222Rn Exhalation Rate Research Articles

Prediction of areas presenting a high radon exhalation potential: A new methodology based on the properties of geological formations and soils

A research program carried out since 1997 produced a methodology for predicting areas with a strong potential for radon exhalation at the soil surface. This methodology is based on a quantification of the Rn exhalation rate, from a precise characterization of the mam local geological and pedological parameters that control the radon source and its transport to the soil/atmosphere interface. It combines a cross mapping analysis of parameters used in a Geographic Information System with a model of the vertical transport of Rn by diffusion trough the soil. This code (TRACHGEO) calculates the radon flux density at the surface as a function of the properties of the rock and the soil. This approach is validated in 4 typical areas with different geological contexts, starting from in situ measurements of radon fluxes and of radon concentrations in dwellings. A lithogeochemic al classificatio n of the geological formations as a function of their U contents and their confrontation to Rn level measurements demonstrate the primordial influence of the U content of the basement on Rn exhalation. This study leads to an initial map of the exhalation potential by assigning a potential class to each lithogeochemistry. Nevertheless, in situ radon measurements reveal a high spatial variability on uraniferous lithologies. Tests made by the TRACHGEO tool show the need to take account of spatial heterogeneity of soils (in addition of geochemistry) to improve the mapping resolution. The TRACHGEO forecasts explain the variability of the Rn exhalation on a larger scale.

Observations of atmospheric variability and soil exhalation rate of radon-222 at a Russian forest site. Technical approach and deployment for boundary layer studies

A monitor for continuous observations of the atmospheric 222Rn daughter activity has been improved and successfully implemented in a field study in the European Taiga (Fyodorovskoye Forest Reserve). The α-activity of the short-lived 222Rn and 220Rn (212Pb) decay products, which are attached to aerosols, is accumulated on a quartz aerosol filter and assayed on line by α-spectroscopy. The α-activity from the 212Pb daughters is determined by spectroscopy and corrected for. This monitor is suitable to measure 222Rn activities at hourly resolution down to 0.5 Bq m−3 with an uncertainty well below ±20%. The prototype of this monitor is run in Heidelberg on the roof of the Institute's building about 20 m above ground. For this site, the atmospheric radioactive disequilibrium was determined between the 222Rn daughter 214Po and 222Rn, which has to be known in order to derive the atmospheric 222Rn activity with the static filter method. We derived a mean disequilibrium 214Po/222Rn = 0.704 ± 0.081 for various meteorological conditions through parallel222Rn gas measurements with a slow pulse ionisation chamber. At the Russian field site, continuous activity observations were performed from July 1998 until July 2000 with half a year's interruption in summer/fall 1999. During intensive campaigns, a second monitor was installed at Fyodorovskoye at 15.6 m (July/August 1998), and at 1.8 m (July/August 1999 and October 1999) above ground. As expected, pronounced diurnal cycles of the 222Rn daughter activity were observed at all sites, particularly during summer when the vertical mixing conditions in the atmospheric surface layer vary strongly between day and night. The lower envelope of the continuous measurements at Fyodorovskoye and at Heidelberg changes on synoptic timescales by a factor of 4–10 due to long-range transport changes between continental to more maritime situations. Generally, the 222Rn activity at 26.3 m height at Fyodorovskoye is lower by a factor of 2–3 compared to Heidelberg at 20 m above ground. This unexpected result is due to considerably lower 222Rn exhalation rates from the soils measured in the footprint of the Fyodorovskoye Forest tower compared to Heidelberg. With the inverted chamber technique 222Rn exhalation rates in the range 3.3–7.9 Bq m−2 h−1 were determined at Fyodorovskoye for summer 1998 and autumn 1999 (wet conditions with water table depths between 5 and 70 cm). Only during the very dry summer of 1999 the mean222Rn exhalation rate increased by about a factor of five. All measured exhalation rates at the Fyodorovskoye Forest are considerably smaller by a factor of 2–10 compared to observations in the vicinity of Heidelberg (ca. 50–60 Bq m−2 h−1) and generally in Western Europe.

