Effect of Grain Size on Radon Exhalation Rate in the Soils of Hassan District of Southern India

The radon concentration and radon exhalation rates were studied in 39 soil samples collected from Hassan district of southern India. LR-115 Type II solid-state nuclear track detector was used to measure the radon exhalation rate using the sealed can technique. The radon exhalation rate increases with a decrease in the soil grain size. A strong positive correlation was observed between the radon exhalation rate and effective radium content. The α index and annual effective dose were also determined.     

Effect of moisture on the radon exhalation rate from soil, sand and brick samples collected from NWFP and FATA, Pakistan

A series of experiments were carried out to study the effectof the moisture content on the radon exhalation rate from soil,sand and brick samples that were collected from the North WestFrontier Province and Federally Administered Tribal Areas ofPakistan, using CR-39-based radon dosimeters. After processing,samples were prepared by adding 15, 30 and 45% moisture contents(by weight) and were placed in plastic containers. The dosimeterswere installed in it at heights of 25 cm above the surface ofthe samples. These containers were then hermetically sealedand the dosimeters were exposed to radon for 60 to 65 days.After exposure, CR-39 detectors were etched in 25% NaOH at 80°Cfor 16 h, and track densities were counted. From the measuredtrack densities, exhalation rate was determined using two differentapproaches. Maximum average radon exhalation rates of 385 ±86, 393 ± 31 and 362 ± 36 mBq m^–2 h^–1were observed at 30% moisture content from soil, sand and bricksamples, respectively. A slight decrease in exhalation ratewas observed in all samples at moisture content of 45%. Accordingto the t-test, change in the exhalation rate as a function ofhumidity is significant at 95% confidence level.     

Radon survey in schools in north-east Italy

During the year 2000 the Regional Agency for Environmental Protection (ARPA) of Friuli Venezia Giulia together with the Pordenone Province carried out a survey to determine the radon concentration in the schools. About 900 measurements have been carried out in 300 schools located both in the mountainous and in the flat territory. Moreover, geological information was gathered. both on a regional scale and, where possible, on a small detailed scale. The purpose of this study is to consider the possibility of using all the data collected to discover some radon prone areas. The first results of this study seem to locate some radon prone areas where the cover consists of very permeable gravelly deposits.     

Radon exhalation rate from the soil, sand and brick samples collected from NWFP and FATA, Pakistan

In order to characterise the building materials as an indoor radon source, knowledge of the radon exhalation rate from these materials is very important. In this regard, soil, sand and brick samples were collected from different places of the North West Frontier Province (NWFP) and Federally Administered Tribal Areas (FATA), Pakistan. The samples were processed and placed in plastic containers. NRPB radon dosemeters were installed in it at heights of 25 cm above the surface of the samples and containers were then hermetically sealed. After 40-80 d of exposure to radon, CR-39 detectors were removed from the dosemeter holders and etched in 25% NaOH at 80 degrees C for 16 h. From the measured radon concentration values, (222)Rn exhalation rates were determined. Exhalation rate form soil, sand and brick samples was found to vary from 114 +/- 11 to 416 +/- 9 mBq m(-2) h(-1), 205 +/- 16 to 291 +/- 13 mBq m(-2) h(-1) and 245 +/- 12 to 365 +/- 11 mBq m(-2) h(-1), respectively.     

Estimates of the dose due to 222Rn concentrations in water

About 300 samples of groundwater were collected in the region of Extremadura (Spain) in order to analyse their radon activity concentrations. Correlations with the geological characteristics of the aquifer soil were studied. Internal doses by inhalation due to radon exhalation from the water sample and doses by ingestion were estimated. A model was used to calculate the lung dose due to inhalation of radon exhaled from the water. The estimated lung dose range found for the samples was from 2.1 x 10(-3) to 13 mSv a(-1) (the average contribution to the dose due to radon inhalation in Spain being approximately 1.2 mSv a(-1)). The estimated dose by ingestion ranged from 4.1 x 10(-4) to 3.3 mSv a(-1).     

CFD modelling of thoron and thoron progeny in the indoor environment

Thoron (220Rn) exhalation from building materials has become increasingly recognised as a potential source for radiation exposure in residences. However, contrary to radon (222Rn), limited information on thoron exposure is available. The purpose of this study is to estimate the concentration of thoron and its progeny products in a typical Dutch living room using computational fluid dynamics. The predicted thoron concentration is ～9 Bq m(-3) using a source term of 14 Bq s(-1) for the thoron exhalation from building materials. The concentration varies from 15 Bq m(-3) near the building materials to 2.7 Bq m(-3) in the centre of the living room. The mean effective dose from thoron progeny is calculated as 0.09 mSv y(-1), with a total effective dose from radon and thoron progeny of 0.38 mSv y(-1).     

