Radon emanation from soil samples

The soil or bedrock beneath a building is one of the sources of radon gas in the indoor air. The ²³⁸U content of samples of the soil or the bedrock can be measured by gamma ray spectrometry and is of interest because the uranium content in the soil is a precursor of the presence of the radon gas in the soil. The emanation of radon gas from different types of material can be estimated to some extent if the content of ²³⁸U of a sample is known and the ²²⁶Ra content is only minorly affected. The true emanation is, however, affected by various parameters. One of these parameters is the possibility or not for the gas to come out from the grains into the air in the space between the grains of the sample.

In this study we report the results from measurements of radon gas emanating from samples of soil frequent in the Lund region in Sweden and in the Barcelona region in Spain. As soils have different grain size it is important to know the type of soil. The ²³⁸U content of the soil is measured with gamma ray spectrometry. The radon measurements are made by Kodak plastic film in closed cans, filled with the soil according to a technique, developed for radon measurements in water samples.

The result shows, that the combination of grain size and uranium content is important for the emanation of the radon gas from the grains of the soil.     

Radon exhalation studies in an Indian uranium tailings pile

A study was taken up to quantify the source term arising due to radon exhalation from Uranium(U) tailings pile at Singbhum shear zone in Jharkhand state of India. In-situ experiments were conducted at 40 locations of the U tailings pile in three seasons namely summer, rainy and winter to measure the radon fluxes. The fluxes were also predicted by a diffusion model using the measured parameters such as Ra-226 content, bulk density, diffusion coefficient, radon emanation factor, moisture content and temperature in the U tailings. It was observed that the predicted fluxes using the in-situ diffusion length and emanation factor were closer to measured values by accumulator technique than that predicted using empirically estimated diffusion coefficient and emanation factor. A conversion factor has been established between radon fluxes and Ra-226 content in U tailings for Jaduguda. The source term arising due to the radon exhalation from U tailings pile at Jaduguda has determined using the measured data of radon fluxes.     

The dust emission law in the wind erosion process on soil surface

The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment. The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the grain size composition in the soil surface. Supported by the National Natural Science Foundation of China (Grant No. 50706031) and the Natural Science Foundation of Shanxi Province of China (Grant No. 2008021005)     

Observation and removal of daily quasi-periodic components in soil radon data

We report (quasi) periodic oscillations observed in soil radon emanation data especially during summer period. Soil radon has been continuously monitored in the Marmara region of Turkey over the past nine years to reveal possible relationships between soil radon and seismic activities. This long term monitoring has clearly demonstrated that soil radon concentrations are affected by various parameters such as seasonal and daily changes in atmospheric parameters (temperature, pressure, precipitation). Sometimes, soil temperature variations as well as barometric pressure and precipitation may dominantly influence the soil radon concentration; leading to seemingly complex radon time series. One may need to remove such components for better analysis of the possible relationships between soil radon emanation and seismic activities. Here, we suggest using an algorithm to detect and remove daily-oscillations from the raw data. The detection and separation (extraction) algorithm is based on Empirical Mode Decomposition method which is a signal-adaptive method that automatically decompose the signal into its characteristic modes. The algorithm is applied to the data collected from three different soil radon monitoring stations (Bal?kesir, Gönen, and Armutlu) in Marmara region of Turkey and the results are provided.     

The influence of fractal size distribution of covers on radon exhalation from uranium mill tailings

Tailings produced during mining and milling of uranium ores represent potentially large volumes of low level radioactive materials. A typical environmental problem associated with mill tailings is radon emanation. Covering tailings is widely applied to reduce radon exhalation rate. In this paper, the fractal theories and field covering tests are used to study the fractal characters of size distribution of six types of covering materials, including waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite, and their influences on radon exhalation. The size distributions of uranium tailings and the six aforementioned covering materials all exhibit a good fractal structure. The contents of fine grain increase with the increasing value of fractal dimension. The results of field radon measurement show that the radon emanation rate of tailings without covers is 14.7–18.6 Bq/m² s. Covering tests were carried out of the six abovementioned covering materials with thickness of 0.4 m, 0.8 m, 1.2 m, 1.6 m and 2.0 m. The results indicate that the application of these materials for cover layers can decrease the radon exhalation rate markedly. The effectiveness of a cover layer in reducing radon exhalation is related to its fractal texture of size distribution. Under the same thickness conditions, the attenuation coefficient of radon exhalation rate increases with the increasing fractal dimension of size distribution of covers. The empirical expressions of the attenuation coefficients in relation to fractal dimension D of size distribution and thickness x of covers is obtained for evaluating the effectiveness of final covers for uranium tailings impoundments.     

