Journal of Maps, 2014
http://dx.doi.org/10.1080/17445647.2014.923348
SCIENCE
Total natural radioactivity, Veneto (Italy)
∗
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V. Stratia,b , M. Baldoncinia,c, G.P. Bezzonb, C. Brogginid, G.P. Busob, A. Caciollid,
I. Callegarie, L. Carmignanie, T. Colonnae, G. Fiorentinia,b,c, E. Guastaldie, M. Kac¸eli
Xhixhaf, F. Mantovania,c, R. Menegazzod, L. Moub, C. Rossi Alvarezd, G. Xhixhaac and
A. Zanonb
a
Department of Physics and Earth Sciences, University of Ferrara, Ferrara, Italy; bLegnaro National
Laboratory, INFN, Legnaro, Padova, Italy; cINFN Ferrara section, Ferrara, Italy; dINFN Padova
section, Padova, Italy; eCentre for GeoTechnologies, University of Siena, San Giovanni Valdarno,
Arezzo, Italy; fDepartment of Natural Science and Habitat, University of Sassari, Sassari, Italy
(Received 4 February 2014; resubmitted 6 May 2014; accepted 8 May 2014)
We present the first detailed map of the terrestrial natural radioactivity of the Veneto Region
(Italy), a 18,264 km2 densely populated area, previously investigated through indoor radon
surveys. The activity concentration in 709 representative samples of the main Alpine
lithostratigraphic units was measured by using a high-purity germanium (HPGe) g-ray
spectrometer to characterize the radioactivity content of the 41 cartographic units of the
Veneto Lithostratigraphic map at 1:250,000 scale. An area accounting for 61% of the
territory, comprising alluvial plains was investigated through airborne g-ray measurements.
The large-volume NaI detectors were mounted on an ultralight aircraft, flying a 7000 km
line. The data were interpolated using Ordinary Kriging, and a distribution model of the
radioactivity content was produced. The result of the data analysis is a total natural
radioactivity map of Veneto at 1:250,000 scale in which the activity concentration of the
territory is visualized in seven classes, according to the percentile values calculated on the
total dataset of measurements.
Keywords: natural radioactivity; airborne gamma ray spectrometry; Veneto; activity
concentration; rock radioactivity; geological and soil mapping
1. Introduction
Following the International Atomic Energy Agency (IAEA) recommendation for the development of radioelement baseline maps (IAEA, 2010), here we present the total radioactivity map
of the Veneto Region (Italy), based on g-ray spectroscopy measurements. A map of the natural
radioactivity content is a basic component for supporting research in physics, Earth and life
sciences. Many research projects have focused on the absorbed dose distribution due to the
natural background radiation (Grasty, 2004) or on mapping geogenic radon considering the distribution of geological units (Kemski, Siehl, Stegemann, & Valdivia-Manchego, 2001). Although
different research teams in the Veneto Region have studied indoor exposure to natural
∗
Corresponding author. Email: strati@fe.infn.it
# 2014 Virginia Strati
2
V. Strati et al.
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radioactivity (Trotti et al., 1994) and mapped the areas with elevated indoor radon levels (Trotti
et al., 1998), a map of the activity concentration is still a missing piece of knowledge in a region
with one of the highest population densities in Europe.
The mountainous areas were investigated based upon the geological map with reconnaissance
of lithostratigraphical units at a scale of 1:250,000: a sampling strategy was planned to characterize the 41 Cartographic Units (CU) on the basis of the radiometric responses of 709 representative
rock samples. In the Quaternary plain deposits, the distribution of activity concentration was
obtained by geostatistical interpolation of airborne g-ray measurements, interpolated using Ordinary Kriging. We produced the map of total natural radioactivity of the Veneto Region using statistical techniques for combining all the data into a single, coherent, cartographic reference frame.
2. Geological setting
The mountainous areas of Veneto are characterized, from the geological perspective, of rocks
deformed during the Alpine orogeny, a mountain-building event that affected a broad segment
of Southern Europe and the Mediterranean region during the Paleogene and Neogene periods
(65.5 to 2.6 millions of years ago).
