Radon Concentration In Soil Air Research Articles

New-designed in-situ measurement system for radon concentration in soil air and its application in vertical profile observation

ABSTRACT Radon in soil is a valuable radioactive tracer in earth science, especially for earthquake and volcanic precursors. For the purpose of continuous measurement of radon-in-soil concentration in-situ, a new-designed measurement system was developed. Calibration and experiments for humidity response correction were carried out in details, and field measurement of vertical profile with 7 radon probes at different depths was performed. Calibration results show that the sensitivity of the radon probes is 16.1 ± 1.0 cph (kBq m−3)−1, and the lower level detection limit is 231 ± 15 Bq m−3 for 1-hour measurement cycle under the absolute humidity of 32.8 g m−3. Field measurement results show that radon concentrations at different depths change with time and increase with depth in the soil. The vertical profile presents a negative exponential distribution with different diffusion length in sunny days, while rainfall can disturb the vertical distribution and lead to increase of radon concentration in the near ground surface. Radon concentration in underground deeper than 80 cm appears quite stable and hardly affected by rainfall in our observation.

Analysis of radon depth profile in soil air after a rainfall by using diffusion model

Abstract The radon concentrations in soil air were measured before and after a rainfall. 226Ra concentration, porosity, moisture content and temperature in soil were measured at Kyungpook National University in Daegu. As the results of measurement and analysis, the arithmetic mean of measured 222Rn concentration increased from 12100 ± 500 Bq/m3 to 16200 ± 600 Bq/m3 after the rainfall. And the measured 226Ra concentration was 61.4 ± 5.7 Bq/kg and the measured porosity was 0.5 in soil. The estimated values of 226Ra concentration and porosity using diffusion model of 222Rn in soil were 60.3 Bq/kg and 0.509, respectively. The estimated values were similar to the measured values. 222Rn concentration in soil increased with depth and moisture content. The estimations were obtained through fitting based on the diffusion model of 222Rn using the measurement values. The measured depth profiles of 222Rn were similar to the calculated depth profiles of 222Rn in soil. We hope that the results of this study will be useful for environmental radiation analysis.

Radon in the soil air of Estonia

Several investigations in Estonia during 1996¬-1999 have shown that permissible level (200 Bq/m3) of radon (222Rn) in indoor air is exceeded in 33% of the inspected dwellings. This makes Estonia one of the five countries with highest radon risk in Europe (Fig 1). Due to correlation between the soil radon risk level and radon concentration in houses, small scale radon risk mapping of soil air was carried out (one study point per 70–100 km2). It turned out that one-third of Estonian mainland has high radon risk potential, where radon concentration in soil air exceeds safe limit of 50 kBq/m3.In order to estimate radon content in soil air, two different methods developed in Sweden were used simultaneously. Besides measuring radon content from soil air at the depth of 80 cm with an emanometer (RnM), maximum potential content of radon in soil (RnG) was estimated based on the rate of eU (226Ra) concentration in soil, which was acquired by using gamma-ray spectrometer.Mapping and following studies revealed that simultaneously measured RnG and RnM in study points may often differ. To inspect the cause, several monitoring points were set up in places with different geological conditions. It appeared that unlike the RnG content, which remains close to average level in repeated measurements, the RnM content may differ more than three times periodically. After continuous observations it turned out that concentration of directly measured radon depended on various factors being mostly controlled by mineral composition of soil, properties of topsoil as well as different factors influencing aeration of soil.The results of Rn monitoring show that reliable level of radon risk in Estonian soils can only be acquired by using calculated Rn-concentration in soil air based on eU content and directly measured radon content of soil air in combination with interpreting specific geological and geochemical situations in the study points.

Seasonal variations of radon concentration in soil air in different geological conditions on the example of Estonia

Radon risk in Estonia is among the highest in Europe, influencing human health in many areas. The measured radon level in soil air differs considerably between spring– summer and autumn–winter periods at the same measuring point. Such variations are an obvious obstacle in interpreting reliably the radon risk level in the soil. To tackle with this problem, a monitoring system was established. Radon ( 222 Rn) concentrations in soil air were investigated in four geologically different sites at three depths during three years every 26–40 days. The results showed that at every site the concentration of radon in soil air depended on the eU ( 238 U) concentration in Quaternary deposits and underlying bedrock, on rock types, as well as on aeration circumstances during measuring, such as temperature, topsoil aeration, precipitation and air pressure. The measured radon level concentration starts to increase in autumn when the topsoil turns wet, air humidity increases and ground begins to freeze. It reached the maximum in late winter, when the ground is most frozen. The radon concentration is at its lowest during the warm and dry summer period when topsoil aeration and radon permeability are at their maximum.

