Title
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity
journal homepage: www.elsevier.com/locate/jenvrad
Digital version of the European Atlas of natural radiation
Giorgia Cinellia,, Tore Tollefsena, Peter Bossewb, Valeria Gruberc, Konstantins Bogucarskisa,
Luca De Felicea, Marc De Corta
a European Commission, Joint Research Centre, Directorate for Nuclear Safety & Security, Ispra, Italy
b German Federal Office for Radiation Protection (BfS), Berlin, Germany
c Austrian Agency for Health and Food Safety (AGES), Linz, Austria
A R T I C L E I N F O
Keywords:
Europe
Digital Atlas
Natural radiation
Mapping
A B S T R A C T
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.
1. Introduction
The Joint Research Centre (JRC) of the European Commission
decided to embark on a European Atlas of Natural Radiation (EANR)
(De Cort et al., 2011), in line with its mission, based on the Euratom
Treaty (EU, 2012), which is to collect, validate and report information
on radioactivity levels in the environment. This Atlas is intended to
familiarize the public with the natural radioactive environment, to give
a more balanced view of the annual dose that it may receive from
natural radioactivity and to provide reference material and generate
harmonized data for the scientific community.
Natural ionizing radiation is considered to be the largest contributor
to the collective effective dose received by the world population
(UNSCEAR, 2008: Annex B). The human population is continuously
exposed to ionizing radiation from several natural sources that can be
classified in two broad categories: high-energy cosmic rays incident on
the Earth’s atmosphere and releasing secondary radiation (cosmic
contribution); and radioactive nuclides generated during the formation
of the Earth and still present in the Earth’s crust (terrestrial contribu-
tion). Terrestrial radioactivity is mostly produced by uranium (238U and
235U) and thorium (232Th) radioactive families together with potassium
(4 K), which is a long-lived radioactive isotope of the element po-
tassium. In most circumstances, radon (222Rn), a noble gas produced in
the radioactive decay of 238U, is the major contributor to the total dose
(UNSCEAR, 2008: Annex B, Table 12 and Fig. 36).
The Atlas is a collection of maps of Europe displaying the levels of
natural radioactivity caused by different sources: from cosmic radiation
to terrestrial radionuclides. As a first task, the JRC started to prepare a
European Indoor Radon Map (EIRM), given its great radiological im-
portance (WHO, 2009). Second, the JRC committed itself to map a
variable which measures what earth delivers in terms of geogenic
radon potential (RP), due to the heterogeneity of data sources across
https://doi.org/10.1016/j.jenvrad.2018.02.008
Received 31 August 2017; Received in revised form 7 February 2018; Accepted 14 February 2018
Corresponding author.
E-mail address: [emailprotected] (G. Cinelli).
Journal of Environmental Radioactivity 196 (2019) 240252
Available online 27 February 2018
0265-931X/ 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
T
http://www.sciencedirect.com/science/journal/0265931X
https://www.elsevier.com/locate/jenvrad
https://doi.org/10.1016/j.jenvrad.2018.02.008
https://doi.org/10.1016/j.jenvrad.2018.02.008
mailto:[emailprotected]
https://doi.org/10.1016/j.jenvrad.2018.02.008
http://crossmark.crossref.org/dialog/?doi=10.1016/j.jenvrad.2018.02.008&domain=pdf
Europe and the need to develop models for estimating a harmonized
quantity which adequately measures or classifies the RP. The European
Geogenic Radon Map (EGRM) will also give the possibility to char-
acterize areas for radon risk where indoor radon measurements are not
available (Gruber et al., 2013a, 2013b; Bossew et al., 2015). A multi-
variate classification approach to estimate the geogenic radon potential
has been developed and was proposed to the scientific community
during the 12th International Workshop on the Geological Aspects of
Radon Risk Mapping in September 2014 in Prague (https://remon.jrc.
