Soil Gas Radon Concentration Research Articles

Investigation aspects of the geogenic radon potential on Bulgarian territory

Radon (222Rn) is a radioactive gas formed as a result of the radioactive decay of radium (226Ra). Radon is identified as one of the dominant sources of population exposure that could lead to lung cancer, accounting for between 3% and 14% of all lung cancers. Rocks in the Earth’s crust are a primary source of radon in the atmosphere. In this context, the geogenic radon potential (GRP) of a terrain refers to the probability of high radon concentrations being present in a building. The radon index is a concept used to characterize the geogenic potential of the terrain, providing the likelihood of radon concentration in a building, which is directly related to the influence of the Earth's surface. One approach to quantifying the radon index is based on multivariate cross-tabulation, involving two parameters: radon concentration in soil gas and the gas permeability of the earth layer, both measured at 80 cm below the surface. In Bulgaria, focused investigations on the connection between radon gas and geology, resp. on GRP have begun in the last five. As a result of the accumulated experience from field studies conducted so far related to the characterization of GRP, two important aspects have been identified that impact field measurements and the determination of radon gas in the soil, thus the methodology for calculating the radon index. The first aspect is connected with the theoretical and model-based investigations about possible state of soil saturation. The second aspect is about the GRP and fault systems in Sofia. This article makes an attempt to summarize all the studies concerning these two aspects and to suggest some further steps in the geogenic radon potential studies.

Assessment of soil gas radon migration and transport through the estimation of radon diffusion length and diffusion coefficient in the soil matrix

Naturally occurring radioactive gas, radon is a decay product of radium present in the soil. Radon flux reaches the atmosphere through exhalation from soil surface. This study aims to estimate the radon diffusion length and diffusion coefficient in soil matrix on the premises of HNB Garhwal University campus at Tehri Garhwal, India. Soil gas radon concentration was measured at different depths (15, 30, 45, 60, 75, and 90 cm) using a Smart RnDuo (Scintillation-detector) at 14 different locations in the university campus. Simultaneous measurement of surface and mass exhalation rates was also carried out for each location. Gamma-ray spectrometry was used to estimate the radium content in soil samples. Results of the present study suggest that soil gas radon concentration increases with increasing sampling depth. The diffusion coefficient and length were calculated using the soil gas radon concentration gradient within the soil matrix. The average value of diffusion length (l) and diffusion coefficient (D) were obtained as, ls = 0.70 ± 0.22 m, Ds = 0.0054 ± 0.0049 m2 sec-1 and la = 0.77 ± 0.63 m, Da = 0.0073 ± 0.014 m2 sec-1 by Fick’s diffusion model and analytic models, respectively.

A review of approaches to assessment of potential radon hazard of land plots

According to Rosstat statistics, in recent years there has been a tendency in the Russian Federation to increase the intensity of construction, while both the number of buildings put into operation and their total area are increasing. The assessment of the potential radon hazard of land plots for construction provides the possibility of timely inclusion of the necessary protective (preventive) measures against radon in the design of buildings. This is a legal requirement in cases where the density of radon flux from the ground surface within the building area exceeds the established hygienic standards (action levels). The paper presents a review of Russian and foreign approaches to assessing the potential radon hazard of land plots conducted within the framework of engineering and environmental surveys. The current regulatory requirements to radiation safety indicators of land plots for construction of residential, public and industrial buildings and facilities in the Russian Federation are analyzed. The main drawbacks of the algorithm for determining the potential radon hazard of land plots, used in the current guidelines MU 2.6.1.2398-08 approved at the federal level more than 15 years ago, are described. Critical remarks (the unsuitability of the value of density of radon flux from the ground surface for designing radon protective and mitigation (remedial) measures, lack of consideration of seasonal variations of radon flux density, etc.) accumulated over the years as a result of practical application of these guidelines are presented. Benefits and drawbacks of foreign approaches to assessing the potential radon hazard of the territory based on the results of measurements of radon concentration in soil gas, as well as the very possibility of a transition in Russian regulations from the density of radon flux from the ground surface to the radon concentration in soil gas, are analyzed. Some rational proposals of various Russian research teams on improving the algorithm for determining the potential radon hazard of land plots are considered.

