dose received by the public. The measured values of thoron concentrations were used for the calculation of annual effective doses. The estimated values of the annual effective dose due to thoron exposure were observed in the range of 0.2-14.7 mSv. The estimated radiation doses responsible for thoron exposure were observed considerably high in the region. The results obtained are compared with those obtained in other studies performed so far in the study area and a review of different studies involving different measurement techniques is presented in the paper. The results of this study support the preliminary studies showing high values of thoron levels in the study area.

Site-specific dose conversion factors for radon progeny based on ambient aerosol characteristics in an outdoor environment and a tourist cave.

Site-specific Dose Conversion Factors (DCFs) for radon progeny were estimated based on the aerosol measurement results in an outdoor environment and a tourist cave. The Activity Median Diameter (AMD) and unattached fraction were measured and used to calculate the effective dose per unit intake of radon progeny. The AMDs in the outdoor environment was in the range of 0.24-0.71 µm with the unattached fraction of 0.17. In the tourist cave, two peaks were found in the aerosol size distribution at nucleation and accumulation modes and the unattached fraction was measured to be 0.69 with a range of 0.36-0.85. The DCFs at the outdoor environment did not differ from those from the publication of the International Commission on Radiological Protection; however, the DCF in the tourist cave was significantly higher due to the discrepancy in the unattached fraction and the aerosol size distribution. It was found that these two factors would significantly affect the DCF so that we should be aware of it.

Electrostatic precipitator collection efficiency studies using atmospheric radon progeny as aerosol analogs for nuclear explosion radionuclides.

Electrostatic precipitation (ESP) is an attractive low-powered collection mechanism for mobile and fixed aerosol detection of radionuclides (RNs) for Nuclear Explosion Monitoring (NEM). Aerosol samplers deployed in the International Monitoring System use a blower to draw air through a filter media to collect particulates. ESP-based samplers collect aerosols without a filter, which can greatly increase volumetric flow capacity per watt of power consumed. ESP-based collectors may be optimized to perform low-power mobile RN collection or to improve the air throughput of existing monitoring stations. This effort describes the use of unknown concentrations of atmospheric RNs to determine the collection efficiency of a compact ESP design. For this analysis, naturally occurring radon progeny are simultaneously collected by a single stage wire-plate ESP and a filter-based sampler with a known collection efficiency. The activity of resulting samples is measured with gamma-spectroscopy and decay corrected for analysis time offsets. RN collection efficiencies are then derived for an experimental survey of ESP operational parameters that influence the ionization, transit, and collection of aerosols. At volumetric flow rates of 1.5-2 CMM, the optimized collection efficiency was calculated as 21±2%, and slower rates around 0.5 CMM resulted in 55 ±5% collection efficiency. The monitoring performance of the ESP-based collector was assessed for a simplified nuclear explosion source term by calculating the minimal detectable concentrations of short-lived fission & activation products. Results of the study suggest that a low-power ESP is feasible for NEM at distances of 100s of km.

226Ra measurement via gamma-ray spectrometry of 222Rn progeny - quantification of radon losses from sample capsules.

Radium-226 detection in sediment samples is generally executed by means of gamma-ray spectrometry. Data evaluation relies (besides the 186.2 keV 226Ra gamma peak) on the combined analysis of major gamma peaks that are produced by the short-lived radon (222Rn) daughters 214Pb and 214Bi. Precondition for this detection approach is equilibrium decay of all members of the decay chain between 226Ra and 214Bi. In closed systems, this equilibrium is reached after about five half-lives of 222Rn (19 days). However, a closed system can only be guaranteed if the capsule which contains the sample prevents diffusive escape of radon. Such radon-tightness cannot be guaranteed for a wide range of plastic materials. Due to its polymer structure, plastic material generally tends to allow radon diffusion and hence radon loss from the sample resulting in a disturbance of the required decay equilibrium. The paper introduces an approach that allows quantifying radon loss from sample capsules by direct radon measurements using mobile radon detection equipment. The experimental findings are supported by theoretical considerations. An examined alternative approach based on the offset of the 186.2 keV data point from an efficiency function that is calculated exclusively from short-lived radon progeny peaks in the gamma-ray spectrum did not prove to be applicable due to a lack of supporting peaks in the low-energy section of the spectrum.

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.

Radon progeny measurements in a ventilated filter system to study respiratory-supported exposure.

