222Rn studies and mapping in the city of Curitiba - Brazil
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222
Rn studies and mapping in the city of Curitiba - Brazil
Janine Nicolosi Corrêa*a, Loriane Fiora, Sergei A. Paschuka, Hugo R. Schelina,
Brigitte R. S. Pecequilob, Vicente de Paula Meloc,
a
Federal University of Technology - Paraná, UTFPR, Av. Sete de Setembro, 3165,
Curitiba, PR, 80230-901, Brazil
b
Institute of Nuclear and Energetic Researches, IPEN, CNEN, Av. Prof. Lineu Prestes,
2242-/05508-000 São Paulo, Brazil
c
Institute of Radioprotection, IRD, CNEN, Av. Salvador Allende, Rio de Janeiro, RJ,
Brazil.
Abstract. This work describes radon monitoring performed in cooperation between the Laboratory of Ionizing
Radiations of the Federal University of Technology – Paraná (UTFPR), the Institute of Nuclear and Energetic
Researches (IPEN) and the Institute of Radiation Protection and Dosimetry (IRD), from the Brazilian Nuclear
Energy Commission (CNEN), during the last two years. For 222Rn concentration measurements related to different
construction materials as well as for the studies of radon emanation and its reduction, the sealed cell chambers, of
approximately 60 x 60cm2, was built using ceramic and concrete blocks. This construction was performed within
a protected and isolated laboratory environment to maintain the air humidity and temperature stable. These long
term measurements have been performed using polycarbonate alpha track passive detectors. The exposure time
was set to 15 days considering previous calibration performed at IRD, where a efficiency of 70% was obtained for
the density of alpha particle tracks about 13.8cm-2 per exposure day and per kBq/m3 of radon activity
concentration. The chemical development of the alpha tracks was achieved by electrochemical etching. The track
identification and counting were done using a code based on the MATLAB Image Processing Toolbox. The cell
chambers were built following four main steps: 1) assembling the walls using the blocks and mortar; 2) plaster
installation; 3) wall surface finishing using lime; 4) wall surface insulation by paint. By comparison between three
layers installed at the masonry walls from concrete and ceramic blocks, it was concluded that only wall painting
with acrylic varnish attended the expectation and reduced the radon emanation flow by a factor of approximately
2.5. The construction materials were submitted to the instant measurements of radon concentration using a
ALPHA GUARD Professional detector. The samples of the construction materials were stored inside an acrylic
container (sealed up chamber) connected to the instant ALPHA GUARD detector. The equipment was adjusted
with an air flow of 0.5 L/min and the 222Rn concentration was registered every 10 minutes. Among the analyzed
materials were sand, structure concrete blocks, granite and concrete paving stones, cement, etc. The measured
instant 222Rn concentrations were also compared with the results of long term measurements using alpha track
detectors.
KEYWORDS: NORM; Rn-222; Construction Materials; Track Detectors; Alpha Particles.
1. Introduction
Considering the risk associated with 222Rn inhalation by the human being and lung cancer, it is very
important to carry out a systematic monitoring, measuring and identifying radon and its progeny [1 -
3]. The present work describes a procedure and presents the results of 222Rn concentration
measurements in air and its correlation with construction materials used in the Brazilian industry as
well as discusses some possibilities of radon infiltration reduction by plastering, coating and painting
of masonry walls.
These studies were performed in cooperation between the Laboratory of Ionizing Radiations of the
Federal University of Technology – Paraná (UTFPR), the Institute of Nuclear and Energetic
*
Presenting autho r, E-mail : j ani ne_ nic olosi@ho tma il .co m
1Researches (IPEN) and the Institute of Radiation Protection and Dosimetry (IRD), from the Brazilian
Nuclear Energy Commission (CNEN), during the last two years [4 – 9].
As was reported previously [14], this collaboration performed a systematical sampling of radon
concentration within dwellings of urban areas in the cities of Curitiba and Campo Largo in the state of
Paraná, Brazil. At that time about 100 LEXAN (GE) track detectors were exposed in air (indoor and
outdoor) during the summer and winter period. It was found that 88% of the studied places presented
222
Rn concentration below the action level of 200 Bq/m3, established by the World Health
Organization (WHO). Ten percent of the studied places presented Radon concentration within 200
Bq/m3 and 400 Bq/m3, which is considered an action level by most of the European Community.