The first results of studies of temporary variations in soil-radon activity of faults in Western Pribaikalie

Radon concentrations in soil air are variable depending on factors that are considered external (planetary) and internal (geodynamic) relative to the Earth. In active fault zones, variations of gas emanations are most intense. A permanent monitoring station was established near Tyrgan settlement in Western Pribaikalie to study temporal variations of soil radon concentration, Q, in the faults of the Baikal rift, East Siberia. This station is located in the zone of the Primorsky normal fault that is the largest in the region. The station is equipped with radon radiometer PPA01M03 that records Q values every 85 minutes and also monitors a number of meteorological parameters, including atmospheric pressure, humidity, and air temperature. We analysed records of two measurement sessions (148 and 66 days) covering a part of the year during which field measurement of Q are possible in the cold climate conditions of the area under study. According to the available monitoring data, variations of radon concentrations in the Primorsky fault zone may vary by more than one order of magnitude through a springsummerautumn period, and such variations are oscillatory. Significant changes of permeability in time occur due to intensive changes in the state of stresses of the rock massives under the impacts of the planetary and geodynamic factors. The influence of the first group of factors, i.e. planetary ones, is manifested by synchronous oscillations of radon concentrations and atmospheric pressure, which phases of occurrence are opposed. Domination of daily and fourday periods gives evidence that the state of stresses of the rock massives is impacted by the lunar tides and cyclonic phenomena associated with the interaction between the Earth and the Sun. The influence of the second group of factors, i.e. geodynamic ones, is suggested by an evident relation between radon emanations and seismic events, including the catastrophic earthquake in Japan (March 11, 2011, M=9.0). Tectonophysics The external and internal factors are acting together, but their roles are different with regard to variations of radon concentrations in different periods of time. In the monitoring periods, radon emanation variations were mainly controlled by the planetary factors. Radon exhalation increases and decreases according to periodic variations in atmospheric pressure, which, in additional to ‘pumping’ effects, may lead to opening/closure of pores and cracks in the rocks. While external pressures are reduced, internal stresses are released by relatively weak earthquakes. The guiding influence of atmospheric pressure on the yield of radon is disturbed when internal stresses are in excess of a certain level due to intensive movements along faults in the Baikal rift or displacements of plates in neighbouring active zones (for example, due to the strongest earthquake in Japan). In such relatively short periods of time, when seismic activity is increased, the influence of tectonic stresses on permeability of rocks and radon emanations becomes dominant. Based on our analysis of the measurements of soil radon concentrations obtained on the local site in the Primorsky fault zone through the monitoring period, it became possible, for the first time for Pribaikalie, to reveal and theoretically model the principal specific features of variation of soil radon concentrations, Q, in time and the dependence of such variations on the external and internal factors. Prospects of these studies are related to installation of a network of monitoring stations in the territory of the Baikal rift and assurance of longterm monitoring sessions.

RESEARCH ON CHANGES IN THE VOLUMETRIC ACTIVITY OF RADON IN SOIL AIR DEPENDING ON DEPTH / TŪRINIO RADONO AKTYVUMO DIRVOŽEMIO ORE KAITOS PAGAL GYLĮ TYRIMAS

The article discusses radon concentrations measured in the upper and deeper sandy-loam soil air. The conducted research has disclosed that the volumetric activity of radon in soil at various depths depends on soil porosity, ambient temperature, humidity, atmospheric pressure and the density of radium in soil. The paper shows that radon concentrations in soil air is distributed as follows: 3,0 ± 0,8 kBq/m3 (0,4 m), 9,0 ± 2,4 kBq/m3 (0,6 m), 11.5 kBq/m3 ± 1.2 (0,8 m). The intensity of exhalation of the respective depths makes 8,0 ± 0,9 mBq/m2s, 9,2 ± 1,3 mBq/m2s, 10,0 ± 0,1 mBq/m2s. Santrauka Tūrinis radono aktyvumas išmatuotas viršutiniame ir gilesniuose priesmėlio-priemolio dirvožemio oro sluoksniuose. Nustatyta, kad radono tūrinis aktyvumas įvairiuose dirvožemio gyliuose priklauso nuo dirvožemio porėtumo, aplinkos temperatūros, drėgmės, atmosferos slėgio, radžio kiekio dirvožemyje ir tankio. Pastebėtos tokios priklausomybės: kuo didesnis dirvožemio gylis, savitasis radžio aktyvumas dirvožemio ore, temperatūrų skirtumas tarp dirvožemio oro ir pažemio oro, tuo didesnis tūrinis radono aktyvumas dirvožemio ore bei ekshaliacijos intensyvumas. Nustatyta, kad tūrinis radono aktyvumas dirvožemio ore pasiskirstęs taip: 3,0 ± 0,8 kBq/m3(0,4 m gylyje); 9,0 ± 2,4 kBq/m3 (0,6 m gylyje); 11,5 ± 1,2 kBq/m3 (0,8 m gylyje). Ekshaliacijos intensyvumas atitinkamuose gyliuose yra 8,0 ± 0,9 mBq/m2·s; 9,2 ± 1,3 mBq/m2·s; 10,0 ± 0,1 mBq/m2·s.

