A STUDY OF RADON CONCENTRATION IN KINDERGARTENS IN THE UPPER , B. Kozlowska1, M. Kordiak1, M. Wysocka2 1 Institute of Physics, University of Silesia, , Poland. 2 Laboratory of Radiometry, Central Mining Institute, Katowice, Poland

Abstract The project is related to the studies of radon levels in dwellings (mainly kindergartens) in the Region and is planed to be carried out for a few years. The main task is to investigate relationship between measurement results and geological structure of the area in correlation with mining industry. Statistical analyses of obtained results have been performed with the use of the program HISTO from IAEA. The inhalation doses which children obtain in kindergarten halls have also been calculated.

Introduction

Upper Silesia region is located in the south of Poland. High population of people and urbanization is very characteristic for this region. The area owes its development to the presence of natural resources both in the past and nowadays. In connection with this mining industry has been developed through ages. There are still working coal mines but in the past there was also zinc and lead ore mining. Rich coal deposits ensure its exploitation for the next fifty years. The goal of this project is to determine the correlation between radon concentration results in kindergarten’s buildings in a few Upper Silesia towns and geological and mining activity in the investigated region. The reason why the kindergartens have been chosen was the fact that children’s bodies are more likely the subject to ionization radiation than adults. Radon is a radioactive noble gas which increases the risk of lung cancer. The permissible limit of the concentration of this gas in dwellings in Poland for new buildings (i.e. built after 1998) is equal to 200Bq/m3, for older buildings 400Bq/m3. Three Upper Silesia were initially selected for studies: , Jaworzno and Katowice. Presently conducted research has been supplemented with previously obtained results by the Central Mining Institute for Piekary Śląskie kindergartens [1] because of its interesting location close to the town Bytom. During the examination of geological maps of this area and present mining industry situation it has been found that some parts of the Upper Silesia may be regions with enhanced radon risk. Districts of Bytom, Jaworzno and Piekary Śląskie are located at the Triassic synclines where radon migration and exhalation is simplified. Katowice is located in Quaternary formations which geological structure makes radon migration and exhalation more difficult. Moreover, in all these regions mining operation both in the past and at the present time makes the migration of the gas easier. It has been established that the main sources of radon penetration into the buildings are fissures in rocks, loosening of the ground and damages of building’s structure.

Measurements

Two methods of radon measurements in kindergarten’s buildings were performed: short term measurements with the use of charcoal Pico-Rad detectors from Packard (by University of Silesia) and long-term measurements based on solid state nuclear track detectors (SSNTD) LR-115 from Kodak (by Central Mining Institute).

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Fig.1. Areas under investigation at Upper Silesia region. Faults are marked with black thick lines.

The Pico-Rad detector is a plastic vial with a 3g of charcoal container placed at the top. In order to perform a measurement one has to place an open detector at the investigated hall. After the established exposition time the vial is tightly closed and taken at the shortest possible time to the laboratory. Recommended exposition time is equal to 48 hours. The exposition time cannot be shorter than 12 hours and longer than 96 hours. The analysis at the laboratory is based on determining detector’s alpha and beta activity by the liquid scintillation counting (LSC) The LSC used at the Laboratory of Low Activities at the University of Silesia is WinSpectral α/β 1414 from Wallac. Before the LSC measurement 10 ml of liquid scyntylator cocktail is poured to the detector. The cocktail fills the bottom of the vial without touching the charcoal. A sample prepared this way is left closely caped by a certain amount of time for desorption of radon from charcoal to the liquid scyntylator (here Insta Fluor based on xylene). Desorption of radon takes place through gaseous phase i.e. xylene vapor and lasts from a few to several hours. After the measurement of alpha and beta radioactivity emitted by radon and its radioactive progenies (222Rn, 218Po, 214Po – alpha counts, 214Pb, 214Bi –beta counts) radon activity concentration is calculated. LSC measurement cannot be performed later than 192 hours (8 days) after the exposition of the detectors. For the long term radon measurements the passive method based on LR-115 detectors, strippable type, was used. Diffusion caps with SSNTD were exposed for at least two months period. After this time the LR-115 plastic detectors were removed from the caps and taken for chemical treatment. In a water bath at a temperature of 60oC the foils were etched in 2M KOH solution. After drying the foils were analyzed at a mechanical spark counter. The lower limit of detection for this method is 10 Bq/m3. With the use of this passive method one can evaluate the average value of radon concentration in the exposed detector time.

2 Radon measurements were performed at 46 buildings, mainly kindergartens apart from a few neighboring houses. Pico-Rad detectors were placed in cellars (1 detector) and ground floor halls (2 detectors). In case of SSNTD there were four detectors placed at every investigated building, two at cellars and two at children’s halls.

