Radon and thoron progeny concentration variability in relation to meteorological conditions at Bucharest (Romania)

Study on seasonal variation of radon, thoron, and their progeny levels in indoor environments and their radiological effects on human health

Indoor radon (222Rn), thoron (220Rn) and their progeny concentrations have been measured in different types of buildings at different locations in different dwellings in different seasons in Hassan city, Karnataka, using time-integrated passive radon dosemeters containing LR-115 Type II solid-state nuclear track detectors. The annual effective dose due to radon and thoron has been estimated. The activity concentrations were observed to be highest in winter and lowest in summer, and the data also shows that bathrooms and kitchens have significantly higher radon-thoron concentrations and annual effective doses.

Meteorological Approach in the Identification of Local and Remote Potential Sources of Radon: An Example in Northern Iberian Peninsula

This paper presents a meteorological approach to identify local and remote sources driving the variability of surface daily radon concentrations. To this purpose, hourly ²²²Rn concentration and surface meteorological measurements, and air mass trajectories at Bilbao station (northern Iberian Peninsula) during the period 2017-2018 have been taken as reference. To investigate the potential transport pathways and potential ²²²Rn sources, the backward trajectory cluster analysis, trajectory sector analysis (TSA), and potential source contribution function (PSCF) are applied. On average, the diurnal ²²²Rn cycle shows the expected behaviour, with larger concentrations during the night and minimum concentrations during the daylight hours, with differences in the seasonal amplitudes. According to daily differences between maximum and baseline values, ²²²Rn daily cycles were grouped into six groups to identify meteorological conditions associated with each amplitude, and potential source areas and transport routes of ²²²Rn over Bilbao. The trajectory cluster and the TSA method show that the main airflow pathways are from the south, with small displacement, and the northeast, while the analysis of surface wind speed and direction indicates that the highest amplitudes of ²²²Rn concentrations are registered under the development of sea-land breezes. The PSCF method identified south-western and north-eastern areas highly contributing to the ²²²Rn concentration. These areas are confirmed by comparing with the radon flux map and the European map of uranium concentration in soil. The results have demonstrated the need in combining the analysis of local and regional/synoptic factors in explaining the origin and variability of ²²²Rn concentrations.

Spatial and Temporal Variations of Indoor Airborne Radon Decay Product Dose Rate and Surface-Deposited Radon Decay Products in Homes

The temporal variations of the airborne radon decay product dose rate and deposited radon decay product activities, as well as the within-house and house-to-house variations of radon concentrations, were evaluated through repeated field measurements. Long-term average radon and surface-deposited radon decay product concentrations were measured in 76 rooms of 38 houses. Temporal variation of radon, as well as airborne and surface-deposited radon decay products, were measured in 11 of the 38 houses during two different seasons. Environmental factors that have the potential to influence airborne dose rate and deposited radon decay products were also studied. Airborne dose rates were calculated from the unattached and attached potential alpha energy concentrations using two dosimetric models. For one model, the observed dose variations were 103%, 74%, 58%, and 60% for the total, house-to-house, within-house, and within-room temporal variations, respectively. For the other model, the dose variations were 100%, 66%, 61%, and 46%, respectively. Surface-deposited Po showed variations of 79%, 57%, 42%, and 48%, respectively. These substantial radon decay product concentration variations suggest that multiple locations and time-integrated measurements are needed to make an accurate assessment of the chronic radon-related doses in homes. Smoking was the environmental factor that had the largest temporal and spatial effect on airborne radon decay product dose rates.

THE NRPI MULTI-PURPOSE ON-LINE MONITORING STATION FOR MEASUREMENT OF NATURAL RADIOACTIVITY IN THE AMBIENT ATMOSPHERE AND IN THE SOIL

During years 2010-12 an automated, on-line and wireless outdoor measurement station of atmospheric radon, gamma dose rate and meteorological parameters was realised at the National Radiation Protection Institute (NRPI) in Prague. At the turn of the year 2013 an expansion of the existing station was completed. Under the project funded by the Czech Technological Agency a new updated station was established, additionally equipped with modules for measurement of atmospheric radon/thoron short-lived decay products, radon in water and soil and radon exhalation rate from soil. After the introduction of the station updated key detection parameters and benefits, its use for atmospheric modelling and monitoring is demonstrated. There are summarised results from the 3-year measurement period in the NRPI outdoor area in Prague and from simultaneous annual measurement performed by another similar station located near uranium mud fields in DIAMO, state enterprise, Stráž pod Ralskem. Observed seasonal and diurnal variations of atmospheric radon concentrations and variability of the equilibrium factor, F, are illustrated and compared.

Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock

Radon (²²²Rn), thoron (²²⁰Rn) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 μSvh^-1 at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y^-1. However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for better instrumentation when dealing with outdoor TnP.