However what really calls attention is that 2% of the studied places presented Radon concentration
above 600 Bq/m3, which can be considered as a level of immediate remediation. In general, the
obtained 222Rn concentration levels are in good agreement with previously performed geological
studies [11] in this region. Moreover, the measured 222Rn concentration levels in Curitiba as well as in
Campo Largo are compatible with values found in Monte Alegre (PA), Campinas (SP) and Poços de
Caldas (MG) [10, 13, 15 – 17]. Some small discrepancies are easily explained taking into account
different habitual ventilation practices in different regions of Brazil.
As a continuation of this work it has been performed a more accurate correlation analysis between
radon concentration and used construction materials, where the measurements were initiated with
emanation chambers and samples of construction materials such as granites, sands, cements, ceramics
and bricks, structure concrete blocks, etc. In this case the active method of detection was used. As a
step following those studies the measurements were performed and the radon monitoring was carried
out using long term plastic alpha particle track detectors exposed in the air of a constructed closed
environment, which can be named as a cell chamber.
2. Materials and Methods
Instant measurements of radon concentration using ALPHA GUARD Professional detector were made
for the studied construction materials. These measurements were done in the UTFPR and in the Radon
Laboratory from the IRD where the samples of construction materials were submitted to instant
measurements of radon concentration using the ALPHA GUARD Professional detector. The samples
were stored inside an acrylic container (sealed up chamber) connected to the instant ALPHA GUARD
detector. The equipment was adjusted with an air flow of 0.5 L/min and the 222Rn concentration was
registered every 10 minutes. Some general details of those measurements can be seen in Figure 1.
Figure 1. (a) General view of the samples of construction materials; (b) ALPHA GUARD detector; (c)
the construction materials stored in the acrylic chamber.
For the 222Rn concentration measurements in air related to different construction materials as well as
for the studies of Rn emanation and its reduction, the cell chambers, of approximately 60 x 60 cm2,
were built using ceramic and concrete blocks. This construction was performed within a protected and
isolated laboratory environment maintaining the air humidity and temperature stable. The details of the
“cell-house” construction can be seen in Figure 2. During the radon long term measurements the cell
chambers were sealed by wooden caps.
2Figure 2. Cell chambers built from concrete and ceramic blocks.
The cell chambers have been built following four principle steps: 1) assembling the walls using the
blocks and mortar; 2) plaster installation; 3) wall surface finishing using the lime; 4) wall surface
insulation with paint.
LEXAN film were chosen as track detectors since its 100 μm protection layer creates the Bragg peak
of alpha particle energy loss just at the surface of the LEXAN film which makes the procedure of
chemical track development more simple. The chamber construction, with the filter (to prevent
aerosols) and the polymer LEXAN detector are shown in Figure 3. During each step of the
measurements 6 exposition chambers with LEXAN detector were installed inside every built cell. The
exposure time was set to 15 days considering previous calibration performed at IRD, where a
efficiency of 70% was obtained for the density of alpha particle tracks about 13.8cm-2 per exposure
day and per 1 kBq/m3 of radon activity. In other words, such track density in the developed (etched)
detector guarantees that 70% of the detected events will not be superposed and could be easily
identified and counted. Following this recommendation and considering the expected radon
concentration levels in air within 200 Bq/m3 and 2000 Bq/m3 the exposition time was estimated.
Figure 3. General view of the internal structure of exposition chambers with LEXAN layer inside.
With the purpose to track the developed alpha particles, an electrochemical EKOTRONIC bath was
used which allows to work simultaneously with more than 30 polycarbonate passive alpha track
detectors. Exposed LEXAN layers were chemically pre-etched (1000V at 100Hz) during 40 minutes
and later etched (800V at 3000Hz) at 30oC in a solution of 6N KOH + 80% of C2H5OH during 3
hours. Such pre-etching and etching timing was chosen to obtain the size of alpha – particle track of
about 100 μm, which could be easily identified and visualized by computer scanning within 1200 dpi
resolution [10]. For exposition chamber cleaning and deactivation a solution EDTA
(Ethylenediaminetetraacetic acid in aqueous solution) was used.
