Differences of natural radioactivity and radon emanation fraction among constituent minerals of rock or soil

We examined differences in the radioactive characteristics among the main minerals forming granite materials. Using a non-toxic high-density agent, minerals were separated from rock (granite–gneiss) and soil (weathered granite) samples. The natural radioactivity (²³⁸U and ²²⁶Ra) and radon emanation fraction of the minerals were then studied by gamma-ray spectrometry. The radon emanation fractions (27–43%) of the minerals from the soil were much higher than those (0.6–4.6%) of the rock minerals. Additionally, the emanation fractions differed greatly among the minerals separated from both the bulk rock and soil. These results were discussed in terms of the differences of surface area and radium distribution in the mineral grains. It was noticeable that a higher emanation fraction than expected for quartz was commonly observed in the rock and soil samples. We then estimated the contribution of each constituent mineral to the total radon exhalation from the bulk samples. The result depended not only on the radon emanation fraction, but also on the ²²⁶Ra activity and the mineral content. Furthermore, using the obtained data, we also discussed the effect of grain size on radon emanation and why this has been reported to vary markedly in previous studies.     

Application of the can technique and radon gas analyzer for radon exhalation measurements

A passive “can technique” and an active radon gas analyzer with an emanation container were applied for radon exhalation rate measurements from different construction materials, viz. five marble seven ceramic and 100 granite tiles used in Saudi Arabia. The marble and ceramic tiles did not show detectable radon exhalation using the active radon gas analyzer system. However the granite tiles showed relatively high radon exhalations, indicating a relatively high uranium content. A comparison of the radon exhalation rates measured by the two techniques showed a linear correlation coefficient of 0.57. The radon exhalation rates from the granites varied from 0.02 to 6.58 Bq m⁻² h⁻¹ with an average of 1.35±1.40 Bq m⁻² h⁻¹. The geometric mean and the geometric standard deviation of the frequency distribution were found to be 0.80 and 3.1, respectively. The track density found on the nuclear track detectors in the can technique exposed to the granites, having high exhalation rates, varied linearly with exposure time with a linear correlation coefficient of 0.99. This experimental finding agrees with the theoretical prediction. The can technique showed sensitivity to low radon exhalation rates from ceramic, marble and some granite over a period of 2 months, which were not detectable by the active radon gas analyzer system. The reproducibility of data with both measuring techniques was found to be within a 7% deviation.     

A study of radon and thoron release from Egyptian building materials using polymeric nuclear track detectors.

The free exhalation rates of both thoron and radon, the specific activities of 224Ra, and 226Ra, and the physical properties, such as the emanation coefficients and radon effective diffusion coefficient of several building material samples were determined using LR-115 and CR-39 polymeric nuclear track detectors. The free areal exhalation rate was measured by the sealed cup-technique, whereas the radium content was obtained by the alpha-autoradiographic method. The calibration coefficient for thoron measurements in air using cylindrical cup equipped with LR-115 detector was estimated. Moreover, the calibration coefficients for measurements of the specific activities of 224Ra and 226Ra were also evaluated. New method was developed for evaluating the emanation coefficient as well as the diffusion coefficient of radon isotopes in the studied materials.     

Distribution of radionuclides in the river sediments and coastal soils of Chittagong, Bangladesh and evaluation of the radiation hazard

The concentrations and distribution of natural and anthropogenic radioactive materials in sediments and soils from around the two major rivers and coastal area of Chittagong, Bangladesh were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. In the sediment and soils in general, the concentration of ²³²Th was found to be higher than that of the ²³⁸U and the activities of ²³²Th and ²³⁸U in this area are higher than the world average. ¹³⁷Cs was observed in all the samples, ranging from 0.4 to 3.88 Bq kg⁻¹. The radium equivalent activities, emanation coefficients and radon exhalation rates were estimated for the sediment and soils; the emanation coefficients, radon exhalation rates and dose rates were found to be higher than the world average values.     

Determination of 222Rn emanation fraction and diffusion coefficient in concrete using accumulation chambers and the influence of humidity and radium distribution.

In this paper we present a laboratory method for the determination of diffusion coefficient, D, as well as the 222Rn emanation fraction, f, in concrete core samples. It is based either on the analyses of the growth curves of the radon in the air volume surrounding a sample enclosed in an accumulation chamber (Lucas cell or RADIM device) or using the charcoal adsorption method. Samples used have a special geometry allowing the assumption of a one-dimensional diffusion of radon in material. Radium was enhanced in the concrete samples by adding radium bromide solution or uranium ore. A strong dependence of the emanation fraction on the enhancing method was observed. For the sample enhanced with uranium ore the specific exhalation rate was about ten times smaller. A marked dependence of radon exhalation on the water content was also observed.     