An experimental method for measuring the radon-222 emanation factor in rocks

An experimental method, based on a 21-day accumulation technique, is proposed for measuring the radon-222 emanation factor in undisturbed consolidated materials. The leakage rate is determined from the form of the radon growth curve in the measurement chamber. It was comparable to the radon decay. In order to obtain the “true” radon emanation factor, the thickness of the sample must be less than the radon diffusion length in the porous material. The method was used to measure the radon emanation factor in water-saturated claystones (argillites). The radon emanation factor, determined from experiments on a rock sample with a thickness of 5 mm, was 15%, a value typical for this kind of material.     

Dependence of grain boundary character distribution on the initial grain size of 304 austenitic stainless steel

Abstract

In order to study the dependence of the grain boundary character distributions (GBCD) on the grain size, annealing treatment was carried out on 304 austenitic stainless steel with different initial grain sizes. The evolution of the GBCD was analysed by electron backscatter diffraction. The experimental results showed that abnormal grain growth (AGG) occurred when grain size was small. With a smaller initial grain size, the number density of abnormally large grains and the fraction of low-Σ CSL boundaries increased but the size of abnormally large grains decreased and the random boundaries presented a continuous network. With a larger initial grain size, the fraction of low-Σ CSL boundaries also increased as well as the size of abnormally large grains but the number density of abnormally large grains decreased and the connectivity of random boundary network was disrupted by low-Σ CSL boundaries, especially Σ3ⁿ (n = 1, 2, 3) boundaries. However, with a very large initial grain size, normal grain growth (NGG) occurred, which had no effect on the fraction of low-Σ CSL boundaries and the connectivity of random boundary network.     

Emanations and “induced” radioactivity: From mystery to (mis)use

Radon, Rn; atomic number Z=85; is a (gaseous) chemical element of which no stable but only radioactive isotopes exist. Three of them, namely actinon (²¹⁹Rn), thoron (²²⁰Rn) and radon (²²²Rn) are the decay products of naturally occurring radioisotopes of radium:²²³Ra,²²⁴Ra and²²⁶Ra, respectively. The natural Rn isotopes were discovered within the period 1899–1902 and at that time referred to as emanations because they came out (emanated) of sources/materials containing actinium, thorium and radium, respectively. The (somewhat mysterious) emanations appeared to disintegrate into radioactive decay products which by depositing at solid surfaces gave rise to “induced” radioactivity i.e. radioactive substances with various half-lives. Following the discovery of the emanations the volume of the research involving them and their disintegration products grew steeply. The identity of a number of these radioactive products was soon established. Radium- emanation was soon used as a source of RaD (²¹⁰Pb) to be applied as an “indicator” (radiotracer) for lead in a study on the solubility of lead sulphide and lead chromate. Moreover, radium and its emanation were introduced into the medical practice. Inhaling radon and drinking radon-containing water became an accepted medicinal use (or misuse?) of that gas. Shortly after the turn of the century, the healing (?) action of natural springs (spas) was attributed to their radium emanation i.e. radon. Bathing in radioactive spring water and drinking it became very popular. Even today, bathing in radon-containing water is still a common medical treatment in Jáchymov, Czech Republic.     

Seasonal variation on radon emission from soil and water

Radon is being measured continuously in spring water and soil-gas at Badshahi Thaul Campus, Tehri Garhwal in Himalayan region by using radon Emanometer since December 2002. An effort was made to correlate the variance of radon concentrations in spring water and soil-gas with meteorological parameters at the same location. The main meteorological parameters that affect the radon emanation from host material is surrounding temperature, barometric pressure, wind velocity, rain fall and water level of the spring. The correlation coefficient between radon concentration in spring water and different atmospheric parameters was computed. The correlation coefficient between radon concentration in spring water and the maximum atmospheric temperature was 0.3, while it was 0.4 for minimum atmospheric temperature at the monitoring site. The correlation coefficient for radon concentration in spring water with minimum and maximum relative humidity was 0.4. Spring water radon concentration was found positively correlated (0.6) with water discharge rate of the spring. A weak correlation (0.09) was observed between the radon concentration in spring water and rain fall during the measurement period. As temperature of near surface soil increases, the radon emanation coefficient from the soil surface also increases. The possible effects due to global warming and other climatic changes on environment radiation level were also discussed in detail.      