The correlation between indoor and soil gas radon concentrations in Kiraz district, İzmir.

All humans are exposed to radon, the primary source of natural radiation, which can harm people due to natural processes rather than human activity. Thus, it is of significant importance to determine the levels of radon in indoor, soil gas, water, and outdoors. Radon concentration (CRn) was measured in Kiraz district, İzmir, and the correlation between the indoor and soil gas CRn values was investigated. The indoor CRn values measured in 40 randomly selected dwellings in Kiraz exhibited a wide range from 19.50 ± 2.50 to 204.70 ± 8.00Bqm-3 with an average value of 61.11 ± 4.23Bqm-3. The measured indoor CRn values were compared to the reference levels in the world to help control radon in the dwellings. Indoor CRn values were lower than the ICRP reference level of 300Bqm-3 in all of the dwellings studied. Furthermore, in 34 dwellings (representing 85% of the total number of dwellings studied), indoor CRn values were lower than the WHO reference level of 100Bqm-3. Health hazard indices, namely annual effective dose (AED) and excess lifetime cancer risk (ELCR), were also calculated for each dwelling and compared with internationally acceptable levels to estimate the risk to human health. The AED values varied from 0.49 ± 0.06 to 5.16 ± 0.20mSv y-1 with an average value of 1.54 ± 0.11mSv y-1, which exceeds the world average of 1.15mSv y-1 as reported by UNSCEAR. The ELCR values ranged from 2.05 ± 0.26 × 10-3 to 21.55 ± 0.84 × 10-3 with an average value of 6.43 ± 0.44 × 10-3, exceeding the world average of 0.29 × 10-3 as reported by UNSCEAR. The soil gas CRn values measured exhibited a wide variation ranging from 129.25 ± 6.38Bqm-3 to 6172.64 ± 44.06Bqm-3 with an average value of 1291.79 ± 18.70Bqm-3. The soil gas CRn values were less than 10,000Bqm-3; hence, the research area is categorized as "low radon risk areas" according to Sweden Criteria, and so no special constructions are required in the studied area. When soil gas CRn values were compared to indoor CRn values, no linear relationship was found between the CRn values. However, a strong positive linear correlation was found between indoor and soil gas CRn values less than 200Bqm-3 and 2500Bqm-3, respectively.

Radon and carbon dioxide emissions from the surface rupture zone produced by the 1920 Haiyuan M8.5 earthquake in Northwest China

A M8.5 earthquake struck the Haiyuan area in 1920 and resulted in a 240-km long surface rupture zone along the Haiyuan fault (HYF). In this study, to determine the spatial relationship between soil gases and fault activity on a regional scale, radon (Rn) and carbon dioxide (CO2) concentrations in soil gas were measured in situ with a grid spacing of 5 ∼ 10 km along the Haiyuan surface rupture zone (HYSRZ). Ordinary Kriging (OK) and Inverse Distance Weight (IDW) interpolation were used to investigate spatial variations in Rn and CO2 concentrations. Synchronous soil gas anomalies were identified in southern Haiyuan County and at the southern end of the HYSRZ, and were correlated with higher slip rate, larger deformation, and larger degree rupture size than other segments. Moreover, soil gas anomalies were spatially highly coupled with seismically active zones and low b value areas, suggesting that the permeability and porosity of gas emissions are enhanced by higher stress. Two seismic velocity profiles across the gas anomaly area confirmed that low-velocity bodies exist at 0 ∼ 10 km below the surface, as revealed by magnetotelluric (MT) sounding results, indicating that gas emissions are associated with the migration of deep fluids. Our results provide new insight into the source of fluids in the HYSRZ and offer support for the design of a continuous geochemical measurement network in this area.