Effects of source rocks, soil features and climate on natural gamma radioactivity in the Crati valley (Calabria, Southern Italy)

The study, which represents an innovative scientific strategy to approach the study of natural radioactivity in terms of spatial and temporal variability, was aimed to characterize the background levels of natural radionuclides in soil and rock in the urban and peri-urban soil of a southern Italy area; to quantify their variations due to radionuclide bearing minerals and soil properties, taking into account nature and extent of seasonality influence. Its main novelty is taking into account the effect of climate in controlling natural gamma radioactivity as well as analysing soil radioactivity in terms of soil properties and pedogenetic processes. In different bedrocks and soils, activities of natural radionuclides ((238)U, (232)Th (4) K) and total radioactivity were measured at 181 locations by means of scintillation γ-ray spectrometry. In addition, selected rocks samples were collected and analysed, using a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS) and an X-Ray Powder Diffraction (XRPD), to assess the main sources of radionuclides. The natural-gamma background is intimately related to differing petrologic features of crystalline source rocks and to peculiar pedogenetic features and processes. The radioactivity survey was conducted during two different seasons with marked changes in the main climatic characteristics, namely dry summer and moist winter, to evaluate possible effects of seasonal climatic variations and soil properties on radioactivity measurements. Seasonal variations of radionuclides activities show their peak values in summer. The activities of (238)U, (232)Th and (4) K exhibit a positive correlation with the air temperature and are negatively correlated with precipitations.

Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: Characterising the atmospheric mixing state

A radon-based nocturnal stability classification scheme is developed for a flat inland site near Bucharest, Romania, characterised by significant local surface roughness heterogeneity, and compared with traditional meteorologically-based techniques. Eight months of hourly meteorological and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility are analysed. Heterogeneous surface roughness conditions in the 1 km radius exclusion zone around the site hinder accurate characterisation of nocturnal atmospheric mixing conditions using conventional meteorological techniques, so a radon-based scheme is trialled. When the nocturnal boundary layer is very stable, the Pasquill-Gifford "radiation" scheme overestimates the atmosphere's capacity to dilute pollutants with near-surface sources (such as tritiated water vapour) by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s(-1) and nocturnal mixing depths vary from ∼ 25 m to less than 10 m above ground level (a.g.l.). Combining nocturnal radon with daytime ceilometer data, we were able to reconstruct the full diurnal cycle of mixing depths. Average daytime mixing depths at this flat inland site range from 1200 to 1800 m a.g.l. in summer, and 500-900 m a.g.l. in winter. Using tower observations to constrain the nocturnal radon-derived effective mixing depth, we were able to estimate the seasonal range in the Bucharest regional radon flux as: 12 mBq m(-2) s(-1) in winter to 14 mBq m(-2) s(-1) in summer.

Radiological characterisation and radon equilibrium factor in the outdoor air of a post-industrial urban area

The radiological characterisation of outdoor air is always a complicated task due to the several radioactive emissions coming from the different radionuclides and also because of the very short half-lives of radionuclides in the natural radioactive series. In some places, this characterisation could result in unusual values because the natural presence of radionuclides with terrestrial origin can be modified by manmade activities. Nonetheless, this characterisation is useful not only for air quality control purposes but also because radon and its progeny in the outdoor air are the main contributors to human exposure from natural sources. In this study, we have carried out air particle sampling, followed by gamma-ray spectrometry, alpha spectrometry and beta counting determinations for this purpose. Subsequently, the outdoor air has been radiologically characterised through the obtained data and using a pre-existing analytical method to take into account the radioactive decays of short half-life radionuclides during sampling, sample preparation and measuring times. Bilbao was chosen to carry out this work. It is a medium-sized town located in northern Spain, close to the Atlantic Ocean and at sea level. This city has a recent industrial past as there were numerous steel mills and other heavy industries, including some quarries, and some open pit mines close to it, which concluded in a remediation program. So, it is a place where the air is potentially modified by manmade activities. The obtained results show that activity concentration values for long-lived radionuclides that precede radon and thoron are in the order of 10(-6) Bq m(-3) and long-lived ones after radon are around 10(-4) Bq m(-3). Thoron progeny are around 2 × 10(-2) Bq m(-3) and radon progeny are around 1.8 Bq m(-3). The mean radon equilibrium factor was 0.18. All of these values are close to the minimum UNSCEAR values, but show some variability, which highlights the importance of determining activity concentrations for each naturally occurring radionuclide and the equilibrium factor in the outdoor air.

Development of a primary thoron activity standard for the calibration of thoron measurement instruments

The LNHB and IRSN are working on a reference atmosphere for thoron ((220)Rn) instrument calibration. The LNHB, as the national metrology institute for activity measurement in France, has to create a new thoron reference standard in order to estimate with accuracy the thoron concentration of a reference atmosphere. The measurement system presented in this paper is based on a reference volume using an alpha detector, which is able to measure thoron and its decay products to define the thoron concentration of a thoron reference atmosphere. This paper presents the first results with this new system using a well-known radon ((222)Rn) atmosphere and a thoron ((220)Rn) atmosphere.