ec.europa.eu/About/Atlas-of-Natural-Radiation/Geogenic-radon/
Geogenic-radon). In this context, multivariate estimation means to use
information from several quantities which are physically related to
radon, to assess a radon quantity of interest. Some countries, which
have several input quantities available, have already been testing this
approach (Miles and Appleton, 2005; Appleton and Miles, 2010; Szab
et al., 2014; Garcia-Talavera et al., 2013; Ielsch et al., 2017; Drolet
et al., 2013, 2014). Although work on the geogenic radon map has been
under way for several years, it has proven more complicated than
thought initially. For these reasons, in our project we have decided to
give priority to the development of those maps that should be part of
the EANR but also be used as input parameters in the EGRM, such as the
uranium map in soil or bedrock and terrestrial gamma dose rate.
Maps of uranium, thorium and potassium in soil, covering most
European countries, have been created. In addition, a methodology was
developed to estimate the terrestrial gamma dose rate using EURDEP data
(https://remon.jrc.ec.europa.eu/About/Rad-Data-Exchange) (Bossew et al.,
2017), and this map-s is now available. Maps of uranium, thorium and
potassium concentration in bedrock are available for some countries.
Moreover, the annual cosmic-ray dose map has been completed.
Finally, the first version of the European Atlas of Natural Radiation
is available in digital format through a web portal (https://remon.jrc.
ec.europa.eu/About/Atlas-of-Natural-Radiation), in which all the maps
are collected and displayed with the related information.
This paper is structured as follows: Section 2 explains how the
website has been designed and the map visualization tools used. In
section 3 the different maps are described according to the general
schema: a) Introduction, b) Materials and Methods, and c) Results and
Discussion.
2. Web design and map visualization issues
2.1. Web design
The goal of the Radioactive Environmental Monitoring (REMon)
web portal (https://remon.jrc.ec.europa.eu) is to provide a single point
of access for up-to-date radiological information, allowing the general
public to improve their understanding of environmental radioactivity.
The portal offers geo-referenced data in the form of interactive maps,
for general use, in an easy and straightforward manner. It contains a list
of associated scientific publications and offers a number of interactive
tools to the users.
The following data and services are currently available via the
portal (Fig. 1):
real-time monitoring information collected from automatic surveil-
lance systems in most European countries by the European
Radiological Data Exchange Platform (EURDEP). The map shows
measurements of environmental radioactivity in the form of gamma
dose rate averages and maxima for the last 24 h. These measure-
ments originate from some 5500 monitoring sites operated by
competent national authorities in most European countries and
worldwide (so far 39 countries in total). Each station displays time
series of averaged gamma dose rates for the last 30 days and last
24 h. Moreover, registered users can create custom maps, such as
real-time gamma dose rates tracking for user’s POI (points of in-
terest).
information about national radioactivity in Europe through the
European Atlas of Natural Radiation (EANR), the topic of this paper.
The portal offers a direct navigation through all main sections of the
portal such as:
general information about activities, e.g. Real-Time monitoring,
Natural Radioactivity;
maps and services, scientific publications;
contact and other relevant information.
The entire web portal has been developed using a modern re-
sponsive design, in order to make all web pages automatically detect
the visitor’s screen size and orientation and change the layout accord-
ingly. The map viewer has been developed using standard interactive
mapping tools (https://remap.jrc.ec.europa.eu) in order to display
complex radiological data in a simple, intuitive way.
2.2. Projection
The majority of maps reported in the Atlas have been developed
using a 10 km 10 km grid based on the old standard projection for the
European Commission at the continental scale, viz. the GISCO-Lambert
azimuthal equal-area coordinate reference system with spherical earth
and centre of projection at 9 E and 48 N (hereafter referred to as
GISCO-LAEA). The reason is historical: by the time the JRC had laun-
ched the first map, the European Indoor Radon Map, in 2006, several
base maps had been developed before the European Commission
decided in 2002 to adopt a new standard projection. This new standard
is known as the European Terrestrial Reference System 1989 – Lambert
azimuthal equal-area coordinate reference system with spherical earth
and centre of projection at 10 E and 50 N (hereafter referred to as
ETRS89-LAEA). Several radioecological maps had been developed in
the old reference frame. More importantly, the European Soil properties
thematic layers in raster format were available in the first version, still
in the old GISCO-LAEA coordinate reference system (for the second
version in ETRS89-LAEA, see Van Liedekerke et al., 2006). The inten-
tion was to overlay the indoor radon maps on these soil maps and study
relationships. For further details on GISCO- vs. ETRS89-LAEA co-
ordinate reference systems, see the EC and EuroGeographics report on
map projections for Europe (Annoni et al., 2001).
