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.      

Soil radon time series: Surveys in seismic and volcanic areas

Soil radon surveys have been performed in a long term monitoring basis with SSNTD (LR 115 type II), in order to observe possible fluctuations due to high magnitude seismic events and volcanic eruptions. Five-year radon time series are available in stations located in an intense seismic zone located along the Pacific coast of Mexico. The series analyses have been performed as a function of the local seismicity and geological characteristics. A discussion is intended to explain the lack of biunivocal relation between single radon peaks and earthquakes for the long term monitoring data using SSNTDs. Examples of short term radon anomalies obtained with continuous probes are also discussed as a function of local earthquakes and meteorological perturbations. Additionally, complementary results from recent changes in the activity pattern of an active volcano indicate that degassing process induced anomalous soil radon emanation correlated with the volcanic activity changes.     

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.     

Variation of radon flux along active fault zones in association with earthquake occurrence

Radon flux measurements were carried out at three radon stations along an active fault zone in the Langadas basin, Northern Greece by various techniques for earthquake prediction studies. Specially made devices with alpha track-etch detectors (ATDs) were installed by using LR-115, type II, non-strippable cellulose nitrate films (integrating method of measurements). Continuous monitoring of radon gas exhaling from the ground was also performed by using silicon diode detectors, Barasol and Clipperton type, in association with various probes and sensors including simultaneously registration of the meteorological parameters, such as precipitation height (rainfall events), temperature and barometric pressure. The obtained radon data were studied in parallel with the data of seismic events, such as the magnitude, M_L of earthquakes, the epicentral distance, the hypocentral distance and the energy released during the earthquake event occurred at the fault zone during the period of measurements to find out any association between the rad on flux and the meteorological and seismological parameters. Seismic events with magnitude M_L ≥ 4.0 appeared to be preceded by large precursory signals produced a well-defined “anomaly” (peak) of radon flux prior to the event. In the results, the radon peaks in the obtained spectra appeared to be sharp and narrow. The rise time of a radon peak, that is the time period from the onset of a radon peak until the time of radon flux maximum is about a week, while the after time, that is the time interval between the time of radon flux maximum and the time of a seismic event ranges from about 3 weeks or more.     

Zusammenhänge Zwischen Radonanomalien und Schwarm-Erdbeben im Oberen Vogtland

Abstract

The results of continuous radon measurements in soil air and the water of a mineral spring at Bad Brambach are presented. They are discussed in connection with meteorological, hydrological parameters, and seismic events with magnitudes <3. The atmospheric pressure (especially pressure gradient), the temperature, and the groundwater level gradient have a significant influence onto radon activity of soil air.

The gamma-activity in spring water is influenced by the water flow rate only.

The results show that the soil air (mean Rn activity 130 Bq · l^?1) and especially the water of the Radonquelle of Bad Brambach (mean Rn activity 25 kBq · l^?1) react upon micro earthquakes with small epicentral distances. Frequently there are precursor effects, that means radon maxima due to the building up of tectonic stress/strain.

About 60% of the seismic events had been attended by radon anomalies during the registration period.

The long term measurements will be continued to investigate possible influences of earthquakes with higher epicentral distances and magnitudes >5 onto the radon regime of the bad Brambach area.     

Processing of radon time series in underground environments: Implications for volcanic surveillance in the island of Tenerife,Canary Islands,Spain

The analysis of temporal and spatial variations in the flux of soil gases across the soil–air interface is a useful tool to study geo-dynamical processes associated with volcanic and/or seismic activity. However, many of these variations are induced by external variables, such as temperature, barometric pressure, rainfall and other meteorological variables. In an attempt to filter out non-endogenous variations in the emissions of gases, the optimal choice of the monitoring sites with numerical filtering techniques based on multi-variate and frequency domain analysis of the time series for gaseous emissions were combined, in the case of radon (²²²Rn). Monitoring sites are located in underground galleries in the volcanic island of Tenerife, Canary Islands, Spain. Since the effect of wind, rainfall and temperature variations are very small inside galleries, a first natural filtering process of external parameters in the emissions of gases was achieved. This new approach has been successfully tested and as a result, the background level for radon emissions at various locations has been defined, by which correlations between gaseous emissions and the volcanic and/or seismic activity could be carried out.     