The Alpine orogeny has been linked with the Cretaceous-Tertiary convergence that led to the
disappearance of the Piemont-Liguria Ocean and to the subduction of the European plate beneath
the African plate (Miocene). The Alps belong to the Alps-Himalaya orogenetic system, composed
of relatively young mountains (Cretaceous-Paleogene) having a crustal structure characterized by
opposite vergence. Two main tectonic systems are distinguishable: the European chain, with a
W-NW vergence, and the Southern Alps, with a S-SE vergence.
The stratigraphic succession of the Veneto Region, included within the Subalpine Domain, is
formed by a Paleozoic crystalline basement and by sequences of sedimentary and volcanic covers
(from Permian to Quaternary) (Figure 1).
The crystalline basement, made up of metamorphic rocks (metasandstones, metabasalts, phyllites, metarhyolites), is the product of the recrystallization and deformation of sedimentary and
volcanic rocks. The basement outcrops are confined in the Recoaro (western sector of Veneto
Region), Comelico and Agordo (northern sector) areas.
The extended sedimentary cover (see Figure 1) is characterized by the presence of Paleozoic
rocks (volcanic, sandstone, limestones and marls), Mesozoic rocks (mainly dolomites, limestone
and marls) and Tertiary sequences (sandstones and conglomerates) in flysch and molasses facies.
The volcanic rocks, mainly outcropping in the Recoaro area and Euganean Hills, represent the
evidence of two different magmatic cycles. The first cycle (Triassic, Recoaro area) refers to early
products of rhyolitic, rhyodacitic and dacitic composition, followed by rhyolitic-dacitic flows and
products of andesitic and basaltic composition. The second cycle (Paleogene, Euganean Hills) is
related to an intense effusive activity, characterized by the presence of basalt lava flows, hyaloclastite, breccias and volcanic dikes.
The Subalpine Domain is covered by Quaternary sediments formed by erosion and transport
processes. These sediments include moraine deposits and sequences of alluvional materials made
up of fluvial, lake and marsh deposits.
3.
Methods
3.1. Reference geological map and sampling strategy
The geological map of Veneto at 1:250,000 scale (Antonelli et al., 1990) was used as a guide
for the natural radioactivity survey. The Veneto Region (18,264 km2) is classified into the
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Figure 1. Schematic lithostratigraphic map of the Veneto Region.
Southern Alpine sector and Hill areas (SAH), covering approximately 39% of the territory, and
into a wide River Plain area (RP) for the remaining 61% of the territory, formed of Quaternary
alluvial deposits of the Po, Adige, Brenta, Piave and Tagliamento rivers. The 41 CU in the
SAH areas were investigated by collecting 709 rock samples, following the sampling strategy
described in (Callegari et al., 2013), and obtaining an overall average of one data point per
25 km2. In particular, outcrops representative of each CU were explored collecting fresh
rock samples. The Quaternary deposits of the RP areas were investigated using airborne
g-ray spectrometry (AGRS) measurements (Guastaldi et al., 2013) performed during approximately 75 h of effective flight, which correspond to a 7000 km line. Figure 2 shows the
locations of the collected rock samples and the effective flight lines performed during the
AGRS survey.
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V. Strati et al.
Figure 2. The locations of the collected rock samples and the effective flight lines: the maximum line
spacing is approximately 2.5 km.
3.2. HPGe laboratory measurements and data analysis
The activity concentrations of 40K, eU (equivalent uranium) and eTh (equivalent thorium) in
709 representative rock samples was measured using a fully automated HPGe g-ray spectrometer, called the MCA_Rad (Xhixha et al., 2013). The MCA_Rad is composed of two
60% relative efficiency coaxial HPGe p-type detectors, having an energy resolution of approximately 1.9 keV at 1332.5 keV (60Co). The efficiency was calibrated using standard point
sources with an overall uncertainty of less than 5%. Prior to measurement, each rock
sample was crushed, homogenized and sealed in a cylindrical polycarbonate container with
a volume of 180 cm3.