The developed LEXAN detectors were scanned and the obtained images were analyzed by a simple
code based on the MATLAB Image Toolbox. Except for alpha track identification, this code calculates
the total track number, defines the density and the coordinates of tracks [9].
3. Results
For radon concentration detection using the active method, the samples of concrete and ceramic blocks
were placed in an isolated chamber connected directly to the ALPHAGUARD detector. Concentration
measurements were performed during approximately 2 hours with the programmed constant air
3outflow of 0.5 L/min. Measured 222Rn concentrations were 154 +/- 10 Bq/m3 and 281 +/- 40 Bq/m3
respectively. During these measurements, humidity and pressure inside the chamber were also
monitored.
The results of the performed gamma spectrometry analysis concerning the activity of 226Ra, 232
Th and
40
K in the samples of ceramic and concrete blocks can be seen at Table 1.
Table 1. Obtained activity values of 226Ra, 232Th and 40K in the ceramic and concrete blocks.
226 232 40
Ra Th K
Material
(Bq/kg) (Bq/kg) (Bq/kg)
Ceramic block 38,9 1,7 46,1 1,8 188 12
Concrete block 21,1 0,9 19,7 0,9 737 44
It can be concluded that the activity levels within 38, 46 e 188 Bq/kg are comparable with the results
described in the literature [19, 20, 21] where in the case of ceramic blocks an activity within 12 and
109 Bq/kg for 226Ra, within 41 and 89 Bq/kg for 232Th and within 24 and 1200 Bq/kg for 40K
respectively was observed.
The summary of the experimental results concerning 222Rn concentration is presented in Figure 4. The
very small (about 0.2 m3) internal volume of cell chambers received radon concentrations of about 600
Bq/m3 and 1000 Bq/m3. These values are higher than the action level of 200 Bq/m3, established by the
World Health Organization (WHO). Even more: the three first steps of cell chambers construction
presented radon concentration above 600 Bq/m3 which is the level of immediate remediation
considered by most of the European Community. However extrapolating these results to the dimension
of a real room with few cubic meters of air volume and considering equal radon emanation flow from
the walls, one can conclude that, in this case, the radon concentration would be below 200 Bq/m3 and
does not represent specific danger for the human being. In general, the obtained 222Rn concentration
levels are in good agreement with previously performed monitoring studies [4, 9, 11, 13] in this
region.
Figure 4. 222Rn concentration in air measured during four steps of cell chambers construction.
44. Conclusions
The rather high 222Rn concentration levels, associated with construction materials, do not represent a
big danger since the results were obtained within a very small cell chamber volume (about 0.2 m3).
The obtained results concerning the four steps of cell chamber construction doesn't show significant
differences between radon concentration levels created by concrete and ceramic bricks which is in
rather good agreement with the instant measurements performed with the ALPHA GUARD
professional detector.
The observed almost two times divergence between the instant and long term measurements can be
easily explained taking into account the small volume of used the acrylic container (about 8 L) for the
storage of material samples and the used pump outflow about 0.5 L/min. These permanent
measurements will be repeated with higher precision in the nearest future. Moreover, the observed
radon concentration increase after the lime layer installation that requires special attention and
measurements, since such finishing materials usually are considered as sealant in radon mitigation
techniques [12]. Comparing the radon reduction between the three layers installed at the masonry
walls of concrete and ceramic blocks, one can see that only wall painting with acrylic varnish attended
the expectation and reduced the radon emanation flow by the factor of 2.5 approximately.
Acknowledgements
The authors are very thankful to Brazilian agencies CNPq and Fundação Araucária for financial
support of this work as well as to colleagues from the IRD and from the Institute of Nuclear and
Energetic Researches (IPEN/CNEN) for permanent positive discussions and assistance in the
measurements.
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