Airborne Gamma-ray Spectrometry Research Articles

Distribution of U and Th in an Iberian U-fertile granitic complex (NW, Spain): airborne-radiometry, chemical and statistical approaches

The behaviour and distribution of U and Th have been studied in an Iberian Hercynian granitic complex known as Cadalso-Casillas de Flores batholith. This batholith is composed of two granitic intrusions known as El Payo and Peñaparda complexes. To explain the geochemical behaviour, the distribution of uranium and thorium and determine the fertility in U of these granites in search for mineral resources, three different approaches have been used: Interpretation of airborne radiometric data, chemical analysis of whole-rock and accessory minerals and statistical calculations.The obtained results indicate that: (a) the airborne gamma-ray spectrometry is a powerful mapping and exploration tool; (b) U/Th ratios in whole-rock samples increase with the evolution and the chemical analysis of radio-element bearing accessory minerals showed that both elements were segregated in accessory minerals during magmatic fractional crystallisation. This primary distribution of U and Th was affected by superimposed post-magmatic, hydrothermal and meteoric alterations; and (c) the statistical approach, approximately defined that the proportion of U linked to U-rich mineral phases especially uraninite differs in both granitic complexes. It also identified those independent variables that are positively correlated with uranium and hence any U not unaccounted for by these elements was interpreted as uraninite or its alteration products. The statistical analysis also highlighted the lack of positive correlations between uranium and thorium.Accordingly, the studied granites were grouped into two different genetically unrelated intrusions, where the behaviour of U and Th-bearing accessory minerals was also different and only the granitic units G2 and G3 of the El Payo complex and G6 of the Peñaparda complex could be classified as fertile in U.

Airborne gamma-spectrometry and its potential

Considered are the examples of the use of airborne gamma-ray spectrometry for studying the radioactive contamination of big territories and for other purposes.

Environmental hazards and distribution of radioactive black sand along the Rosetta coastal zone in Egypt using airborne spectrometric and remote sensing data

High-resolution airborne gamma ray spectrometry, conducted in 2003, was used to estimate radioactive elements spatial abundance along the Rosetta coastal zone area. It was noticed that both Uranium and Thorium are concentrated in the black sand deposits along the beach. In contrary, Potassium was observed in high level abundance at the cultivated Nile Delta lands due to the accumulated usage of fertilizers. Exposure Rate (ER), Absorbed Dose Rate (ADR) and Annual Effective Dose Rate (AEDR) were calculated to evaluate the radiation background influence in human. Results indicated that the human body in the study sites is subjected to radiation hazards exceeds the accepted limit for long duration exposure. In addition, the areas covered by the highest concentration of Uranium and Thorium show the highest level of radiogenic heat production. Detection the environmental hazards of the radioactive black sands in the study site encouraged this research to monitor the spatial and temporal distribution of these sediments. The Landsat Thematic Mapper images acquired in 1990, 2003 and 2013 were analyzed using remote sensing image processing techniques. Image enhancements, classification and changes detection indicated a positive significant relationship between the patterns of coastline changes and distribution of the radioactive black sand in the study sites. The radioactive black sands are usually concentrated in the eroded areas. Therefore, in 1990 high concentration of the radioactive black sands were observed along the eastern and western flanks of the Rosetta promontory. Distribution of these sediments decreased due to the construction of the protective sea walls. Most of the radioactive black sands are transported toward the east in Abu Khashaba bay under the effect of the longshore currents and toward the west in Alexandria and Abu Quir bay under the action of the seasonal reverse currents.

Precipitation correction of airborne gamma-ray spectrometry data using monitoring profiles: methodology and case study

Variations of soil moisture content caused by precipitation often complicate the interpretation of airborne gamma-ray spectrometry data. This is particularly the case in repeated surveys designed to monitor the change of near surface abundances of radioactive elements or in large and time-consuming surveys.To counter this precipitation effect we propose a correction method based on repeated survey flights over a monitoring profile. Assuming that the weather and the soil conditions at the monitoring profile are representative for the survey area, the weather dependent effect of soil moisture can be observed and sufficiently corrected.