Assessment of Indoor and Soil-Gas Radon Concentration of a Quarry Site in Eiyekorin, Kwara State

The toxic health effect of human exposure to radon gas which is radioactive in nature has attracted extensive research attention worldwide. Since direct experiments on the effect of earthquakes on radon release are difficult to conduct, a possible alternative is to use man-made explosions as an earthquake surrogate and investigate the corresponding effect on radon concentration. This study aims at investigating the soil-gas radon concentration in an active quarry site and areas outside the quarry, and the infiltration of the gas into the indoor environment was measured in order to access the occupational exposure risk. Soil gas radon concentration was taken at 30 random locations within the quarry and areas outside the quarry using RAD7, likewise 10 indoor radon gas in offices and homes were measured using an active radon detector manufactured by Durridge Incorporation in USA and comparative analysis of the difference between the two locations were done. The mean of the soil-gas radon concentration in the quarry site is 24968.84 ± 6913.204Bq/m3 while that of outside the quarry is 9664.67 ± 4992.86 Bq/m3. The result shows higher values of radon-gas concentration in the quarry site compared with area outside the quarry and when compared to the International Commission on Radiation Protection (ICRP) suggested value of radon concentration in soil and sediment, which is in the range of 0.4 to 40 KBqm-3, result shows that most location within the study area are higher than these limits. Also, the radon in air indoor and outdoor was taken at the offices located within the quarry and occupational exposure risk was carried out. The average of radon in air indoor and outdoor was found to be 31.12 Bqm–3 and 10.12 Bqm–3 respectively with higher values found indoor. However, the values are found to be below the recommended value of 300 Bq/m3 by ICRP publication for homes and workplaces.

Effect of Seasonal Variation and Soil Parameters on Soil-Gas Radon Concentration in Ogbomoso, South Western Nigeria

Radon 222Rn, an inert natural radioactive gas, a daughter product in the 238U natural decay series, a source of alpha radiation. It accounts for about 55% of the total radiation from natural sources. Radon is known for its substantial variations in concentration due to both seasonal changes and variations in soil parameters. Soil, fractures in rocks and water are the main source of radon and they are the routes through which individual is exposed to it, in which this study is aimed at examining the effects of seasonal variation, soil parameters, on soil radon concentration. A total of hundred (100) in-situ soil radon measurements were carried out for both seasons (wet and dry) in Ogbomoso using an active electronic device RAD 7. Soil parameters were measured using a 4-in-1 digital metre. The obtained experimental data were subjected to a statistical tool (SPSS) Version 23, with statistical significance set at p < 0.01. The result showed that the effect of seasonal variation on soil-gas radon concentration was discovered to be maximum during the dry season with the radon concentration of 1900.01 Bq/m3 and minimum during the wet season with the radon concentration of 711.81 Bq/m3.The mean value of radon in soil-gas was found to be 553.48 Bq/m3 and 1366.34 Bq/m3 for wet and dry season respectively. Soil parameters considered in this work have notable influence on soil gas radon concentration in both seasons. Thus, providing valuable insight into the dynamics of radon migration in the soil. The results will help to develop effective mitigation strategies by policies makers and reducing the risk of radon related lung cancer in the study area.

Assessment of Radon Potential along Local Fault System in Sofia, Bulgaria (at Specific Test Site)