Study of a predictive methodology for quantification and mapping of the radon-222 exhalation rate

We propose a new methodology for predicting areas with a strong potential for radon ( 222Rn) exhalation at the soil surface. This methodology is based on the Rn exhalation rate quantification, starting from a precise characterisation of the main local geological and pedological parameters that control the radon source and its transport to the soil/atmosphere interface. It combines a cross mapping analysis of these parameters into a geographic information system with a model of the Rn vertical transport by diffusion in the soil. The rock and soil chemical and physical properties define the entry parameters of this code (named TRACHGEO) which calculates the radon flux density at the surface. This methodology is validated from in situ measurements of radon levels at the soil/atmosphere interface and in dwellings. We apply this approach to an area located in western France and characterised by a basement displaying a heterogeneous radon source potential, as previously demonstrated by Ielsch et al. (J. Environ. Radioactivity 53(1) (2001) 75). The new results obtained show that spatial heterogeneity of pedological characteristics—in addition to basement geochemistry—must be taken into account to improve the mapping resolution. The TRACHGEO forecasts explain the Rn exhalation variability on a larger scale and in general correlate well with in situ observations. Moreover, the radon-prone sectors identified by this approach generally correspond to the location of the dwellings showing the highest radon concentrations.

Radon permeability and radon exhalation of building materials

High radon concentrations indoors usually depend on the possibilities of radon penetration from the surrounding soil into the buildings. Radon concentrations in dwellings up to 100 kBq/m 3 were found in some special regions (i.e. Schneeberg/Saxony, Umhausen/Tyrol), where the soil shows a high uranium content and additionally, a fast radon transport in the soil is possible. To reduce the radon exposure of the inhabitants in these ‘radon prone areas’ it is necessary to look for building and insulating materials with low radon permeability. We examined several building materials, like cements, concretes and bricks of different constitutions for their diffusion coefficients and their exhalation rates. The insulating materials, like foils and bitumen were tested also on their radon tightness. The measurements were performed with an online radon measuring device, using electrostatic deposition of 218Po ions onto a surface barrier detector and subsequent alpha spectroscopy. The mean diffusion lengths for the investigated building materials range from lower than 0.7 mm (i.e. for plastic foil), up to 1.1 m for gypsum. The diffusion length R was calculated from the diffusion coefficient D with R= D/λ . If the thickness of the material is more than 3 times the diffusion length, then it is called radon-tight. The mean 222Rn exhalation rates for the building materials varied between 0.05 and 0.4 mBq/m 2s. The samples were investigated as stones, plates, blocks, foils, coatings, powders etc., no statement can be made about working at the construction site of a building. Also the fabrication and processing of the materials has to be considered, because the material characteristics may have changed.

Light weight concrete: [formula omitted], [formula omitted], [formula omitted] contents and dose reduction assessment

Four types of light weight concrete (LWC) commonly used in Hong Kong, namely, autoclave aerated concrete (plus lime), autoclave aerated concrete (plus Pulverized Fuel Ash or PFA), concrete with synthetic aggregate ‘Leca’ and concrete with polystyrene bean as aggregate were measured for their 226 Ra , 232 Th and 40 K contents using high-resolution gamma spectrometry. All the radionuclide contents except those for the PFA autoclave aerated concrete were below the world averages of building materials. The Ra-equivalents for these four LWC were 49.6, 249, 122 and 44.2 Bq kg −1, respectively, and were much smaller than a recommended limit of 370 Bq kg −1 for construction materials for dwellings. The gamma-dose rate for an indoor environment with partition walls built with LWC was estimated to be about 20 × 10 −8 Gy h −1, which corresponded to a reduction in the effective dose of about 0.25 mSv y −1 when compared to that obtained for an indoor environment built with normal concrete (NC) only. The Rn exhalation rates from the three lowest Ra-equivalent LWC were calculated as 0.509, 1.28, and 0.335 mBq m −2 s −1, respectively, which corresponded to a reduction in the indoor Rn concentration of around 14 Bq m −3 and reduction in the tracheobronchial dose reaching 1 mSv y −1 by using the James lung-dosimetry model, when compared to the case of NC.

Effects of Using Light-Weight Concrete on Indoor Radon Concentration in High-Rise Buildings

Light-weight concrete (LWC) (or drywall construction) has been used for partition walls in public housing in Hong Kong for about 10 years. A previous laboratory investigation showed that all types of LWC had considerably smaller Rn exhalation rates than those from normal concrete (NC), and could thus theoretically reduce the indoor Rn concentrations and the corresponding radiation dose from Rn. In the present investigation, a survey of Rn exhalation rates and indoor Rn concentrations at 39 dwelling sites built using LWC were carried out using charcoal canisters and ?-spectroscopy. The mean Rn exhalation rate and the mean Rn concentration were around 1.6 mBq.s-1.m-2 and 19 Bq.m-3, respectively, which were significantly smaller than the corresponding values of 12 mBq.s-1.m-2 and 33 Bq.m-3 for NC sites. The statistical t-test showed that both the mean Rn exhalation rate and the mean Rn concentration for NC and LWC sites walls were different at the 100% confidence level. The Rn exhalation rate from an LWC surface was, on average, only about 14% of that from an NC surface, while the Rn concentration in an LWC site was, on average, about 58% of that in an NC site, which were significant. A person living at an LWC site receives an average annual equivalent dose smaller than one living at an NC site by an amount as large as 1 mSv. Therefore, the use of LWC for partition walls can be a simple and economical way to reduce the indoor Rn concentrations and the corresponding radiation dose from Rn. Furthermore, the mean Rn concentration theoretically predicted from the mean Rn exhalation rate agreed excellently with that from measurements.

