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2009 International Nuclear Atlantic Conference - INAC 2009 ,RJ, , September27 to October 2, 2009 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-03-8

Radon in Soil Gas Survey in (Brazil).

Sergei A. Paschuk1, Janine Nicolosi Corrêa1, Hugo R. Schelin1, Laercio Barbosa1, Tatyana Sadula1, Cristiana A. Matsuzaki1

1 Federal University of Technology – Paraná, UTFPR Av. 7 de Setembro 3165, Curitiba - PR, Brazil [email protected], [email protected]

ABSTRACT

This work describes the radon in soil gas measurements performed during the last two years in cooperation between the Laboratory of Applied Nuclear Physics of the Federal University of Technology (UTFPR), the Nuclear Technology Development Center (CDTN) and the Institute of Radiation Protection and Dosimetry (IRD) from the Brazilian Nuclear Energy Commission (CNEN). Following previously concluded measurements of radon concentration in dwellings and the measurements of 222Rn activity in drinking water collected at artesian bores of Curitiba , present step of activities has been dedicated to measurements of radon concentration in soil gas. Experimental setup was based on the Professional Radon Monitor (ALPHA GUARD) connected to specially developed for such measurements Soil Gas Probe through the air pump and filter system. After the Probe was inserted, the ground has been tamped down around the probe, to prevent air from moving vertically along the outside of the shaft. The equipment was adjusted with air flow of 0.03 L/min and the measurements were performed during 90 min approximately. The 222Rn concentration levels were detected and analyzed by the computer every 5 minutes using the software DataEXPERT by GENITRON Instruments. Collected average levels of 222Rn concentration were processed taking into account the internal volume of Soil Probe and connection vessels. Radon sampling was performed at a depth of 50 – 70 cm. Obtained experimental data of radon concentration present rather big variation but correlates perfectly with previously obtained results for 222Rn activity in drinking water. Further measurements are planned to be performed at other regions of Parana State and will involve the mineral analysis of soil samples.

1. INTRODUCTION

After the decades of systematic and numerous studies performed at different countries of the World, it has been concluded that radon as well as its progeny is the main cause of lung cancer [1]. Radon is heavy noble radioactive gas generated within three main radioactive series. Specifically, 222Rn is produced by the 238U decay series and proceeding from  -decay of 226Ra [2, 3].

It is well known that more than 50% of the effective annual radiation dose received by a being is related to the radon and its progenies. Among the principle mechanisms that bring the radon inside the dwelling is the soil exhalation as well as exhalation and release from the water [2, 3].

Radon concentration in the soil and its transport (emanation, diffusion, advection and adsorption) to the surface depends on different physical, geological and ambient parameters such as the geology of the area, geochemical composition of the soil, its porosity and permeability, grain size, soil , bottom sediments and inputs from streams, temperature, atmospheric pressure, etc. [4]. Since the main part of indoor radon originates in the soil, the measurements of radon concentration in soil gas have to be considered as an important tool and indicator of probable high levels of radon inside the dwellings [5].

Curitiba - the Capital of Paraná State is big industrial located in Southern Brazil. The urban area of the city is situated at the First Paranaense Plateau located between the Mountain and Devoniana Cliff which makes part of the hydrographic basin of Alto Iguaçu River. The average altitude of Curitiba is about 920 m. The soil of Curitiba consists of poorly consolidated sediments (clay stones, clayey sands and sandstones) with contributions of the silt and sandy fractions [6]. The principal composition of Curitiba soils is Cambisol (60%), following by Latosol (17%) and Organosol (10.5%) [7].

2. MATERIALS AND METHODS

Measurements were performed at Curitiba urban area during the autumn of 2008. The areas for the test were chosen following the results concerning the high concentration levels of radon in samples of drinking water from artesian wells or, in some cases, obtained high concentration levels of radon inside the dwellings. In all cases the tests were performed at the native (rough) soil excluding the terrains submitted to strong grading and earth-moving.

Studies were performed at the Laboratory of Applied Nuclear Physics of the Federal University of Technology – Paraná (UTFPR, Curitiba, Brazil) on base of the Professional Radon Monitor (ALPHA GUARD) connected to specially prepared for such measurements Soil Gas Probe through the air pump and filter system. The general view of the ALPHA GUARD detector during the measurements could be seen in Figure 1.

Figure 1. ALPHA GUARD Detector (GENITRON Instruments) in measurements with Soil Gas Probe.

The instant radon detector AlphaGUARD (Genitron Instruments) is suitable for continuous monitoring of radon concentrations in the range of 2 – 2*106 Bq/m³. This detector (pulse- counting ionization chamber suitable for alpha spectroscopy) is a portable, battery- or net- operated radon monitor with high storage capacity which records, using the integrated

INAC 2009, Rio de Janeiro, RJ, Brazil. sensors, simultaneously with detected radon activity the ambient temperature, relative humidity and atmospheric pressure [8].