Interpretation of airborne and ground magnetic and gamma-ray spectrometry data in prospecting for base metals in the central-north part of the Itabuna-Salvador-Curaçá Block, Bahia, Brazil

Interpretation of airborne and ground magnetic and radiometric geophysical data is fundamental to provide support for geologic mapping and exploration of mineral resources. This is particularly important of the Itabuna-Salvador-Curaçá Block component of the São Francisco Craton in the state of Bahia, Brazil, which bears important base metal mineralization in ultramafic intrusions. The interpreted airborne data covered part of the northern segment, and the ground data comprised an area of [Formula: see text] in the northern segment of that Archean block. The radiometric interpretation was only qualitative, and the magnetic interpretation was qualitative and quantitative. The qualitative interpretation defined distinct configurations of the geophysical signatures. So, it furnished possible regional and local geologic models and also helped to infer the distribution of magnetization and radiometric content in the rocks. The quantitative interpretation started with Werner deconvolution for a preliminary identification of the magnetic sources, and 2D magnetic modeling improved the definition of the anomalous bodies in terms of geometry, depth to the top, and magnetic susceptibility. The combined qualitative and quantitative interpretation allowed mapping of the rocks that contain magnetic and metallic minerals, as well as felsic lithology, such as granites and orthogneisses, and mafic lithology, such as gabbros and amphibolites. It also suggested that most of the northwest–southeast lineaments related to felsic and mafic magnetic intrusions. The analysis may extend to other areas of the block and be integrated with field and laboratory geologic, geophysical, and geochemical studies for an adequate exploration of nickel, copper, and chromium that are potentially present in the region.

Integrated interpretation of satellite imagery, aeromagnetic, aeroradiometric and ground exploration data-sets to delineate favorable target zones for unconformity related uranium mineralization, Khariar basin, Central India

The Mesoproterozoic Khariar basin, to the SE of Chhattisgarh basin, comprises 1000 m thick arenaceous-argillaceous sediments. For the first time, a multidisciplinary approach has been made to the integrate interpreted satellite imagery, aero-magnetic and aero-radiometric data with available ground exploration data sets with an objective to understand structural fabric and to establish various parameters for unconformity related uranium mineralization in the environs of Khariar basin. Total Magnetic Intensity (TMI) anomaly image has been useful to mark major faults (ENE-WSW), magnetic bodies and overall basement characteristics. Combination of first vertical derivative (1VD) and tilt derivative magnetic images brought out presence of NW-SE magnetic linear (dominant) with minor ENE-WSW and NNE-SSW trends. Basic dykes and quartz veins are the surface manifestations of NW-SE trend in basement. Radially averaged power spectrum indicates the approximate basement configuration. Enhanced Thematic Mapper satellite imagery (Landsat ETM+) interpretation has shown lineaments along NW-SE, NNE-SSW, ENE-WSW and ENW-WSE directions. These observations are corroborated by interpreted results of magnetic data. Analysis of both results indicate NW-SE and ENE-WSW trends as post depositional. Aero-radiometric images (U, Th, K and ternary U-Th-K) show overall radio-elemental distribution for various litho-units. Besides, Th and K images along with interpreted ETM+ satellite imagery (RGB: 432/752/751) are useful to map small outliers and to modify basement-sediment contact. Geochemical data from basement rocks around Khariar basin suggests the younger Bundeli granitoids and its equivalents are good source of uranium in the western margin. Presence of labile uranium is inferred from higher concentration of uranium in water samples. The Airborne gamma-ray spectrometry (AGRS) and hydro-geochemical anomalies fall along fault zones and intersection of fault zones. The western and southern margin of Khariar basin are also characterized by presence of paleosol at unconformity, which are favorable factors for unconformity type uranium mineralization. Based on the present study, part of western and southern margin emerge as potential target areas for further exploration of uranium.

Appraisal of long-term radiation trends in the environs of nuclear power plants – Examples from Switzerland

Abstract Annually since 1989, biannually since 1994 the sites of the Swiss nuclear facilities (4 power plant sites, a nuclear research institute and a waste storage facility) are surveyed flying the same survey lines by airborne gamma ray spectrometry. The equipment and the data processing software used for those surveys was built and developed at the Institute of Geophysics, ETH Zurich. For mapping the ground radiation around the nuclear facilities a pixel representation and a modified Spectrum Dose Index (SDI) method is used. In the search for long-term trends the local dose-rates are calculated first and in turn the net dose rates over the time span 1992–2010. So far no significant change in the radiation levels was detected over the last 18 years outside of the fenced sites of the nuclear facilities, except for the operation of an industrial radiation facility in 1995.

