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.     

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.     

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.     

大气降雨俘获空气中短寿命氡子体实验研究

为了研究降雨对空气中短寿命氡子体的清洗机制,设计了分别模拟大气降雨的水汽凝结过程和雨粒下降过程的两个实验装置,并进行了多次实验,实验水样采用低本底 能谱仪进行测量。实验结果表明:凝结水的短寿命放射性计数与本底相近,说明水汽凝结不能俘获短寿命氡子体。某一次自来水冲刷空气后获得了高出本底30.9% 的初始 计数,其半衰期为35.7 min,纯净水冲刷空气后获得了高出本底19.6%的初始计数,这些计数主要是由氡子体214Pb 和214Bi 引起的。可见,无论是自来水还是纯净水,它们冲刷空气后都能俘获短寿命氡子体,且半衰期和放射性核素种类均与雨水相似。这一实验结果充分说明:大气降雨的短寿命放射性不是在水汽凝结阶段而是在降落阶段对空气的冲刷获得的,是在降落过程中俘获了空气中的短寿命氡子体214Pb 和214Bi 而引起的。本次实验结果为降雨对空气中短寿命氡子体的冲刷清洗机制提供了最有力的证据。To investigate the underpinning mechanism of rainfall-scavenging of the atmospheric short-lived radon daughters, two experiments simulating water vapor condensing procedure and raindrop falling procedure were conducted. The radioactivity of the tested water was measured by low-background   γ spectrometry. The obtained results showed that the γ-ray counts of condensed water was on the same level as the background,which proved that water vapor condensation cannot trap short-lived radon daughters. In contrast, the initial γ-ray count of washout water (35.7 min half-life) was increased by 30.9% after washing the atmosphere with tap water. Similarly, the initial  -ray count of washout water was increased by 19.6% after washing the atmosphere with puri ed water. These counts originated mainly from radon daughters 214Pb and 214Bi. Obviously, both tap water and puri ed water can trap short-lived radon daughters when washing the atmosphere. Furthermore, the half-life and the kinds of radioactive nuclides in the washout water are similar to that in the rainfall water.These experimental results are able to ascertain that short-lived radon daughters in precipitation come mainly from scavenging (washout) and not from water vapor condensation within the cloud. It is in the process of falling that raindrops trapped short-lived radon daughters 214Pb and 214Bi. The obtained results as demonstrated here provide a powerful evidence for understanding the washout mechanism of short-lived radon daughters from theatmosphere by rainfall.     

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.     

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.     

Application of a radon model to explain indoor radon levels in a Swedish house

Radon entry from soil into indoor air and its accumulation indoors depends on several parameters, the values of which normally depend on the specific characteristics of the site. The effect of a specific parameter is often difficult to explain from the result of indoor radon measurements only. The adaptation of the RAGENA (RAdon Generation, ENtry and Accumulation indoors) model to a Swedish house to characterise indoor radon levels and the relative importance of the different radon sources and entry mechanisms is presented. The building is a single-zone house with a naturally-ventilated crawl space in one part and a concrete floor in another part, leading to different radon levels in the two parts of the building. The soil under the house is moraine, which is relatively permeable to radon gas. The house is naturally-ventilated. The mean indoor radon concentration values measured with nuclear track detectors in the crawl-space and concrete parts of the house are respectively 75±30 and 200±80 Bq m⁻³. Results of the model adaptation to the house indicate that soil constitutes the most relevant radon source in both parts of the house. The radon concentration values predicted by the model indoors fall into the same range as the experimental results.     

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.     

Experimental and theoretical study of radon levels and entry mechanisms in a mediterranean climate house

An experimental study has been carried out in an inhabited single-family house. Radon concentration in the different rooms of the house and in its garden soil has been measured with Nuclear Track Detectors. No high differences of radon concentration have been observed between the different rooms of the house, so that the proximity of the room level to the soil seems not to affect the radon concentration. The annual radon concentration obtained indoors and in the soil has been respectively 35 Bq m⁻³ and 24 kBq m⁻³. Since radon generation in the source, entry into indoor air and accumulation indoors depend on several parameters, the effect of a specific parameter on indoor radon concentration is difficult to explain from the radon measurements only. The RAGENA (RAdon Generation, ENtry and Accumulation indoors) model has been adapted to the room in the basement of the house. The mean radon concentration values obtained with the model are compared to experimental results derived from measurements using Nuclear Track Detectors. The use of the model, together with the experimental study, has allowed characterising radon sources, levels and entry mechanisms in the house. The concrete walls have been found to be the most relevant radon source, while the contribution of the soil is negligible in this case. The indoor radon level is given by the balance of the permanent exhalation from concrete and the removal due to ventilation. The indoor radon levels are close to the average value for the Barcelona area which, in turn, is close to the world averaged value.     

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.     

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.     