Verification of German methane emission inventories and their recent changes based on atmospheric observations

Continuous methane concentration records and stable isotope observations measured in the suburbs of Heidelberg, Germany, are presented. While δ13C‐CH4 shows a significant trend of −0.14‰ per year, toward more depleted values, no trend is observed in the concentration data. Comparison of the Heidelberg records with clean air observations in the North Atlantic at Izaña station (Tenerife) allows the determination of the continental methane excess at Heidelberg, decreasing by 20% from 190 ppb in 1992 to 150 ppb in 1997. The isotope ratio which is associated with this continental methane pileup in the Heidelberg catchment area shows a significant trend to more depleted values from δ13Csource = −47.4 ± 1.2‰ in 1992 to −52.9 ± 0.4‰ in 1995/1996, pointing to a significant change in the methane source mix. Total methane emissions in the Heidelberg catchment area are estimated using the 222radon (222Rn) tracer method: from the correlations of half‐hourly 222Rn and CH4 mixing ratios from 1995 to 1997, and the mean 222Rn exhalation rate from typical soils in the Rhine valley, a mean methane flux of 0.24 ± 0.5 g CH4 km−2 s−1 is derived. For the Heidelberg catchment area with an estimated radius of approximately 150 km, Core Inventories Air 1990 (CORINAIR90) emission estimates yield a flux of 0.47 g CH4 km−2 s−1, which is about 40% higher than the 222Rn‐derived number if extrapolated to 1990. The discrepancy can be explained by overestimated emissions from waste management in the CORINAIR90 statistical assessment. The observed decrease in total emissions can be accounted for by decreasing contributions from fossil sources (mainly coal mining) and from cattle breeding. This finding is also supported by the observed decrease in mean source isotopic signatures.

Radon exhalation rates and gamma doses from ceramic tiles.

This study was carried out to assess the possible radiological hazard resulting from the use of zircon in glaze applied to tiles used in buildings. The 226Ra content of various stains and glazing compounds was measured using gamma spectroscopy and the 222Rn exhalation rates for these materials were measured using adsorption on activated charcoal. The radon exhalation rates were found to be close to or less than the minimum detectable values for the equipment used. This limit was much lower than the estimated exhalation rates, which were calculated assuming that the parameters controlling the emanation and diffusion of 222Rn in the materials studied were similar to those of soil. This implied that the 222Rn emanation coefficients and/or diffusion coefficients for most of the materials studied were very much lower than expected. Measurements on zircon powders showed that the 222Rn emanation coefficient for zircon was much lower than that for soil, indicating that only a small fraction of the 222Rn produced by the decay of 226Ra was able to escape from the zircon grains. The estimated increase in radon concentration in room air and the estimated external gamma radiation dose resulting from the use of zircon glaze are both much lower than the relevant action level and dose limit.

Radon exhalation rate from some fertilizers, clay and potatoes in Egypt

Large amounts of uranium, radium and radium products are redistributed throughout the environment owing to the use of phosphate fertilizers. Potential radiological impacts resulting from direct exposure, inhalation and ingestion of foods grown with fertilizers are discussed. This paper describes a simple method to measure exhalation rate of 222RN from phosphate fertilizers, clay and potatoes in a laboratory and in a more economical way. Three Egyptian factories of phosphate fertilizers were selected in this study (Assuit, Abu Zaable and Kafr El Ziat).

The effect of the composition and production process of concrete on the 222Rn exhalation rate

In a series of 18 concrete samples, the influence of several parameters related to composition and production processes on the radon exhalation rate was studied. The investigated parameters were: amount and type of cement, water-cement ratio, curing conditions and curing time, type of aggregates, compressive strength, and water evaporation rate during conditioning. Strong positive correlations with the calculated radon emanating power were found for the evaporation rate and the water-cement ratio. A negative correlation was found for the compressive strength. The results are discussed with respect to the capillary pore volume and pore size of the concrete samples.

