Radon Diffusion Coefficient Research Articles

Assessment of soil gas radon migration and transport through the estimation of radon diffusion length and diffusion coefficient in the soil matrix

Naturally occurring radioactive gas, radon is a decay product of radium present in the soil. Radon flux reaches the atmosphere through exhalation from soil surface. This study aims to estimate the radon diffusion length and diffusion coefficient in soil matrix on the premises of HNB Garhwal University campus at Tehri Garhwal, India. Soil gas radon concentration was measured at different depths (15, 30, 45, 60, 75, and 90 cm) using a Smart RnDuo (Scintillation-detector) at 14 different locations in the university campus. Simultaneous measurement of surface and mass exhalation rates was also carried out for each location. Gamma-ray spectrometry was used to estimate the radium content in soil samples. Results of the present study suggest that soil gas radon concentration increases with increasing sampling depth. The diffusion coefficient and length were calculated using the soil gas radon concentration gradient within the soil matrix. The average value of diffusion length (l) and diffusion coefficient (D) were obtained as, ls = 0.70 ± 0.22 m, Ds = 0.0054 ± 0.0049 m2 sec-1 and la = 0.77 ± 0.63 m, Da = 0.0073 ± 0.014 m2 sec-1 by Fick’s diffusion model and analytic models, respectively.

The influence of radon penetration through joints on the overall radon barrier properties of waterproof membranes

Waterproofing membranes with a proven ability to prevent radon penetration are commonly used to provide basic protection of buildings against radon from the subsoil. The goal of our research was to find out which types of joints of the pre-applied membranes are radon-tight and which, on the other hand, are radon permeable. Another goal was to find out how significant radon penetration through the joints can be, and how it can affect the ability of the whole radon-proof course to prevent radon penetration into the house. Six types of joints were investigated by determining the radon diffusion coefficient. Four of these types had a radon diffusion coefficient up to three orders of magnitude greater than the membranes themselves. A procedure was proposed for taking into consideration the high radon diffusion coefficient of joints in the calculation of the radon resistance of the whole radon-proof course. It has been proven that leaks in the joints can reduce the radon resistance of the whole radon-proof course by two to three orders of magnitude. For this reason, the course may not meet the minimum radon resistance requirements. Numerical simulation revealed that the leaks were due to the use of unsuitable sealing materials and technologies. A correct sealing technology for problematic joints was designed and subsequently verified.

Study of the use of wallpaper to mitigate radon exhalation from building materials in indoor spaces

Radon gas is known to exhale from the ground and can enter and accumulate inside buildings. Many countries set radon limit concentrations and propose mitigation techniques applied in the outdoors to prevent radon from entering buildings. However, radon can also exhale from building materials, e.g. cement, bricks, marble or tiles, contributing high concentrations indoors. Space ventilation is the most used technique to reduce the indoor radon concentration to safe limits, but sometimes, it is not enough. In these cases, it is necessary to apply alternative techniques. This work exposes a prevention technique to reduce radon concentration in indoor spaces that come from building materials or from the subsoil diffusing through basement walls, based on the use of wallpapers. The use of wallpapers is a common decorative technique in homes and buildings, which is compatible with interior finishes and is simple to apply, easily accessible, commercially available and inexpensive. Different commercial wallpapers were selected with a cellulosic and polymeric base and vinylic, cellulosic, latex or non-woven coating material. Configurations of single and double layers of wallpaper and a triple configuration by adding an intermediate layer of aluminium film have been tested. Tests to determine the reduction of radon concentration were performed, and diffusion coefficient and diffusion length were calculated following an adaptation of ISO/TS 11665–13 standard. Radon reduction of 90%, low-medium radon resistance and a diffusion coefficient around 10−11 m2/s were reached for single-layer configuration, and up to 98% of radon reduction, medium radon resistance and diffusion coefficient of 10−12 m2/s with double-layer configuration for dense non-porous base wallpapers with vinylic and non-woven coatings. Adding an aluminium foil intermediate in the double configuration improves the results of all wallpapers tested regarding radon reduction concentration, radon resistance, diffusion length and diffusion coefficient. Moreover, for the dense non-porous base made of non-woven fabric with a vinyl coating layer wallpaper, the diffusion length is shorter than the thickness of the sample in this configuration so the amount of penetrating radon will be reduced by the decay of radon in the wallpaper. Therefore, most radon would disintegrate along the sample and the concentration in the interior space would be lower. These results open a new alternative to protect indoor spaces from radon that access through walls or building materials based on a simple, easy and low-cost technique.