Results and Discussion

Fig. 2 shows results obtained for Pico-Rad detectors measurements. Radon 222Rn activity concentration in Bq/m3 for four selected cities is presented at the histogram. From the preliminary results one can see that radon concentration activity values in the kindergartens can vary in a wide region. It depends on the season of the year, the frequency of room’s ventilation, buildings constriction air tightness etc. Large differences in radon activities occur sometimes in the neighboring buildings (for example building 7 and a few meters farther building 8).

Rn-222 concentration activity in kindergartens in the Upper Silesia (Pico-Rad)

Cellar Ground floor Norm 1 Norm 2

1000

900 Polish Norm for buildings built Polish Norm for buildings built 800 before 1998r after 1998r

] 700 3 m / 600 q B 500 222 [ - 400 n R 300 200 100 0

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P P P P

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Fig.2. Summary comparison of the short term measurements results with the use of charcoal detectors in Bytom, Jaworzno, Katowice and Piekary Śląskie.

Measurements results have been statistically examined using the program HISTO [2] obtained by courtesy of researchers from the Analytical Quality Control Services at International Atomic Energy Agency’s Laboratories at Seibersdorf, Vienna. Kurtosis and skewness tests and the histogram of the results show that the radon activity values both for cellars and for ground floor halls do not form a normal distribution plot. In the case of the cellars there were five outliers found in a region of high concentration values. These values were obtained for five randomly situated kindergartens in Katowice and Bytom. In the case of ground floor halls there were eight outlier values obtained at kindergartens in Piekary Śląskie, Katowice and Jaworzno. Enhanced radon concentration values at a few separate buildings point at the movement of the geological strata around the buildings. The fact that they are randomly located in the studied area shows that a local geological fault connecting these places cannot be found. Radon concentration activity values obtained for cellars are higher than in ground floor halls. After outlier rejection the normal distribution of the values was obtained and for that there

3 were an arithmetic mean, median and the robust value calculated. These values almost overlapped and the robust values for cellars and for ground floor halls were equal to 106 Bq/m3 and 28 Bq/m3, respectively. The ratio of the robust values for cellars to ground floor halls was calculated:

C Rn( cellar ) 106Bq / m3 = = 3.8 , C Rn( ground _ floor ) 28Bq / m3 where:

3 C Rn( cellar )- robust value for cellars results (Pico-Rad) – 106 Bq/m , 3 C Rn( ground _ floor )- robust value for ground floors results (Pico-Rad) – 28 Bq/m .

The ratio is equal to 3.8:1. High radon values for the cellars explicitly confirm that the main source of radon emanation is soil with features enabling emanation, migration and exhalation of this gas. The second method used for radon measurement was SSNTD with LR-115 plastic foils. Results obtained with these studies are shown in Fig. 3.

Rn-222 concentration activity in kindergartens in the Upper Silesia (LR-115)

Cellar Ground floor Norm 1 Norm 2

450 400 Polish Norm for buildings built 350 before 1998r ]

3 300 m

/ Polish Norm for buildings built after

q 250

B 1998r. 200 222 [ - n 150 R 100 50 0 ng 1 ng 2 ng 3 ng 4 ng 5 ng 6 ng 7 ng 8 ng 9 ng 1 ng 2 ng 3 ng 4 ng 5 ng 6 ng 7 i i i i ng 1 ng 2 ng 3 ng 4 ng 5 ng 6 ng 7 ng 8 ng 9 i ng 1 ng 2 ng 3 ng 4 ng 5 ng 6 ng 7 i i i i i i i i i i i i i i i i i i i i i i i i i i i ng 10 ng 11 ng 12 ng 13 ng 14 ng 15 ng 16 ng 17 d d d d d ng 10 ng 11 ng 12 ng 13 ng 14 d d d d i i i i i i i i d d d d d d d l l l l d d d d d d d d d l d d d d d d d i i i i i l l l l l l l l l l l l l l l l l l l l l l l l l l l d d d d d d d d d d d d d l l l l l l l l l l l l l bui bui bui bui bui bui bui bui bui bui bui bui bui bui bui bui e bui e bui e bui e bui e bui e bui e bui e bui e bui i i i i e e e e e e e e e i bui bui bui bui bui i i i i m m m m m m m e bui e bui e bui e bui e bui e bui e bui e bui k k k k no bui no bui no bui no bui no bui no bui no bui c c c c c c c c c e e e e e k k k k k i i i i i i i i o o o o o o o i i i i i i i i i t t t t t t t s s s s z z z z z z z c c c c c s s s s s k k k k k k k k i i i i i r r r r r r r y y y y y y y ą w w w w w w w w w ą ą ą ą ą ą ą ą s s s s s s s s l l l l l l l l l o o o o o o o o o o o o o o o o w w w w w ą ą ą ą ą ą ą ą B B B B B B B t t t t t t t t t l l l l l l l l Ś Ś Ś Ś Ś Ś Ś Ś Ś o o o o o w w w w w w w