Radon (222Rn) and its progeny are responsible for half of the annual dose from natural radiation and the most frequent cause for lung cancer induction after smoking. During inhalation, progeny nuclides accumulate in the respiratory tract while most of the radon gas is exhaled. The decay of progeny nuclides in the lung together with the high radiosensitivity of this tissue lead to equivalent doses implying a significant cancer risk. Here, we use gamma spectroscopy to measure the attachment of radon progeny on an air-ventilated filter system within a radon enriched atmosphere, mimicking the respiratory tract. A mathematical model was developed to describe the measured time-dependent activities of radon progeny on the filter system. We verified a linear relation between the ambient radon activity concentration during exposure and the amount of decay products on the filter system. The measured activities on the filters and its mathematical description are in good agreement. The developed experimental set-up can thus serve to further investigate the deposition of radon progeny in the respiratory tract under varying conditions for determination of dose conversion factors in radiation protection, which we demonstrate by deriving dose estimations in mouse lung.

Cold season dose rate contributions from gamma, radon, thoron or progeny in legacy mines with high natural background radiation.

In areas with high natural background radiation, underground cavities tend to have high levels of airborne radionuclides. Within mines, occupancy may involve significant exposure to airborne radionuclides like radon (222Rn), thoron (220Rn) and progeny. The Fen carbonatite complex in Norway has legacy mines going through bedrock with significantly elevated levels of uranium (238U) and especially thorium (232Th), and significant levels of their progeny 222Rn and 220Rn. There are also significantly elevated levels of gamma radiation in these mines. These mines are naturally chimney ventilated and release large volumes of air to the outdoors giving a large local outdoor impact. We placed alpha track detectors at several localities within these mines to measure airborne radionuclides and measured gamma radiation of bedrock at each locality. The bedrock within the mines shows levels up to 1900 Bq kg-1 for 238U, 12 000 Bq kg-1 for 232Th and gamma dose rates up to 11 µSv h-1. Maximum levels of airborne radionuclides were 45 000 Bq m-3 for 220Rn and 6900 Bq m-3 for 222Rn. In addition, we measured levels of thoron progeny (TnP). In order to estimate radiation dose contribution, TnP should be assessed rather than 220Rn, but deposition-based detectors may be biased by the airflow of mine-draft. We present dose rate contributions using UNSCEAR dose conversion factors, and correcting for airflow bias, finding a combined cold season dose rate within these mines of 17-24 µSv h-1. Interestingly, fractional dose rate contributions vary from 0.02 to 0.6 for gamma, 0.33 to 0.95 for radon and 0.1 to 0.25 for TnP.

Changes induced in the human respiratory tract by chronic cigarette smoking can reduce the dose to the lungs from exposure to radon progeny.

Chronic cigarette smoking leads to changes in the respiratory tract that might affect the dose received from exposure to radon progeny. In this study, changes induced by cigarette smoking in the respiratory tract were collected from the literature and used for calculation of the dose received by the lungs and organs outside the respiratory tract. Morphological and physiological parameters affected by chronic smoking were implemented in the human respiratory tract model (HRTM) used by the International Commission of Radiological Protection (ICRP). Smokers were found to receive lung doses 3% smaller than the ICRP reference worker (non-smoking reference adult male) in mines and 14% smaller in indoor workplaces and tourist caves. A similar dose reduction was found for the extrathoracic region of the HRTM. Conversely, kidneys, brain, and bone marrow of smokers were found to receive from 2.3- up to 3-fold of the dose received by the respective organ in the ICRP reference worker, although they remained at least two orders of magnitude smaller than the lung dose. These results indicate that the differences in the lung dose from radon progeny exposure in cigarette smokers and non-smokers are smaller than 15%.

Experimental Setups for In Vitro Studies on Radon Exposure in Mammalian Cells-A Critical Overview.

Naturally occurring radon and its short lived progeny are the second leading cause of lung cancer after smoking, and the main risk factor for non-smokers. The radon progeny, mainly Polonium-218 (218Po) and Polonium-214 (214Po), are responsible for the highest dose deposition in the bronchial epithelium via alpha-decay. These alpha-particles release a large amount of energy over a short penetration range, which results in severe and complex DNA damage. In order to unravel the underlying biological mechanisms which are triggered by this complex DNA damage and eventually give rise to carcinogenesis, in vitro radiobiology experiments on mammalian cells have been performed using radon exposure setups, or radon analogues, which mimic alpha-particle exposure. This review provides an overview of the different experimental setups, which have been developed and used over the past decades for in vitro radon experiments. In order to guarantee reliable results, the design and dosimetry of these setups require careful consideration, which will be emphasized in this work. Results of these in vitro experiments, particularly on bronchial epithelial cells, can provide valuable information on biomarkers, which can assist to identify exposures, as well as to study the effects of localized high dose depositions and the heterogeneous dose distribution of radon.