Effect of modified graphene nanosheets on the properties of 222Rn and gamma ray multifunctional shielding polymer composite materials

AbstractDevelopment of shielding materials for 222Rn and γ radiation has crucial implications for ensuring the safety of individuals. This paper reports the synthesis of modified graphene nanosheets (MGNPs) via the reaction of KH560 with graphene nanosheets (GNPs), while melt blending and hot‐press molding technique were used to fabricate a multifunctional polymer composite shielding material, MGNP/WB/PMMA (polymethyl methacrylate). Successful synthesis of MGNP was confirmed by Fourier transform infrared spectroscopy, and scanning electron microscope (SEM) analysis was utilized to assess the distribution of functional fillers within the cross‐section of the polymer composite. Additionally, thermogravimetric analysis (TGA) demonstrated that MGNP and WB particles enhance the thermal stability of the polymer composite materials. Compared to pure PMMA, 98.7% decrease in the radon diffusion coefficient was observed for MGNP1.5 wt%/PMMA composite material. In addition to enhance the radon‐blocking characteristics of the polymer composites, inclusion of WB particles also boosts their shielding capacity against gamma radiation. The 222Rn diffusion coefficient of MGNP1.5 wt%/WB25wt%/PMMA polymer composite material decreased by 99.6% and at energies of 60 KeV, 80 KeV, 122 KeV, 365 KeV, the mass attenuation coefficient (MAC) for the composite material increased by 0.79, 1.97, 0.57, and 0.05 cm2/g, respectively, compared to pure PMMA.Highlights The PMMA composite materials doped with graphene nanosheets demonstrate outstanding resistance to 222Rn. Graphene nanosheets modified by KH560 exhibit favorable dispersion within PMMA. WB can further enhance the radon resistance of MGNP/WB/PMMA composite materials. The polymer composites exhibit excellent 222Rn and gamma ray shielding properties.

Numerical simulations of radon exhalation from surrounding rocks of single and double underground roadways

The radon exhalation rate of surrounding rocks in underground roadways is an important parameter in determining radon exhalation capacity and ventilation flowrate for radon removal. By approximating the roadways as thick-walled, porous cylinders, this study investigates radon exhalation from their surrounding rocks via simulations using computational fluid dynamics (CFD). Radon exhalation rates of single and double underground roadways were computed and analysed under different pressure differences, radon diffusion coefficients, permeabilities of rocks, single roadway locations and additional parallel roadway orientation. The radon regulating zone was presented and the effect of pressure difference on it was analysed. By fitting the data from simulation results, an estimation model was obtained for the radon exhalation rate of a single roadway. For two adjacent parallel roadways with a distance greater than or equal to 50m, the model is also suitable for estimating the radon exhalation rate when the rock permeability is less than 1 × 10−14 m2 and the ratio of permeability to diffusion coefficient is less than 5 × 10−9.

Methodology for assessment of radon diffusion coefficients in membranes, used as radon barriers in construction and refurbishment

In the near future, research on new materials for radon barriers can be expected to rise in order to meet a greater demand of radon mitigation solutions because of the increasingly lower radon levels that the EU legislation aims to. Such research would need a method for the determination of the radon diffusion coefficient and this paper presents an inexpensive method for that purpose, using affordable radon detectors and a simple experimental setup that does not require any tubing or any pumping. Besides the use of two Electronic Integration Devices as radon detectors, the experimental setup used in our method consists only in a two-chamber container made of steel and a small-sized radon source, which was produced in our lab using a 226Ra solution. The radon diffusion coefficient is determined by measuring radon levels in both chambers of the container, which are separated by a membrane made of the material whose radon diffusion coefficient is to be determined. Radon diffuses from a source chamber to a receiver chamber trough the membrane, being the amount of radon that has passed through and the rate at which it has done so the key parameters in the calculation of the radon diffusion coefficient. Our method can handily measure materials with a radon diffusion coefficient above or equal to 10-11 m2 s-1 or, provided that the sample is thin enough, verify that the coefficient is lower than 10-12 m2 s-1. Its precision is good enough to provide radon coefficient diffusion values with a good repeatability as the RSD is as low as a 35% for materials in which the coefficient is in the order of 10-11 m2 s-1. This means that our method is valid for screening materials for radon barriers and checking their compliance with technical specifications.