The role of mesoscale meteorology in modulating the (222)Rn concentrations in Huelva (Spain)--impact of phosphogypsum piles

The combined analysis of (222)Rn activity concentrations and mesoscale meteorological conditions at Huelva city (Spain) was addressed in this study to understand the potential impact of phosphogypsum piles on the (222)Rn activity concentrations registered at this area. Hourly mean data from April 2012 to February 2013 registered at two sampling sites (Huelva city and in the background station of El Arenosillo, located 27 km to the south-east) have been used in the study. The results of the present study showed a large difference in mean radon concentrations between the two stations during the sampling period, 6.3 ± 0.4 Bq m(-3) at Huelva and 3.0 ± 0.2 Bq m(-3) at El Arenosillo. The analysis has demonstrated that hourly (222)Rn concentrations at Huelva city above 22 Bq m(-3), with nocturnal peaks up to 50 Bq/m(3), mainly coincided with the occurrence of a pure sea-land breeze cycle. Mesoscale circulations in this region are mainly characterized by two patterns of sea-land breeze, pure and non-pure, with the phosphosypsum piles directly upstream (south) of the city during the afternoon on pure sea-breeze days. The difference between mean (222)Rn activity concentrations at Huelva city were 9.9 ± 1.5 Bq m(-3) for the pure pattern and 3.3 ± 0.5 Bq m(-3) for the non-pure pattern, while in the background station concentrations were 3.9 ± 0.4 Bq m(-3) and 2.8 ± 0.4 Bq m(-3) respectively. Considering these large differences, a detailed analysis of composites and case studies of representative sea-land breeze cycles of both types and their impact on (222)Rn activity concentration was performed. The results suggested that the presence of the phosphogypsum piles was necessary in order to justify the high (222)Rn activity concentrations observed at Huelva compared with the background station in the afternoons on pure sea breeze days (1.5-2.0 Bq m(-3)). On the other hand, large night time differences between the two sites on these days were likely to be associated with a combination of shallow density currents travelling down the Guadalquivir valley and, again, the presence of phosphogypsum piles. The results have demonstrated a significant impact of the phosphogypsum piles on (222)Rn activity concentrations in Huelva city during the occurrence of pure sea breeze days.

Diurnal and seasonal variability of outdoor radon concentration in the area of the NRPI Prague

In autumn 2010, an outdoor measuring station for measurement of atmospheric radon, gamma equivalent dose rate in the range of 100 nSv h(-1)-1 Sv h(-1) and proper meteorological parameters such as thermal air gradient, relative air humidity, wind speed and direction and solar radiation intensity was built in the area of the National Radiation Protection Institute vvi. The station was designed to be independent of an electrical network and enables on-line wireless transfer of all data. After introduction of the station, illustrations of its measurement properties and the results of measured diurnal and seasonal variability of atmospheric radon, based on annual continuous measurement using a high-volume scintillation cell at a height of 2.5 m above the ground, are presented.

Radon and thoron doses in kindergartens and elementary schools

Exposing the Raduet Rn-Tn solid-state nuclear track detectors, radon (Rn: (222)Rn) and thoron (Tn: (220)Rn) activity concentrations have been measured in 7 kindergartens and 18 elementary schools in Slovenia. Diurnal variations of both gases were monitored using a Rad7 device. The Rn concentration was in the range from 145 to 794 Bq m(-3) in kindergartens and from 70 to 770 Bq m(-3) in schools, and the Tn concentration was in the range from 21 to 73 Bq m(-3) in kindergartens and from 4 to 91 Bq m(-3) in schools. The Tn versus Rn concentration ratio varied from 0.02 to 0.83. Monthly effective doses due to radon and its decay products ranged from 109 to 600 μSv month(-1) in kindergartens and from 21 to 232 μSv month(-1) in schools, and those due to thoron and its decay products ranged from 3.8 to 13.3 μSv month(-1) in kindergartens and from 0.29 to 6.62 μSv month(-1) in schools. The contribution of thoron to the total effective dose was from 1.3 to 11 % in kindergartens and from 0.4 to 17 % in schools.