Radon exhalation rate measurement in the environment of Hassan district of southern India

The radon exhalation rate from soil and building materials collected from the Hassan district of southern India was studied by the sealed can technique. The surface exhalation rates of the building materials were found to vary from 13.07 ± 0.19 to 430 ± 9 mBq m^–2 h^–1 with a mean value of 141 ± 4 mBq m^–2 h^–1. The surface exhalation rates of the soil samples were found to vary from 36.5 ± 0.8 mBq m^–2 h^–1 to 376 ± 7 mBq m^–2 h^–1 with a mean value of 140 ± 4 mBq m^–2 h^–1. Good positive correlation was observed between the effective radium content and radon exhalation rate for both soil and building materials. Annual effective dose and α-index have also been estimated for the population of the region.     

A survey of ²²²Rn in drinking water in Mexico City

In Mexico City there are more than 22 millions of inhabitants (10 in the metropolitan area and 12 in the suburban zone) exposed to drinking water. The local epidemiological authorities recognised that exposure to radon contaminated drinking water is a potential health hazard, as has been considered worldwide. The United States Environmental Protection Agency has proposed a limit of 11.1 Bq l(-1) for the radon level in drinking water. In Mexico a maximum contamination level of radon in drinking water has not yet even considered. In this work, a (222)Rn study of drinking water in Mexico City has revealed a range of concentrations from background level to 3.8 Bq l(-1). (222)Rn was calculated using a portable degassing system (AquaKIT) associated with an AlphaGUARD measuring system. Samples from 70 wells of the water system of the south of the Valley Basin of Mexico City and from houses of some other political administrative divisions of Mexico City were taken.     

An automatic device for measuring the effect of meteorological factors on radon-222 flux from soils in the long-term

An automatic method for measuring the radon flux at soil surfaces is described. The proposed experimental design minimises the disturbance induced by the accumulator technique widely used to measure radon exhalation from the ground. By exposing the ground surface to the normal weather conditions between two consecutive measurements, this method can be used to study, in the long term, the effects of meteorological factors on the radon flux density at the soil-atmosphere interface.     

The US radon problem, policy, program and industry: achievements, challenges and strategies

US radon research, policy and programs have stalled since their start in the late 1980s and early 1990s. In 2005, more homes had radon above the US Environmental Protection Agency (EPA) Reference Level than anytime in history since more homes were added to the housing stock that had indoor radon concentrations exceeding 150 Bq m(-3) than had been mitigated. Funding for the US radon program has declined two-thirds from 1997 to 2007. Despite impressive goals for radon reduction, EPA lacks sound progress indicators especially in new construction radon control systems. School radon reduction has been at a standstill since the early 1990s. There has been no significant radon risk reduction in low-income sectors of the population. There is need for effective partnerships between the public and private sectors of the US radon professional communities as well as with the international programs and professionals.     

氡析出率测量中的218Po非平衡修正

通过对传统的累积法测量氡析出率模型实验验证,发现得到的氡析出率明显偏低。对测氡仪器的工作原理与集氡罩中氡的浓度变化规律进行分析,发现是由于被测介质表面析出的氡不断进入集氡罩,218Po与氡没有平衡,造成测量的氡浓度明显偏低。通过非平衡修正得到了修正后的氡析出率测量理论模型。利用修正后的该模型得到的介质表面氡析出率与参考值符合得较好,误差小于7%。此外比较优值函数的取值也可发现:修正后的理论模型优值函数的取值小于传统模型,这表明修正后的理论模型更符合实际,该理论模型可应用于氡析出率仪的研制与改进。     

Soil gas radon measurements in a region of the Bohemian Massif: investigations in the framework of an Austrian pilot study

Soil gas radon measurements are carried out in a pilot study in three municipalities in Upper Austria. The selected municipalities are characterised by a high radon potential. Sixty measuring sites--well distributed over the region and over the different geological areas--were selected. Additionally, the permeability of the soil was determined where the soil gas samples were taken and at various sites where soil samples were analysed by gamma spectrometry. Long-term soil-gas radon concentration measurements are carried out at several sites to study the long-term behaviour of radon activity concentration in soil, the influence of meteorological parameters and seasonal variations. The final goal of the project is to correlate the collected data with geological data and indoor radon concentration. First results of this ongoing study are presented and discussed.     