The role of airborne geophysics for detecting hydrocarbon microseepages and related structural features: The case of Remanso do Fogo, Brazil

The first direct indication of hydrocarbon occurrence in Remanso do Fogo area (Minas Gerais State, Brazil) was the existence of microseepages. However, Quaternary sedimentary cover in the area made the identification of new occurrences and associated controlling structures quite difficult. This study investigated the spatial distribution of hydrocarbon related gases in shallower to intrasedimentary depths in Remanso do Fogo area, using airborne gamma-ray spectrometry and magnetic data. The geophysical data were processed using techniques designed to suppress the influence of regional geological signatures. Known and possible new occurrences of microseepages were detected by mapping low residual potassium values and high uranium residual values in relation to potassium, termed as DRAD values, which resulted from the subtraction of potassium from uranium residual values, using a Thorium (Th)-normalizing approach. The validation of these occurrences was done based on existing gas geochemistry data in the soil. For the magnetic data, the amplitude of the analytic signal, combined with the total horizontal gradient of the subtraction between the 1200- and 400-meter upward continuations, enhanced the northwest–southeast and east–west magnetic lineaments, which are partially related to the microseepages and the drainage of the area. The distinction of near-surface and deep signatures also allowed the general identification of intrasedimentary and basement structures, which are potentially controlling the occurrences of seepages in the area.

Mapping the terrestrial air-absorbed gamma dose rate based on the data of airborne gamma-ray spectrometry in southern cities of China

An environmental radioactivity survey by Airborne Gamma-ray Spectrometry (AGS) on a large scale was undertaken in Zhuhai Zone (ZZ) and Shenzhen Zone (SZ), which include major cities in southern China, covering areas of 3800 km2 and 4660 km2, respectively. The estimated dose rates by AGS have been compared with observed results by ionization chamber and portable dosemeter. Maps of the terrestrial dose rate at 1m above ground level have been calculated based on the data of AGS. The mean dose rates are 84.37 ± 51.69 and 82.10 ± 32.98 nGy/h in ZZ and SZ, and the maximum rates are 343.11 and 368.36 nGy/h, respectively. Dose rates in some places are above 180 nGy/h; the areas covered where 149 km2 in ZZ and 43 km2 in SZ. The dominant geological conditions that evidently contribute to the radioactive anomalies are outcrops of Middle and Late Jurassic and Cretaceous biotitic-granite. The growth of industrialization and urbanization has dramatically altered radiation background. Stone mining results in the increase of radiation levels with maximum dose rates approaching 368.36 nGy/h in an open pit. The investigation results provide valuable background data and give a good example for mapping nationwide natural radiation terrestrial dose rates in China by AGS.

A geophysically constrained litho-structural analysis of the Eburnean greenstone belts and associated granitoid domains, Burkina Faso, West Africa

Interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho-structural framework in a poorly exposed Paleoproterozoic granite-greenstone terrain of the West African Craton. The geophysical data portray with sufficient detail all of the lithological units and structural features present. The results suggest that the granitoid domains are formed by numerous small to medium-sized plutons. The existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model. The magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late-orogenic plutons were reliably identified. Relic F1 fold hinges were recognized in the Houndé and Boromo greenstone belts. The D1 penetrative structures are generally affected by the D2 transcurrent shear zones, which often form as well the granite-greenstone belt boundaries. Previously unreported S2 shear zones including the Bossié shear zone, transecting the Sidéradougou granitoid domain and abundant small-scale shear zones affecting all of the lithologies represent prospective areas for gold exploration. Airborne gamma-ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the Banfora greenstone belt. The magnetic data revealed at least three generations of doleritic dykes crosscutting the western Burkina Faso.