Environmental spread of radon gas (222Rn) has been intensively investigated in the last few years due to its harmful effects on human health. A concept of radon index is used to characterize the geogenic radon potential of the terrain, as the latter gives the probability of the presence of radon gas concentration in a building, the genesis of which is directly related to the influence of the earth's surface. One of the approaches for quantifying the radon index is based on a multivariate cross-tabulation, which includes two parameters – radon concentration in soil gas and gas permeability of the earth layer (at 80 cm). The geology of the specific site (approx. 350 m2) is characterized by the Pliocene clayey-sandy Formation, covered with Quaternary sediments. From tectonic point of view, the site as a part of Sofia Graben, has being subject of events related mainly with the Late Alpine deformations heading to very complex structures and fault systems. In situ measurements performed in the summer of 2023 at ten distinct points at the surface and 11 distinct points at two meters in depth from the surface vary as follows: from 44.2 to 189.0 kBq/m3 (radon soil gas), from 2.0E-11 to 1.8E-13 m2 (soil gas permeability), and from 0.10 to 0.17 µSv/h (gamma dose rate). Based on that, the radon index of the site is determined from “medium” to “high”, with a predominance of the latter. One of the reasons for the high radon potential is the presence of sub-faults connected with the major Sofia fault system and their influence on the radon concentration. Therefore, in future investigations of the radon index, a very detailed survey of the site's geology is needed in the territory with appearing fault systems. In addition, based on the determination of the radon index, the forthcoming construction activities in such areas will be advised to use preventive measures during the construction of the new building to avoid future radon gas influxes on the premises.

Radon indoors source potential from soil gas in a temperate climate: impact of infiltration rate and seismicity

Indoor radon source potential from unground soil was monitored using prototype devices approaching a dwelling with a cellar basement at 1 depth from the soil-atmosphere interface. Therefore, the radon concentrations in soil gas were monitored at 1 m depth. Integrated radon measurements were performed, and the results correlated with meteorological parameters. The influence of the difference in outdoor and device-soil temperature was considered, and the infiltration rate was calculated. The effect of the soil temperature gradient on the soil radon entry rate was evaluated. The indoor radon entry rate due to the soil gas was 7.0 ± 2.7 Bq m−3 h−1. The radon entry rate was 5.0 ± 0.8 Bq m−3 h−1 due to diffusion. In contrast, the advection-drive flow of soil gas is ranged up to ± 4.0 Bq m−3 h−1. So, the infiltration rate of the model dwelling was 0.7 (± 0.5) × 10−1 h−1 if only the stack effect occurred. The radon levels in tap water were measured, and the radon entry rate was estimated at 1.3 ± 0.7 Bq m−3 h−1. If the ventilation rate is low or seismic faulting appears, the soil radon entry is increased by one order of magnitude. The soil radon appeared like the building materials, having 1/3 of the total indoor radon entry, while outdoor air was slightly lower (28%), with tap water at 5%. The resident’s mortality risk occurred at < 2.5% for typical dwellings in temperate climate areas founded on sand-gravel underground. The risk rises to 34% with an extremely low ventilation rate between indoors and outdoors or high radon entry from the soil due to seismic faulting.

Assessment of Radiological Risks due to Indoor Radon, Thoron and Progeny, and Soil Gas Radon in Thorium-Bearing Areas of the Centre and South Regions of Cameroon

Indoor radon, thoron and thoron progeny concentrations, along with the equilibrium factor for thoron progeny and soil gas radon concentrations, have been measured to assess radiological risks in the centre and south regions of Cameroon. Indoor radon and thoron concentrations were estimated using radon–thoron discriminative detectors (RADUET), while thoron progeny monitors measured the equilibrium equivalent thoron concentration (EETC). Radon concentrations in the soil were determined using a MARKUS 10 detector. It was found that radon, thoron and thoron progeny concentrations range between 19 and 62 Bq m−3, 10 and 394 Bq m−3 and 0.05 and 21.8 Bq m−3, with geometric means of 32 Bq m−3, 98 Bq m−3 and 4.9 Bq m−3, respectively. The thoron equilibrium factor ranges between 0.007 and 0.24, with an arithmetic mean of 0.06 ± 0.03; this is higher than the world average value of 0.02 provided by the United Nations Scientific Commission on the Effects of Atomic Radiation(UNSCEAR, New York, USA). The level of the soil radon concentration ranges from 4.8 to 57.3 kBq m−3, with a geometric mean of 12.1 kBq m−3 at a depth of 0.7 m. Of the sampling points, 66% fall within normal radon risk areas, and 3% of the sampling areas are high radon risk areas exceeding 50 kBq m−3. The annual effective dose was found to be 0.03 ± 0.01 mSv for radon, 0.08 ± 0.05 mSv for thoron, 0.63 ± 0.12 mSv for radon progeny and 1.40 ± 0.84 mSv for thoron progeny. The total dose is estimated to be 2.14 mSv y−1. The mean estimated indoor excess lifetime cancer risk values due to radon, thoron, radon progeny and thoron progeny are 0.12 × 10−3, 0.31 × 10−3, 2.51 × 10−3 and 5.58 × 10−3, respectively. Thoron progeny contributed 60% to the effective dose. Thus, thoron progeny cannot be neglected in dose assessments, in order to avoid biased results in radio-epidemiological studies.