Evaluation of radon gas concentration in the air of soil and dwellings of Hawar and Foara villages, using (CR-39) detectors

The present study has measured radon concentration in dwellings and soil of two villages of Hawar and Foara by using a passive dosimeter containing a solid-state nuclear track plastic detector commercially known as (CR-39). About 224 dosimeters were distributed inside houses of both villages. Additionally, 56 dosimeters were placed in the soil of each village at 50 cm depth. Soil dosimeters were retrieved after 14 days while house dosimeters were retrieved after three months. The collected dosimeters were chemically etched and then counted using an optical microscope. The study found that indoor radon concentration in Hawar village ranged from 31.6 ± 4.4 Bq m - 3 in the south area to 41.7 ± 5 Bq m - 3 in the west area, and in Foara village, varied between 39.9 ± 9 Bq m - 3 in the east area to 47.9 ± 10.8 Bq m - 3 in the south area. Moreover, the indoor radon concentration in the living rooms at Hawar village was 33.2 ± 2.2 Bq m - 3 which is almost the same as that in the guest rooms, 40.1 ± 3.3 Bq m - 3 , whereas the indoor radon concentration in living rooms at Foara was 36.6 ± 7.5 Bq m - 3 and in the guest rooms was 50.8 ± 5.4 Bq m - 3 . The study indicated also that radon concentration in soil air at Hawar village was 3.7 ± 0.2 kBq m - 3 and in Foara village was 4.3 ± 0.9 kBq m - 3 . The average indoor radon concentrations were comparable in both villages Hawar and Foara. Radon concentration in the study area is comparable to the national radon concentration.

Natural radioactivity due to radon in Soum region, Jordan

Indoor and in soil radon levels were measured using closed- and open-can techniques. Measurements were carried during three different seasons (fall, winter and spring) in Soum area northwest of Jordan. The highest average radon concentrations indoor were measured during winter, while in fall and spring its values were almost equals. The average radon concentration was 144 Bq m −3 , which is below the indoor radon concentration action level recommended by ICRP. This indoor average is about three times the Jordanian national average which may be due to the geological settings of the study area that composed of carbonate sedimentary rocks bearing high radioactive material. The average radon concentration in soil air was about 15 kBq m −3 and it ranges from 4 to 21 kBq m −3 in winter and fall, respectively. Ignoring other sources of radon in the dwellings, every 1000 Bq m −3 in the soil contributes about 10 Bq m −3 . The equilibrium factor was calculated to be 0.4.

A method for estimating the convective radon transport velocity in soils

A method for estimating the convective radon transport velocity in soils is developed. The approach under review is based on measurements of the radon concentration in soil air. Mathematical models for describing the convective radon transport velocity are discussed. Data on the convective radon transport velocity in commonly encountered soil types are presented. The results obtained from a 2-month experiment aimed at investigating the effect of the atmospheric condition on the convective radon transport velocity are reported. The soil gas radon concentration at 30– 70 cm depth was measured by means of passive track detectors (Type III-b SSNTDs) with 72– 96 h exposure time.

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 kBq m −3 (1.7– 24 kBq m −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).

