Emanation Fraction Research Articles

Exploring radon emanation fraction in dry and wet conditions: a study in the main Boundary Thrust Region of Garhwal Himlaya

Exploring radon emanation fraction in dry and wet conditions: a study in the main Boundary Thrust Region of Garhwal Himlaya

Evaluation of potential radiological hazards of unfired construction materials containing fly ash in Vietnam.

In this study, the specific activities of 226Ra, 232Th and 40K in the unfired construction materials (solid card bricks, 4-hole bricks, pavement bricks) containing fly ashand bottom ash from a coal-fired thermal power plant in Vietnam were measured using the low-level gamma-ray spectrometer with HPGe detector. Also, the 222Rn concentrations in these materials were analyzed using RAD7 radon monitor and then radon mass exhalation rate and emanation fraction of these materials were calculated. The potential radiological hazards for residents living in the model room made of these materials were evaluated. The average specific activity of 226Ra, 232Th and 40K were found as 67.7, 79.3 and 703.5Bqkg-1, respectively. The total annual effective dose (due to external gamma exposure and internal radon exposure for resident living in the CEN model room made of the unfired brick samples) was found as 0.9mSvy-1 which is lower than the worldwide average dose of 2.4mSvy-1. Calculations from ResRad-Build code showed that the doses due to radon exposure account for from 62.3% (at the first year) to 98.8% (at the next 30years) of the total gamma and radon dose. Under low air exchange to the outside environment, from the 6th year onwards, the total dose may exceed the average dose value from natural radiation exposure sources.

Radon emanation from dust of varying composition and size

222Rn emanating from environmental dust constitutes an important background component for many low-energy, low-rate experiments. Radon emanation rates from dust and rock, thus, are important for experiment planning. In this paper, we report measured radon emanation fractions for five types of dry dust differing in grain size and composition. These data were obtained by a novel technique in γ-spectroscopy, measuring emanated and non-emanated 222Rn progeny activities as well as the parent 226Ra activity in a time series. The range of observed radon emanation fractions is (3.7 ± 2.0)% to (16.2 ± 0.9)%. Four of the five samples are standardized samples available commercially, so additional investigations of these samples may be readily carried out.

Quantification of 37Ar emanation fractions from irradiated natural rock samples and field applications

Underground-produced 37Ar can be used for underground nuclear explosions (UNE) detection and for groundwater dating. The quantification of the emanation, that is the fraction of activity produced in the rock that escapes to the pore space, is essential for predicting the background activity expected in natural environments. We propose an experiment in which artificial CaCO3 powder and natural rock particles are irradiated with neutrons in a routinely operated medical cyclotron, whose energy spectrum is experimentally measured. The produced activity was quantified and compared with the emanated activity to determine the emanating fraction. The results showed consistent and reproducible patterns with a dominance of the recoil process at small scales (<2 mm). We observed emanation values ≤1% with a dependency on the grain size and the inner geometry of particles. Soil weathering and the presence of water increased the recoil emanation. The atoms produced that were instantaneously recoiled in the intra- or inter-granular pore space left macroscopic samples by diffusion on timescales of days to weeks (Deff = 10−12 – 10−16 m2 s−1). This diffusive transport determines the activity that prevails in the fluid-filled pore space accessible for groundwater or soil gas sampling.

Radiological assessment of urban soil samples in the residents of a central Anatolian volcanic province, Turkey

ABSTRACT The concentration of natural and anthropogenic radionuclides, emanation fraction (EF), and mass (χM) and area (χA) exhalation rate of 222Rn in urban soil samples collected from dwelling areas in Nevşehir city located in a region known as the central Anatolian volcanic province of Turkey were determined using gamma-ray spectroscopy. The average activity concentrations of 226Ra, 228Ra, 40K and 137Cs were measured as 60.2 ± 3.8, 50.1 ± 2.8, 631.0 ± 29.7 and 5.5 ± 0.4 Bq/kg, respectively. The average concentration of 222Rn in soil and air was estimated as 27 kBq/m3 and 84 Bq/m3, respectively. The average values of EF, χM and χA were found as 20%, 25.4 μBq/kg⋅s and 20.2 mBq/m2⋅s, respectively. The average values of outdoor absorbed gamma dose rate, external and internal annual effective dose and lifetime cancer risk estimated for radiological assessment were found as 85 nGy/h, 104 µSv/y, 797 µSv/y and 4.1 × 10−4, respectively.

