Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the
AlphaGUARD and from 2013- with RM-2 measuring systems, while soil permeability
was measured with the Radon-JOK device since 2015. Measurements of both
parameters were performed at 412 locations, mostly in the vicinity of schools and
kindergartens and the obtained average value of radon in soil gas was 48 kBq m-3 with
standard deviation of 52 kBq m-3. It is important to emphasize that there are areas with
radon concentrations up to 550 kBq m3
.
Geogenic radon potential (GRP) has been constructed by “Neznal approach” and a
new subclassification with 7 classes (1- very low, 2 – low, 3 – medium lower, 4 –
medium higher, 5 – high, 6 – very high, 7 – extremely high) is being introduced. The
obtained average GRP of 28 ± 29 (“Neznal equation”) or 3.30 ± 0.96 (classes)
classifies the soil of Croatia into soil of medium GRP.Koncentracije radona u tlu u Republici Hrvatskoj su mjerene AlphaGUARD mjernim
sustavom (Genitron Instruments) od 2005. do 2013., a potom se mjere RM-2 mjernim
uređajem (Radon v.o.s., Češka Republika). Premeabilnost tla mjeri se od 2015. godine
Radon-JOK uređajem (Radon v.o.s., Češka Republika). Mjerenja se uglavnom obavljaju
u blizini škola i vrtića. Dosad je izvršeno 412 mjerenja oba parametra. Prosječna
koncentracija radona u tlu iznosi 48 kBq m-3 s pripadnom standardnom devijacijom od
52 kBq m-3. No, postoje i područja u kojima je mjerena koncentracija radona u tlu i do
550 kBq m-3
.
Geogenski radonski potencijal (GRP) je izračunat tzv. češkim pristupom iz empirijske
jednadžbe, a uvedena je i nova subklasifikacija kojom se kontinuirane vrijednosti
GRP-a svrstavaju u klase: (1- vrlo nizak, 2 – nizak, 3 – niži srednji, 4 – viši srednji, 5 –
visok, 6 – vrlo visok, 7 – izrazito visok). Izračunate vrijednosti GRP-a iznose 28 ± 29
(empirijska kontinuirana vrijednost) odnosno 3,30 ± 0,96 (klase) čime se tlo u Republici
Hrvatskoj, u prosjeku, klasificira u srednji geogenski radonski potencijal

Miklavčić, Igor

Poje Sovilj, Marina

Radolić, Vanja

Stanić, Denis

VinaR - Repository of the Vinča Institute of Nuclear Sciences

ДРУШТВО ЗА ЗАШТИТУ ОД ЗРАЧЕЊА 
СРБИЈЕ И ЦРНЕ ГОРЕ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
XXIX СИМПОЗИЈУМ ДЗЗСЦГ 
Сребрно језеро 
27- 29. септембар 2017. године 
 
 
 
 
 
 
 
 
 
Београд 
2017. године 
ЗБОРНИК 
РАДОВА 
 SOCIETY FOR RADIATION PROTECTION OF  
SERBIA AND MONTENEGRO 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
XXIX SYMPOSIUM DZZSCG 
Srebrno jezero 
27- 29. September 2017 
 
 
 
 
 
 
 
 
 
 
Belgrade 
2017 
PROCEEDINGS 
 
ЗБОРНИК РАДОВА 
 
XXIX СИМПОЗИЈУМ ДЗЗСЦГ 
27-29.09.2017. 
 
 
 
 
 
 
 
 
 
Издавачи: 
Институт за нуклеарне науке „Винча“ 
Друштво за заштиту од зрачења Србије и Црне Горе 
 
 
За извршног издавача: 
Др Борислав Грубор  
 
Уредници: 
Др Јелена Станковић Петровић 
 Др Гордана Пантелић 
  
 
 
ISBN 978-86-7306-144-3 
 
ÓInstitut za nuklearne nauke „Vinča“ 
 
Техничка обрада:  
Јелена Станковић Петровић, Гордана Пантелић 
 
Штампа: 
 Институт за нуклеарне науке ”Винча”, Мике Петровића Аласа 12-14, 11351 
Винча, Београд, Србија 
 
Тираж: 
 150 примерака 
 
Година издања: 
Септембар 2017. 
 