Then the JRC considered how to manage all the maps, originally
developed using the GISCO-LAEA spatial reference system into the
ETRS89-LAEA projection for displaying the data (see all maps reported
in this paper, thumbnails in the digital Atlas). Since for some data, such
as indoor radon, the original sample point co-ordinates are not avail-
able but only spatial averages over the grid cells, it was decided to
simply display the grid with its statistical values in the ETRS89-LAEA
projection. This led to the current, compromise solution.
Fig. 1. Schema of the REMon website.
G. Cinelli et al. Journal of Environmental Radioactivity 196 (2019) 240252
241
https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation/Geogenic-radon/Geogenic-radon
https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation/Geogenic-radon/Geogenic-radon
https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation/Geogenic-radon/Geogenic-radon
https://remon.jrc.ec.europa.eu/About/Rad-Data-Exchange
https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation
https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation
https://remon.jrc.ec.europa.eu
https://remap.jrc.ec.europa.eu
Instead the map viewer in the digital version of the Atlas uses Web
Mercator projection. As described above, the data (based on ETRS89-
LAEA L52 M10 grid for the majority of the maps) have simply been
projected and displayed in the Web Mercator projection.
2.3. Other tools
Geostatistical analysis and data mapping have been performed using
ArcGIS (Esri) and Surfer 11 (Golden Software, LLC) software.
With the goal to prepare all geospatial data, the Quantum GIS
Geographic Information System software has been used (Open Source
Geospatial Foundation Project, http://qgis.osgeo.org) while Geoserver,
an open source server for sharing geospatial data (http://geoserver.
org/), has been used for publishing all geospatial data using OGC (Open
Geospatial Consortium) open standards.
3. Maps
So far the digital version of European Atlas of Natural Radiation
consists of the followings maps:
European annual cosmic-ray dose map
European indoor radon concentration map
European indoor radon – number of measurements
European uranium concentration in soil map
European thorium concentration in soil map
European potassium concentration in soil map
European terrestrial gamma dose rate map
European uranium concentration in bedrock map
European thorium concentration in bedrock map
European potassium concentration in bedrock map
European map of soil permeability
For each map, data have been collected, statistically analysed and
mapped using the most appropriate methods available. They will be
briefly described below. The classes chosen to display the data in the
maps do not refer to any limit, reference, action level.
3.1. European annual cosmic-ray dose map
3.1.1. Introduction
The Earth is continually bombarded by high-energy cosmic-ray
particles, and the worldwide average exposure to cosmic rays re-
presents about 13% of the total annual effective dose received by the
population. Therefore the assessment of cosmic-ray exposure at ground
level is of great interest to better understand population exposure to
ionizing radiation.
3.1.2. Materials and methods
The methodology used for developing the European Annual Cosmic-
Ray Dose map has been extensively described in Cinelli et al. (2017b),
and below we briefly report the main aspects:
the values displayed depend only on elevation, and hence this map
clearly reflects the elevation map;
the dose has been assessed according to methods described in
UNSCEAR (UNSCEAR, 2008: Volume 1, Annex B, Chap. 2);
a global digital elevation model (DEM), called the GTOPO30 dataset
(https://lta.cr.usgs.gov/GTOPO30), was used. This dataset was de-
rived from several raster and vector sources of topographic in-
formation and is a raster georeferenced TIFF with a horizontal grid
spacing of 30 arc seconds (approximately 1 km at the Equator);
the accuracy of the simple and easy approach based only on ele-
vation data has been confirmed by comparing the results with those
obtained using other models.