Experience from using plastic film in radon measurement

Plastic film is a useful detector of radon gas. The method of detection of the gas is used for several decades to measure radon concentrations both indoors and in soil. Experiences from radon measurements in Sweden indoors, in soil and in water using the plastic film Kodak LR 115-II are discussed in this report. Some examples are given from various projects. One example is taken from a large scale mapping of indoor radon levels in houses, where the building material is the main source of radon. In anotther example the measurements from a large scale soil radon mapping are discussed. The use of the plastic film for measurements of radon levels in water is also discussed. All the investigations are made in order to give the authorities concerned information of the radon situation and to study the connection between high indoor radon levels and various types of cancers.     

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.     

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.      

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.     

The potential health hazard due to elevated radioactivity in old uranium mines in Dolina Białego,Tatra Mountains,Poland

Natural radioactivity is one of the essential components of the environment. Unlike the Sudety mountains area in Poland, the Tatra Mountains were not the subject of wide survey as regards the levels of natural radioactivity. Especially, the concentrations of radon (natural radioactive gas) have not been investigated there in terms of their possible negative health impact. Within the frame of bilateral cooperation between the Institute of Nuclear Physics in Kraków, Poland, and the Jo?ef Stefan Institute in Ljubljana, Slovenia, the measurements of natural radioactive elements in old uranium mines in the Tatra National Park were performed in June 2010. The investigated sites were located in Dolina Bia?ego (The Valley of the White). One of the mines is situated near the tourist path. The paper presents the results of complex measurements of natural radioactivity in both uranium drifts. The concentration of radon gas inside the mining drifts exceeded 28,000 Bq m^?3. Also, very high gamma dose rates were observed (up to 5600 nSv h^?1). The maximum concentrations of natural radioactive elements (potassium ⁴⁰K, radium ²²⁶Ra, thorium ²³²Th) in rock samples amounted to 535, 2137, and 18 Bq kg^?1, respectively. The effective dose rates due to radon and thoron inhalation have been assessed as 0.013 mSv h^?1 (for the lowest concentration) and 0.121 mSv h^?1 (for the highest concentration).     

Study of the response of silicon detectors for alpha particles

Numerous radon measurements are carried out using silicon detectors directly in the environment. This new kind of alpha radiation measurement has been developed because the reduced cost makes it possible to replace the usual plastic track detectors. At our laboratory, an alpha particle detector has been designed from a commercial silicon photodiode. This type of detector can determine the device response perfectly in any kind of environment. Different spectrum analyses have been conducted in the laboratory and field to define the exact origin of counted alpha particles. We studied the response for different radon and thoron concentration levels and observed the energy of the detected alpha particles. We carried out some of these experiments with gas flux, and some without, to show the effects of interactions with surfaces to obtain thermodynamic equilibrium in the detection chamber. Finally, the silicon diodes that we tested measure the alpha particles of the decay products (polonium) from the radon and the thoron, but very weakly from the gases themselves. Thus, it is possible to make mistakes when measuring the radon if the count of alpha particles is performed without spectrum analysis. One reason for this is that the decay progenies of the radon are solid radio-elements with thermodynamic proprieties different from gases.     

Airborne radioactivity levels in dwellings of Khammam district, Andhra Pradesh, India

Radon/thoron levels are estimated in Khammam district as a part of “Radon/thoron mapping” program in Andhra Pradesh, India. About 100 dwellings were chosen at random covering most parts of Khammam district. Twin chamber cup dosimeters consisting of solid-state nuclear track detectors (SSNTDs, LR-115, Type-II) were used to evaluate the radiation levels at quarterly intervals for a period of one calendar year. The average radon and thoron concentrations were found to be 39.1±13.3 and 19.4±14.9 Bq/m³, respectively. Seasonal variations of radon/thoron levels were also studied. Variations of radon/thoron concentration levels with different types of dwellings have been studied. In the bare flooring dwellings thoron levels were found to be highest in comparison to concrete, limestone and marble floorings.     

The use of nuclear prospecting measurements for characterizing the radioactive status of Al-Bayyarat and Sabkhet Mouh areas,southern Palmyrides,Syria

Al-Bayyarat and Sabkhet Mouh areas in southern Palmyride have been radioactively characterized by using different nuclear prospecting measurements. Those measurements include the application of airborne, carborne spectrometric gamma, radon emanation and borehole techniques. The merging of airborne, carborne spectrometric gamma data enables to establish the normalized eU, eTh, and K% maps in the study area. Radon emanation and spectrometric gamma measurements have been applied only in Al- Bayyarat area, where radioactive anomalous zone has been observed. The radioactive characteristics of the study area has been explained through studying and analyzing a profile of 30 Km long, where a plausible geo-radioactive model has been proposed for the uranium leaching and its transport.     

Indoor radon survey in dwellings of some regions in Yemen

Indoor radon survey in a total of 241 dwellings, distributed in some regions of Yemen was performed, using CR-39 based radon monitors. The objective of this radon survey is to get representative indoor radon data of three regions, namely Dhamar, Taiz and Hodeidah, situated at different altitudes above sea level. The radon concentrations varied from 3 to 270 Bqm⁻³ with an average of 42 Bqm⁻³. It was found that the average radon concentration in the surveyed areas increases with altitudes. The highest average radon concentration of 59 Bqm⁻³ was found in Dhamar city while the lowest average concentration of 8 Bqm⁻³ was found in Hodeidah city.