XXIX	Симпозијум	ДЗЗСЦГ	
 
192 
 
RADON IN SOIL GAS AND CONSTRUCTED GEOGENIC RADON 
POTENTIAL IN CROATIA 
Vanja RADOLIĆ, Marina POJE SOVILJ, Denis STANIĆ and Igor MIKLAVČIĆ 
J. J. Strossmayer University of Osijek, Department of Physics, Osijek, Croatia 
vanja@fizika.unios.hr 
 
ABSTRACT 
Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the 
AlphaGUARD and from 2013- with RM-2 measuring systems, while soil permeability 
was measured with the Radon-JOK device since 2015. Measurements of both 
parameters were performed at 412 locations, mostly in the vicinity of schools and 
kindergartens and the obtained average value of radon in soil gas was 48 kBq m
-3
 with 
standard deviation of 52 kBq m
-3
. It is important to emphasize that there are areas with 
radon concentrations up to 550 kBq m
3
.  
Geogenic radon potential (GRP) has been constructed by “Neznal approach” and a 
new subclassification with 7 classes (1- very low, 2 – low, 3 – medium lower, 4 – 
medium higher, 5 – high, 6 – very high, 7 – extremely high) is being introduced. The 
obtained average GRP of 28 ± 29 (“Neznal equation”) or 3.30 ± 0.96 (classes) 
classifies the soil of Croatia into soil of medium GRP. 
 
1.  INTRODUCTION 
Radon (222Rn) is continuously generated in rocks and soil as a product of radioactive 
decay of radium (226Ra) in the natural decay series of uranium (238U). A very small 
fraction of radon emanates from its place of origin into the air-filled pore spaces of 
rocks. Driven by some transport mechanisms, such as advection (due to pressure 
differences), convection (temperature differences) or diffusion (concentration differen-
ces), it moves toward the surface and exhalates to the atmosphere or enters into the 
buildings above. The resulting indoor radon concentration in buildings is a function of 
natural (“what the Earth delivers”) and anthropogenic factors (construction types: state 
and age of building, building materials used, presence of basement or not, and living 
habits of the residents: ventilation rate, type of heating and air-conditioning etc.) and 
therefore it is temporally variable and unique for each particular house or building. 
From the radon mapping point of view, it is wise to use that kind of parameter which is 
more or less constant over a long period of time. Such parameter should take into 
consideration as much physical processes as possible which contributes to conditions 
for potential indoor radon. The most used input quantities are: radon in soil gas (c, 
kBq/m-3) at certain depth which is the result of production (radioactive decay of radium) 
and emanation from minerals while soil permeability (k, m2) describes an advective 
transport process which usually dominates over the others in most cases. Recently, these 
two variables were combined and define so called geogenic radon potential (GRP) 
which is widely used as a measure of geogenic hazard of “what Earth delivers” in term 
of radon [1-3]. Although, there are several very different definitions and meanings of 
GRP in literature [4-7], we are using the Czech approach, the parameter called 
“Neznal’s” GRP which has been developed from radon index (RI) of building site [8]. 
That GRP is defined in the following way: 
Радон	
 
193 
 
!"# = 	
&
-()*+,--./
  .	  GRP=
!
-#$%&'()*+
         (1) 
In the Czech Republic, three classes of GRP are used and they are correlated to radon 
index: low (GRP < 10), medium (10 ≤ GRP < 35) and high ( 35 ≤ GRP). 
The main goal of this paper is to present GRP maps based on radon in soil gas and soil 
permeability measurements in Croatia. The difference between continuous (by using 
equation (1)) and discrete (classes) GRP approach will be investigated and the 
subclassification of GRPs will be introduced and justified due to very different and 
diverse geological structures as well as climatological conditions in Croatia. 
 
2.  MATERIAL AND METHODS 
Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the 
AlphaGUARD (Manufacturer: Genitron Instruments, Germany) and from 2013- with 
the RM-2 (Manufacturer Radon v.o.s., Czech Republic) measuring systems, while soil 
permeability was measured with the Radon-JOK device (Manufacturer: Radon v.o.s., 
Czech Republic) from 2015. Measurements of both parameters were performed at 412 
locations, mostly in the vicinity of schools and kindergartens. Radon in soil gas 
measurements were generally performed immediately after the soil permeability 
measurements at the same soil probe and at the depth of 0.8 m (with 5 cm of sampling 
geometry). Up to 2013, radon was measured by the AlphaGUARD measuring system 
according to sampling protocol from manufacturer (AlphaGUARD manual). In both 
types of radon detectors for soil gas measurements, thoron was excluded from the 
results because measurements were performed 15 minutes after gas sampling. 
In fact, soil permeability was calculated from Darcy’s law according to measurement of 
time needed to withdraw certain amount of soil air by means of negative pressure 
established by Radon-JOK measurement set-up (Radon-JOK manual).  
Geogenic radon potential for each measuring location was calculated by using equation 
(1) and taking into account the maximum measured value of radon in soil gas and the 
average soil permeability value. The obtained values were classified into classes 
according to Table 1. 
 
