Validation of a database of mean uranium, thorium and potassium concentrations in rock samples of Portuguese geological units, generated of literature data.

The European Atlas of Natural Radiation, recently published, contains a collection of maps of Europe showing the levels of natural sources of radiation. Among the lacunae of the Atlas are maps of U, Th and K concentrations in rocks due to lack of European-wide geochemical surveys of bedrock units. The objective of this paper is to investigate the usability of scattered geochemical data of rock samples for large-scale mapping of U, Th and K concentrations in geological units. For this purpose, geochemical data were compiled from literature sources to produce a geochemical database (LIT database) that includes 2817 entries of U, Th and K concentrations measured in rock samples of geological units outcropping in Portugal. Given the methodical heterogeneity within LIT database, the influence of the geochemical analysis techniques was assessed through a three-way analysis of variance (ANOVA) using geological units, geochemical analysis techniques and loss on ignition (LOI) as categorical variables. The percentage of variation explained by geological factors was large (>35%), while the percentage of variation explained by the geochemical analysis techniques and LOI was generally lower than 5%. The geological factors were the main source of variability in the data, followed by the error component which can be assumed to represent the true spatial variability of geochemical concentrations. The pairwise comparison of the least square (LS) means computed through the ANOVA for each geochemical analysis technique indicates that LIT database can be considered consistent within itself, thus, reliable. In order to validate the usability of literature data the terrestrial gamma dose rate (TGDR) calculated from LIT database (TGDRcalc) was compared to the TGDR displayed in the Radiometric Map of Portugal (TGDRobs). The correlation between TGDRcalc and TGDRobs was highly significant (p < 0.001) and the results of a paired sample t-test and Wilcoxon median tests indicate that the differences between the arithmetic means of TGDRcalc and TGDRobs were not statistically significant (p = 0.126 and p = 0.14, respectively). Distributions of TGDRcalc and TGDRobs were seemingly equal according to the Kolmogorov-Smirnov and Anderson-Darling tests. Although, systematic discrepancies between TGDRcalc and TGDRobs were observed for sedimentary rocks, the compatibility of the RMP and LIT databases can be considered acceptable, which implies that the estimation of the contents of terrestrial radionuclides using literature data for large-scale mapping of U, Th and K contents in geological units is reasonable.

Development of a Geogenic Radon Hazard Index-Concept, History, Experiences.

Exposure to indoor radon at home and in workplaces constitutes a serious public health risk and is the second most prevalent cause of lung cancer after tobacco smoking. Indoor radon concentration is to a large extent controlled by so-called geogenic radon, which is radon generated in the ground. While indoor radon has been mapped in many parts of Europe, this is not the case for its geogenic control, which has been surveyed exhaustively in only a few countries or regions. Since geogenic radon is an important predictor of indoor radon, knowing the local potential of geogenic radon can assist radon mitigation policy in allocating resources and tuning regulations to focus on where it needs to be prioritized. The contribution of geogenic to indoor radon can be quantified in different ways: the geogenic radon potential (GRP) and the geogenic radon hazard index (GRHI). Both are constructed from geogenic quantities, with their differences tending to be, but not always, their type of geographical support and optimality as indoor radon predictors. An important feature of the GRHI is consistency across borders between regions with different data availability and Rn survey policies, which has so far impeded the creation of a European map of geogenic radon. The GRHI can be understood as a generalization or extension of the GRP. In this paper, the concepts of GRP and GRHI are discussed and a review of previous GRHI approaches is presented, including methods of GRHI estimation and some preliminary results. A methodology to create GRHI maps that cover most of Europe appears at hand and appropriate; however, further fine tuning and validation remains on the agenda.

Digital version of the European Atlas of natural radiation.

The European Atlas of Natural Radiation is a collection of maps displaying the levels of natural radioactivity caused by different sources. It has been developed and is being maintained by the Joint Research Centre (JRC) of the European Commission, in line with its mission, based on the Euratom Treaty: to collect, validate and report information on radioactivity levels in the environment of the EU Member States. This work describes the first version of the European Atlas of Natural Radiation, available in digital format through a web portal, as well as the methodology and results for the maps already developed. So far the digital Atlas contains: an annual cosmic-ray dose map; a map of indoor radon concentration; maps of uranium, thorium and potassium concentration in soil and in bedrock; a terrestrial gamma dose rate map; and a map of soil permeability. Through these maps, the public will be able to: familiarize itself with natural environmental radioactivity; be informed about the levels of natural radioactivity caused by different sources; have a more balanced view of the annual dose received by the European population, to which natural radioactivity is the largest contributor; and make direct comparisons between doses from natural sources of ionizing radiation and those from man-made (artificial) ones, hence, to better assess the latter. Work will continue on the European Geogenic Radon Map and on estimating the annual dose that the public may receive from natural radioactivity, by combining all the information from the different maps. More maps could be added to the Atlas, such us radon in outdoor air and in water and concentration of radionuclides in water, even if these sources usually contribute less to the total exposure.

Mapping uranium concentration in soil: Belgian experience towards a European map.

A map of uranium concentration in soil has been planned for the European Atlas of Natural Radiation. This Atlas is being developed by the Radioactivity Environmental Monitoring (REM) group of the Joint Research Centre (JRC) of the European Commission. The great interest in uranium compared to other terrestrial radionuclides stems from the fact that radon (222Rn) is in the decay chain of uranium (238U) and that public exposure to natural ionizing radiation is largely due to indoor radon. With several different databases available, including data (albeit not calibrated) from an airborne survey, Belgium is a favourable case for exploring the methodology of uranium mapping. A harmonized database of uranium in soil was built by merging radiological (not airborne) and geochemical data. Using this harmonized database it was possible to calibrate the data from the airborne survey. Several methods were used to perform spatial interpolation and to smooth the data: moving average without constraint, by soil class and by geological unit. When using the harmonized database, it is first necessary to evaluate the uranium concentration in areas without data or with an insufficient number of data points. Overall, there is a reasonable agreement between the maps on a 1 km × 1 km grid obtained with the two datasets (airborne U and harmonized soil U) with all the methods. The agreement is better when the maps are reduced to a 10 km × 10 km grid; the latter could be used for the European map of uranium concentration in soil.

Investigations on indoor Radon in Austria, part 2: Geological classes as categorical external drift for spatial modelling of the Radon potential.

Geological classes are used to model the deterministic (drift or trend) component of the Radon potential (Friedmann's RP) in Austria. It is shown that the RP can be grouped according to geological classes, but also according to individual geological units belonging to the same class. Geological classes can thus serve as predictors for mean RP within the classes. Variability of the RP within classes or units is interpreted as the stochastic part of the regionalized variable RP; however, there does not seem to exist a smallest unit which would naturally divide the RP into a deterministic and a stochastic part. Rather, this depends on the scale of the geological maps used, down to which size of geological units is used for modelling the trend. In practice, there must be a sufficient number of data points (measurements) distributed as uniformly as possible within one unit to allow reasonable determination of the trend component.