Radon exhalation behavior and determination of diffusion migration parameters in spherical porous emanation media

There is a significant impact of the radon diffusion coefficient and the free radon production rate on the exhalation of radon from porous materials that can be regarded as spheres, hexahedrons, or cylinders. To understand this effect, the radon exhalation rules of spherical porous media with different radii were studied according to the radon diffusion migration theory. A specialized method for simultaneous determination of the radon diffusion coefficient and the free radon production rate of the spherical porous media was proposed, and applied to determine the above two parameters for two hemispherical test blocks with different radii. The results show that:(1) For spherical porous media with a certain radon diffusion length (Ld), as the radius (r0) of the sphere increases, the radon exhalation rate first increases, and tends to stabilize at r0≥6Ld; The free radon release share gradually decreases from approximately 1, and drops to a steady state at r0≥18Ld. (2) Compared with conventional methods, the relative error of the free radon production rate determined by the proposed method is within 3.9%, which verifies the reliability of the new method.

Influence of temperature on the radon concentration distribution in ramp under low-speed wind field: A numerical simulation study

By introducing the parameters of radon exhalation rate and radon diffusion coefficient, the distribution of radon concentration field on ramp under the condition of superposition of temperature field and flow field is simulated. The simulation results show that the distribution of radon concentration in the ramp under the condition of low-speed ventilation is greatly affected by the temperature field and flow field, and the change of radon exhalation caused by temperature is the main factor leading to the change of radon concentration in the ramp. The change of temperature will cause the overall increase of radon concentration in the ramp. Under the condition of constant flow field, the radon concentration in the chamber is more than two times higher than the average radon concentration in the ramp. Some areas severely exceeded the limit.

Research of radon diffusion behavior in liquid scintillator

Radon and its daughters are one of the most important background sources for low-background liquid scintillator (LS) detectors. The study of the diffusion behavior of radon in the LS contributes to the analysis of the related background caused by radon. Methodologies and devices for measuring radon's diffusion coefficient and solubility in materials are developed and described. The radon diffusion coefficient in the LS was measured for the first time and the solubility coefficient was also obtained. In addition, the radon diffusion coefficient in the polyolefine film which is consistent with data in the literature was measured to verify the reliability of the diffusion device.

Semi-empirical modeling of the temporal variation of indoor radon concentration over short periods

The time rate of change of the indoor radon concentration is studied in a semi-empirical frame. The differential equation that describes the radon mass-balance inside a room is used, with taking into account all sources of indoor radon. Rather than solving the equation numerically, an analytical form is obtained with applying some approximations that are based on experimental observations. This makes the describing model more realistic and updatable. After fitting some of the parameters to the experimental data, the model is found to be successful for describing the indoor radon concentration over a couple of days. Moreover, the model predicts some important characteristics of the radon flow to the indoors from the soil and from the building materials. For the room considered in this study, it is found that the radon diffusion transfer coefficient inside the building material is while the radon diffusion and advection transfer coefficients inside the soil are and respectively. The model can also predict the amount of contribution to the indoor radon by any sources that may be unknown. It was found to be The obtained results show the feasibility and convenience of the model.

A study on radon diffusion and exhalation of soils under transient conditions: Theoretical and experimental approach

A practical method is presented for the short-time transient-diffusion measurement of radon flux and concentration in large soil samples (porous materials) and the radon diffusion coefficients. An experimental apparatus was designed and tested to verify the theoretical validity and technical accuracy of the presented technique by the transient-diffusion method. The concentration data measured inside the accumulator determines the radon flux for various soil thicknesses. Good agreement was observed between values of the measured radon flux and those expected by the theoretical model based on the diffusion theory. The relative standard deviation of 16% was obtained in measurements with dry soil by the short-time transient-diffusion method. Diffusion coefficients of soils were derived from the curve fit of measured flux data to the theoretical expression based on Fick’s law. Comparing the measured diffusion coefficient and that obtained by empirical correlation provides a good agreement with a relative uncertainty of 11%. The present transient-diffusion measurement technique could provide low cost, good precision, short time experiment, no radioactive waste (residue) generation, and good validity.