Table 1. Subclassification of geogenic radon potential (GRP) 
 
GRP – ”Czech” 
approach 
Class 
Radon 
index 
GRP – 
”Croatian” 
subdivision 
Class Description 
GRP < 10 1 Low 
GRP < 5 1 Very low 
5 ≤ GRP < 10 2 Low 
10 ≤ GRP < 35 2 Medium 
10 ≤ GRP < 22.5 3 Medium lower 
22.5 ≤ GRP < 35 4 Medium 
higher 
GRP ≥ 35 3 High 
35 ≤ GRP < 60 5 High 
60 ≤ GRP < 125 6 Very high 
GRP ≥ 125 7 Extremely 
high  
Radon values as well as GRPs were presented in the form of maps based on 
internationally suggested 10 x 10 km square grid which has been used for the European 
indoor radon map as well as for the future European geogenic radon map [1, 9].  
XXIX	Симпозијум	ДЗЗСЦГ	
 
194 
 
3.  RESULTS AND DISCUSSION 
The obtained results of radon in soil gas measurements in Croatia as well as calculated 
(by Equation (1)) and constructed (according to classification described in Table 1) 
geogenic radon potential are summarized in Table 2. The arithmetic mean of all 
measurements of radon in soil gas is 48 kBqm-3 with standard deviation of 52 kBqm-3. 
while the average GRP with its standard deviation is 28 ± 29. According to the used 
subclassification, it belongs to higher medium GRP. Normal probability plots of 
logarithmic values for both parameters are presented in Figures 1A and 1B. The applied 
statistical tests for normality (Lilliefors, Kolmogorov-Smirnov, Shapiro-Wilk) show 
that both parameters do not obey log-normal distribution, which was expected, since the 
measuring locations were not randomly chosen. The measurements of radon in soil gas 
and soil permeability were mostly performed in the vicinity of schools and 
kindergartens as a part of targeted surveys of indoor radon.  
 
Table 2. The basic statistical analysis of radon in soil gas measurements and 
calculated and constructed geogenic radon potential (GRP) for Croatia (AM – 
arithmetic mean, SD – standard deviation, GM – geometric mean, GSD – 
geometric standard deviation) 
 Radon in soil gas 
[kBq m
-3
] 
GRP GRP-classes 
Number of measurements 874 795 
Number of locations 785 412 
AM 47.6 28.4 3.30 
SD 52.1 28.7 0.96 
Median 34.7 15.9 3 
GM 33.0 16.8 3.0 
GSD 2.4 2.6 1.6 
Min - Max 1.0 - 566.0 0.3 - 470.4 1 - 7 
 
 
  
Figure 1A. Normal probability plot of 
logarithmic values of radon in soil gas 
in Croatia 
Figure 1B. Normal probability plot of 
logarithmic values of GRPs in Croatia 
 
The strong influence of water content in soil on radon concentration in soil gas is 
presented in Figure 2. In two consecutive years (2014 and 2015), the measurements of 
radon in soil gas were performed in the vicinity of schools and kindergartens in 
Радон	
 
195 
 
Požega-Slavonia county and repeated a year later. In 2014, there were severe rainfalls 
with lots of floods in the area of interest a week before measuring campaign and a year 
later (in 2015), there were normal weather conditions (the cumulative precipitation for 
September 2014 and 2015 for Požega weather measuring station are presented as the 
right part of Figure 2). Radon in soil gas were approximately twice higher during the 
period with significant water content in soil than during the period with normal 
conditions (normal quantity of precipitation for that area).  
 
 
 
 
Figure 2. Comparison of radon in soil gas concentrations measured in 
Požega-Slavonia county at the same locations in two consecutive years. In 2014, the 
measurements were performed a week after severe rainfalls (upper right) and in 
2015 during normal weather conditions (lower right). The line (y(x) = x) on the 
graphical presentation of empirical results suggests no difference between 
measured values. 
 
 
In order to examine temporal variations of local GRP associated to meteorological and 
climate variations, the measurements of radon in soil gas and soil permeability were 
undertaken several times a week during the whole year (from April 2015 until April 
2016). The obtained results of calculated GRP are presented in Figure 3. There were 82 
measurements and the average value and its standard deviation of adjoint GRP class 
was 3.76 ± 0.58. In 93% of cases, the associated GRPs belonged to medium GRP class. 
Two values, at the end of the presented measuring cycle, were significantly different 
from the other results. These anomalies were associated with the preparation for 
construction work by heavy machinery nearby the measurement point. This was, at the 
end, the reason to stop measurements at that measuring site. 
 
 
 
 
 
 
 
XXIX	Симпозијум	ДЗЗСЦГ	
 
196 
 
 
Figure 3. Time series of GRP values calculated from measurements of radon in soil 
gas and soil permeability at one measuring point in the courtyard of Department 
of Physics in Osijek. Yellow areas represent the medium (lower and higher) GRP. 
 