Moreover, in Cinelli et al. (2017b) the annual cosmic-ray collective
dose has been evaluated, and population-weighted average annual ef-
fective dose (per capita) due to cosmic ray has been estimated for each
European country considered in the work.
3.1.3. Results and discussion
The European Annual Cosmic-Ray Dose map reports the annual
effective dose that a person may receive from photons, direct ionizing
and neutron components of cosmic radiation at ground level (Cinelli
et al., 2017b; Tollefsen et al., 2016-01). This is the dose that a person
may receive if she/he spends all the time at that elevation, considering
365 days per year and 24 h per day.
3.2. European indoor radon map
3.2.1. Introduction
The European Indoor Radon Map (EIRM) intends to show means
over 10 km 10 km grid cells of long-term (ideally, mean annual) in-
door radon concentration in ground-floor rooms of dwellings.
3.2.2. Materials and methods
The participants, counting national competent authorities, labora-
tories, universities etc., aggregate their raw data into cells over a
10 km 10 km grid covering Europe. Defined by the JRC, this grid uses
the GISCO-LAEA coordinate reference system. Exceptions have been
made for Ireland and Malta which used their own 10 km 10 km grids
based on their national coordinate reference systems.
Specifically, data providers fill the cells with the following statistics
calculated from their original data: the arithmetic mean (AM), standard
deviation (SD), AM and SD of the ln-transformed data, median,
minimum and maximum, as well as the number of original measure-
ments in the cell. This procedure was agreed upon to ensure data
protection, because the original data and their exact location are not
given away, but remain at the national level, thus guaranteeing data
privacy. The methods and procedures to collect and process the raw
data have been further described in Dubois et al. (2010) and Tollefsen
et al. (2011).
The choice of variable to be mapped can be seen as a compromise
between an indoor radon map and a geogenic radon potential map.
Moreover, restricting the data to annual mean radon concentration on
ground-floor rooms means that data providers have to estimate this
quantity, ideally from long-term measurements. Whenever measure-
ments have been made over shorter periods, some intermediate mod-
elling involving seasonal corrections may be necessary to estimate an-
nual means. Admittedly, most people do not actually live on ground
floors, especially in urban areas. In spite of its limitations, this approach
was adopted simply because most data are available for this variable.
As a consequence, the statistics over the chosen quantity do not
represent the ones of exposure. For that purpose, either data must result
from a carefully design-based survey which reflects demographic reality
(samples representative for population density and house and dwelling
characteristics), or alternatively model-based correction to account for
demographic representativeness must be performed. Since few national
radon surveys are design-based, and demographic data with continental
coverage have only recently become available (see e.g. Batista e Silva
and Lavalle, 2013), neither the design-based nor the model-based
approach could be chosen for generating a European radon exposure
map; it must therefore be left to future efforts.
3.2.3. Results and discussion
As of August 2017, 32 European countries participate to the EIRM.
More than 27,000 cells have been filled with data, based on more than
1,100,000 individual measurements in total (Table 1). As can be seen
from Fig. 2, the number of measurements per cell and coverage of
territory vary widely between countries and between regions of in-
dividual countries. The number of measurements per cell range from a
G. Cinelli et al. Journal of Environmental Radioactivity 196 (2019) 240252
242
http://qgis.osgeo.org/
http://geoserver.org/
http://geoserver.org/
https://lta.cr.usgs.gov/GTOPO30
single one up to a maximum of nearly 24,000 (for a cell in the UK). Still,
there are many empty cells. The map thus mirrors the status of national
surveys of indoor radon monitoring in Europe, at least up to the data
released by national authorities to the JRC.