Figure 2. General view of steel probe developed for soil-gas radon measurements.

For air sampling and radon concentration measurements in the soil it has been developed steel probe and auxiliary drill (Figure 2). Geometrical parameters of the probe and drill are: total length – 1400mm, drill and probe external diameter – 35mm, internal probe diameter – 22mm, estimated internal volume of the probe – 0.348L, the depth of probe penetration in the soil – 1000mm.

Following the recommendations and considerations of other authors [9], air samples were taken from depth of about 70 – 80cm from the ground level. After the steel probe was inserted, the ground has been tamped down around the probe, to prevent air from moving vertically along the outside of the shaft. The equipment was adjusted with air flow of 0.03 L/min and the measurements were performed during 90 min approximately. The 222Rn concentration levels were detected and analyzed by the computer every 5 minutes using the software DataEXPERT by GENITRON Instruments.

3. RESULTS AND CONCLUSIONS

Table 1. Some numerical examples of 222Rn concentration measurements in soil gas.

AVERAGE 222Rn REGION OF SAMPLE COLLECTION (CURITIBA, PR, CONCENTRATION OF SOIL BRAZIL) GAS SAMPLE, [Bq/m3] Umbará - Region 1 38523 +/- 2630 Umbará - Region 2 120 +/- 30 Jardim das Américas - Region 1, Campus UFPR 2 +/- 5 Jardim das Américas - Region 2, Campus UFPR 1026 +/- 145 Jardim das Américas - Region 3, Campus UFPR 9 +/- 5 Bom Retiro – Region 1 35300 +/- 3070

INAC 2009, Rio de Janeiro, RJ, Brazil.

Some sample of collected experimental data concerning the soil gas radon is presented in Table 1. It could be concluded that almost half of obtained values is much higher than previously obtained data at other regions of Brazilian territory [10]. The concentration of radon in soil gas at the level of few dozens kBq/m3 usually classify the terrain as high risk where some special measures have to be taken for prevention of radon accumulation inside the dwellings. This observation is very important considering rapid development of Curitiba and its urban infrastructure.

In the nearest future it is planned to perform the measurements of natural radionuclides content in loess samples with an objective to find the concentration 238U, 226Ra, 232Th and 40K and to compare obtained data with radon concentration in the soil.

ACKNOWLEDGMENTS

The authors are very thankful to CNPq, CNEN and Fundação Araucária (Paraná St.) for financial support of this work as well as to colleagues from the Institute of Radiation Protection and Dosimetry (IRD/CNEN) and from the Center of Nuclear Technology Development (CDTN/CNEN) for permanent positive discussions and assistance in the measurements.

REFERENCES

1. NRC, National Research Council, 1988. Committee on the Biological effects of Ionizing Radiations. Health Risks of Radon and other Internally Deposited Alpha-Emitters BEIR IV- Washington, D.C.: National Academy Press. 602 pp. 2. ICRP 60 - International Commission on Radiological Protection. Recommendations of the International Commission on Radiological Protection, Oxford: Pergamon Press, 1991. 3. UNSCEAR. Sources and effects of ionizing radiation , New York, 1993. 4. K. Sun, Q. Guo and J. Cheng, “The Effect of Some Soil Characteristics on Soil Radon Concentration and Radon Exhalation from Soil Surface”, Journal of NUCLEAR SCIENCE and TECHNOLOGY, 41, 11, pp. 1113–1117 (2004). 5. “Radon Risk Classification”, http://www.radon.eu/services.html. 6. A.C. Duarte Pires, V. de Freitas Melo, A.C. Vargas Motta, V.C. , “Majors soil classes of the metropolitan region of Curitiba (PR), Brazil: II - interaction of Pb with mineral and organic constituents”, Braz. arch. biol. technol. 50, 2, pp.183-192 (2007). 7. Empresa Brasileira de Pesquisa Agropecuária – EMBRAPA, Sistema brasileiro de classificação de solos. EMBRAPA, Rio de Janeiro (1999). 8. GENTIRON INSTRUMENTS. AlphaGUARD portable radon monitors user manual. 1998. 9. M. Neznal, M. Neznal and J. Smarda, “INTERCOMPARISON MEASUREMENT OF SOIL-GAS RADON CONCENTRATION” Radiation Protection Dosimetry, 72, 2, pp. 139–144 (1997). 10. MARQUES, A.L.; GERALDO, L. P.; SANTOS, W. Níveis de radioatividade natural decorrente do radonio no complexo rochoso da Serra de São Vicente, SP. Radiologia Brasileira. V. 39, 3. , 2006.

INAC 2009, Rio de Janeiro, RJ, Brazil.