 
Geogenic radon potential maps of two selected counties (Istria and Osijek-Baranja) 
using grid approach were created and presented in Figure 4. These two counties have a 
very different geological structure. Istria consists of a limestone plateau and dolomites 
formed in Late Cretaceous, much of which lacks water owing to its karst topography 
while carbonate rocks, especially flysch are significantly formed during Paleogene 
period. Osijek-Baranja county consists geologically mainly of sandstones and soft clay 
while sediments are of gravels, loess and silts. All these sediments are the product of 
mostly continental environments and alluvial fans. Differences in geological structure of 
these two areas inevitable have, as a consequence, very different geogenic radon 
potential as it can be seen in Figure 4. 
 
Радон	
 
197 
 
 
 
 
Figure 4. Geogenic radon potential maps of Istria (left) and Osijek-Baranja (right) 
counties 
 
In more than 2/3 of the Istrian peninsula there are high (or even very high) GRP while 
in Osijek-Baranja county medium GRP prevails. This kind of maps could be useful for 
identification [10] as well as definition of so called radon-prone areas which have been 
under special attention in EU BSS [11]. The next phase of research is to connect GRP 
and indoor radon maps and to find some kind of functional or geostatistical relationship 
between those spatial variables as well as to introduce new ones (other terrestrial 
radionuclide maps, climate maps, geology maps, etc.). 
 
4.  CONCLUSION 
Radon in soil gas and soil permeability were measured in more than 400 locations in 
Croatia. The geogenic radon potential for each location was calculated and the obtained 
results show that the average GRP in Croatia is in medium class. Although, there are 
areas with very high (or even extremely high) GRP. It was shown that radon in soil gas 
concentration itself is highly sensitive on water content in soil. The variations of GRP 
throughout a year are much smaller than radon in soil gas and it is wise to use this 
quantity to describe the potential hazard of radon. GRP maps of several Croatian 
counties were created and can be used as a tool for identification or even for definition 
of radon-prone areas. Nevertheless, it should be pointed out that no map can fully reflect 
the true reality of variations of radon potential due to heterogeneity of soil under the 
surface. Moreover, such maps can provide an useful information about soil as the main 
XXIX	Симпозијум	ДЗЗСЦГ	
 
198 
 
radon source in buildings but they cannot be used for direct extrapolation and estimation 
on indoor radon concentrations inside the buildings at some areas of interest. 
 
5.  ACKNOWLEDGEMENT 
The part of this research has been supported and funded by the internal project 
IZIP-2014-100 of J.J.Strossmayer University of Osijek.  
 
6.  REFERENCES 
[1]  V. Gruber, P. Bossew, M. De Cort, T. Tollefsen. The European map of the geogenic 
radon potential. J. Radiol. Prot. 33, 2013, 51–60. 
[2]  K.Z. Szabo, G. Jordan, A. Horvath, C. Szabo. Mapping the geogenic radon 
potential: methodology and spatial analysis for central Hungary. J. Environ. 
Radioact. 129, 2014, 107-120. 
[3]  G. Ielsch, M.E. Cushing, Ph. Combes, M. Cuney. Mapping of the geogenic radon 
potential in France to improve radon risk management: methodology and first 
application to region Bourgogne. J. Environ. Radioact. 101, 2010, 813-820. 
[4]  J. Chen, R. Falcomer, L. Bergman, J. Wierdsma, J. Ly. Correlation of soil radon and 
permeability with indoor radon potential in Ottawa. Radiat. Prot. Dosim. 136, 2009, 
56-60. 
[5]  H. Friedmann. Final results of the Austrian radon project. Health Phys. 89, 2005, 
339-348. 
[6]  J. Kemski, A. Siehl, R. Stegemann, M. Valdivia-Manchego. Mapping the geogenic 
radon potential in Germany. Sci. Tot. Environ. 272, 2001, 217-230. 
[7]  J.H.C. Miles, J.D. Appleton. Mapping variation in radon potential both between and 
within geological units. J. Radiol. Prot. 25, 2005, 257–276. 
[8]  M. Neznal, M. Neznal, M. Matolin, I. Barnet, J. Miksova. The new method for 
assessing the radon risk of building sites. Czech Geol. Survey Special papers, 16 
(2004), Czech Geol. Survey, 47 p.: http://www.radon-vos.cz/pdf/metodika.pdf (last 
access 25.2.2017). 
[9]  G. Dubois. P. Bossew, T. Tollefsen, M. De Cort. First steps towards a European 
atlas of natural radiation: status of the European indoor radon map. J. Environ. 
Radioact. 101, 2010, 786-798.  
[10]  V. Radolić, I. Miklavčić, D. Stanić, M. Poje, I. Krpan, M. Mužević, B. Petrinec, B. 
Vuković. Identification and mapping of radon-prone areas in Croatia - preliminary 
results for Lika-Senj and the southern part of Karlovac Counties, Radiat. Prot. 
Dosim. 162, 2014, 29-33. 
[11]  Council directive 2013/59/EURATOM of laying down basic safety standards for 
protection against the dangers arising from exposure to ionising radiation. Office 
Journal of the European Union, 5 December 2013; L13: 1-73. 
 