Natural radioactivity level in fly ash samples and radiological hazard at the landfill area of the coal-fired power plant complex, Vietnam

In this study, natural radioactivity concentrations and dosimetric values of fly ash samples were evaluated for the landfill area of the coal-fired power plant (CFPP) complex at Binh Thuan, Vietnam. The average activity concentrations of 238U, 226Ra, 232Th and 40K were 93, 77, 92 and 938 Bq kg−1, respectively. The average results for radon dose, indoor external, internal, and total effective dose equivalent (TEDE) were 5.27, 1.22, 0.16, and 6.65 mSv y−1, respectively. The average emanation fraction for fly ash were 0.028. The excess lifetime cancer risks (ELCR) were recorded as 20.30 ×10−3, 4.26 ×10−3, 0.62 ×10−3, and 25.61 ×10−3 for radon, indoor, outdoor exposures, and total ELCR, respectively. The results indicated that the cover of shielding materials above the landfill area significantly decreased the gamma radiation from the ash and slag in the ascending order: Zeolite < PVC < Soil < Concrete. Total dose of all radionuclides in the landfill site reached its peak at 19.8 years. The obtained data are useful for evaluation of radiation safety when fly ash is used for building material as well as the radiation risk and the overload of the landfill area from operation of these plants for population and workers.

Semi-experimental evaluation for radon exhalation rate and excess lifetime cancer risk from potential radon exposure for using fly ash building materials

In this work, the radon exhalation, annual effective dose and excess lifetime cancer risks due to the exposure of radon released from raw building materials containing fly ash of different fractions were evaluated. The 226Ra and 222Rn concentrations were evaluated by the measurements on HPGe gamma spectrometer, RAD 7 radon detector combined with model calculation of radon exhalation for standard rooms. The results indicated that the emanation fraction for fly ash is lower than the corresponding value for soils and rocks. The surveyed building materials of containing fly ash can result in an indoor radon concentration up to 1.7 Bq m−3 which is below the recommended value of 100 Bq m−3 by WHO, the annual effective dose increases from 0.007 to 0.022 mSv year−1, the excess lifetime cancer risks ranges from 0.027 × 10–3 to 0.085 × 10–3 with the ratio of 3.2 for the additional fly ash content in cement up to 75%. In the meanwhile, it has a down trend and influences inconsiderably on these parameters for sand. The obtained mean annual effective doses are lower than the dose limitation of 10 mSv year−1 recommended for occupational workers.

Radiological characterization of building materials used in Malaysia and assessment of external and internal doses

In this study, the activity concentrations of 226Ra, 232Th, 222Rn, and 40K, emanation fractions (P), equilibrium equivalent concentration (EEC), and mass exhalation rates (Em) of radon released from building materials used in Malaysia were studied using gamma-ray spectrometer with HPGe detector. Radiological parameters [activity concentration index (ACI), indoor air-absorbed dose rate (Din), annual effective dose (AEDin) from external and internal (ERn), soft tissues (HST) and lung (HL), and effective dose equivalent (Heff)] were estimated to evaluate radiological hazards due to the use of these building materials: sand, cement, gravel, bricks, tiles, fly ash, white cement, and ceramic raw materials. The measured P, EEC, and Em vary from 10 to 30%, 0.9 to 22 Bq m−3, and 33 to 674 mBq h−1 kg−1, respectively, while the calculated ACI and AEDin vary from 0.1 ± 0.01 to 2.1 ± 0.1 and 0.1 ± 0.01 to 2.4 ± 0.6 mSv y−1, respectively. On the other hand, the internal annual effective dose ranges from 0.1 to 1.4 mSv y−1. The estimated radiological risk parameters were below the recommended maximum values, and radiological hazards associated with building materials under investigation are therefore negligible.