Results of special 220Rn measurements

Measurements of the activity concentration of the 220Rn progeny were performed inside German dwellings (n=148) and in the open air (n=100) by air sampling. The median value C indoor = 0.25 Bq/m 3 of the 220 Rn progeny concentration indoors was found four times higher than outdoors C outdoor = 0.05 Bq/m 3. The indoor 220Rn progeny concentrations were compared to the ventilation rate of the rooms. There was no clear correlation. Due to the changing ventilation behaviour throughout a year, a wave-like variation of the indoor 220Rn progeny concentration was observed, with its minimum in July and its maximum during the winter months. These measured data were compared to model calculations that derived indoor 220Rn concentrations from 220Rn exhalation out of the building materials. Measurements of a large sample of commercial building materials showed 220Rn exhalation rates ranging from 0.01 Bq/m 2s up to 1 Bq/m 2 s. A mean 220Rn exhalation rate of 50 mBq/m 2 s results in an indoor 220Rn concentration of 8 Bq/m 3. That means that, for inhalation of airborne radioactivity in dwellings, the contribution of the 220Rn progeny to the effective dose may not be neglected.

A mysterious spot on the outdoor concentration of radon isotopes

Temporal and spatial distribution of 222Rn and 220Rn and their progeny concentrations in the open atmosphere, 222Rn and 220 Rn exhalation rates, radioactivities in soil and underground water, including some meteorological factors, were measured at a spot of high 222Rn and 220 Rn concentrations to investigate the source and occurrence mechanism. Hourly mean concentrations of 222Rn and 220Rn during August 1993 were about 230 Bq m −3 and 130 Bq m −3 at 1 m above ground surface. Diurnal variations were high at daytime and low at nighttime, which gives an inverse variation compared with the typical variation in the normal environment. 222Rn concentrations varied quickly in a few minutes and reached a maximum of about 14 kBq m −3. The maximum daily mean 222Rn concentration at 5 cm above ground surface was 11 kBq m −3. Concentrations of 218Po, 214Pb, 214Bi, and 220Rn progeny were 8∼61 Bqm −3, 1∼7 Bqm −3, 0.5∼5 Bq m −3, and 0.02∼0.14 Bq m −3, respectively. The equilibrium factor for 222Rn was estimated to be 0.01∼0.2. The main source of the mysterious spot of high 222Rn and 220Rn concentrations was a small but deep channel between the basement of the building and the surrounding soil, and the extremely localized weather condition.

Measurements of Thoron Concentration by Passive Cup Method and Its Application to Dose, Assessment

A new type of passive integrating cup monitors was developed by using a 50 mm radius stainless steel hemisphere to measured indoor radon (222Rn) and thoron (220Rn) concentrations. By placing a pair of cup monitors with an air exchange opening of diameter 5 mm and four openings of diameter 20mm at a 20cm distance from wall during about three months, the concentrations of both gases could be assessed from the a track densities on the cellulose nitrate (CN) films. The 222Rn and 220Rn concentrations were surveyed with the cup monitors in the different types of dwellings around Nagoya in Japan over three years. The 220Rn concentrations were rather high in the dwellings with soil wall, and the mean 220Rn concentration was 160±12 Bq·m−3. The 220Rn exhalation rate from wall and the 220Rn diffusion were evaluated from the distribution of 220Rn concentrations in the dwellings. The results of the surveys have also clarified the relationship between the 220Rn concentrations a t a 20cm distance from wall and the 220Rn...

Reduction of the Radon Entry Rate from Building Materials by Industrial Surface Coatings

Abstract The retaining effect of over 20 different surface coatings on the free 222Rn exhalation rate has been studied. Coatings that are normally applied for decoration of walls and ceilings in homes were found to be ineffective. Reductions of up to 75% were found for other coatings studied, when applied to all sides of the test walls. If the surface coating is applied to only one side of the wall, coatings on the basis of epoxy resin and polyurethane could reduce the exhalation rate by 95% according to model calculations.

Radon release from building materials in Hong Kong.

Indoor 222Rn in high-rise buildings originates inside the building materials, then diffuses gradually through the intergranular spaces of the material into the room atmosphere. Therefore, the radionuclide contents and the physical properties of the building materials are important for indoor 222Rn levels in Hong Kong. In this paper, the radionuclide contents of typical building materials used locally were determined by gamma spectrometry, and the results indicate that the average 226Ra, 232Th, and 40K contents in Hong Kong concrete are the highest known in the world. Physical properties, such as the emanation coefficients and 222Rn diffusion coefficients, were measured in these materials and they are not much different from those in other countries. The effect of surface coatings on 222Rn exhalation rate was studied and the observed reduction was from 2-68%. The 222Rn exhalation rate was found to increase steadily with temperature up to 50 degrees C; at 50 degrees C, the 222Rn exhalation rate can be as high as four times the rate at 20 degrees C.