Large areas with high sampling density are found in e.g. the Czech
Republic, Austria, Switzerland, North Italy, Belgium, the UK, South
Finland and Luxembourg. The median number of measurements per cell
equals 4, with a median absolute deviation (MAD) of 4.4 (Table 1). This
heterogeneity of sampling density clearly influences the statistical un-
certainty of the means as estimates of the expected concentration
within a cell, as it does for the standard deviation and other statistics.
Fig. 3 shows the geographical distribution of arithmetic means over
10 km 10 km cells. The map reveals a spatial trend in indoor radon
concentrations across Europe and essentially reflects the underlying
geology. Regions of high radon concentrations are found in the granite
areas of the Bohemian Massif, the Iberian granite province, the Massif
Central, the Fennoscandian Shield, Corsica, Cornwall and the Vosges
Mountains, in the crystalline rocks of the Central Alps and karst rocks of
the Swiss Jura and the Dinarides, the black shales in North Estonia and
in certain volcanic structures in Central Italy.
The mean of all non-empty cells in all of Europe (for participating
countries) is 103 Bq/m3, while the median is 60 Bq/m3. See Table 1 for
descriptive statistics of the dataset which underlies the map. For all
participating countries, more than 30% of the non-empty cells have an
arithmetic mean above 100 Bq/m3 and 4% of them above 300 Bq/m3
(Table 1). The descriptive statistics for each country as well as the
percentage of cells with AM above 100 and 300 Bq/m3 are reported in
the supplementary materials.
Again it should be emphasized that the cell mean (AM or median
over cell means) is an estimate of the spatial mean of the quantity
long-term mean radon concentration in dwellings in ground-floor
rooms, but neither (a) the mean over radon in ground-floor dwellings,
nor (b) the mean over all dwellings, i.e. an estimate of exposure. For (a)
one would have to calculate a weighted mean with population density
by cells as weights; for (b) the distribution of dwellings over floors
would have to be included as weight, together with a model which
accounts for floor level. Since (a) population centres are preferentially
located in valleys and flatlands, in many cases over quaternary geology
which in most cases has lower radon potential, and (b) radon con-
centration decreases with floor level, on the average, demographically
weighted mean radon concentrations and mean exposure are generally
lower than the spatial mean of the quantity discussed here.
3.3. U, Th and K in soil
3.3.1. Introduction
Due to the important contribution of uranium, thorium and po-
tassium radionuclides in the total annual effective dose received by the
population both for external and internal exposure (UNSCEAR, 2008,
Annex B), maps of these radionuclides in soil, covering most European
countries, have been created. These maps can be used as input para-
meters for the EGRM, but also as stand-alone maps in the Atlas for the
outline about natural radioactivity levels in Europe.
Table 1
Descriptive statistics for the dataset on which the EIRM is based, as of August 2017.
Number of non-empty cells 27,544
Total number of measurements 1,154,373
Measurements per cell, MED (MAD) 4 (4.4)
Min/Max number of measurements per cell 1/23,993
Cell mean, AM CV % 103.2 Bq/m3 139%
Cell median, MED (MADI) 60.0 ( 46.0) Bq/m3
Percentage cell AM > 300 Bq/m3 4.34%
Percentage cell AM > 100 Bq/m3 34.3%
CV within cells, MED ( MAD) 66.8 (34.0) %
GSD within cells, MED (MAD) 1.88 (0.68)
CV, coefficient of variation, where CV = SD/AM; MAD = MED(x-MED(x)).
Fig. 2. Number of measurements per 10 km 10 km cell of long-term radon concentration in ground-floor rooms of 32 European countries (ETRS89-LAEA frame). Latest update, August
2017. Source: European Commission, DG JRC (Tollefsen et al., 2010-03).
G. Cinelli et al. Journal of Environmental Radioactivity 196 (2019) 240252
243
3.3.2. Materials and methods
Databases. A research was carried out and identified two geo-
chemical databases available for all the territory of Europe for mapping
the uranium (U), thorium (Th) and potassium (K) concentration in soil.