Радон	
 
199 
 
RADON U TLU I IZRAČUNATI GEOGENSKI RADONSKI 
POTENCIJAL U HRVATSKOJ 
Vanja RADOLIĆ, Marina POJE SOVILJ, Denis STANIĆ and Igor MIKLAVČIĆ 
J. J. Strossmayer University of Osijek, Department of Physics, Osijek, Croatia, 
vanja@fizika.unios.hr 
 
APSTRAKT 
Koncentracije radona u tlu u Republici Hrvatskoj su mjerene AlphaGUARD mjernim 
sustavom (Genitron Instruments) od 2005. do 2013., a potom se mjere RM-2 mjernim 
uređajem (Radon v.o.s., Češka Republika). Premeabilnost tla mjeri se od 2015. godine 
Radon-JOK uređajem (Radon v.o.s., Češka Republika). Mjerenja se uglavnom obavljaju 
u blizini škola i vrtića. Dosad je izvršeno 412 mjerenja oba parametra. Prosječna 
koncentracija radona u tlu iznosi 48 kBq m
-3
 s pripadnom standardnom devijacijom od 
52 kBq m
-3
. No, postoje i područja u kojima je mjerena koncentracija radona u tlu i do 
550 kBq m
-3
. 
Geogenski radonski potencijal (GRP) je izračunat tzv. češkim pristupom iz empirijske 
jednadžbe, a uvedena je i nova subklasifikacija kojom se kontinuirane vrijednosti 
GRP-a svrstavaju u klase: (1- vrlo nizak, 2 – nizak, 3 – niži srednji, 4 – viši srednji, 5 – 
visok, 6 – vrlo visok, 7 – izrazito visok). Izračunate vrijednosti GRP-a iznose 28 ± 29 
(empirijska kontinuirana vrijednost) odnosno 3,30 ± 0,96 (klase) čime se tlo u Republici 
Hrvatskoj, u prosjeku, klasificira u srednji geogenski radonski potencijal. 


Radon u tlu i izračunati geogenski radonski potencijal u Hrvatskoj

Repository of the Vinča Nuclear Institute (VinaR)