A method to quantify the 37Ar emanation fraction in powders and rocks

In order to make predictions of the potential 37Ar signal from an underground nuclear explosion, a value for the 37Ar emanation fraction is needed. A system was developed to quantify the emanation fraction from samples ranging in size from powder to small rocks. Assorted rock samples were irradiated with Watt fission spectrum neutrons to produce radioactive argon gas via activation of calcium. The argon produced was extracted on a custom apparatus and cryogenically trapped. The extracted gas was then processed to separate the argon and load it into a proportional counter for counting. The emanation fraction of argon gas from the rock samples was then calculated by comparing the measured and predicted activities.

Determination of the radon emanation fraction from rocks by simple gamma-ray spectrometry

A simple method for the determination of the radon emanation fraction (EF) from rocks has been studied in this work. Growth and decay curves of radium—radon—daughters and the double counting technique using the same gamma-ray spectrometry were applied to determine the EF from eleven rocks at different lithologies. Aluminium Marinelli beakers were used to prevent the leakage of radon during the equilibration period of around 30 days. And also, nitrogen purging system was constructed to replace the surrounding air of the detector for obtaining a stable background and reducing the interference of radon daughter nuclides from the atmosphere.

ASSESSMENT OF RADIUM ACTIVITY CONCENTRATION AND RADON EXHALATION RATES IN IBERIAN PENINSULA BUILDING MATERIALS.

Radium (226Ra) is a natural radioactive element of the uranium decay series, which could also be present in building materials. Radon (222Rn) is continuously produced by the decay of 226Ra and its presence inside buildings can contribute to the increase of the population exposure to ionizing radiation. In this work, the amount of radium activity concentration and radon exhalation rates in several types of building materials that are commonly used in the Iberian Peninsula have been tested. The radium activity concentration was measured by gamma-ray spectrometry, whereas the radon exhalation rates were carried out using a continuous radon monitor (active measuring technique) and a solid state nuclear track detectors (passive measuring technique). The 226Ra mean values range from 5.0 to 123.4 Bq kg-1. As expected, the results show that the radon exhalation rate is higher in granites samples relatively to others building materials analysed. A positive correlation was found between radium activity concentration and radon exhalation rates in both techniques. The emanation fraction and alpha index were also calculated.

Investigation of some factors affecting on release of radon-222 from phosphogypsum waste associated with phosphate ore processing

The aim of this study is oriented to investigate the influence of some physicochemical factors such as radium distribution, grain size, moisture content and chemical constituents on releases of radon-222 from the accumulated phosphogypsum (PG) waste. The emanation fraction, activity concentration in the pore and the surface exhalation rate of radon-222 in the bulk PG waste are 34.5 ± 0.3%, 238.6 ± 7.8 kBq m−3 and 213 ± 6.9 mBq m−2 s−1, respectively. These values were varied and enhanced slightly in the fine grain sizes (F1 < 0.125 mm) by a factor of 1.05 folds compared to the bulk residue. It was also found that release of radon from residue PG waste was controlled positively by radium (Ra-226), calcium (CaSO4) and strontium (SrO). About 67% of radon release attributed to the grain size below 0.5 mm, while 33% due to the large grain size above 0.5 mm. The emanation fraction of Rn-222 is increased with moisture content and the maximum emanation is ∼43% of moisture of 3–8%. It reduced slowly with the continuous increase in moisture till 20%. Due to PG waste in situ can be enhancing the background to the surround workers and/or public. Therefore, the environmental negative impacts due to release of Rn-222 can be minimized by legislation to restrict its civil uses, or increasing its moisture to ∼10%, or by the particle size separation of the fine fraction containing the high levels of Ra-226 followed by a suitable chemical treatment or disposal; whereas the low release amount can be diluted and used in cement industry, roads or dam construction.

Dependence of radon emanation of soil on lithology

In soil samples collected from 58 points of 7 different lithological units that appear most often in Slovenia, emanation fraction of 222Rn and porosity have been determined. Emanation fraction ranged from 0.010 to 0.547 and varied substantially among lithological units, as well as within the same lithological unit. The highest average value was found in soil over sea and lake deposits (0.340) and the lowest, over metamorphic rocks (0.029). Based on the data measured, radon concentration in soil gas was calculated and compared with the values obtained previously at the same points by exposing solid state nuclear track detectors.