FOREGS: the Geochemical Atlas of Europe, hereafter referred to as
FOREGS, has about 1800 samples collected in Europe between 1997
and 2001, corresponding to a sampling density of about one sample per
4700 km2. The European contribution to the programme has been
carried out by government institutions from 26 countries under the
auspices of the Forum of European Geological Surveys (FOREGS). Two
different depth-related samples were taken at each site: a topsoil sample
from 0 to 25 cm (excluding material from the organic layer where
present), and a subsoil sample from a 25 cm thick section within a depth
range of 50200 cm (http://weppi.gtk.fi/publ/foregsatlas/article.php?
id=10). The samples have been collected in forested and unused lands;
greenland and pastures; and non-cultivated parts of agricultural land.
U, Th and K have been measured using inductively coupled plasma
mass spectrometry (ICP-MS).
GEMAS: the Geochemical Mapping of Agricultural and Grazing
Land Soil project, hereafter referred to as GEMAS (Reimann et al.,
2014a, b; http://gemas.geolba.ac.at/), involving 33 European coun-
tries, is a cooperation project between EuroGeoSurveys through its
Geochemical Expert Group, and Eurometaux, the European Association
of Metals. The GEMAS project collected samples of agricultural soil (Ap
– horizon, 0-20 cm, regularly ploughed fields) and samples from land
under permanent grass cover (Gr – grazing land soil, 0-10 cm). The
sampling was completed in the beginning of 2009. The sampling den-
sity is about one sample per 2500 km2 (about 3000 samples of Ap and
3000 of Gr for all of Europe). The determination of K was made by XRF.
U and Th have been measured by ICP-MS with aqua regia extraction.
The U and Th data have been corrected using the value of extractability
of elements analysed by XRF, delivering true total concentrations, in an
aqua regia extraction reported in Table 12.4 of Reimann et al. (2014a).
Data analysis, comparison and merging. Since the GEMAS
samples were collected at 0-10 cm and 0-20 cm depth, the FOREGS
Topsoil has been chosen as the reference group for FOREGS data. Ob-
serving the Q-Q plots (see supplementary materials), it has been as-
sumed that both databases, FOREGS Topsoil data and GEMAS
(Ap + Gr), can be described by the following distributions:
Normal distribution for K2O
Lognormal distribution for Th and U.
To compare the two databases, first the ratio between the arithmetic
mean and median of K2O, natural logarithmic of U (hereafter ln-U) and
of Th (hereafter ln-Th) has been calculated.
The comparison between the distributions of the two databases,
FOREGS Topsoil and GEMAS (Ap + Gr), reported in Fig. 4, confirms the
results of the ratios between the mean and median (Table 2); in details:
K2O: the mean and median are similar and also the distributions;
ln-U: the comparison of the mean (0.92) is much better than the
median (0.75). The distributions appear quite similar;
ln-Th: the comparison of the mean (1.05) is better than the median
(1.10). The distributions appear quite different.
Our purpose is to have a database (hence a map) that best represents
the European soil. FOREGS Topsoil and GEMAS data in this respect are
complementary because they taking into account different kinds of soil
(Agricultural, Grazing and residual soil-undisturbed), collected at dif-
ferent locations with the same methodology. After testing the possibi-
lity to harmonize the databases, it was realised that the best solution
was to merge the two databases without any correction-harmonization.
To check the spatial correlation of the merged database, Surfer 11
software (Golden Software, LLC) has been used. Choosing the stan-
dardized estimator, experimental variograms have been computed for
K2O, ln-U and ln-Th of the merged database (Fig. 5).
The K2O, ln-U and ln-Th have been interpolated using the Surfer
11
Fig. 3. Arithmetic means (AM) over 10 km 10 km cells of long-term radon concentration in ground-floor rooms of 32 European countries (ETRS89-LAEA frame). Latest update, August
2017. (The cell mean is neither an estimate of the population exposure, nor of the risk.) Source: European Commission, DG JRC (Tollefsen et al., 2010-02).