A CFD-based approach to study the deposition and distribution behaviour of 212Pb in a calibration chamber.

Among the several aspects of decay products behavior, deposition is of special significance because of its prominent role in the activity removal from the environment, which eventually results in the occurrence of decay product disequilibrium with the parent gas. This point is particularly important in case of thoron dosimetry where thoron progeny 212Pb accounts for the most of the radiological dose. The deposition depends on the size distribution of decay products and the structure of air turbulence at the air-surface interface. In the present work, the effect of varying air-flow (fan speed) and aerosol count median diameter (CMD) was studied on the deposition and distribution profile of 212Pb using computational fluid dynamics (CFD). The simulations have been carried out in a cubical calibration chamber of volume 8 m3, facilitated at RP&AD, BARC. Simulated results showed that the increase of total depositional loss rate of attached fraction of 212Pb due to increase of the fan speed was significant for CMD up to 400 nm, beyond which this effect started becoming less prominent with increasing diameter. Besides, a minimum of the total depositional loss rate curve was seen to be shifted to the higher CMD with increase of the fan speed. CFD results were found to be in good agreement with experimental observations obtained in the controlled conditions with thoron source.

Impact of humidity and flowrate on the thoron measurement sensitivity of electrostatic radon monitors.

The accurate measurement of thoron activity concentration is an important issue in both thoron exposure evaluation and in reducing its influence on radon measurement. For radon monitors based on electrostatic collection technique and an alpha spectrometry analyser, air humidity and sampling flowrate are key factors influencing the sensitivity of thoron activity concentration measurement. For the purpose of improving thoron measurement sensitivity and stability, theoretical derivation and experimental studies were systemically performed in this study. The results show that thoron measurement sensitivity decreases as a negative exponential function with absolute humidity increasing, and the sensitivity of thoron is much lower than that of radon under the same conditions, which is mainly caused by the small value of the concentration ratio of thoron inside to outside of the chamber. When the air exchange rate of the measurement chamber (sampling flowrate/inner volume) increases, the measurement sensitivity of thoron gas first increases rapidly and then decreases slowly after reaching its maximum at the air exchange rate of 0.24 s-1. In practice, in the normal air exchange rate range (for example <0.05 s-1), increasing the sampling flowrate could greatly improve the thoron measurement sensitivity, which consequently suggests an effective way to update thoron measurement under the present conditions of the monitor.

Indoor radon survey in Greenland and dose assessment.

Indoor radon and its decay products are the primary sources of the population's exposure to background ionizing radiation. Radon decay products are one of the leading causes of lung cancer, with a higher lung cancer risk for smokers due to the synergistic effects of radon decay products and cigarette smoking. A total of 459 year-long radon measurements in 257 detached and semi-detached residential homes in southwest and south Greenland were carried out, and a dose assessment for adults was performed. The annual arithmetic and geometric means of indoor radon concentrations was 10.5 ± 0.2 Bq m-3 and 8.0 ± 2.3 Bq m-3 in Nuuk, 139.0 ± 1.0 Bq m-3 and 97.3 ± 2.1 Bq m-3 in Narsaq, and 42.1 ± 0.7 Bq m-3 and 22.0 ± 3.1 Bq m-3 in Qaqortoq. Arithmetic and geometric mean radon concentration of 79.0 Bq m-3 and 50.3 Bq m-3 were estimated for adult, person-weighted living in south Greenland. The total number of detached and semi-detached residential homes where indoor radon is exceeding 100 Bq m-3, 200 Bq m-3, and 300 Bq m-3 is 37 homes (15.0%), 13 homes (5.2%), and 8 homes (3.2%), respectively. A positive correlation between indoor air radon concentrations and underlying geology was observed. The indoor radon contribution to the annual inhalation effective dose to an average adult was 0.5 mSv in Nuuk, 6.5 mSv in Narsaq, 2.0 mSv in Qaqortoq, and 4.0 mSv for south Greenland adult person weighted. The estimated annual average effective dose to adults in Narsaq is higher than the world's average annual effective dose of 1.3 mSv due to inhalation of indoor radon. Cost-efficient mitigation methods exist to reduce radon in existing buildings, and to prevent radon entry into new buildings.