土壤氡析出率影响因素及估算模型

目的通过对某定点处土壤氡析出率的长期测量观察,分析并总结环境因素对氡析出率的影响规律。方法使用ERS-2静电收集式氡采样测量仪,每次采样累积时间40min,每10分钟测量一次氡浓度,通过线性拟和求算出土壤表面氡析出率;利用已有的数学模型对测量结果进行估算和评价;同时测量环境空气的湿度、温度、土壤含水量和土壤氡浓度。结果春季土壤氡析出率平均值为(24·9±5·6)mBq/(m2·s),夏季平均值为(11·9±3·4)mBq/(m2·s)。结论在影响土壤氡析出率的诸因素中,湿度非常重要,而环境温度对氡析出率的影响相对较小;测量期间环境气压变化不明显,没有观测到气压对析出率的影响。开展土壤射气系数的研究,将有助于阐明多种环境因素对土壤表面氡析出率的影响。     

我国部分地区土壤氡析出率的理论模型

目的 本研究旨在通过理论研究和实验验证初步建立我国部分地区土壤氡析出率的理论模型。方法 通过对氡在土壤中扩散理论的分析，建立土壤氡析出率数学模型，该模型考虑了土壤的镭含量、射气系数、孔隙度和含水饱和度等因素对氡析出率的影响。为验证此模型，我们在北京、贵阳和内蒙古3个不同土壤类型的地区，共30处进行了氡析出率及土壤相关物理性质的实际测量。结果 有近1／3的样品理论值与实测值吻合比较好。结论 实测结果初步显示出模型的有效性。笔者对误差分布规律及产生原因进行了分析，提出了今后土壤氡析出率模型的改进方向。     

A short-time method to measure the radon potential of porous materials

The radiological risk associated with the use of solid materials has been traditionally established according to their radon exhalation rates, the accumulation chamber technique being the most widely used for the determination of this quantity. However, this coupled methodology has two important drawbacks: the calculated exhalation rate value depends strongly on the experimental setup used; hence widely varying values can be calculated for the same material. Furthermore, this technique usually requires long monitoring times (between 1 and 4 weeks).In this paper, we present a fast and reproducible method for the determination of radon potential (as an alternative to the exhalation rate) based on the application of the accumulation chamber technique. Radon potential is proportional to the emanation coefficient, and can be calculated within measuring times of less than 24 h. The theoretical basis is developed and the experimental setup is discussed in detail in this paper.The procedures for the determination of different experimental parameters (leakage constant, slope correction) are shown as essential steps for the later determination of the radon potential. In addition, the robustness of the developed methodology is demonstrated, and the reproducibility tests carried out with the general system performance are shown. Finally, the radon potential for different materials is determined, allowing its prompt categorization according to its associated radiological risk.     

Measurement of radioactivity and radon exhalation rate in different kinds of marbles and granites

Geological materials usually contaminated with naturally occurring radioactive materials (NORM) have become a focus of great attention. These NORM under certain conditions can reach hazardous contamination levels. Some contamination levels may be sufficiently severe that precautions must be taken.

The present study deals with 60 geological samples (marble and granite) from both Egyptian and foreign locations. The studied samples were analyzed and the concentrations in Bq/kg dry weight of radioisotopes were determined by gamma-ray spectrometry using hyper-pure germanium (HPGe) detector in Bq/kg dry weight. The absorbed dose rate due to the natural radioactivity in the samples under investigation ranged from 2.45±0.07 to 64.44±1.93 nGy/h for marble and from 41.55±1.25 to 111.94±3.36 nGy/h for granite. The radium equivalent activity varied from 5.46±0.16 to 150.52±4.52 Bq/kg for marble samples and from 229.52±6.89 to 92.16±2.76 Bq/kg for granite. The representative external hazard index values for the corresponding samples are also estimated and given.

The radon exhalation rates for marble and granite samples were also calculated by using solid state nuclear track detector (CR-39). The value of radium exhalation rate varied from 8.0±2.39 to 30.20±5.06 Bq/m²/d for marble and 6.89±1.72 to 25.79±4.38 Bq/m²/d for granite and the effective radium content was found to vary from 1.700±0.51 to 6.42±1.08 Bq/kg for marble and 1.29±0.32 to 5.63±0.96 Bq/kg for granite. The values of the radon exhalation rate and effective radium content are found to correspond with the values of uranium concentration measured by the HPGe detector in the corresponding sample.     