ДРУШТВО ЗА ЗАШТИТУ ОД ЗРАЧЕЊА СРБИЈЕ И ЦРНЕ ГОРЕ                     XXIX СИМПОЗИЈУМ ДЗЗСЦГ Сребрно језеро 27- 29. септембар 2017. године          Београд 2017. године ЗБОРНИК РАДОВА  SOCIETY FOR RADIATION PROTECTION OF  SERBIA AND MONTENEGRO                       XXIX SYMPOSIUM DZZSCG Srebrno jezero 27- 29. September 2017           Belgrade 2017 PROCEEDINGS  ЗБОРНИК РАДОВА  XXIX СИМПОЗИЈУМ ДЗЗСЦГ 27-29.09.2017.          Издавачи: Институт за нуклеарне науке „Винча“ Друштво за заштиту од зрачења Србије и Црне Горе   За извршног издавача: Др Борислав Грубор   Уредници: Др Јелена Станковић Петровић  Др Гордана Пантелић     ISBN 978-86-7306-144-3  ÓInstitut za nuklearne nauke „Vinča“  Техничка обрада:  Јелена Станковић Петровић, Гордана Пантелић  Штампа:  Институт за нуклеарне науке ”Винча”, Мике Петровића Аласа 12-14, 11351 Винча, Београд, Србија  Тираж:  150 примерака  Година издања: Септембар 2017.  XXIX	Симпозијум	ДЗЗСЦГ	 192  RADON IN SOIL GAS AND CONSTRUCTED GEOGENIC RADON POTENTIAL IN CROATIA Vanja RADOLIĆ, Marina POJE SOVILJ, Denis STANIĆ and Igor MIKLAVČIĆ J. J. Strossmayer University of Osijek, Department of Physics, Osijek, Croatia vanja@fizika.unios.hr  ABSTRACT Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the AlphaGUARD and from 2013- with RM-2 measuring systems, while soil permeability was measured with the Radon-JOK device since 2015. Measurements of both parameters were performed at 412 locations, mostly in the vicinity of schools and kindergartens and the obtained average value of radon in soil gas was 48 kBq m-3 with standard deviation of 52 kBq m-3. It is important to emphasize that there are areas with radon concentrations up to 550 kBq m3.  Geogenic radon potential (GRP) has been constructed by “Neznal approach” and a new subclassification with 7 classes (1- very low, 2 – low, 3 – medium lower, 4 – medium higher, 5 – high, 6 – very high, 7 – extremely high) is being introduced. The obtained average GRP of 28 ± 29 (“Neznal equation”) or 3.30 ± 0.96 (classes) classifies the soil of Croatia into soil of medium GRP.  1.  INTRODUCTION Radon (222Rn) is continuously generated in rocks and soil as a product of radioactive decay of radium (226Ra) in the natural decay series of uranium (238U). A very small fraction of radon emanates from its place of origin into the air-filled pore spaces of rocks. Driven by some transport mechanisms, such as advection (due to pressure differences), convection (temperature differences) or diffusion (concentration differen-ces), it moves toward the surface and exhalates to the atmosphere or enters into the buildings above. The resulting indoor radon concentration in buildings is a function of natural (“what the Earth delivers”) and anthropogenic factors (construction types: state and age of building, building materials used, presence of basement or not, and living habits of the residents: ventilation rate, type of heating and air-conditioning etc.) and therefore it is temporally variable and unique for each particular house or building. From the radon mapping point of view, it is wise to use that kind of parameter which is more or less constant over a long period of time. Such parameter should take into consideration as much physical processes as possible which contributes to conditions for potential indoor radon. The most used input quantities are: radon in soil gas (c, kBq/m-3) at certain depth which is the result of production (radioactive decay of radium) and emanation from minerals while soil permeability (k, m2) describes an advective transport process which usually dominates over the others in most cases. Recently, these two variables were combined and define so called geogenic radon potential (GRP) which is widely used as a measure of geogenic hazard of “what Earth delivers” in term of radon [1-3]. Although, there are several very different definitions and meanings of GRP in literature [4-7], we are using the Czech approach, the parameter called “Neznal’s” GRP which has been developed from radon index (RI) of building site [8]. That GRP is defined in the following way: Радон	 193  !"# = 	&-()*+,--./  .	  GRP=!-#$%&'()*+         (1) In the Czech Republic, three classes of GRP are used and they are correlated to radon index: low (GRP < 10), medium (10 ≤ GRP < 35) and high ( 35 ≤ GRP). The main goal of this paper is to present GRP maps based on radon in soil gas and soil permeability measurements in Croatia. The difference between continuous (by using equation (1)) and discrete (classes) GRP approach will be investigated and the subclassification of GRPs will be introduced and justified due to very different and diverse geological structures as well as climatological conditions in Croatia.  2.  MATERIAL AND METHODS Radon concentrations in soil gas in Croatia were measured from 2005-2013 with the AlphaGUARD (Manufacturer: Genitron Instruments, Germany) and from 2013- with the RM-2 (Manufacturer Radon v.o.s., Czech Republic) measuring systems, while soil permeability was measured with the Radon-JOK device (Manufacturer: Radon v.o.s., Czech Republic) from 2015. Measurements of both parameters were performed at 412 locations, mostly in the vicinity of schools and kindergartens. Radon in soil gas measurements were generally performed immediately after the soil permeability measurements at the same soil probe and at the depth of 0.8 m (with 5 cm of sampling geometry). Up to 2013, radon was measured by the AlphaGUARD measuring system according to sampling protocol from manufacturer (AlphaGUARD manual). In both types of radon detectors for soil gas measurements, thoron was excluded from the results because measurements were performed 15 minutes after gas sampling. In fact, soil permeability was calculated from Darcy’s law according to measurement of time needed to withdraw certain amount of soil air by means of negative pressure established by Radon-JOK measurement set-up (Radon-JOK manual).  