The regional distribution of indoor radon concentration in Germany

According to the recommendations of the ICRP and the German Commission on Radiological Protection, areas should be identified where increased radon concentrations in buildings occur more frequently than on the countrywide average. Based on investigations of radon concentration in soil air, the areas of Germany have been classified. Comparing the soil gas classes with the radon concentrations in dwellings, we found that in regions with a soil gas radon concentration of up to 10 kBq/m 3 (about 25% of the total area of Germany), the probability that indoor concentrations above 400 Bq/m 3 occur is in the order of 0.1%; values of more than 1000 Bq/m 3 can be excluded. The assessment of about 20 000 indoor measurements in areas with radon concentrations in soil air in the range between 10 and 100 kBq/m 3 showed that radon concentrations >400 Bq/m 3 occur only in 0.2% of the investigated dwelling stock. However, occurrences of more than 1000 Bq/m 3 cannot be excluded completely. A rather clear increase of the number of dwellings with radon concentrations greater than 400 and 1000 Bq/m 3 has been found in areas with soil gas radon concentration >100 kBq/m 3 (about 6% of the area).

Parametric changes of radon [formula omitted] concentration in ground water in Northeastern Hungary

Variation of radon concentration in ground water in the area of Northeastern Hungary was investigated. Specific geological features of this region result in high radon concentration in well waters (between 100 and 350 Bq l −1) and in the air of dwellings (occasionally as high as 10 000 Bq m −3). The observed radon concentrations of well waters show unpredictable variability both in space and time. In adjacent wells, concentration values may change by a factor of 10. In the case of some wells, a variation by a factor of 3–6 (between 20 and 180 Bq l −1) was measured during a year. Measurements were made in order to find correlations between radon concentration in soil air, radon concentration in water and meteorological parameters, i.e. external air pressure, temperature, wind speed and air humidity. A good correlation (with correlation coefficient of k=−0.84) between radon concentration in soil air and air pressure was found.

CONCENTRATIONS OF INDOOR AND SOIL RADON IN LITHUANIA/RADONAS GRUNTO ORE IR PATALEOSE LIETUVOJE

Uranium and its daughters including Ra-226 are naturally present in the Earth's crust and other environmental bodies. During decay of Ra-226 radioactive noble gas radon is produced. This gas emanates to the atmosphere from solid matrixes containing Ra-226. It causes a special problem connected with the fact that radon accumulates in the closed spaces of buildings. Increased concentrations of radon indoors in many cases are the significant source of human exposure to ionizing radiation. Radon daughters having been deposited in the airways of human lungs are the source of alpha particles which irradiates the inner surface of airways. Since radiation quality of alpha radiation is high and small volumes of tissues are being irradiated, the influence of indoor radon as a source of ionizing radiation is significant. In order to forecast indoor radon concentrations and to take necessary remedial (in existing buildings) or prevention (in new buildings) measures, the main sources of indoor radon should be known in each country or geographical region. It may be soil, building materials, water and natural gas. It has been determined that the main source of indoor radon in Lithuania is soil. Permanent investigations of radionuclide content of building materials used or manufactured in Lithuania have not revealed any building materials with concentrations of naturally occurring radionuclides exceeding maximum permitted levels determined by the Lithuanian Hygienic Standards HN 40-1994. These investigations are performed by means of gamma spectrometry using the Ge spectrometer by Oxford after sample grinding and drying. A short review of radon risk mapping techniques used in Sweden, USA, Germany and Czech Republic is presented in paper. These techniques may be used for creation of similar technique in Lithuania with corrections connected with local geology. When determining radon risk mainly two parameters should be taken into account: radium content in soil (or radon content in soil air) which is associated with the type of soil and permeability of soil. The Lithuanian system of radon risk determination is not created yet because more detailed data on radon concentrations in soil air should be collected. Data from field measurements of radon concentrations in soil air and concentrations of naturally occurring radionuclides are presented. These measurements were carried out in some potentially important from the point of view of radon risk regions of Lithuania. Concentrations of Ra-226, Th-228 and K-40 in soil have been measured by gamma spectrometer GR-256 by Exploranium on the surface layer (up to 30 cm) of soil. Concentrations of radon in soil have been measured by MARKUS 10 in the depth of 70 cm. The measurements have been performed directly without sampling and sample preparation by digging the detector of Exploranium and pumping rod of MARKUS 10 in the investigated soil. The results indicate that there are some regions in Lithuania with radon concentrations in soil air exceeding 100 kBq/m3. Though radon risk depends on soil permeability these results show that these areas may be identified as areas of medium or even high radon risk. The system for classification of building sites in terms of indoor radon risk should be created in Lithuania in order to follow requirements of Lithuanian radiation protection standards and to keep below determined action levels of indoor radon- 400 Bq/m3 in existing buildings and 200 Bq/m3 in constructed ones. Results of indoor radon measurements are presented as well. The measurements have been performed in 400 randomly selected detached houses during heating season in two lowest permanently used rooms. Duration of one measurement exceeds 3 weeks. E-PERM electrets have been used for this type of measurements. The results show that the average concentration of indoor radon in Lithuania is 55 Bq/m3. In some cases these concentrations exceed the above-mentioned action levels and approach 2000 Bq/m. It shows that indoor radon problems exist in Lithuania as in many other countries. The average concentration of indoor radon in karst region is 125 Bq/m3. It shows that special attention should be paid to such regions because conditions for increased intake of radon to buildings may exist. Indoor radon is one of the main sources of exposure in Lithuania. In some cases it may be the essential source causing tens of milisieverts of annual effective dose. It shows that the problem of indoor radon is important in Lithuania.