Eighteen years of continuous observation of Radon and Thoron progenies atmospheric activity

The eighteen years (1993-2010) of continuous observations of the activity concentrations of Radon ((222)Rn) and Thoron ((220)Rn) progenies within the atmosphere as recorded twice a day in Arad (Romania) are analyzed and discussed in correlation with air temperature, monthly precipitation and sky cloudiness. A detailed statistic analysis of all data revealed more peculiarities such as a systematically higher concentration in the morning compared to midday, a negative correlation between (220)Rn and (222)Rn activity concentrations and precipitation level, temperature and sky cloudiness. Both Morlet wavelet and power spectra confirmed the predominance of the one year periodicity, as well as the presence of some components with a periodicity of 7.2, 2.8, 1.5 and 1.2 years, more evident in the case of (220)Rn. The possible influence of meteorological factors on both (222)Rn and (220)Rn progenies atmospheric activity concentrations are discussed.

Dynamics, deterministic nature and correlations of outdoor (222)Rn and (220)Rn progeny concentrations measured at Bacău, Romania

The long-term variation, nature and correlations of outdoor (222)Rn and (220)Rn progeny concentrations measured during the period 1994-2009 were investigated. The time series of data were obtained within the framework of the monitoring program performed by the Environmental Radioactivity Monitoring Station (ERMS) Bacău, a component part of the National Environmental Radioactivity Survey Network (NERSN), coordinated by National Environmental Protection Agency (NEPA). The measuring method is based on the total beta measurements of atmospheric aerosol filters, using a low background total beta counter and ((90)Sr/Y) reference standard. Analysis of the time series of progeny concentrations in the low atmosphere makes evident different patterns of variation of these concentrations: diurnal, seasonal and annual. A possible relationship of progeny concentration increase with global warming is emphasized. In order to find the dominant frequency of the physical processes determining progeny concentration variability the power spectrum has been used. The deterministic nature of the time series of concentrations has been studied making use of the autocorrelation function and stationarity of the original data and of their phase randomized time series. Also, the correlations with meteorological parameters have been investigated using Pearson's correlation coefficient with corresponding level of significance.

Observations and modelling of thoron and its progeny in the soil-atmosphere-plant system

Samples of pasture vegetation, mainly Trifolium pratensis, were collected at the Botanic Garden of the University of Bologna during the period 1998-2000 and measured by gamma-spectrometry for determining thoron progeny. Concentrations of (212)Pb were between 1.5 and 20 Bq m(-2), with individual peaks up to 70 Bq m(-2). Soil samples were collected at the same location and physically characterised. Their chemical composition (particularly Th and U) was determined by X-ray fluorescence spectroscopy. Lead-212 on plants mainly originates from dry and wet deposition of this isotope generated in the lower atmosphere by the decay of its short-lived precursor (220)Rn, which is produced in the upper soil layers as a member of the natural thorium decay chain and exhales into the atmosphere. Concentrations of (220)Rn in the atmosphere depend on (1) the amount of Th present in soil, (2) the radon fraction which escapes from the soil minerals into the soil pore space, (3) its transport into the atmosphere, and (4) its redistribution within the atmosphere. The mobility of radon in soil pore space can vary by orders of magnitude depending on the soil water content, thus being the main factor for varying concentrations of (220)Rn and (212)Pb in the atmosphere. We present a simple model to predict concentrations of thoron in air and its progeny deposited from the atmosphere, which takes into account varying soil moisture contents calculated by the OPUS code. Results of this model show close agreement with our observations.

Atmospheric radon in Hong Kong

For the first time in Hong Kong, atmospheric radon concentration was continuously monitored between November 2007 and October 2008. This paper presents the results obtained during the 12-month period. The annual mean atmospheric radon concentration in Hong Kong was found to be 9.3 Bqm(-3) which was close to the level at neighbouring places like Guangdong and Taiwan. An estimation of the dose arising from atmospheric radon to the Hong Kong population was made. The meteorological effects on the variation of atmospheric radon concentration were discussed. It was found that the origin of the airmass and stability of the local atmosphere played vital roles in the seasonal and diurnal variations respectively, whereas precipitation caused abrupt changes in rainy days. An attempt was also made to find out the contribution of atmospheric radon to the ambient gamma dose rate.

Concentrations of 222Rn, 220Rn and their decay products measured in outdoor air in various rural zones (Morocco) by using solid-state nuclear track detectors and resulting radiation dose to the rural populations

Alpha and beta activities per unit volume of air due to radon ((222)Rn), thoron ((220)Rn) and their progenies were measured in the outdoor air at different locations in Morocco by using both CR-39 and LR-115 type II solid-state nuclear track detectors (SSNTDs). In addition, the radon concentration was continuously measured in one location by using the methods with SSNTDs and AlphaGuard counter. The influence of the geological and meteorological conditions as well as phosphate and building material dust on the radon concentration in the outdoor air of the areas studied was investigated. The committed equivalent doses due to (218)Po and (214)Po radon short-lived progeny were evaluated in different tissues of the respiratory tract of the members of the public from the inhalation of outdoor air. The annual effective dose due to radon short-lived progeny from the inhalation of outdoor air by the members of the rural population was estimated.