Geogenic radon potential for each measuring location was calculated by using equation (1) and taking into account the maximum measured value of radon in soil gas and the average soil permeability value. The obtained values were classified into classes according to Table 1.  Table 1. Subclassification of geogenic radon potential (GRP)  GRP – ”Czech” approach Class Radon index GRP – ”Croatian” subdivision Class Description GRP < 10 1 Low GRP < 5 1 Very low 5 ≤ GRP < 10 2 Low 10 ≤ GRP < 35 2 Medium 10 ≤ GRP < 22.5 3 Medium lower 22.5 ≤ GRP < 35 4 Medium higher GRP ≥ 35 3 High 35 ≤ GRP < 60 5 High 60 ≤ GRP < 125 6 Very high GRP ≥ 125 7 Extremely high  Radon values as well as GRPs were presented in the form of maps based on internationally suggested 10 x 10 km square grid which has been used for the European indoor radon map as well as for the future European geogenic radon map [1, 9].  XXIX	Симпозијум	ДЗЗСЦГ	 194  3.  RESULTS AND DISCUSSION The obtained results of radon in soil gas measurements in Croatia as well as calculated (by Equation (1)) and constructed (according to classification described in Table 1) geogenic radon potential are summarized in Table 2. The arithmetic mean of all measurements of radon in soil gas is 48 kBqm-3 with standard deviation of 52 kBqm-3. while the average GRP with its standard deviation is 28 ± 29. According to the used subclassification, it belongs to higher medium GRP. Normal probability plots of logarithmic values for both parameters are presented in Figures 1A and 1B. The applied statistical tests for normality (Lilliefors, Kolmogorov-Smirnov, Shapiro-Wilk) show that both parameters do not obey log-normal distribution, which was expected, since the measuring locations were not randomly chosen. The measurements of radon in soil gas and soil permeability were mostly performed in the vicinity of schools and kindergartens as a part of targeted surveys of indoor radon.   Table 2. The basic statistical analysis of radon in soil gas measurements and calculated and constructed geogenic radon potential (GRP) for Croatia (AM – arithmetic mean, SD – standard deviation, GM – geometric mean, GSD – geometric standard deviation)  Radon in soil gas [kBq m-3] GRP GRP-classes Number of measurements 874 795 Number of locations 785 412 AM 47.6 28.4 3.30 SD 52.1 28.7 0.96 Median 34.7 15.9 3 GM 33.0 16.8 3.0 GSD 2.4 2.6 1.6 Min - Max 1.0 - 566.0 0.3 - 470.4 1 - 7     Figure 1A. Normal probability plot of logarithmic values of radon in soil gas in Croatia Figure 1B. Normal probability plot of logarithmic values of GRPs in Croatia  The strong influence of water content in soil on radon concentration in soil gas is presented in Figure 2. In two consecutive years (2014 and 2015), the measurements of radon in soil gas were performed in the vicinity of schools and kindergartens in Радон	 195  Požega-Slavonia county and repeated a year later. In 2014, there were severe rainfalls with lots of floods in the area of interest a week before measuring campaign and a year later (in 2015), there were normal weather conditions (the cumulative precipitation for September 2014 and 2015 for Požega weather measuring station are presented as the right part of Figure 2). Radon in soil gas were approximately twice higher during the period with significant water content in soil than during the period with normal conditions (normal quantity of precipitation for that area).      Figure 2. Comparison of radon in soil gas concentrations measured in Požega-Slavonia county at the same locations in two consecutive years. In 2014, the measurements were performed a week after severe rainfalls (upper right) and in 2015 during normal weather conditions (lower right). The line (y(x) = x) on the graphical presentation of empirical results suggests no difference between measured values.   In order to examine temporal variations of local GRP associated to meteorological and climate variations, the measurements of radon in soil gas and soil permeability were undertaken several times a week during the whole year (from April 2015 until April 2016). The obtained results of calculated GRP are presented in Figure 3. There were 82 measurements and the average value and its standard deviation of adjoint GRP class was 3.76 ± 0.58. In 93% of cases, the associated GRPs belonged to medium GRP class. Two values, at the end of the presented measuring cycle, were significantly different from the other results. These anomalies were associated with the preparation for construction work by heavy machinery nearby the measurement point. This was, at the end, the reason to stop measurements at that measuring site.        XXIX	Симпозијум	ДЗЗСЦГ	 196   Figure 3. Time series of GRP values calculated from measurements of radon in soil gas and soil permeability at one measuring point in the courtyard of Department of Physics in Osijek. Yellow areas represent the medium (lower and higher) GRP.   Geogenic radon potential maps of two selected counties (Istria and Osijek-Baranja) using grid approach were created and presented in Figure 4. These two counties have a very different geological structure. Istria consists of a limestone plateau and dolomites formed in Late Cretaceous, much of which lacks water owing to its karst topography while carbonate rocks, especially flysch are significantly formed during Paleogene period. Osijek-Baranja county consists geologically mainly of sandstones and soft clay while sediments are of gravels, loess and silts. All these sediments are the product of mostly continental environments and alluvial fans. Differences in geological structure of these two areas inevitable have, as a consequence, very different geogenic radon potential as it can be seen in Figure 4.  