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.     

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。     

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.     

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.     

开环式测量氡析出率

对开环式测量氡析出率方法进行了验证,测得的介质表面氡析出率与参考值符合得较好。通过理论分析得到了集氡罩内的氡浓度趋于恒定值的时间表达式;提出了采用底面积较大的集氡罩,并加一调节阀来调低泵的流量的方法来提高集氡罩内的氡浓度,减小RAD7测量时的统计涨落。     

标准测氡仪的量值溯源方法研究

研究了利用氡活度绝对测量装置制备高准确度标准氡源的方法,得到了活度扩展不确定度为0.8%(k=2)的量传用氡源。依据计算标准氡体积活度的基本原理,对用于氡源活度量传所配套的小氡室的有效体积进行了校准,其有效体积的扩展不确定度为0.46%(k=2),对一般氡标准装置(标准氡室)所用的参考仪器(AlphaGUARD型标准测氡仪)进行校准,得到其平均体积活度响应为1.01,体积活度响应的扩展不确定度为3.2%(k=2)。     

Anomalous indoor radon concentration in a dwelling in Qatif City, Saudi Arabia

An indoor radon survey was carried out recently in nine cities of Saudi Arabia using nuclear track detectors (NTD)-based passive radon detectors. The survey included Qatif City in the Eastern Province of Saudi Arabia, where 225 detectors were collected back successfully. It was found that the average indoor radon concentration in the dwellings was 22 +/- 15 Bq m(-3). However, one of the dwellings showed an anomalous radon concentration of 535 +/- 23 Bq m(-3). This finding led to a detailed investigation of this dwelling using active and passive techniques. In the active technique, an AlphaGUARD 2000 PRQ radon gas analyser was used. In the passive technique, CR-39 based passive radon detectors were used in all the rooms of the dwelling. Radon exhalation from the wall and the floor was also measured using the can technique. The active measurement confirms the passive one. Before placing the passive radon detectors in all the rooms of the two-storey building, the inhabitant was advised to ventilate his house regularly. The radon concentration in the different rooms was found to vary from 124 to 302 Bq m(-3). Radon exhalation from the floor and the wall of the room with the anomalous radon concentration was found to vary from 0.5 to 0.8 Bq m(-2) h(-1). These low radon exhalation rates suggest that the anomalous radon concentration is most probably due to underground radon diffusion into the dwelling through cracks and joints in the concrete floor.     

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.     

Calibration of Scintillation Cells for Radon-222 Measurements at the U.S. Environmental Protection Agency

Zinc sulfide coated scintillation cells are the primary method for measuring radon-222 at the U.S. Environmental Protection Agency (EPA), Office of Radiation Programs (ORP), Eastern Environmental Radiation Facility (EERF). These cells are used to measure concentrations of radon in exposure chambers that are used to calibrate or test other devices or instruments. Individual cells are calibrated by analyzing samples of air with known concentrations of radon produced by emanation of radon from standard radium-226 solutions obtained from the National Institute of Standards and Technology. The calibration procedure includes ingrowth of radon-222 into equilibrium with the radium in the standard solution, transfer from the solution into an evacuated container, and dilution with a measured volume of air. Samples of the radon in air mixture are transferred to evacuated scintillation cells and sealed for 4 h prior to counting, which allows secular equilibrium to be established between the radon and its decay products.Calibration factors for each individual cell are computed by decay correcting the radon to the time of collection and calculating the ratio of count rate (cpm), corrected for background, to radon activity (Bq) for the specific volume of the cell. Four or more calibration factors are determined for each cell and aver-aged to provide the calibration factor used for measurements. Calibrations are repeated at 6-mo intervals, and the results of each calibration are compared to the previous averages. When calibration factors fall outside the 95% confidence interval, they are rejected and the cell is checked for defects prior to recalibration.     

Lung cancer risks due to the radon in cigarette tobacco

Thirty-one tobacco samples were evaluated for the activity concentrations of radon and radium using solid-state nuclear track detectors (CR-39). The detectors were exposed for a period of 150 days to different types of cigarette tobacco. The highest values of 364 Bq m^–3 for radon and 31.4 Bq kg^–1 for radium were obtained for MIA2 sample, and the lowest values of 20.2 Bq m^–3 for radon and 1.74 Bq kg^–1 for radium, for SUM sample. According to the estimate, this range of radon levels corresponds to the lung cancer incidence in the range 22–396 cases per million smoker per year. The annual effective dose in general and for lungs in particular, the surface and mass exhalation rate, the equivalent equilibrium concentration of radon, and absorbed dose to tissues and lungs were calculated. The highest values were obtained for MIA2 sample, and the lowest values, for SUM sample.     