Exposure to radon in the radon spa Niška Banja,Serbia

There is a well-known radon spa Ni?ka Banja in south-east of Serbia. In Ni?ka Banja spa there is a medical complex and radon is used for therapeutic purposes for many different diseases. This paper presents elevated radon levels in the Ni?ka Banja spa. Indoor radon and radon in water activity concentration measurements in thermal pools and therapy rooms are presented. There are also results from gamma spectrometry measurements of soil, rock and therapy mud. A special attention is paid to the medical staff exposure to radon around thermal pools. The annual effective doses from radon for staff working around the thermal pools in Ni?ka Banja spa are very high comparing to the maximum recommendation level. The maximal radon concentration of (22.90 ± 0.57) kBq m^?3 was measured in the basement of the hotel-dispensary “Radon”. This hotel is settled on “bigar” rock – travertine, which has high content of ²²⁶Ra.     

A simple model for automatically measuring radon exhalation rate from medium surface

A simple model to measure radon exhalation rate from medium surface is developed in this paper. This model is based on a combination of the “accumulation chamber” technique and a radon monitor. The radon monitor is used to perform measurement of radon concentration evolution inside the accumulation chamber, and radon exhalation rate is evaluated via nonlinear least-square fitting of the measured data. If the flow rate of the pump is high enough, radon concentration in the detector's internal cell becomes to be equal to that in the accumulation chamber quickly, and the simple model for measuring the radon exhalation rate can be generated analytically. Generally, the pump flow rate of radon monitor is low, not satisfying the condition. We find other sufficient conditions of this simplified model. On these conditions, the radon exhalation rate can be calculated accurately through this model even the flow rate of the pump is not so high. This method can be applied to develop and improve the instruments for measuring the radon exhalation rate.     

土壤的光谱特征及氮含量的预测研究

应用近红外光谱分析技术(NIR)测定土壤参数具有快速、方便的特点.文章分析了不同含水率、不同颗粒大小的土壤样本在不同测试角、不同测试高度对土壤光谱的影响,并得到了不同含水率和不同粒径土壤的含氮量预测模型.研究了这些因素对含氮率测量的影响,分析了NIR技术在田间实地应用预测的可能性.研究表明,光谱仪在距土壤高度为100 mm,测试角为45°时,具有最大的吸光度.土壤粒径和含水率这2个参数明显影响,当粒径在0.5～5 mm变化时,含氮量预测相关系数r为0.81左右,当土壤粒径在＜0.25和＞5 mm模型的预测能力变差.当土壤样品呈天然潮湿状态时,氮的预测结果较差.而样品干燥以后,预测相关系数较高.为土壤原位光谱测试提供了依据.     

An approach to discriminatively determine thoron and radon emanation rates for a granular material with a scintillation cell

A powder sandwich technique was applied to determine thoron (²²⁰Rn) and radon (²²²Rn) emanation rates for a granular material. The feature of this technique is the sample preparation, in which a granular material is put and fixed between two membrane filters. Airflow is directly given to this sandwich sample, will include thoron and radon emanated from the material, and then is transferred to the detector. This method makes sure that thoron and radon emanated are not retained in pore space within the sample volume, which is crucial for the appropriate emanation test. This technique was first introduced by Kanse et al. (2013) with the intention to measure the emanation of thoron - but not of radon - from materials having much higher ²²⁴Ra activity than ²²⁶Ra. In the present study, the methodology for the discriminative determination of thoron and radon emanation rates from a granular material has been examined using a flow-through scintillation cell and sandwich sample. The mathematical model was developed to differentiate total alpha counts into thoron- and radon-associated counts. With a sample of uranium ore, this model was experimentally validated by comparison between the scintillation cell and a reference detector that can discriminatively measure thoron and radon concentrations. Furthermore, the detection limits and uncertainties were evaluated to discuss the characteristics of this method. Key parameters for improving the determination of thoron and radon emanations were found to be the background radon concentration and the leakage of radon from the measurement system, respectively. It was concluded that the present method is advantageous to a sample that has much higher ²²⁶Ra activity than ²²⁴Ra.     