Theoretical calculation of radon emanation fraction

Emanation fraction of radon atoms created in a granular material was estimated using Monte Carlo method. Two models based on different arrangements of grains were considered: one of them representing simple cubic structure and the other one based on face centered cubic structure. As it was expected, the structure that provided higher density of grain packing (FCCS) gave lower values of radon emanation fraction. Both models showed that the probability of radon embedding in the neighboring grains would approach zero for large values of grain radius. Assuming homogenous distribution of 226Ra within the whole grain volume, radon emanation fraction decreased with increasing grain radius while it showed the opposite behavior in the case of surface distribution of 226Ra. The order of magnitude of radon emanation fraction decreased from 10−2% (for grain radius of few micrometers) to 10−4% (for grain radius larger than few millimeters) when homogenous distribution of 226Ra was considered. If the distribution of 226Ra was assumed only within the surface layer of a grain, emanation increased from less than 1% (obtained for grain size of few micrometers) to almost 25% (for large grain radius). The effect of moisture on the emanation fraction was confirmed by examining the case of water filling the space among the grains. Radon emanation was also considered analytically and the results were compared with Monte Carlo calculations.

Calculation of temperature dependence of radon emanation due to alpha recoil

Many experimental and modeling studies have examined several factors affecting radon emanation. Of these factors, the effect of temperature shown in earlier experiments has not been discussed with model calculations. In the present study, radon emanation fractions were calculated for various temperatures, namely different air densities, using a simple model into which the emanation processes originating from alpha recoil were incorporated. As a result, the slightly negative correlation that the radon emanation fraction decreased with increasing temperature was observed within a certain range of grain size, while temperature had no effect within the other range. Considering the current knowledge of processes through which radon emanation occurs, this result would be expected to be qualitatively reasonable. However, the result is not similar to all previous experimental results showing the positive correlation. These papers occasionally explain that the positive correlation is attributable to the adsorption of radon on solids during its transfer among grains. Since the general definition of radon emanation includes no transfer process after its release from a grain, their explanation could not be well established. The discrepancy between the calculated and measured data may suggest the needs of review and improvement of experimental and/or modeling techniques.

Radon emanation fractions from concretes containing fly ash and metakaolin

Radon (222Rn) and progenies emanate from soil and building components and can create an indoor air quality hazard. In this study, nine concrete constituents, including the supplementary cementitious materials (SCMs) fly ash and metakaolin, were used to create eleven different concrete mixtures. We investigated the effect of constituent radium specific activity, radon effective activity and emanation fraction on the concrete emanation fraction and the radon exhalation rate. Given the serious health effects associated with radionuclide exposure, experimental results were coupled with Monte Carlo simulations to demonstrate predictive differences in the indoor radon concentration due to concrete mixture design. The results from this study show that, on average, fly ash constituents possessed radium specific activities ranging from 100Bq/kg to 200Bq/kg and emanation fractions ranging from 1.1% to 2.5%. The lowest emitting concrete mixture containing fly ash resulted in a 3.4% reduction in the concrete emanation fraction, owing to the relatively low emanation that exists when fly ash is part of concrete. On average, the metakaolin constituents contained radium specific activities ranging from 67Bq/kg to 600Bq/kg and emanation fractions ranging from 8.4% to 15.5%, and changed the total concrete emanation fraction by roughly ±5% relative to control samples. The results from this study suggest that SCMs can reduce indoor radon exposure from concrete, contingent upon SCM radionucleotide content and emanation fraction. Lastly, the experimental results provide SCM-specific concrete emanation fractions for indoor radon exposure modeling.

Radon emanation from low-grade uranium ore

Estimation of radon emanation in uranium mines is given top priority to minimize the risk of inhalation exposure due to short-lived radon progeny. This paper describes the radon emanation studies conducted in the laboratory as well as inside an operating underground uranium mine at Jaduguda, India. Some of the important parameters, such as grade/226Ra activity, moisture content, bulk density, porosity and emanation fraction of ore, governing the migration of radon through the ore were determined. Emanation from the ore samples in terms of emanation rate and emanation fraction was measured in the laboratory under airtight condition in glass jar. The in situ radon emanation rate inside the mine was measured from drill holes made in the ore body. The in situ222Rn emanation rate from the mine walls varied in the range of 0.22–51.84 × 10−3 Bq m−2 s−1 with the geometric mean of 8.68 × 10−3 Bq m−2 s−1. A significant positive linear correlation (r = 0.99, p < 0.001) between in situ222Rn emanation rate and the ore grade was observed. The emanation fraction of the ore samples, which varied in the range of 0.004–0.089 with mean value of 0.025 ± 0.02, showed poor correlation with ore grade and porosity. Empirical relationships between radon emanation rate and the ore grade/226Ra were also established for quick prediction of radon emanation rate from the ore body.