土壤物理性质对土壤氡浓度及地表氡析出率的影响

目的探讨土壤性质对土壤氡浓度及地表氡析出率的影响。方法在北京、贵阳、呼和浩特的31个测量点进行土壤氡浓度及析出率的现场实测。采集土壤样品，在实验室进行土壤镭含量、含水量、孔隙度和粒径分布等物理性质测量。用线性拟合方法分析了实测土壤氡、析出率数据之间的相关性，以及它们与土壤镭含量的关系。结果地表氡析出率与土壤氡浓度和土壤镭含量有正相关关系；土壤含水饱和度过高或过低均会使析出率和土壤氡浓度降低；贵阳地区土壤镭含量较高，但其粉砂黏土壤的特性使土壤氡浓度很难准确采样，导致结果偏低。结论地表氡析出率和土壤氡浓度虽然与土壤镭含量有正相关关系，但在实际环境中易受含水量等多因素影响，而且土壤氡浓度的准确测量受土壤特性限制较大。     

First model of the effect of grain size on radon emanation

The present model represents an improvement on previous models of radon emanation from soil by incorporating soil grain size in addition to moisture. Monte Carlo simulation was employed in the calculation since it was difficult to mathematically express the radon emanation fraction for the present soil model. Grain size is one of the most important factors in describing the properties of soil. Grain size was demonstrated to affect the radon emanation fraction, depending on moisture content. Although the emanation fraction is generally considered to be proportional to grain size, the result of the model calculation suggested that the effect of grain size is not so simple. This study should serve as an initial step toward improving the modeling of this radon emanation.     

Quantification of the dependency of radon emanation power on soil temperature

A study on the quantification of the dependency of the radon emanation power on soil temperature has been made using the accumulation method. The emanation from dry soil was studied at temperatures between −20°C and 45°C. A formula to calculate the radon emanation power as a function of the temperatures has been developed. The formula would contribute to the modeling of radon transport in soils and building materials.     

Radon exhalation rate and uranium estimation in rock samples from Bihar uranium and copper mines using the SSNTD technique.

Widespread uranium mineralization is associated with copper, nickel and other sulphides in the Singhbhum shear zone developed at the northern margin of the Singhbhum craton in the state of Bihar of India. The south-eastern part of the shear zone between Surda-Mosabani-Badia is rich in copper mineralization while the central part between Jaduguda-Bhatin-Nimdih and Narwapahar-Garadih-Turamdih is enriched in uranium. In the present study, trace uranium concentration in geological samples from the Mosabani copper mine and the Narwapahar and Jaduguda uranium mine areas have been determined using fission track registration technique. For the measurement of the radon exhalation rate, the 'can technique' using alpha sensitive LR-115 type II plastic track detectors were used. Uranium concentrations were found to vary from 1.5 to 2097.9 ppm whereas the radon exhalation rate varied from 0.2 to 19.2 Bq m-2 h-1. The values of radon exhalation rate from crushed rock and soil samples are found to correspond with the measured values of uranium in the corresponding samples. A positive correlation has been found between radon exhalation rate and uranium concentration in the samples. The linear coefficients are found to be 0.40, 0.98 and 0.95 in the Mosabani, Narwapahar and Jaduguda mine areas respectively. High values of radon exhalation in subsurface mines like Jaduguda (depth approximately 800 m) and Mosabani (depth > 1000 m) seem to emphasize the need for adequate ventilation for the removal of radon and its progenies from the mines.     

Measurement of radon emanation factor from granular samples: effects of additives in cement.

Two methods for radon emanation factor determination were performed and compared regarding their measuring accuracy: (a) by hermetically closing the sample in an airtight container and measuring the induced radon activity, and (b) by mixing charcoal and sealing the sample hermetically and after placing the sample in an open vessel with no charcoal addition, measuring each time the 226Ra content using gamma-spectrometry. Measurements of radon emanation factor of cement and pozzolanic additives, i.e. fly ash and phosphogypsum were also performed.     

Natural radioactivity and radon exhalation rate of soil in southern Egypt

The level of natural radioactivity in soil of 30 mining samples collected from six locations in southern Egypt was measured. Concentrations of radionuclides in samples were determined by γ-ray spectrometer using HPGe detector with a specially designed shield. The obtained results of uranium and thorium series as well as potassium (K-40) are discussed. The present data were compared with data obtained from different areas in Egypt.

Also, a solid state nuclear track detector SSNTD (Cr-39) was used to measure the radon concentration as well as exhalation rate for these samples. The radon concentrations were found to vary from 1.54 to 5.37 Bq/kg. The exhalation rates were found to vary from 338.81 to 1426.47 Bq/m²d. The values of the radon exhalation rate are found to correspond with the uranium concentration values measured by the germanium detector in the corresponding soil samples.     