Measurement of radon concentration in soil gas and radon exhalation rate from soil samples along and across the Main Central Thrust of Garhwal Himalaya, India.

The present study focuses on measuring radon concentrations in soil gas at various depths, radon exhalation rate (surface and mass) from soil samples, and gamma dose rate along and across the Main Central Thrust of Garhwal Himalaya, India. Radon concentration in soil gas, surface, and mass exhalation rates was measured using a portable SMART radon monitor (RnDuo). Furthermore, the gamma dose rate was measured using a pocket radiation monitor. The soil gas radon concentration varied from 15 ± 4 to 579 ± 82Bqm-3 at a depth of 25cm, 10 ± 2 to 533 ± 75Bqm-3 at a depth of 30cm, and 9 ± 1 to 680 ± 95Bqm-3 at a depth of 35cm. The surface and mass exhalation rates were found 3 ± 0.7 to 98 ± 3Bqm-2h-1 (with AM ± SD = 36 ± 28Bqm-2h-1) and 1 ± 0.2 to 95 ± 2mBqkg-1h-1 (with AM ± SD = 30 ± 22mBqkg-1h-1), respectively. The gamma dose rate for the present study area varies from 0.11 ± 0.05 to 0.28 ± 0.05µSvh-1 with a mean value of 0.17 ± 0.05µSvh-1. The correlation analysis between the exhalation rates (mass and surface) and radon concentration of soil gas at various depths was carried out in the current study.

Public exposure in the Orenburg region due to natural sources of ionizing radiation. Part 2: Doses to the population of the eastern districts of the Orenburg region

The paper presents the estimated doses to the population of six eastern districts of the Orenburg region, Russia, based on the results of a comprehensive radiation survey conducted in 2019 in 34 settlements with previously found elevated levels of activity concentration of natural radionuclides in tap water from groundwater sources of drinking water supply. It is shown that the average individual annual effective dose due to all natural sources of ionizing radiation in 18 of 34 settlements corresponds to ‘elevated level’ of exposure due to natural sources according to established classification (from 5 to 10 mSv/year), and in another 7 settlements to ‘high level’ (over 10 mSv/year) with radon being the main contributor to the dose. Four settlements of Kvarkensky and Adamovsky districts, where the highest indoor radon concentrations had been found, were selected for a detailed survey, which included measurements of density of radon flux from the soil, radon concentration in soil gas, activity concentration of natural radionuclides in samples of building materials and in soil samples, and activity concentration of radon in tap water from groundwater sources of drinking water supply. Results of the detailed survey proved that the main source of radon in the buildings was the soil gas infiltration; compared to it, the contribution of waterborne radon release was insignificant.

Estimated versus field measured soil gas radon concentration and soil gas permeability