Regional mapping of soil parent material by machine learning based on point data

A machine learning system (MART) has been used to predict soil parent material (SPM) at the regional scale with a 50-m resolution. The use of point-specific soil observations as training data was tested as a replacement for the soil maps introduced in previous studies, with the aim of generating a more even distribution of training data over the study area and reducing information uncertainty. The 27,020-km 2 study area (Brittany, northwestern France) contains mainly metamorphic, igneous and sedimentary substrates. However, superficial deposits (aeolian loam, colluvial and alluvial deposits) very often represent the actual SPM and are typically under-represented in existing geological maps. In order to calibrate the predictive model, a total of 4920 point soil descriptions were used as training data along with 17 environmental predictors (terrain attributes derived from a 50-m DEM, as well as emissions of K, Th and U obtained by means of airborne gamma-ray spectrometry, geological variables at the 1:250,000 scale and land use maps obtained by remote sensing). Model predictions were then compared: i) during SPM model creation to point data not used in model calibration (internal validation), ii) to the entire point dataset (point validation), and iii) to existing detailed soil maps (external validation). The internal, point and external validation accuracy rates were 56%, 81% and 54%, respectively. Aeolian loam was one of the three most closely predicted substrates. Poor prediction results were associated with uncommon materials and areas with high geological complexity, i.e. areas where existing maps used for external validation were also imprecise. The resultant predictive map turned out to be more accurate than existing geological maps and moreover indicated surface deposits whose spatial coverage is consistent with actual knowledge of the area. This method proves quite useful in predicting SPM within areas where conventional mapping techniques might be too costly or lengthy or where soil maps are insufficient for use as training data. In addition, this method allows producing repeatable and interpretable results, whose accuracy can be assessed objectively.

Radon potential mapping of the Tralee–Castleisland and Cavan areas (Ireland) based onairborne gamma-ray spectrometry and geology

The probability of homes in Ireland having high indoor radon concentrations isestimated on the basis of known in-house radon measurements averaged over10 km × 10 km grid squares. The scope for using airborne gamma-ray spectrometer data for theTralee–Castleisland area of county Kerry and county Cavan to predict the radon potential(RP) in two distinct areas of Ireland is evaluated in this study. Airborne data arecompared statistically with in-house radon measurements in conjunction withgeological and ground permeability data to establish linear regression models andproduce radon potential maps. The best agreement between the percentage ofdwellings exceeding the reference level (RL) for radon concentrations in Ireland (% > RL), estimated from indoor radon data, and modelled RP in the Tralee–Castleisland area isproduced using models based on airborne gamma-ray spectrometry equivalent uranium(eU) and ground permeability data. Good agreement was obtained between the% > RL from indoor radon data and RP estimated from eU data in the Cavan area using terrainspecific models. In both areas, RP maps derived from eU data are spatially more detailedthan the published 10 km grid map. The results show the potential for using airborneradiometric data for producing RP maps.

Extrapolation at regional scale of local soil knowledge using boosted classification trees: A two-step approach

Digital soil mapping can be helpful in providing pedological information over wide areas where existing soil information is limited. The aim of this study was to predict soil properties at a regional scale by parametrizing soil-landscape models using a machine-learning method recently applied to soil science concerns: boosted classification and regression trees. To examine soil properties interdependence, a two-step approach was tested: first soil parent material (PM), including bedrock formations and superficial deposits, was predicted; then, predicted PM was included as a predictive variable to estimate natural soil drainage (SD). Others predictive variables included environmental data representing known soil-forming factors: terrain attributes (elevation, slope, profile and plan curvatures, sub-watershed hillslope length, hydrological distance from the nearest stream, aspect, relative elevation above the nearest stream and a Compound Index initially proposed by Beven and Kirkby (1979) and modified by Mérot et al. (1995)), geological data, airborne gamma-ray spectrometry (K:Th ratio, deviation from mean K emissions of the related lithological unit) and landscape data (derived from remotely sensed data). The study area is located in Brittany (northwestern France) and covers 4645km². The training dataset was constructed from existing detailed soil maps (scale 1:25,000) available for 11% of the study area. An additional set of 1148 punctual soil observations spread over the study area represented an independent validation dataset. Based on 20,000 randomly selected pixels from the training area, PM and SD were predicted with overall accuracies of 73 and 70% respectively. While calculated on punctual observations, correct agreement between prediction and observation decreased to 49% for PM and 52% for SD. Predicted PM was the most influential variable for SD prediction, illustrating the relevance of the two-step approach tested. Boosted classification tree appeared to be a particularly adequate and robust procedure for predicting soil properties. Probability of occurrence of the predicted PM was demonstrated to be a relevant indication of prediction quality, allowing distinction between well-predicted and poorly-predicted situations.