Dislocation and diffusion deformation mechanisms in ultrafine grained materials and free volume role

The effect of average grain size on the mechanisms of polycrystal deformation are considered in the range of grain sizes from 1nm to 1cm. Critical grain sizes are selected. The activity of dislocation and diffusion mechanisms is analyzed. The deformation distribution in grains of different sizes is considered for a polycrystal as a whole within the grain size distribution.     

Calculation of radon diffusion coefficient and diffusion length for different building construction materials

The diffusion of radon in dwellings is a process determined by the radon concentration gradient across the building material structure between the radon source and the surrounding air, and can be a significant contributor to indoor radon inflow. Radon can originate from the deeply buried deposit beneath homes and can migrate to the surface of earth. Radon emanates to the surfaces mainly by diffusion processes from the point of origin following α-decay of ²²⁶Ra in underground soil and building materials used, in the construction of floors, walls, and ceilings. In the present study radon diffusion through some building materials viz. coarse sand and stone dust of different grain size has been carried out using LR-115 type II solid-state nuclear track detectors (SSNTDs). The radon diffusion coefficients and diffusion lengths through these building construction materials have been calculated. The effect of grain size on radon diffusion through these building materials shows the decrease in radon diffusion with decrease in grain size.     

NdFeB纳米复合永磁材料的交换耦合相互作用和有效各向异性

以Nd₂Fe₁₄B/αFe为例，采用立方体晶粒结构模型，研究了纳米复合永磁材料中不同磁性晶粒间的交换耦合相互作用和有效各向异性.纳米复合永磁材料的有效各向异性Keff等于软、硬磁性相各向异性的统计平均值，每个晶粒的各向异性由晶粒表面交换耦合部分和晶粒内部未交换耦合部分的各向异性共同确定.计算结果表明，软、硬磁性相晶粒尺寸分布显著地影响有效各向异性Keff的值.当软、硬磁性晶粒尺寸D相同时，Keff随晶粒尺寸和硬磁性相体积分数的降低而减小, 当D<20nm 时，K 关键词： 纳米复合永磁材料 交换耦合相互作用 有效各向异性 晶粒尺寸     

颗粒介质尺度效应的抗剪试验及物理机理分析

针对颗粒介质力学特性的颗粒尺度效应研究,选用土矿物颗粒制备不同颗粒尺度的抗剪试样,进行一系列直剪快剪和三轴抗剪试验,测得了不同颗粒粒径和体分比试样的变形曲线及剪应力强度;基于颗粒间微观作用力与重力比值和胞元体模型,首次从微观和细观角度解释颗粒尺度效应的物理机理.结果表明,随着介质中粗颗粒的比例增加和粒径减小,介质变形特性增强,剪应力强度也随之提高;体分比对变形和强度特性的影响比粒径的影响更加显著.基于介质特性尺度效应物理机理分析,提出衡量介质颗粒聚集和摩擦效应的微重比判别参数以及应变梯度和变形协调微裂纹引起颗粒尺度效应的细观机理解释;文中提出的胞元体模型大大减少了颗粒物质体系的计算自由度,为工业和工程设计的计算建模提供一种可行途径.     

Measurements of soil radon in South Russia for seismological application: Some results

Results of soil radon concentration measurements at the surface in Northern Caucasus (Krasnodar territory) in different geological features are shown. Measurements were made in mud volcanoes, faults, mineral deposits and landslips. The data were compared to seismicity. Before earthquakes, the changes in the concentration of radon appear as “humps” or “splashes” of various durations. Monthly, daily and hourly changes of the concentration of soil radon during the earthquakes are shown for each zone of researches. The simultaneous measurement of radon in the big area has shown the movement of the increased concentration of radon to the epicenter several days prior to the earthquake.     

Effects of some physical conditions on leaching rate of radon from radioactive minerals originating from some hot springs

In order to determine the best physical conditions for leaching more radon from minerals into water, we measured the leaching rate of radon from radioactive minerals under the conditions of some different grain sizes and water temperatures. Water temperature affected the leaching rate of radon although the grain size did not significantly affect it. Furthermore, we proposed ultrasonic irradiation to the mixture of a mineral and water as the method of leaching more radon. Ultrasonic irradiation was efficient to leach more radon from the mineral soaked in water because of ultrasonic cavitation.