Prediction of areas with elevated natural radiation is fundamental for the prevention of human exposure. Soil gas radon activity concentration and soil gas permeability are predictive parameters for the radon potential, which has great importance in areas where future urban development is planned. In this study, the soil gas radon equilibrium concentration (C∞) and soil gas permeability (K) were estimated through the application of theoretical and empirical models found in the literature. These models apply soil properties as input parameters. Using already existing soil parameters to predict the radon potential of an area would be useful in avoiding direct field measurements. Therefore, in this study, we examined whether the estimated soil gas radon activity concentration and soil gas permeability values match the values measured in the field. The soil gas radon activity concentration estimated by two theoretical models is about 50% of the measured value in the studied area. This underestimation can be attributed to the assumption that the radon activity concentration measured in the field depends only on soil parameters and the models do not take into account the underlying bedrock. Additionally, these models neglect the radon transport by advection and consider only the radon availability and migration in homogeneous media. Furthermore, they do not count certain characteristics of the soil that can be relevant, e.g. organic matter and clay content in the soil. To investigate more in detail such soil characteristics, seven samples located roughly along the slope, were selected to determine the soil chemical composition by ICP-MS. Evaluating the physical and chemical properties of the soil, it was found that the sampling sites with pH < 8 (low calcium content) the preferential adsorption was a dominant process. This causes radium enrichment in organic matter and clay, which directly influence the soil gas radon activity concentration. At pH > 8, radium is no longer preferentially adsorbed on organic matter but continues to be adsorbed on clays albeit this process is weak because radium competes with calcium cations. Also, there are other factors that may affect radon emanation in soil such as radium concentration and distribution, porosity and water content. In contrast, empirical model of soil gas permeability overestimates the measured value in the study area by an order of magnitude. A new model was made by modifying the previously proposed one, which can be used as a guide for the estimation of the median value of soil gas permeability in granitic areas, but not as an accurate predictor due to the lack of correlation between the estimated and measured values.

Distribution of soil gas radon concentration in north-eastern Sicily (Italy): hazard evaluation and tectonic implications

Distribution of soil gas radon concentration in north-eastern Sicily (Italy): hazard evaluation and tectonic implications

Radon and thoron activity concentration in soil gas of Johor state: a statistical relationship with proxies

Radon and thoron activity concentration in soil gas of Johor state: a statistical relationship with proxies

Status of the geogenic radon potential investigations in Bulgaria

Radon (222Rn) is a radioactive gas and formed as a result of the radioactive decay of radium. 222Rn relieved from the ground could accumulate in the building and contribute to human exposure. Exposure to indoor radon and its decay products contributes to half of the annual dose received by the public from all natural radioactive sources. Radon is recognized as a carcinogenic agent by the WHO and is the second leading cause of lung cancer after tobacco smoke. The radon concentration in buildings and the exposure to radon depend on many factors, but it can be assumed that geology is the main factor influencing the variation of indoor radon. In this regard, the geogenic radon potential (GRP) of the terrain is the probability of the presence of high radon concentration in a building, the genesis of which is directly related to the influence of the earth's surface, and not e.g. from building materials. In addition, there is a concept “radon index”, which is used to characterize GRP. One of the approaches for quantifying the radon index is based on a multivariate cross-tabulation, which includes two parameters – radon concentration in soil gas and gas permeability of the earth layer. Till 2019, complex studies concerning correlation between the measured radon concentrations and bedrock geology in Bulgaria are only scarce and quite general. In the last three years, there are attempts for detailed investigations for evaluation of the bedrock and superficial geology associating with radon potential or/and radon index determinations. Therefore, research works on geogenic radon so far in Bulgaria can be divided into two main groups: regional research works related to the "radon-rock" relationship and local research aimed at determining the radon index at specific sites. In the first group appertain investigations about defining the rock formations in Bulgaria, in their outcrop presence, with possible high radon potential based on geological and published more general “radon–rock correlations” data. Based on that, a GIS based map for the spatial distribution of the particular rock types in accordance with the expected radon potential is made. Also to this group belongs a study concerning spatial sampling design for the use of the polygons (Sliven Province) as the unit of sampling, data collection, and analysis and reduces the number of observations, as well as would optimize the gathering, analysis and systematization of the data for the preparation of a methodology for the preparation of geogenic radon potential map. In the second group appertain investigations of the radon index determination at the two pilot sites affected by fault systems in Sofia.