G. Cinelli et al. Journal of Environmental Radioactivity 196 (2019) 240252
244
http://weppi.gtk.fi/publ/foregsatlas/article.php?id=10
http://weppi.gtk.fi/publ/foregsatlas/article.php?id=10
http://gemas.geolba.ac.at/
software (Golden Software, LLC) on the 10 km 10 km GISCO-LAEA
grid used for the indoor radon map, already described in sections 2 and
3.2. The smoothing interpolator that has been used is kriging (block
type), applied to ln-U and ln-Th and not transformed data for K2O, and
using the variogram models reported in Fig. 5. Then the interpolated
values for K2O (Fig. 8) and the exponential for U and Th, i.e. the geo-
metrical mean-GM (Figs. 6 and 7) have been displayed using ArcGIS
software (Esri, 2011) with the ETRS89-LAEA frame.
3.3.3. Results and discussion
Figs. 6 and 7 display respectively the geometrical means (GM) in
mg/kg of the concentration of uranium and thorium in soil over
10 km 10 km grid cells, while Fig. 8 displays the concentration in
percent of K2O. These maps have been estimated using FOREGS and
GEMAS European databases.
From a rough visual analysis of the three maps we can notice a
correlation between the three elements. Areas characterized by the
highest values for all the considered elements are in central Italy,
North-West Iberia, East Sweden, South Finland and Central France.
Moreover we can notice a correspondence with the highest regions
identified in the European Indoor Radon Map (Fig. 3). Further work has
been planned to best study the correlation between the 3 elements and
between U and indoor radon concentrations.
Countries having additional databases available at national level
could decide to use their own data to develop the maps of Th, U and
K2O concentration in soil. Belgium was a favourable case for exploring
the methodology of Th, U and K2O mapping using several different
databases available. A harmonized database was built by merging
radiological (not airborne) and geochemical data. Using this harmo-
nized database it was possible to calibrate the data from the airborne
survey (Cinelli et al., 2017a, 2018).
So far Belgium, the Czech Republic and Estonia provided aggregated
data from their national databases to be displayed in the maps of U, Th
and K2O concentration in soil and the associated references. The maps
of U, Th and K2O concentration in soil displaying the data from the
countries mentioned above are reported in the digital version of the
European Atlas of Natural Radiation (Tollefsen et al., 2016-04;
Tollefsen et al., 2016-05; Tollefsen et al., 2016-06).
3.4. Terrestrial gamma dose rate
3.4.1. Introduction
Terrestrial gamma dose is another non-negligible contribution to
total dose to humans from natural or enhanced-natural sources. Its
origin is gamma emitting natural radionuclides which are ubiquitous in
the environment, in particular in soil and rock.
Specifically, these are the primordial radionuclides 4 K and members
of the 238U and 232Th series. Altogether there are about 35 primordial
radionuclides, naturally occurring in the environment (among gamma
radiators, except the mentioned ones, most known are members of the
235U series and 138La), but their contribution to dose is negligible, in
comparison to the former.
Gamma dose rate above ground depends on source strength, i.e.
radionuclide concentration in the ground, and attenuation by the
ground, depending on chemical composition of soil or rock and hu-
midity. In general, U and Th decay chains are not in equilibrium in the
environment. This is owed to different chemical and physical properties
of the decay products, which leads to chemical and physical fractio-
nation in environmental media, mainly due to different solubility in
water. 222Rn and 220Rn which belong to the 238U and 232Th chain, re-
spectively, can migrate in the ground, depending on permeability. They
can exhale into the atmosphere and gamma radiating Rn decay pro-
ducts can be precipitated back to the ground with precipitation. As a
result of these geochemical processes, the sources of gamma radiation
Fig. 4. Quantile-quantile plots of K2O, ln-U and ln-Th of FOREGS Topsoil and GEMAS (Ap + Gr) databases considering a normal distribution.
Table 2
Ratio between the arithmetic mean and median of K2O, ln-Th and ln-U of FOREGS Topsoil
and GEMAS (Ap + Gr) databases.
Arithmetic mean
GEMAS/FOREGS
Medi