The activity concentrations of 40K, eU, eTh of the 41 CU were measured using 709 rock
samples. The dataset is composed of a relevant fraction of the Minimum Detectable Activity
(MDA) values, corresponding approximately to 9.4 Bq/kg for 40K, 2.5 Bq/kg for eU and
Journal of Maps
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3.7 Bq/kg for eTh, mainly found in the carbonate rocks. The distribution function for each dataset
was graphically studied using univariate statistics by means of both frequency histograms and
percentage-probability P-P plots to gain an insight into the data structure. The KolmogorovSmirnov statistical test was applied to discriminate the normal and lognormal distributions, providing a p-value (usually p , 0.05) for rejecting the null hypothesis. The MDA values were
treated on the basis of the statistical arguments described in (Helsel, 1990). We verified that
the distributions of 40K, eU and eTh are generally well fitted by a lognormal function. The
total activity was calculated for each CU and the uncertainty propagation was evaluated using
a Monte-Carlo method (BIPM et al., 2008).
3.3.
Airborne g-ray data and data analysis
The AGRS measurements were performed using a modular instrument called the AGRS_16.0 L,
composed of four NaI(Tl) detectors (10 cm × 10 cm × 40 cm each) with a total volume of
approximately 16 Liters mounted on an autogyro (Guastaldi et al., 2013). The system is
further equipped with an ‘upward-looking’ NaI(Tl) detector of 1 L, partially shielded from
ground radiation and used to account for an atmospheric radon correction. The position of the
AGRS_16.0 L system was recorded using a global positioning system (GPS) receiver, and the
height above the ground was calculated by applying the Laplace formula, using pressure and
temperature values measured by dedicated sensors.
The radiometric data acquired during the AGRS survey was analyzed by first integrating the
measured events in 12s interval g-spectra. The g-spectra are then calibrated and analyzed using
the Full Spectrum Analysis with Non-Negative Least Squares constraints (FSA-NNLS) as
described in (Caciolli et al., 2012). The activity concentrations of 40K, eU and eTh at ground
level were determined by applying several corrections to the measured signals, as described in
(Guastaldi et al., 2013): cosmic background corrections, topography corrections, variation in
flying altitude and height corrections and atmospheric radon corrections. Finally, approximately
19×103 radiometric data for the 40K, eU and eTh concentrations were obtained and used to calculate the total activity concentration.
3.4.
Mapping radiometric data
The frequency distribution of the total activity concentration of the overall geo-dataset obtained
by laboratory and airborne g-ray measurements are shown in Figure 3. The map of the total
activity concentration is obtained by interpolating the radioactivity content measured in representative samples of the 41 CU in the SAH areas and in the airborne g-ray surveys in the RP area. In
particular, the median value of the total activity concentration for each CU is assigned to the corresponding polygons in the SAH areas (Callegari et al., 2013). For each radionuclide (40K, eU and
eTh) in the RP areas, omnidirectional Experimental Semi-Variograms (ESV) composed by 12
lags of 1 km were computed and modeled. To check the goodness of the ESV models, a cross
validation procedure was used. The interpolation of the activity concentrations of 40K, eU and
eTh were rasterized in a 200 m × 200 m grid and used to calculate the total activity
concentration.
The legend of the Main Map was constructed following the recommendations of (Reimann,
2005). The total activity concentrations were grouped into seven classes of percentiles, calculated
on the total dataset of 19,735 records. In particular, the intervals of the classes were appropriately
identified as the 5th, 20th, 50th, 80th, 95th and 100th percentiles.
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V. Strati et al.
Figure 3. The frequency distributions of the total activity concentration in rock samples (blue) and airborne
g-ray data measurements (red). The samples on the left of the dashed line are characterized by at least one
concentration of K, U and Th below the MDA.
4.
Conclusions
We present the first detailed investigation of the terrestrial natural radioactivity of the Veneto
Region (Italy), obtained using g-ray spectroscopy measurements. In particular the activity concentrations of SAH areas refer to rock reservoirs, while the radiometric data collected by
AGRS surveys come from the top soil of RP areas.
Following the lithostratigraphic map at 1:250,000 scale (Antonelli et al., 1990), the 41 CU of
the SAH areas were characterized with respect to the total activity concentration by means of 709
measurements on rock samples performed using a HPGe g-ray spectrometer. Over 50% of the
SAH areas primarily consists of limestones and dolomites, characterized by a low total activity,
often resulting in MDA values. The highest values of total activity in the SAH areas are found in
the magmatic rocks of the Euganean Hills and the Recoaro area, together with the crystalline
basement.