CONCENTRATIONS OF INDOOR AND SOIL RADON IN LITHUANIA

Summary Uranium and its daughters including Ra-226 are naturally present in the Earth's crust and other environmental bodies. During decay of Ra-226 radioactive noble gas radon is produced. This gas emanates to the atmosphere from solid matrixes containing Ra-226. It causes a special problem connected with the fact that radon accumulates in the closed spaces of buildings. Increased concentrations of radon indoors in many cases are the significant source of human exposure to ionizing radiation. Radon daughters having been deposited in the airways of human lungs are the source of alpha particles which irradiates the inner surface of airways. Since radiation quality of alpha radiation is high and small volumes of tissues are being irradiated, the influence of indoor radon as a source of ionizing radiation is significant. In order to forecast indoor radon concentrations and to take necessary remedial (in existing buildings) or prevention (in new buildings) measures, the main sources of indoor radon should be known in each country or geographical region. It may be soil, building materials, water and natural gas. It has been determined that the main source of indoor radon in Lithuania is soil. Permanent investigations of radionuclide content of building materials used or manufactured in Lithuania have not revealed any building materials with concentrations of naturally occurring radionuclides exceeding maximum permitted levels determined by the Lithuanian Hygienic Standards HN 40-1994. These investigations are performed by means of gamma spectrometry using the Ge spectrometer by Oxford after sample grinding and drying. A short review of radon risk mapping techniques used in Sweden, USA, Germany and Czech Republic is presented in paper. These techniques may be used for creation of similar technique in Lithuania with corrections connected with local geology. When determining radon risk mainly two parameters should be taken into account: radium content in soil (or radon content in soil air) which is associated with the type of soil and permeability of soil. The Lithuanian system of radon risk determination is not created yet because more detailed data on radon concentrations in soil air should be collected. Data from field measurements of radon concentrations in soil air and concentrations of naturally occurring radionuclides are presented. These measurements were carried out in some potentially important from the point of view of radon risk regions of Lithuania. Concentrations of Ra-226, Th-228 and K-40 in soil have been measured by gamma spectrometer GR-256 by Exploranium on the surface layer (up to 30 cm) of soil. Concentrations of radon in soil have been measured by MARKUS 10 in the depth of 70 cm. The measurements have been performed directly without sampling and sample preparation by digging the detector of Exploranium and pumping rod of MARKUS 10 in the investigated soil. The results indicate that there are some regions in Lithuania with radon concentrations in soil air exceeding 100 kBq/m3. Though radon risk depends on soil permeability these results show that these areas may be identified as areas of medium or even high radon risk. The system for classification of building sites in terms of indoor radon risk should be created in Lithuania in order to follow requirements of Lithuanian radiation protection standards and to keep below determined action levels of indoor radon- 400 Bq/m3 in existing buildings and 200 Bq/m3 in constructed ones. Results of indoor radon measurements are presented as well. The measurements have been performed in 400 randomly selected detached houses during heating season in two lowest permanently used rooms. Duration of one measurement exceeds 3 weeks. E-PERM electrets have been used for this type of measurements. The results show that the average concentration of indoor radon in Lithuania is 55 Bq/m3. In some cases these concentrations exceed the above-mentioned action levels and approach 2000 Bq/m. It shows that indoor radon problems exist in Lithuania as in many other countries. The average concentration of indoor radon in karst region is 125 Bq/m3. It shows that special attention should be paid to such regions because conditions for increased intake of radon to buildings may exist. Indoor radon is one of the main sources of exposure in Lithuania. In some cases it may be the essential source causing tens of milisieverts of annual effective dose. It shows that the problem of indoor radon is important in Lithuania.