Measurements of radon exhalation rate for monitoring cement hydration

The paper deals with one of the physical methods, which can be used for monitoring hydration of cementitious materials: the radon exhalation method. Experiments with two types of hydrating cement paste (made with water to cement ratios of 0.25 and 0.33) are described. The kinetics of shrinkage and hydration heat development are discussed. Different mechanisms influencing the radon exhalation rate E from cement and hydration products are considered. The initial E-values determined in the beginning of the tests were 0.01–0.02 mBq  kg⁻¹ s⁻¹ for the cement pastes made at water/cement ratios of 0.25 and 0.33, respectively. In 3 days both pastes showed E = 0.04 mBq  kg⁻¹ s⁻¹. However, the most important finding seems to be the dramatic increase of the radon exhalation rate up to the maximum observed a few hours after mixing with water (0.66 and 0.58 mBq  kg⁻¹ s⁻¹ for 0.25 and 0.33 pastes, respectively). This was registered in the radon chamber within the time period usually classified as set. The test results showed a strong correlation between radon exhalation rate and liberation of hydration heat. Peaks of the radon exhalation rate coincide with those of temperature measured on the surface of the cement paste. Analysis of the literature data shows that heating of the materials weakens physical adsorption of radon gas atoms on newly formed solid surfaces and can enhance the radon exhalation rate by several times. However, the performed experiment shows that the radon exhalation rate drastically increases (by dozens of times), and then decreases again. Such a dramatic growth can be explained by a synergy between temperature effect and two more phenomena: (a) intensive formation of microstructure with an extremely high specific surface area, when cement sets and while porosity is still high and (b) intensive flow of water, which traps radon from the newly formed solid surfaces of C-S-H and brings it to the sample surface, enhancing the radon flux.     

Theory of radon exhalation into accumulators placed at the soil-atmosphere interface

A theoretical analysis is provided for the phenomenon of radon diffusion into cylindrical accumulators (inverted cups), which are commonly used for the measurement of radon exhalation rates from the earth's surface. Analytical solutions to the diffusion equations in the soil and the cup spaces are obtained by a two-dimensional (2-D) analysis that takes into account the perturbation in the horizontal and vertical radon concentration profiles brought about by the presence of the cup. The mixed nature of the boundary conditions at the soil surface and the cup-soil interface is handled by dual integral equation techniques. The treatment includes steady-state and time-dependent situations with and without ventilation. Formulae are derived for the effective time constant of radon build-up in the cup and for the back diffusion correction factors in different experimental situations. It is found that the effective time constant of radon build-up is much larger than the radon decay constant and it increases for smaller cups. The back diffusion correction factors to be employed in one-time measurement methods also increase as the cup dimensions decrease. The present work provides an analytical basis of an earlier numerical treatment for the growth curve analysis of the same problem. Although the results are based on the assumptions of somewhat ideal nature for mathematical tractability, they provide upper bound estimates of the phenomenon of back diffusion. Some practical applications of the results for extracting diffusion length of radon in materials are also suggested.     

A theoretical and experimental investigation of spatial distribution of radon in a typical ventilated room

The aim of this work is to studying indoor radon distribution using the Finite Volume Method (FVM). This paper focuses on effects of exhalation from different sources (wall, floor and ceiling) and the ventilation profile on distribution the concentrations of radon indoor. The rate of radon exhalation and ventilation were measured and are used as input in FVM simulation. It has been found that the radon concentration is distributed in non homogeneous way in the room. The radon concentration is much larger near floor, and decreases in the middle of the room. The experimental validation was performed by measuring radon concentration at different locations in room using active and passive techniques. We notice that the results of simulation and experimental are in agreement. The annual effective dose of radon in the model room has been also investigated.     