The Quaternary sediments of the RP area were investigated by means of airborne g-ray
surveys, accounting for 75 h of effective time of flight. The extended area with mediumhigh values of total activity concentration could be related to anthropogenic activities (Wetterlind et al., 2012) and selective fluvial deposition of the main river basins. In particular, we
observed that the S-E area surrounding the Euganean Hills is characterized by enrichment
in the radionuclides, probably due to the erosion and transport processes undergone by magmatic rocks.
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Software
The geostatistical analysis was performed using Geovariances ISATISw. The map was produced
using ESRI ArcGIS 9.3.
Acknowledgments
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The authors thank the cartographic support of the Veneto Region – directorate of regional geology and
mining activities. The authors are grateful to Antongiovanni M., Pagotto C., Shyti M. and Bortolami
A. We wish to thank Joachim Kemski, Chris Orton and Mirko Reguzzoni for their detailed and thoughtful
reviews.
Funding
This work is partly supported by the Fondazione Cassa di Risparmio di Padova e Rovigo, the Istituto Nazionale di Fisica Nucleare (INFN), the Centre for GeoTechnologies (University of Siena) and by the MIUR
(ITALRAD Project).
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TOTAL NATURAL RADIOACTIVITY MAP OF VENETO (ITALY)
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Strati V.a,b , Baldoncini M a,c, Bezzon G.P.b Broggini C.d , Buso G. P.b , Caciolli A.d , Callegari I.e, Carmignani L.e, Colonna T.e, Fiorentini G.a,b,c,
Guastaldi E.e, Kaçeli Xhixha M.f, Mantovani F.a,c, Menegazzo R.d , Mou L.b , Rossi Alvarez C.d , Xhixha G.a,c, Zanon A.b
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of Ferrara, Physics and Earth Science Department, Via Saragat, 1 - 44100 Ferrara, Italy.
b INFN, Legnaro National Laboratory, Via dell’Università, 2 - 35020 Legnaro, Padova, Italy.
c INFN, Ferrara Section, Via Saragat, 1 - 44100 Ferrara, Italy.
d INFN, Padova Section, Via Marzolo 8 - 35131 Padova, Italy.
e University of Siena, Centre for GeoTechnologies, Via Vetri Vecchi, 34 - 52027 San Giovanni Valdarno, Arezzo, Italy.
f University of Sassari, Botanical, Ecological and Geological Sciences Department, Piazza Università 21- 07100 Sassari, Italy.
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20
0
20
0
20
200
800
80 0
20
200
0
20
200
00
20
! Marostica
0
0
20 0
20
80 0
20 00
0
! Tezze
80 0
0
0
0
! Castelfranco
! Vedelago
TREVISO
! Paese
Veneto
! Malo
0
1400
14 00
140 0
80
! Valdagno
200
1400
00
14 00
14
80
80
0
20 0
! Trebaseleghe
800
0
0
20
80
0
0
0
20
20 0
200
800
800
200
0
20
200
80 0
0
! Creazzo
20 0
VICENZA
! Torri
! Piazzola
sul Brenta
di Quartesolo
0
20
0
20 0
! Montecchio
200
200
er
! Campodarsego
20
Arzignano
200
0
!
200
20
Grezzana
!
San Pietro in Cariano
!
0
200
g ol a
80
! Negrar
20
Maggiore
! Noale
!
! Martellago
! Santa
Maria di Sala
! Mirano !
Spinea
20
0
20 0
0
20
200
200
0
20
0
20
200
0
cch
ne
20 0
! Lonigo
200
20 0
Teolo
20
0
d'Azzano
20
!
! Abano
0
20 0
200
20
Bonifacio
0
Cadoneghe
! Musile
di Piave
Mogliano Veneto
! Marcon
! Caorle
! Eraclea
Sile
Legend
! Jesolo
d
lio
g
i
av
el B
! Mira
! Mestre
CITIES
! Cavallino-Treporti
!