a a a a a a a a a t t t t t Ś Ś Ś Ś Ś Ś Ś Ś a a a a a a a y y y y y y y y y

a a a a a K K K K K K K K K J J J J J J J y y y y y y y y K K K K K ar ar ar ar ar ar ar ar ar ar ar ar ar ar ar ar ar ek ek ek ek ek ek ek ek ek i i i i i i i i i ek ek ek ek ek ek ek ek i i i i i i i i P P P P P P P P P P P P P P P P P

Fig. 3. Summary comparison of the long term measurements results with the use of LR-115 detectors in Bytom, Jaworzno, Katowice and Piekary Śląskie.

The results have also been statistically examined using the program HISTO. The histogram of the results and kurtosis and skewness tests show that the distribution of radon values for cellars is normal but for ground floor halls one can reject one outlier value. The results for cellars are, similarly to Pico-Rad detectors values, higher than for ground floor halls. The

4 robust values were equal to 118 Bq/m3 and 37 Bq/m3 for cellars and ground floor halls, respectively. The ratio of the robust values was calculated:

C Rn( cellar ) 118Bq / m3 = = 3.2 . C Rn( ground _ floor ) 37Bq / m3

The ratio is equal to 3.2:1 and confirms the conclusion obtained for Pico-Rad detectors studies. Radon concentration activity results obtained with the use of Pico-Rad detectors and SSNTD may vary significantly. These differences result from the character of these two methods. Pico-Rad detectors are used for short term measurement for screening. Plastic detectors LR- 115 are used for long term measurement. A value obtained with Pico-Rad detector corresponds to radon activity in dwelling during two or three days. A result obtained with LR- 115 plastic detector exposed for a long period of time inform about an average radon activity at that period. Radon activity in buildings may vary in a wide range depending on many factors, so values obtained with these two methods can be different. One factor which can cause discrepancies is the fact that Pico-Rad detectors were exposed during weekends in order to avoid additional factors which may decrease radon activity - like opening the windows.

Conclusions

On the basis of the long term measurement average results the possible effective dose per year which children in kindergartens may absorb was calculated. The doses ranged from 0.08 mSv to 1.4 mSv. In a few buildings in Katowice where the plastic detectors were exposed for much longer period of time than in other cities, i.e. for a year, the estimated effective doses are much lower than in the buildings where the exposition time lasted for two months in spring. It was assumed that children stay in the kindergartens for 10 hours per day what can be an overestimation of the average time. However, enhanced radon levels in some kindergartens buildings should not be disdained. Analysis of this data shows that the Upper Silesia region can be the area of potential radon risk because of its specific geological structure and intensive coal exploitation. Bytom, Piekary Śląskie and a part of Jaworzno are located at the Triassic synclines which are built from limestone and dolomite. Cracks and small spatial density enable radon migration to the surface. This fact is confirmed by the results in Bytom where the highest value obtained with the screening method equalled 667 Bq/m3 and with a long term method 160 Bq/m3 in building 1. Measurements in Katowice were carried out in the buildings in southern districts which are located on Quaternary formations. These layers do not favour radon migration. In spite of that a high local radon concentration value equaling 950 Bq/m3 was observed in building 8. In this region there has been an underground exploitation carried out by two coal mines ‘Staszic’ and ‘Wujek’. Due to output works there are local faults and fissures which enable gas penetration into the buildings. Additionally, the houses construction is often disturbed. Through cracks in floors and walls radon migrates into houses interiors. It should be noticed that high radon levels are not due to enhanced natural radioactivity of hard coal or neighboring rocks [3]. Analyses results obtained in Central Mining Institute and confirmed by the literature show that higher radon levels occur at areas with shallow mining exploitation. Exploitation voids come into existence followed by destruction of coal bed structure and what matters migration of radon and other gases into buildings.

5 Literature:

[1] Skowronek J., Wysocka M., Mielnikow A. PTJ vol.42 (1999) 34. [2] HISTO Outlier Testing, Normality Tests, Histogram, Statistical Values, Radecki, Z., Trinkl, A, Analytical Quality Control Services, Chemistry Unit, Agency's Laboratories Seibersdorf, International Atomic Energy Agency. [3] Wysocka M., Prace naukowe GIG 3/2002.

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