连续测氡仪测定空气中氡浓度方法探讨

在民用建筑工程室内环境中氡浓度的测定方法中,用连续测氡仪测定氡浓度是一种方便、快捷的方法,但在实际检测过程中,由于操作等原因,仪器的测量准确度较低。在标准氡室(HD-1型)里模拟实验用标准氡浓度,以RAD7连续测氡仪为例,探讨了取样测量时间、空气湿度对空气中氡浓度测量的准确性的影响。结果表明,在取样测量时间不低于30min、较低空气湿度(10%)条件下,用连续测氡仪测量空气中氡浓度可以获得满意的数据。     

Spatial correlations between chromophores in thin films by femtosecond hyper-Rayleigh scattering

Femtosecond hyper-Rayleigh scattering has been used to probe the spatial orientational fluctuations between nonlinear optical chromophores as dopants in spincoated polymer films. The fluctuation in the second-order incoherently scattered light intensity upon translating the sample is indicative of the degree of spatial correlation between the chromophores. The decay of the autocorrelation function of this fluctuating signal is characterized by a spatial correlation length. Electric-field poling of chromophores is shown to increase this length. The temporal characteristics of this correlation length have been studied and compared with relaxation times, obtained with coherent second-harmonic generation. This correlation length decays much faster than the second-harmonic intensity. The difference in relaxation time between the incoherent and the coherent process is explained by translational diffusion of free volume over the wavelength and over the coherence length, respectively.     

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.     

Radon Exhalation Rate Study of Sand Samples Collected from Sea Coast of Tirur,Kerala, India Using Track Etch Technique

The sand samples have been collecting from the sea coast (Unniyal beach) of Tirur of Malappuram district of Kerala state (India) by the grab sampling method. Radon exhalation rates have measured by “Sealed Can Technique” using LR-115 type II plastic track detector to estimate the health risk level in the environment. The value of radon activity varies from 444.44 to 2204.44 becquerel meter^?3 (Bq m^?3) with a geometric mean (G.M.)/standard deviation (S.D.) value of 1017.21 Bq m^?3/433.27. The value of mass exhalation rate for radon varies from 0.01 to 0.05 Bq kg^?1 h^?1 with a G.M./S.D. value of 0.024 Bq kg^?1 h^?1/0.010. The value of area exhalation rate for radon varies from 0.27 to 1.33 Bq m^?2 h^?1 with a G.M./S.D. value of 0.62 Bq m^?2 h^?1/0.26. The values of radon emanation ranged from 2.90?×?10^?3 to 2.98?×?10^?3 (%) with a G.M./S.D. value of 2.98?×?10^?3(%)/0.05. The alpha dose equivalent of the studied area is found and it varies from 0.68 to 1.66 milli sievert year^?1 (mSv yr^?1) with a G.M./S.D. value of 1.03 mSv yr^?1/0.24. Good positive correlation is observed between the effective radium content and area exhalation rate for sand samples. Therefore, the obtained result shows that this region is safe as for as the health risk effects of radium and radon exhalation rate are concerned.     

氡室建标中几个技术问题的解决办法

标准氡室在氡浓度量值溯源和传递中起着重要作用。为了保证测氡仪量值统一、准确可靠,建立了测氡仪检定装置。针对在建立标准过程中出现的流气式氡源泄漏、氡室实验累积氡浓度值与理论值不一致和液体镭源结晶等问题,重点研究多重密封、改造洗气管路、优化洗气模式及多重过滤等技术方法,并建立氡室累积氡浓度经验曲线和质量管理措施等。按照新建立的实验方法和实验流程,氡室实验调节氡浓度和理论累积氡浓度相对偏差在±3.8%以内,液体镭源长期稳定性在0.7%以内,符合氡室建标的计量性能要求。     

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).     

Measurement of radon diffusion length in thin membranes

Building regulations in Israel require the insulating of buildings against radon (222)Rn penetration from soil. In radon-prone areas membranes stretched between the soil and the building foundation are used, together with sealing other possible penetration routes. Designing the radon mitigation procedure requires checking that all sealing materials are practically, radon tight, having a thickness of at least three times the radon diffusion length. In this work, a very simple technique to evaluate the radon diffusion length in thin membranes, using a radon source of known activity and an activated charcoal canister as radon detector is presented. The theoretical formalism and measurement results for polyethylene membranes of different densities obtained in a recent comparison exercise are presented.     

Metakaolin as a radon retardant from concrete

Granite aggregates are known to be the radon source in concrete. Recently, metakaolin has been introduced as a partial substitution of Portland cement to produce high strength concrete. It can effectively reduce the porosity of both the matrix and the aggregate/paste transition zone, which suggests its ability to retard radon emission from concrete aggregates. In the present work, radon exhalation rates from concrete cubes substituted with metakaolin were measured using charcoal canisters and gamma spectroscopy, and were considerably lower than those from normal concrete, by about 30%. The indoor radon concentration reduction is estimated as approximately 9 Bq m(-3) calculated using a room model, causing a 30% reduction in the indoor radon concentration and the corresponding radon dose. Therefore, metakaolin is a simple material to reduce the indoor radon concentration and the radon dose.     

Validation of a geographic information system for the evaluation of the soil radon exhalation potential in South-Tyrol and Veneto, Italy

The PERS (soil radon exhalation potential) project was promoted by ANPA (Italian Environmental Protection Agency) together with the Università Cattolica del Sacro Cuore of Rome: the aim was to produce a geographic information system allowing the discovery of regions with different radon exhalation potential starting from some territorial knowledge. Some environmental measurements were carried out within this project in selected areas in South-Tyrol and Veneto. The measurement of radon in springwater and groundwater as well as in soil gas plays a decisive role for the validation of the algorithm for computing the PERS. Along with technical aspects, a possible use of the PERS method by the Regional Environmental Protection Agencies and by other agencies is discussed with the scope of identifying radon prone areas, as stated in the Italian 'Decreto Legislativo' 26 May 2000, n. 241. Moreover the forecasting power of PERS regarding indoor radon concentration is analysed.