Experimental and modeling studies of grain size and moisture content effects on radon emanation

Some models have already been developed to explain the effect of moisture content on the radon emanation fraction of soil. For this purpose, “microscopic” soil models, which are easy to deal with mathematically but cannot take grain size into consideration, have been designed. These previous models consist basically of two opposite grain surfaces and pores between the grains. In the present study, in order to study the effect of not only moisture content but also grain size, we present a simple modeling approach based on two “macroscopic” soil models: (1) a single-grain model and (2) a multiple-grain model. The latter model represents a configuration of spherical grains packed in a simple cubic structure. Based on these soil models and general assumptions, the radon emanation fraction was calculated as a function of grain size or moisture content by Monte Carlo simulation. The results for the multiple-grain model show that the radon emanation fraction is markedly increased with grain sizes ranging from 10 to 100 μm and reaches a constant value of 50% when moisture content is 0% and the radium is uniformly distributed on the grain surface. Moreover, a drastic increase is seen at smaller grain sizes with increasing moisture content. From these results, we concluded that the calculation of radon emanation depends greatly on the pore size between a Ra-bearing grain and a neighboring grain. The validity of the model was also evaluated by comparison to experimental data.     

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.     

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.     

Spatial and temporal variations of radon concentration in soil air

The spatial and temporal variability of the soil gas radon concentration in typical soils is studied. The results obtained will be further used to predict indoor radon levels. To this end, 50 measuring points along geologic sections with known physicogeological parameters of soils were chosen. The soil gas radon concentration was measured with SSNTDs (Type III-b) at a depth of 70 cm from June to October, 2000. The radon exposure time was 72–96 h. The average radon concentration in the soil pore air for an urban area was 11 kBqm⁻³ (1.7–24 kBqm⁻³). Small-scale spatial variations in the concentration were found to lie within a narrower range. The effect of meteorological conditions on the soil gas radon concentration was investigated by performing 8 series of measurements at 5 closely spaced points in September–October, 2000. A significant correlation was found between the soil radon concentration and atmospheric pressure (K=−0.86), ambient temperature (K=0.75), and soil temperature (K=0.75).     

Electric field perturbation caused by an increase in conductivity related to seismicity-induced atmospheric radioactivity growth

The influence of conductivity perturbation in the lower atmosphere on the DC electric field over a seismic region is investigated. This perturbation is related to the emanation of radon and other radioactive elements into the lower atmosphere as the seismic activity increases. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization sources. The altitude dependence of the ion formation rate is calculated. An ionization source changes the atmospheric conductivity because of the appearance of ions with an equilibrium number density. The perturbation of the atmospheric conductivity is calculated as a function of the altitude. Lower atmosphere conductivity changes disturb the electric current that flows in the global atmosphere-ionosphere circuit. This disturbance is caused by an external current over a seismic region. DC electric field perturbations on the Earth’s surface and in the ionosphere are estimated. Published in Russian in Khimicheskaya Fizika, 2007, Vol. 26, No. 4, pp. 39–44. The text was translated by the authors.     

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.     

Emanation power of radon and its concentration in soil and rocks

Experiments were carried out to determine emanation power and radon levels in different kinds of soil and bedrocks. Seven stations were selected in the investigated district, which covers an area of about 2300 km² in the northern and western part of Jordan. Five holes were dug in each station at different depths. Two to three passive dosimeters using plastic detectors (CR-39) were put in each hole. Two weeks later, the dosimeters were collected and chemically etched. Some soil and rock samples from the study area were collected and analyzed for radioactive nuclides using γ-ray spectroscopy. The correspondence between radon levels in the soil gas and its precursor concentrations is not clear. However, the study confirms the exponential increase in radon level with depth. In general, Al-Hisa phosphate limestone showed the highest radon concentration while Amman silicified limestone showed the lowest concentration.     

Zur Entdeckungsgeschichte des Radons

The radioactivity of the noble gas radon and its short-life daughter products as the essential part of natural radioactivity have gained in topically in the last years. For this reason the history of discovery of radon has been summed up. This history is one part of the early research about radioactivity. From the appearance of induced radioactivity the way leads to the discovery of thorium emanation by Rutherford and of radium emanation by Dorn. Finally, the article deals with the detection of radon in the air by Elster and Qeitel and of the radon in well water and springivaler by Thomson because only these results have opened the way for the therapeutical usage of radon.     