Радон	 197     Figure 4. Geogenic radon potential maps of Istria (left) and Osijek-Baranja (right) counties  In more than 2/3 of the Istrian peninsula there are high (or even very high) GRP while in Osijek-Baranja county medium GRP prevails. This kind of maps could be useful for identification [10] as well as definition of so called radon-prone areas which have been under special attention in EU BSS [11]. The next phase of research is to connect GRP and indoor radon maps and to find some kind of functional or geostatistical relationship between those spatial variables as well as to introduce new ones (other terrestrial radionuclide maps, climate maps, geology maps, etc.).  4.  CONCLUSION Radon in soil gas and soil permeability were measured in more than 400 locations in Croatia. The geogenic radon potential for each location was calculated and the obtained results show that the average GRP in Croatia is in medium class. Although, there are areas with very high (or even extremely high) GRP. It was shown that radon in soil gas concentration itself is highly sensitive on water content in soil. The variations of GRP throughout a year are much smaller than radon in soil gas and it is wise to use this quantity to describe the potential hazard of radon. GRP maps of several Croatian counties were created and can be used as a tool for identification or even for definition of radon-prone areas. Nevertheless, it should be pointed out that no map can fully reflect the true reality of variations of radon potential due to heterogeneity of soil under the surface. Moreover, such maps can provide an useful information about soil as the main XXIX	Симпозијум	ДЗЗСЦГ	 198  radon source in buildings but they cannot be used for direct extrapolation and estimation on indoor radon concentrations inside the buildings at some areas of interest.  5.  ACKNOWLEDGEMENT The part of this research has been supported and funded by the internal project IZIP-2014-100 of J.J.Strossmayer University of Osijek.   6.  REFERENCES [1]  V. Gruber, P. Bossew, M. De Cort, T. Tollefsen. The European map of the geogenic radon potential. J. Radiol. Prot. 33, 2013, 51–60. [2]  K.Z. Szabo, G. Jordan, A. Horvath, C. Szabo. Mapping the geogenic radon potential: methodology and spatial analysis for central Hungary. J. Environ. Radioact. 129, 2014, 107-120. [3]  G. Ielsch, M.E. Cushing, Ph. Combes, M. Cuney. Mapping of the geogenic radon potential in France to improve radon risk management: methodology and first application to region Bourgogne. J. Environ. Radioact. 101, 2010, 813-820. [4]  J. Chen, R. Falcomer, L. Bergman, J. Wierdsma, J. Ly. Correlation of soil radon and permeability with indoor radon potential in Ottawa. Radiat. Prot. Dosim. 136, 2009, 56-60. [5]  H. Friedmann. Final results of the Austrian radon project. Health Phys. 89, 2005, 339-348. [6]  J. Kemski, A. Siehl, R. Stegemann, M. Valdivia-Manchego. Mapping the geogenic radon potential in Germany. Sci. Tot. Environ. 272, 2001, 217-230. [7]  J.H.C. Miles, J.D. Appleton. Mapping variation in radon potential both between and within geological units. J. Radiol. Prot. 25, 2005, 257–276. [8]  M. Neznal, M. Neznal, M. Matolin, I. Barnet, J. Miksova. The new method for assessing the radon risk of building sites. Czech Geol. Survey Special papers, 16 (2004), Czech Geol. Survey, 47 p.: http://www.radon-vos.cz/pdf/metodika.pdf (last access 25.2.2017). [9]  G. Dubois. P. Bossew, T. Tollefsen, M. De Cort. First steps towards a European atlas of natural radiation: status of the European indoor radon map. J. Environ. Radioact. 101, 2010, 786-798.  [10]  V. Radolić, I. Miklavčić, D. Stanić, M. Poje, I. Krpan, M. Mužević, B. Petrinec, B. Vuković. Identification and mapping of radon-prone areas in Croatia - preliminary results for Lika-Senj and the southern part of Karlovac Counties, Radiat. Prot. Dosim. 162, 2014, 29-33. [11]  Council directive 2013/59/EURATOM of laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation. Office Journal of the European Union, 5 December 2013; L13: 1-73.  Радон	 199  RADON U TLU I IZRAČUNATI GEOGENSKI RADONSKI POTENCIJAL U HRVATSKOJ Vanja RADOLIĆ, Marina POJE SOVILJ, Denis STANIĆ and Igor MIKLAVČIĆ J. J. Strossmayer University of Osijek, Department of Physics, Osijek, Croatia, vanja@fizika.unios.hr  APSTRAKT Koncentracije radona u tlu u Republici Hrvatskoj su mjerene AlphaGUARD mjernim sustavom (Genitron Instruments) od 2005. do 2013., a potom se mjere RM-2 mjernim uređajem (Radon v.o.s., Češka Republika). Premeabilnost tla mjeri se od 2015. godine Radon-JOK uređajem (Radon v.o.s., Češka Republika). Mjerenja se uglavnom obavljaju u blizini škola i vrtića. Dosad je izvršeno 412 mjerenja oba parametra. Prosječna koncentracija radona u tlu iznosi 48 kBq m-3 s pripadnom standardnom devijacijom od 52 kBq m-3. No, postoje i područja u kojima je mjerena koncentracija radona u tlu i do 550 kBq m-3. Geogenski radonski potencijal (GRP) je izračunat tzv. češkim pristupom iz empirijske jednadžbe, a uvedena je i nova subklasifikacija kojom se kontinuirane vrijednosti GRP-a svrstavaju u klase: (1- vrlo nizak, 2 – nizak, 3 – niži srednji, 4 – viši srednji, 5 – visok, 6 – vrlo visok, 7 – izrazito visok). Izračunate vrijednosti GRP-a iznose 28 ± 29 (empirijska kontinuirana vrijednost) odnosno 3,30 ± 0,96 (klase) čime se tlo u Republici Hrvatskoj, u prosjeku, klasificira u srednji geogenski radonski potencijal. 

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Radon u tlu i izračunati geogenski radonski potencijal u Hrvatskoj

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