Measurement of the Indoor Radon Concentration from Different Building Materials Using CR-39 Nuclear Track Detectors and the Associated Annual Effective Dose Determination

This work presents experimental results concerning the radon concentration from different building materials used for construction of houses in the municipality of Bihac. The passive technique using nuclear track detectors C-39 was used for a period for three months. The highest and lowest radon concentration was found in concrete brick buildings 280±5 Bqm-3 and in stone buildings 122±1 Bqm-3. It depends on the radioactive content of the materials, emanation coefficient and diffusion coefficient of radon in that material, porosity and density of the material. The mean annual effective dose was 3.26 mSv/y. The results obtained also give a correlation between indoor radon levels and the associated level of risk.

Determination of the radon diffusion coefficient of thin polyethene and aluminium foils used as single or multilayer configuration barriers

Radon is a radioactive noble gas exhaled from the soil that can reach high concentrations in enclosed spaces. As elevated concentrations cause serious health problems, legislation has been put in place in many countries to regulate the limit concentration and even establish mitigation techniques. One of the most effective techniques for new buildings is the installation of radon barriers. The most important parameter determining whether the barrier is adequate to protect against radon is the diffusion coefficient, whose measurement methodology is standardized in ISO/TS 11665–13:2017. This work applies a previously tested modification of this standard to calculate the radon diffusion coefficient of different materials used as single or multilayer form barriers. Given that there are wasted laminated materials, composed of polymeric materials and aluminium, which are difficult to recycle, a preliminary study of the possible effectiveness of these materials as radon barriers will be carried out using these materials separately or in combination. The materials to be tested are 10-μm sheets of polyethene (PE) and 15-μm sheets of aluminium (Al), testing in each case one, two and three layers of each material. In addition, combinations of the two materials, i.e., PE-Al-PE and PE-Al-PE-Al-PE, are also studied. The diffusion coefficients obtained vary around 2·10−12 m2/s for PE and around 1·10−13 m2/s in the case of Al. The combination of both materials improved results obtained for single-materials barriers giving a diffusion coefficient between 10−13 and 10−14 m2/s. Radon reductions achieved range from 70 to 87.5% for PE to more than 98% for Al and the materials combinations. The excellent radon shielding capacity of aluminium is observed, which grows with increasing material thickness. Furthermore, it can be stated that the use of multilayer materials of different nature is very effective in reducing the radon concentration reaching an enclosed space and the use of aluminium in some of the layers is essential to achieve a more significant shielding effect.

RADON INFILTRATION BUILDING ENVELOPE TEST SYSTEM: EVALUATION OF BARRIER MATERIALS.

The performance of radon barrier materials currently available for housing foundations was evaluated using a unique radon infiltration building envelope test system that was designed to test radon prevention and mitigation systems using real world construction techniques. The reduction in radon concentration measured across the air barrier in the foundations has been used to evaluate five representative barrier materials installed in the radon infiltration building envelope test facility. The reduction in radon concentration in the mock house varied from 68% for 6 mil polyethylene to 98% for the spray polyurethane foam. The five representative barrier materials were selected after determining the radon diffusion coefficient and the corresponding radon resistance from samples of 14 barrier materials in a radon diffusion testing chamber. The Canadian experience evaluating whether radon barrier materials would satisfy building code requirements was described.

Novel method for measuring temperature-dependent diffusion coefficient of radon in porous media

The temperature-dependent diffusion coefficient of radon is one of the most important parameters for predicting radon migration in porous media. In order to measure this parameter more effectively and accurately, theoretical formulas were derived by the steady-state one-dimensional equation of radon migration in porous media for designing the corresponding experimental device, which was used to measure the diffusion coefficients of radon in uranium mill tailings. The results show that the diffusion coefficient of radon in porous media increases with increasing the temperature, which is in agreement with existing researches, verifying the method effectiveness. The changes of the diffusion coefficient of radon with the absolute temperature follow a power law.

THE INFLUENCE OF PINHOLES IN WATERPROOFING MATERIALS ON THE VALUE OF THE RADON DIFFUSION COEFFICIENT.