Time variations of 222Rn concentration and air exchange rates in a Hungarian cave

A long-term radon concentration monitoring was carried out in the Pál-v?lgy cave, Budapest, Hungary, for 1.5 years. Our major goal was to determine the time dependence of the radon concentration in the cave to characterise the air exchange and define the most important environmental parameters that influence the radon concentration inside the cave. The radon concentration in the cave air was measured continuously by an AlphaGuard radon monitor, and meteorological parameters outside the cave were collected simultaneously. The air's radon concentration in the cave varied between 104 and 7776?Bq?m(-3), the annual average value was 1884±85?Bq?m(-3). The summer to winter radon concentration ratio was as high as 21.8. The outside air temperature showed the strongest correlation with the radon concentration in the cave, the correlation coefficient (R) was 0.76.     

Radon survey and soil gamma doses in primary schools of Batman,Turkey

A survey was conducted to evaluate levels of indoor radon and gamma doses in 42 primary schools located in Batman, southeastern Anatolia, Turkey. Indoor radon measurements were carried out using CR-39 solid-state nuclear track detector-based radon dosimeters. The overall mean annual ²²²Rn activity in the surveyed area was found to be 49 Bq m^?3 (equivalent to an annual effective dose of 0.25 mSv). However, in one of the districts (Besiri) the maximum radon value turned out to be 307 Bq m^?3. The estimated annual effective doses are less than the recommended action level (3–10 mSv). It is found that the radon concentration decreases with increasing floor number. The concentrations of natural and artificial radioisotopes were determined using gamma-ray spectroscopy for soil samples collected in close vicinity of the studied schools. The mean gamma activity concentrations in the soil samples were 31, 25, 329 and 12 Bq kg^?1 for ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs, respectively. The radiological parameters such as the absorbed dose rate in air and the annual effective dose equivalent were calculated. These radiological parameters were evaluated and compared with the internationally recommended values.     

A new method for studying the transport of radon and thoron in various building materials using CR-39 and LR-115 solid state nuclear track detectors

Radon (²²²Rn) and thoron (²²⁰Rn) α-activities per unit volume were measured inside and outside different building materials by using two types of solid state nuclear track detectors (SSNTD) (CR-39 and LR-115 type II). In addition, the radon and thoron emanation coefficients of the studied materials were evaluated. Based on these data, the transport of radon and thoron across parallelepipedic blocks of the building materials could be investigated and radon and thoron global α-activities per unit volume outside different building material blocks were determined. Moreover, the diffusion length and the effective diffusion coefficient of radon in the building materials were evaluated and the total alpha activity due to radon in the atmospheres of different rooms consisting of different building materials was studied.     

Measurement of radon emanation in construction materials

Due to the new proposed Israeli approach for radioactivity in construction materials (IS 5098) issued in 2007, the radon emanation of a construction material, a brick in the form of a box (a rectangular parallelepiped), should be checked when its four faces are insulated in order to achieve the same simulation effect when a concrete block is embedded into a wall. A physical model was developed in order to measure the insulation level (quality) of a building product (bulk concrete, building block, tiles, etc.) when its four sides are insulated by various materials. Under the experimental conditions it was found that the insulation level for bulk concrete was 99.5 ± 0.04% which is in good agreement with the requirement of the new Israeli Standard IS 5098. The influence of aging of concrete materials on radon emanation and the emanation ratio, deduced from measurements of insulated and non-insulated materials, was investigated.     

Radon anomalies along faults in North of Jordan

Radon emanation was sampled in five locations in a limestone quarry area using SSNTDs CR-39. Radon levels in the soil air at four different well-known traceable fault planes were measured along a traverse line perpendicular to each of these faults. Radon levels at the fault were higher by a factor of 3–10 than away from the faults. However, some sites have broader shoulders than the others. The method was applied along a fifth inferred fault zone. The results show anomalous radon level in the sampled station near the fault zone, which gave a radon value higher by three times than background. This study draws its importance from the fact that in Jordan many cities and villages have been established over an intensive faulted land. Also, our study has considerable implications for the future radon mapping. Moreover, radon gas is proved to be a good tool for fault zones detection.     

Soil gas radon as an earthquake precursor: some considerations on data improvement

A data processing technique based on impulse responses from multivariable time series was applied to radon data. It was found that soil gas radon at 50 cm depth was affected more by meteorological parameters than at 100 cm depth. This fact together with the fact that the radon change at the latter depth was larger when an earthquake occurred, radon measurement at 100 cm depth was tested as an earthquake precursor. The result showed correlation between radon anomalies and earthquake events.