Estimating the radon emanation coefficient from crystalline rocks into groundwater.

A simple method is proposed to estimate the coefficient of radon emanation from crystalline rocks into underground waters. In these cases, the crystalline rock seems as both the source and the reservoir of the radon. The calculations are based on a formula proposed by Maché for determining the concentration of radon in underground waters. Due to the inaccuracy of estimating some parameters (e.g. porosity), the results have a significant error. The advantage of this method is its simplicity and the possibility of obtaining results in a relatively short time. The estimated values of the emanation coefficient for selected crystalline rocks of the Sudety Mountains (SW Poland) vary from 7 to 41%, and after considering the error resulting from the estimation of rock porosity, saturation and density, the values range from 5 to 60%. The highest values of emanation coefficient (41, 33 and 21%) have been obtained for rocks in areas of tectonic dislocations and the lowest ones are for rocks outside dislocation zones (9 and 7%). The calculations imply that the emanation coefficient of rocks may have a greater influence on radon concentration in underground waters than the contents of radium in the reservoir rocks.     

An investigation of radon exhalation rate and estimation of radiation doses in coal and fly ash samples.

Coal is a technologically important material used for power generation. Its cinder (fly ash) is used in the manufacturing of bricks, sheets, cement, land filling etc. Coal and its by-products often contain significant amounts of radionuclides, including uranium which is the ultimate source of the radioactive gas radon. Burning of coal and the subsequent atmospheric emission cause the redistribution of toxic radioactive trace elements in the environment. In the present study, radon exhalation rates in coal and fly ash samples from the thermal power plants at Kolaghat (W.B.) and Kasimpur (U.P.) have been measured using sealed Can technique having LR-115 type II detectors. The activity concentrations of 238U, 232Th, and 40K in the samples of Kolaghat power station are also measured. It is observed that the radon exhalation rate from fly ash samples from Kolaghat is higher than from coal samples and activity concentration of radionuclides in fly ash is enhanced after the combustion of coal. Fly ash samples from Kasimpur show no appreciable change in radon exhalation. Radiation doses from the fly ash samples have been estimated from radon exhalation rate and radionuclide concentrations.     

Diffusion of radon through varying depths of cement.

Portland cement was mixed with different concentrations of radium chloride (1200, 2400 and 3600 Bq) to produce radioactive sources. These sources were surrounded with cement of different thickness (1, 2 and 4cm). The release of radon from these sources (before and after being surrounded) was studied. The results showed that radon release from the sources itself was less then its release from the same source after being surrounded by cement, and the release did not change with the thickness of cement. Samples were covered with a thin layer of polyethylene before being surrounded with cement. It was found that this additional layer reduced the radon exhalation. This thin layer stopped any reaction between the source and the surrounding cement during solidification of the cement layers. These reactions are thought to be the reason for the increase of radon exhalation from the sources surrounded by cement.     

The radon emanation power of building materials, soils and rocks

The ²²²Rn emanation power of building materials, soil and rock samples is determined by collecting exhalated radon on activated charcoal. Median values are 0.2 for dry soils and stones, 0.06 for sand, 0.025 for bricks, 0.006 for ceramic tiles, 0.008 for mineral slag and 0.3 for gypsum. The emanation power of soil rises with water content, in accordance with literature. For water content above 10% the emanation power of soil is about twice as high as for dry soil.     

Radon exhalation and radiometric prospecting on rocks associated with Cu–U mineralizations in the Singhbhum shear zone, Bihar

The Singhbhum thrust belt is a 200 km long arcuate orogenic belt in Bihar, eastern India. The huge mineral resources, viz. copper, uranium, magnetite, apatite and molybdenite, etc., make it significant from an economic as well as a geological point of view. The belt hosts three types of mineralization: sulphides of copper and other metals, uranium oxides and apatite-magnetite. Several distinct geological episodes are responsible for the evolution of mineralization and the thrust zone itself. Extensive and reliable radiometric prospecting and assaying have been carried out by us for the past 5 years from Dhobani in the east to Turamdih in the west of the Singhbhum shear zone. The present work indicates uranium mineralization in the Pathargora–Rakha area presently being mined for copper and also within areas in the vicinity of Bhatin. Studies on radon emanation have also been undertaken in some parts of the shear zone which indicate reasonably high radon emanation of the soils and rocks studied. This suggests the need for regular monitoring and suitable controls on the mine environment (air quality) and its vicinity. Radon emanation studies coupled with gamma-ray spectrometry and the subsequent modelling of the radiometric and radon measurements will help in the application of radon as a geophysical tracer in exploration of radioactive ore bodies and in radon risk assessment as well as in delineating active and passive faults and even in petroleum exploration.