This article focuses on an experimental study of the influence of imperfections on the value of the radon diffusion coefficient of various waterproofing materials. Microscopic holes were made by a thin tip or by a microdrill bit to imitate the real damage that can be incurred during construction. To determine the change in the radon diffusion coefficient, each waterproofing material was measured five times. The first measurement was performed on undamaged samples, while the following measurements were performed on samples with one, two, four and eight pinholes. The radon diffusion coefficient was measured under nonstationary conditions, because homemade radon sources with a slow rate of radon emanation were used. The radon diffusion coefficients identified in the study were compared according to the thickness of the material and the number and the size of the pinholes. The exact shape and size of the imperfections were documented by an electron microscope.

Fractal discrete fracture network model for the analysis of radon migration in fractured media

A novel model combined with fractal theory and the discrete fracture network (DFN) model is proposed to simulate radon migration in fractured media. In the novel model, the fracture center and length distribution are determined by a first-order model, and the fracture orientations are modeled with the von Mises-Fisher distribution. The model is further developed into a computer software that can calculate the radon diffusion coefficient and exhalation rate of fractured media. An outcrop map is used to validate the ability of the model to describe complex fractures, and radon migration in natural fractures at an outcrop site is predicted using the model. Results show that the model has good reliability and robustness. Evaluation of the representative elementary volume (REV) indicates the existence of REV during the modeling of radon migration in fracture networks. Following an exponential law, REV size decreases with the increase in the length exponent.

Investigation of diffusive transport of radon through bricks

Radon and their progeny are known indoor lung carcinogens with major sources from the subsoil followed by building materials. The present work was aimed to study the radon permeability of main building materials which is a dominant process for radon entry to indoor environment under normal room conditions. For this purpose, the radon diffusion coefficient and permeability for widely used bricks in the southern coastal region of India were measured with a specially designed twin-chamber experimental set up: a strong source of radon in one chamber and radon and progeny accumulation arrangement in another chamber. Brick samples (with varying thicknesses, firing time and porosity) collected from local kilns were sandwiched between the chambers allowing the radon gas to diffuse through them to get developed in the second chamber. An alpha scintillation based radon monitoring device was connected with both chambers for online radon measurement. Moderately- and lightly-fired bricks show relatively greater permeability than the highly-fired ones, but all the studied bricks are found to be in the radon-tight category. Measured data of radon diffusion coefficient (0.29–0.40) × 10−6 m2s-1 with a mean of (0.35 ± 0.05) × 10−6 m2s-1 and diffusion length (0.37–0.44 m) with a mean of 0.41 ± 0.03 m show a general agreement with the available results in the literature, albeit differing with an earlier study by Chauhan et al. (2008) due to the variation of the sample matrix. Measured data may help the building construction agency to choose a suitable brick to ensure a safer indoor environment for the dwellers.

The effects of some soil characteristics on radon emanation and diffusion

The effects of moisture content, grain size, temperature, major elemental composition, and the pH of soils on the radon emanation and diffusion coefficients were evaluated in this study. The emanation and diffusion coefficients are strongly influenced by moisture content and grain size. The radon emanation coefficient increased and the diffusion coefficient decreased with decreasing particle size. However, for soils with large particle sizes, the radon emanation and diffusion coefficient remain almost unchanged with variation in grain size. Comparing five different sized soil particles, the emanation coefficient increased and the diffusion coefficient decreased with moisture content. The radon emanation coefficient reached a constant value with different moisture contents depending on the range of grain sizes. The saturation emanation coefficient for less than 0.1, 0.1–0.2, 0.2–0.3, 0.3–0.5, and more than 0.5 mm sized soil grain ranges are 0.47, 0.42, 0.35, 0.26 and 0.23, respectively, with saturation moisture contents of 16%, 14%, 10%, 6% and 4%, respectively. A drastic increase in radon emanation is found at smaller grain sizes with increasing moisture content. Based on the content of major elements and pH of the soils, the multiple regression indicates that the radon emanation coefficient appears to be significantly dependent on iron content and pH. Effective diffusion coefficient values calculated in our study agree with the results calculated by a previous model. Experimental values show that the temperature dependence of the radon diffusion coefficient follows Arrhenius behavior.

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.