Evaluation of tectonically enhanced radon in fault zones by quantification of the radon activity index

This work highlights the importance of the Geogenic Radon Potential (GRP) component originated by degassing processes in fault zones. This Tectonically Enhanced Radon (TER) can increase radon concentration in soil gas and the inflow of radon in the buildings (Indoor Radon Concentrations, IRC). Although tectonically related radon enhancement is known in areas characterised by active faults, few studies have investigated radon migration processes in non-active fault zones. The Pusteria Valley (Bolzano, north-eastern Italy) represents an ideal geological setting to study the role of a non-seismic fault system in enhancing the geogenic radon. Here, most of the municipalities are characterised by high IRC. We performed soil gas surveys in three of these municipalities located along a wide section of the non-seismic Pusteria fault system characterised by a dense network of faults and fractures. Results highlight the presence of high Rn concentrations (up to 800 kBq·m−3) with anisotropic spatial patterns oriented along the main strike of the fault system. We calculated a Radon Activity Index (RAI) along north–south profiles across the Pusteria fault system and found that TER is linked to high fault geochemical activities. This evidence confirms that TER constitutes a significant component of GRP also along non-seismic faults.

Dynamics in the radon index measurements at a specific test site

The study deals with the evaluation of the dynamic of the radon index in one pilot site based on second-time pilot investigations of the radon index in Bulgaria. In situ measurements of the radon concentration in soil gas, and soil permeability at three polygons: one over and two – close to fault zone have been performed in October 2020 and October 2022. The results show that higher radon content is detected in the fault zone in both cases.

Detailed Geogenic Radon Potential Mapping Using Geospatial Analysis of Multiple Geo-Variables—A Case Study from a High-Risk Area in SE Ireland

A detailed investigation of geogenic radon potential (GRP) was carried out near Graiguenamanagh town (County Kilkenny, Ireland) by performing a spatial regression analysis on radon-related variables to evaluate the exposure of people to natural radiation (i.e., radon, thoron and gamma radiation). The study area includes an offshoot of the Caledonian Leinster Granite, which is locally intruded into Ordovician metasediments. To model radon release potential at different points, an ordinary least squared (OLS) regression model was developed in which soil gas radon (SGR) concentrations were considered as the response value. Proxy variables such as radionuclide concentrations obtained from airborne radiometric surveys, soil gas permeability, distance from major faults and a digital terrain model were used as the input predictors. ArcGIS and QGIS software together with XLSTAT statistical software were used to visualise, analyse and validate the data and models. The proposed GRP models were validated through diagnostic tests. Empirical Bayesian kriging (EBK) was used to produce the map of the spatial distribution of predicted GRP values and to estimate the prediction uncertainty. The methodology described here can be extended for larger areas and the models could be utilised to estimate the GRPs of other areas where radon-related proxy values are available.

Assessment of soil-gas radon concentration over lithologies: a case study from district Karak, Khyber Pakhtunkhwa, Pakistan.

The current study is aimed to determine the variation of soil-gas radon concentrations over different rock formations representing diverse lithologies in the district of Karak, Khyber Pakhtunkhwa, Pakistan. The stratigraphic units were grouped on the basis of lithological contents into four categories, i.e., limestone, evaporites, claystone/mudstone, and sandstone. The highest average soil-gas 222Rn concentration (544Bq/L) was found in the uranium-bearing Dhok Pathan Formation of the Pliocene age, while the lowest radon levels (0.15Bq/L) were observed in the salt-bearing strata of Bahadurkhel Salt of Eocene age showing the non-uraniferous nature of the salt. High radon potential associated with the Dhok Pathan Formation is likely to be related to the high degree of uranium mineralization which is contributing to the elevated soil-gas radon levels. The study revealed that the soil-gas radon concentration in all lithologies is varying in the order of RnSandstone > RnLimestone > RnClaystone/Mudstone > RnEvaporites with the highest radon levels in the sandstone unit of uranium-bearing Dhok Pathan Formation. High fluctuations of soil-gas radon levels observed in this study evidently show that lithology and uranium mineralization have strong control over the 222Rn concentrations.