A weathering intensity index for the Australian continent using airborne gamma-ray spectrometry and digital terrain analysis

Weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides. As weathering intensity increases there are changes in the hydrological, geochemical and geophysical characteristics of the regolith. Thus, once calibrated, weathering intensity can be used to predict a range of regolith properties. A weathering intensity index (WII) over the Australian continent has been developed at a 100m resolution using regression models based on airborne gamma-ray spectrometry imagery and the Shuttle Radar Topography Mission (SRTM) elevation data. Airborne gamma-ray spectrometry measures the concentration of three radioelements — potassium (K), thorium (Th) and uranium (U) at the Earth's surface. The total gamma-ray flux (dose) is also calculated based on the weighted additions of the three radioelements. Regolith accounts for over 85% of the Australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes. The weathering intensity prediction is based on the integration of two regression models. The first uses relief over landscapes with low gamma-ray emissions and the second incorporates radioelement distributions and relief. The application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of: WII=6.751+−0.851∗K+−1.319∗Relief+2.682∗Th/K+−2.590∗Dose. The WII has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials. The WII correlates well with site based geochemical indices and existing regolith mapping. Interpretation of the WII from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described.

The Radiometric Map of Australia

Geoscience Australia and the Australian State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma-ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth’s surface. However, the individual surveys that comprise the national gamma-ray spectrometric radioelement database are not all registered to the same datum. This limits the usefulness of the database as it is not possible to easily combine surveys into regional compilations or make accurate comparisons between radiometric signatures in different survey areas. To solve these problems, Geoscience Australia has undertaken an Australia-Wide Airborne Geophysical Survey (AWAGS), funded under the Australian Government’s Onshore Energy Security Program, to serve as a radioelement baseline for all current and future airborne gamma-ray spectrometric surveys in Australia.The AWAGS survey has been back-calibrated to the International Atomic Energy Agency’s (IAEA) radioelement datum. We have used the AWAGS data to level the national radioelement database by estimating survey correction factors that, once applied, minimise both the differences in radioelement estimates between surveys (where these surveys overlap) and the differences between the surveys and the AWAGS traverses. The database is thus effectively levelled to the IAEA datum. The levelled database has been used to produce the first ‘Radiometric Map of Australia’ – levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100 m resolution.Interpreters can use the map to reliably compare the radiometric signatures observed over different parts of Australia. This enables the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions with contrasting landscape histories.

Effect of small potassium-rich dykes on regional gamma-spectrometry image of a potassium-poor volcanic complex: A case from the Doupovské hory Volcanic Complex, NW Czech Republic

Basaltic rocks with low K, U and Th contents dominate the entire Volcanic Complex of the Doupovské hory Mts. Significant potassium anomaly exceeding 1.5 atomic wt.% of potassium over an area of 4 × 8 km and 2 atomic wt.% of potassium over an area of 2 × 6 km was defined by airborne gamma-ray spectrometry above the central part of the Doupovské hory Volcanic Complex. The following detailed field study, supported by field and laboratory gamma-spectrometry measurements and geochemical analyses of rock samples, resulted in discovery of a swarm of potassium-rich trachytic dykes. The existence of such highly-differentiated rocks in the volcanic complex was unknown till present. These dykes are commonly less than 1 m wide, but their potassium content varies between 4 and 8 atomic wt.%. Owing to this high-K composition and relative abundance of dykes, the dyke rocks significantly modify the regional pattern of gamma-spectrometry data. The potassium anomaly cannot be explained by the presence of Flurbühl intrusive body dominated by ijolites and essexites, as all these rocks are poor in K, with potassium typically not exceeding 1.5 wt.%. On the other hand, much more extensive intermediate trachybasaltic lavas with K content varying within the range 1.8–3 wt.% cause only minor or undetectable anomalies.

Using airborne geophysics to define the 3D distribution and landscape evolution of Quaternary valley-fill deposits around the Jamestown area, South Australia

The combined analysis of airborne electromagnetics, airborne gamma-ray spectrometry, magnetics and a digital elevation model with ground-based calibration has enabled construction of a 3D architectural and landscape evolution model of valley-fill deposits around the township of Jamestown in South Australia. The valley-fill sediments consist of traction, suspension and debris-flow deposits that range in age (optically stimulated luminescence dating) from 102 ± 12 ka to the present day. A sediment isopach map generated from the airborne electromagnetics dataset reveals the 3D structure of the valley-fill deposits. The sediments are up to 40 m thick in asymmetrical valleys and are the result of colluvial fan, floodplain and sheet-wash processes. The sediments fine upwards with a higher proportion of coarser bedload deposits toward the base and fine sand, silt and clay towards the top of the sequence. A strong linear correlation between airborne K response and soil texture allowed the percentage of surface silt to be modelled over the depositional landforms. The sediments are thought to have been derived by a combination of eolian dust accessions, and weathering and erosion of bedrock materials within the catchment. Older drainage lines reflected in the distribution of relatively closely spaced and well-connected ‘magnetic channels’ differ markedly from present-day streams that are largely ephemeral and interrupted. This is thought to reflect a change in local hydrology and associated geomorphic processes from relatively high to lower energy conditions as the valley alluviated. These hydrological changes are likely to be associated with a drying climate, lower recharge and runoff.