Regional boundaries
800
GUL F O F VE NICE
Rivers
Terme
Lakes and lagoons
di Sacco
Adriatic Sea
20 0
20
0
Percentile
! Monselice
0
! Bovolone
20
della Scala
! Este
Bre
nt
r
Ta
ro
ta
L o m b a r d i a
! Cerea
! Chioggia
95 - 100
a
80 - 95
! Legnago
50 - 80
Fratta
20 - 50
! Cavarzere
5 - 20
Ad
ige
! Badia
4995303
Polesine
0-5
ROVIGO
! Lendinara
! Adria Ca nalb i a n
E m i l i a - R o m a g n a
0
© Journal of Maps, 2014
11°0'0"E
662937
702937
2.5
5
Scale 1:250,000
10
15
20
758 - 921
550 - 758
301 - 550
153 - 301
39 - 153
4995303
45°0'0"N
Tolle
The activity concentration in 709 representative samples of the
Southern Alps sector and the Hill areas (SAH) were measured using
a high-purity germanium (HPGe) gamma-ray spectrometer to
characterize the radioactivity content of the 41 Cartographic Units
(CU) of the Veneto Lithostratigraphic map at 1:250,000 scale. The
average sampling distribution is one sample per 25 km2. The
radioactivity content of the quaternary deposits of the River Plain
(RP) (61% of the territory) was measured through an airborne
gamma-ray survey performed by using a module of 4 NaI(Tl)
crystals of 16 L mounted onto an autogyro, which covered
approximately 7000 line km.
The map at 1:250,000 scale describes the total activity concentration
of the 41 Alpine lithostratigraphic units in the SAH areas and of the
RP deposits obtained using the Ordinary Kriging interpolator. The
seven classes of the legend were calculated on the basis of the
distribution values identifying the 5th, 20th, 50th, 80th, 95th and
100th percentiles.
25
Km
12°0'0"E
921 - 2429
The natural radioactivity of the total area of 18,390 km2 of the
Veneto Region (Italy) was characterized.
! Porto
Po
4955303
622937
Viro
Po
45°0'0"N
Total radioactivity
(Bq/kg)
Descriptive notes
co
! Porto
Po
Contour lines with 200 m interval
Highways
200
! Isola
5035303
Border of SAH areas
Venetian
Lagoon
! Piove
Towns
International boundaries
VENEZIA
re
nt
a
! Camponogara
! Ponte San Nicolò
Terme
! Albignasego
20 0
200
! Dolo
Dentro
! Montegrotto
0
20
N
! Vigonza
PADOVA
Donà di Piave
!
! Selvazzano
0
0
! San
20
20
Giovanni Lupatoto
! Zevio
ig l i o
! Rubano
200
San Martino Buon Albergo
20 0
!
sul Mincio
! Castel
! San
Ba
0
! Sommacampagna
20
!
20
!
20 0
0
20
200
VERONA
! Sona
! Valeggio
! Vigodarzere
200
0
20 0
! Bussolengo
5035303
Fimon
20
! Pescantina
ro
Caorle
Lagoon
a
! Salzano
T
! Chiampo
800
Ze
! Scorzè
! Camposampiero
ina
800
800
Te s
80
! San
! Preganziol
se
800
0
Vicentino
Ta
! Bibione
! Roncade
De
0
80 0
80
! Cornedo
80 0
800
Martino di Lupari
! Dueville
800
800
! San
! Cittadella
Stino di Livenza
L i ve
Biagio di Callalta
20 00
80
Godego
sul Brenta
! San
Sagittaria
nz
80
0
o
Astic
! Thiene
! Villorba
! Rosà
80
Garda
! Schio
! Santo
! Cassola
800
0
14 00
del Grappa
200
80
800
! Montebelluna
742937
5075303
!
e nt o
14
0
20
! Bassano
0
200
20 00
20 0
200
80 0
! Concordia
Michele al Tagliamento
am
gli
1400
14 00
200
200
! Portogruaro San
! Oderzo
20
Romano d'Ezzelino
800
80 0
20 00
80 0
0
0
00
00
20
20
14
14
20 0
!
200
00
200
00
20
14
200
20 0
800
800
00
14
20 0
14 00
0
14
5075303
20
!
!
!
782937
13°0'0"E
4955303
822937
CARTOGRAPHIC REFERENCE SYSTEM WGS 84 UTM ZONE 32 - CARTESIAN LATTICE IN BLACK
GEOGRAPHIC COORDINATES REFER TO THE WGS 84 GEODETIC SYSTEM IN BLUE
!