Regional variations pattern of indoor radon levels in some areas of Punjab and Haryana

The indoor radon concentration levels and their regional variationspattern, for two consecutive half-year periods, in a wide rangeof dwellings of some regions of Punjab and Haryana states havebeen studied. The objective was to find the relation betweenthe variations of indoor radon levels with the sub-soil andlocal geology, type of building materials utilised in the dwellingsof the region. Keeping this in view, indoor radon measurementshave been carried out in the dwellings of 30 villages aroundthe Tusham Ring Complex, Bhiwani district, Haryana, known tobe composed of acidic volcanics and associated granites, alongwith 11 villages of Amritsar District, Punjab. The indoor radonconcentration in the dwellings around Tusham (Haryana) was foundto vary from 120 ± 95 to 915 ± 233 Bq m^–3,whereas radon levels varied from 60 ± 37 to 235 ±96 Bq m^–3 for the dwellings studied in Punjab. We believethat local geology including embedded granitic rocks, and sub-soil,as well as building materials having higher radioactive content,is the major contributor for the higher indoor radon levelsobserved particularly in the dwelling around Tusham Ring complex,where some dwellings are showing higher radon concentrationsthan the ICRP recommendations. The environmental samples fromsome areas of Punjab state and around the Tusham Ring Complexof Haryana state have also been analysed for radon exhalationstudies. Higher values for radon exhalation rates have beenobserved for the Tusham's soil/rock specimens, as compared withsoil samples of the Amritsar region of Punjab.     

Radon risk in Alpine regions in Austria: risk assessment as a settlement planning strategy

Soil gas radon measurements complement indispensable and well-established radon indoor measurements in Austria. Radon in soil gas is a result of geochemical conditions as well as of geology, mineralogy, geophysics and meteorology. Therefore, geological factors can help to predict potential indoor radon concentrations via soil gas. Soil gas radon measurements in well-defined geological units give an estimate of local and regional radon hazards and build the basis for radon risk maps, which could be used for land-use planning and urban development. The creation of maps makes an important contribution to health care. For this purpose, several research projects were carried out in Austria. On the one hand, a study was already conducted in Lower Austria to determine the influence of meteorological and soil physical parameters on radon concentrations in soil gas and to evaluate soil gas radon concentrations with a radon emanation and migration model. On the other hand, radon measurements on different geomorphologic formations in the Austrian Alps, which are potential settlement areas, are of special interest.     

Soil radon measurements in the Canadian cities

Radon has been identified as the second leading cause of lung cancer after tobacco smoking. Information on indoor radon concentrations is required to assess the lung cancer burden due to radon exposure. Since radon in soil is believed to be the main source of radon in homes, measurements of soil gas radon concentrations can be used to estimate variations in radon potential of indoor environments. This study reports surveys of natural background variation in soil radon levels in four cities, Montreal, Gatineau, Kingston and the largest Canadian city of Toronto. A total of 212 sites were surveyed. The average soil gas radon concentrations varied significantly from site to site, and ranged from below detection limit to 157 kBq m(-3). For each site, the soil radon potential (SRP) index was determined with the average soil radon concentration and average soil permeability measured. The average SRP indexes are 20±16, 12±11, 8±9 and 12±10 for Montreal, Gatineau, Kingston and Toronto, respectively. The results provide additional data for the validation of an association between indoor and soil radon potentials and for the development of radon potential map of Canada.     

The Closed-Can Exhalation Method for Measuring Radon

Results from closed-can radon exhalation experiments must be interpreted bearing the time-dependent radon diffusion theory in mind. A rapid change from the free to final steady-state exhalation rate will take place for all samples that are thin compared with the radon diffusion length. The radon gas accumulating in a closed can corresponds to a free exhalation rate only if the outer volume of air is much larger than the pore volume of the enclosed sample, or the thickness of the sample is much larger than the radon diffusion length.     

Indoor radon measurements in the granodiorite area of Bergama (Pergamon)-Kozak, Turkey

Indoor radon levels in 20 dwellings of rural areas at the Kozak-Bergama (Pergamon) granodiorite area in Turkey were measured by the alpha track etch integrated method. These dwellings were monitored for eight successive months. Results show that the radon levels varied widely in the area ranging from 11±1 to 727±11 Bq m(-3) and the geometric mean was found to be 63 Bq m(-3) with a geometric standard deviation of 2 Bq m(-3). A log-normal distribution of the radon concentration was obtained for the studied area. Estimated annual effective doses due to the indoor radon ranged from 0.27 to 18.34 mSv y(-1) with a mean value of 1.95 mSv y(-1), which is lower than the effective dose values 3-10 mSv given as the range of action levels recommended by International Commission on Radiation Protection. All dosimetric calculations were performed based on the guidance of the UNSCEAR 2000 report.