The radiometric map of Australia

Geoscience Australia and State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma-ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth?s surface. The quality of the radiometric data acquired over this period varies markedly. Early surveys (prior to about 1990) were flown with a line spacing of about 1500 m and a 16 litre detector at a flying height of 150 m agl. Later surveys have been flown with a detector volume of 32 litres and a line spacing of 500 m, or closer, and flying heights of 100 m, or better. The use of high-performance survey aircraft have now enabled flying heights to be lowered to heights of 60-80m for regional surveys and even lower for detailed surveys. For early surveys, the results were usually reported in units of counts per second. Thus the magnitudes of these data values depend on both the instrumentation used in the survey (such as crystal volume) and the survey parameters (such as nominal flying height). This means that the results from early surveys that used different instrumentation and survey parameters are not directly comparable. Also, even where survey acquisition systems were calibrated to report results as equivalent concentrations of the radioelements, limitations in the calibration of these instruments and temporal variations in radiation output from the earth often result in mis-matches between surveys along their common boundaries. These problems limit the usefulness of the gamma-ray spectrometric data, as surveys are not easily combined into regional compilations, and quantitative comparisons between radiometric signatures from different surveys are difficult. The solution is to adjust all of Australia?s public-domain gamma-ray spectrometric data to a common datum. This will enable surveys to be easily merged into larger regional compilations, and thus facilitate the recognition and interpretation of broad-scale regional features in the data. This paper describes the adjustment of Australia?s National Radioelement Database to a common datum. We have used an Australia-wide Airborne Geophysical Survey (AWAGS) to adjust all the public-domain radiometric surveys in Australia to the International Atomic Energy Agency?s (IAEA) Global Radioelement Datum. The levelled database has been used to produce the first ?Radiometric Map of Australia? - levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100 m resolution. Interpreters can use these grids to reliably compare the radiometric signatures observed over different parts of Australia. This enables the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions across the continent.

Large-scale radon hazard evaluation in the Oslofjord region of Norway utilizing indoor radon concentrations, airborne gamma ray spectrometry and geological mapping

We test whether airborne gamma ray spectrometer measurements can be used to estimate levels of radon hazard in the Oslofjord region of Norway. We compile 43,000 line kilometres of gamma ray spectrometer data from 8 airborne surveys covering 10,000 km 2 and compare them with 6326 indoor radon measurements. We find a clear spatial correlation between areas with elevated concentrations of uranium daughters in the near surface of the ground and regions with high incidence of elevated radon concentrations in dwellings. This correlation permits cautious use of the airborne data in radon hazard evaluation where direct measurements of indoor radon concentrations are few or absent. In radon hazard evaluation there is a natural synergy between the mapping of radon in indoor air, bedrock and drift geology mapping and airborne gamma ray surveying. We produce radon hazard forecast maps for the Oslofjord region based on a spatial union of hazard indicators from all four of these data sources. Indication of elevated radon hazard in any one of the data sets leads to the classification of a region as having an elevated radon hazard potential. This approach is inclusive in nature and we find that the majority of actual radon hazards lie in the assumed elevated risk regions.

Search for long-term radiation trends in the environs of Swiss nuclear power plants

Annually since 1989, biannually since 1994 the sites of the Swiss nuclear facilities are surveyed flying the same survey lines by airborne gamma ray spectrometry. The equipment and the data processing software used for those surveys were built and developed at the Institute of Geophysics, ETH Zurich. For mapping the ground radiation around the nuclear facilities, a pixel representation and a modified spectrum dose index (SDI) method are used. In the search for long-term trends, the local dose rates are calculated first and in turn the net dose rates. So far, no change in the radiation levels was detected over the last 13 years outside of the fenced sites of the nuclear facilities and, especially, no artificial radioactivity was present that could not be explained by nuclear weapon tests or by the Chernobyl event.