Radon Diffusion in Model Tests on Finnish Esker and Till Soils

In this paper, 222Rn activity has been investigated in some Finnish esker and glacial till areas. Model tests have been carried out to study soil parameters such as the 222Rn production rate, the 222Rn diffusion coefficients, and the 222Rn exhalation rate. The general differential equations for diffusion have been solved with different boundary conditions. Diffusion coefficients calculated from different experimental tests are comparable to each other.

Variation of 222Rn Concentration in Outdoor Air due to Variation of the Atmospheric Boundary Layer

Variation of 222Rn concentration in outdoor air, returns of a monostatic acoustic sounder and sensible heat flux are simultaneously observed at Okayama-shi in Japan. The sensible heat flux is measured with an eddy correlation method using a sonic anemometer and a copper-constantan thermocouple thermometer. Using height of a surface-based inversion layer obtained by the acoustic sounder returns and two 222Rn concentrations during the presence of the surface-based inversion layer, the exhalation rate of 222Rn at this site is estimated to be about 0.01 Bq.m-2.s-1, which agrees well with the exhalation rate of 222Rn estimated at Nagoya-shi in Japan. Using the estimated exhalation rates of 222Rn and the variation of the 222Rn concentration in the daytime, heights of mixing layers are estimated. These heights of the mixing layers are larger than the height of the mixing layer estimated using the sensible heat flux and the representative vertical profile of the autumnal night time air temperature in this area.

Determining the 222Rn Exhalation Rate of Building Materials Using Liquid Scintillation Counting

A new method for determining the free 222Rn exhalation rate from building materials is described. The sample is enclosed in a container from which the exhaled Rn is continuously purged by nitrogen gas. After 2-3 h, when the Rn level in the container has reached a steady-state concentration, the outflowing Rn is trapped on silica gel at about -190 degrees C. About 16 h after sampling, the silica gel is analyzed by liquid scintillation counting to determine the area exhalation rate. The method described has a good repeatability and reproducibility with coefficients of variation of 7.8% and 8.3%, respectively, at 5 Bq m-2 h-1. The low limit of detection of 11 mBq 222Rn offers the opportunity to quantify the exhalation rate of almost all kinds of building materials. It was found that the air humidity strongly influences the exhalation rates of building material and, therefore, should be controlled. Two typical building materials were investigated. For gypsum, an increase in the exhalation rate with increasing water vapor pressure was found, whereas for concrete, a linear decrease with increasing water vapor pressure was observed. The 222Rn area exhalation rates of 20 Dutch building materials, including some experimental ones, were determined at 50% RH, 20 degrees C, showing a range of less than 0.02-15.8 Bq m-2 h-1. The lowest values were found for natural gypsum board, the highest for phosphogypsum blocks. Building materials containing fly ash gave area exhalation rates comparable to those of similar materials without fly ash.

A new approach to measure Rn exhalation rate out of building walls

The novel technique has been developed to measure Rn exhalation out of structural material surfaces. The majority of Rn daughter nuclides are in the form of positive ions right after their alpha decay process. By applying an appropriate electric field between a wall and a Si detector, the positive ions are accumulated directly on the radiation-sensitive electrode of the Si detector, and real-time alpha spectrometry is performed. This new method can be utilized for existing structures without using destructive means. The basic characteristics of the system and experimental results for several building structures are presented. >

Radon Exhalation from the Soil

Abstract The exhalation of radon from the soil is the main source for high radon concentration in dwellings. A study of the mechanism of exhalation, its dependence on various parameters and the entry points for radon in houses are presented. Electrostatic deposition of the radon daughter products on a surface barrier detector and subsequent analysis of the measured alpha spectra allows one to determine the exhalation rates of 222Rn and 220Rn directly from the soil. For a sampling time of two hours, the lower limit of detection of our equipment was found to be 0.3 x 10-3 Bq.m-2.s-1 for 222Rn. In the south-west part of Germany, the 222Rn exhalation rates from the soil vary approximately between 2 x 10-3 and 100 x 10-3 Bq.m-2.s-1. The water content of the investigated soil, its actual porosity and its radium content determine the radon migration through the pores. For example in regions with volcanic rocks the exhalation rates are up to 10 times higher than in sandstone areas. Some special constructive measures to reduce the entry of radon in buildings are proposed.