The contribution of fly ash toward indoor radon pollution from concrete

Owing to concerns about radon exposure, there is a need for understanding risk associated with fly ash in concrete. Monte Carlo simulations were applied, based on the radium specific activity of concrete constituents taken from the literature, to predict probabilities for the radium specific activity and radon exhalation rate. The model was then used to predict the indoor radon concentrations and effective annual doses from two different slab-on-grade concrete floors, one with and one without fly ash, in a typical single-family home in the United States. Due to uncertainty in the literature-reported values, a sensitivity analysis was conducted varying the emanation fraction of the fly ash concrete floors. The results show that concrete floors made without fly ash and a 5% emanation fraction, resulted in 90% of the simulated homes having an indoor radon concentration of less than or equal to 2.3 Bq m−3 and an associated annual dose of less than or equal to 54 μSv y−1. This annual dose represents 4% of the total annual background inhalation dose. A 25wt% fly ash concrete with an emanation fraction of 3% achieved the same exposure probability, but higher assumed emanation fractions raised the exposure probability. In general, the predicted radon exposure from fly ash concrete suggests minimal population health effects. But, given the serious health effects of radon exposure the influence of fly ash on the emanation fraction and radioactive pollution indoors deserves further exploration.

Determination of the radon emanation fraction from phosphogypsum using LSC

A simple method for the determination of the radon emanation fraction was studied using a liquid scintillation counter. The radon activity of the gaseous phase in a closed container was measured 1 day and 35 days after sealing and used to calculate the radon emanation fraction. Radon leakage from the container was investigated using a 226Ra radioactive standard solution (SRM4967, NIST) to plot a radon growth curve. The method was applied to materials that typically contain a high level of radium, such as phosphogypsum, phosphate fertilizer and a rock sample. The effect of temperature on the radon emanation fraction from the materials was investigated at 0, 10, 20, 30 and 40 °C. It was found that there is a linear correlation (R2 = 0.746 − 0.946) between temperature and the emanation fraction. Within the temperature range, the radon emanation fractions were 0.241–0.466 for phosphogypsum, 0.225–0.351 for phosphate fertilizer and 0.154–0.351 for the rock sample.

Natural radionuclides content and radiological hazard of commercial ornamental stones: An integrated radiometric and mineralogical-petrographic study

Abstract Twenty samples of natural building materials commonly employed as ornamental stones in the international market have been investigated for natural radioactivity. External (gamma), as defined and used by the European Commission, and internal (alpha) hazard indexes were calculated and radon specific exhalation rate and emanation fraction were measured. The radiological investigation was complemented by an integrated mineralogical-petrographic and rock characterization approach. The most common radioactive accessory minerals occurring in the investigated samples are apatite, zircon and allanite, with minor monazite, thorite, thorianite, REE and Zr-oxides. Significant correlations with total activity concentration have been observed for K 2 O, Th and Ce concentrations. The emanation fraction is also influenced by both total porosity and porosity distribution. Radon exhalation rate and emanation fraction are very variable ranging from 0.0011 to 0.64 Bq kg −1 h −1 and from 0.2 to 62%, respectively. Most of the materials have radiological hazard indexes that do not exceed the European Commission limit values when used as ornamental or paving or flooring stones. However, three volcanic (Tufo Giallo Riano, Tufo Grigio Riano and Peperino Viterbese) samples could cause significant exposure both from excess radon indoor concentration (>200 Bq m 3 ) and from gamma radiation (>1 mSv y −1 ) when used as structural materials. This study further indicates that limit values for hazard indexes based on natural activity concentration and Rn emanation should take into account the lithological properties and use of the materials.