Measurements of radon exhalation rates in building materials used in ...

Int. Journal of Applied Sciences and Engineering Research, Vol. 4, Issue 4, 2015 © 2015 by the authors – Licensee IJASER- Under Creative Commons License 3.0 Research article

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Measurements of radon exhalation rates in building materials used in Iraqi houses Sahar A. Amin Environmental research center, university of technology, Baghdad-Iraq DOI: 10.6088.ijaser.04043 Abstract: The aim of the present work was to measure radon concentrations and exhalation rates in various construction materials in buildings in Iraq, using a CR-39 solid-state nuclear track detector. Radon concentrations varied from a minimum of 261.3 ± 48.0 Bq m−3 for concrete, to a maximum 761.6 ± 29.4 Bq m−3 for gravel, with a mean of 527.7 ± 50.6 Bq m−3. The radon values were higher than the international recommended value. Radon mass exhalation rates differed from a minimum of (0.65 ± 0.11) × 10−2Bq kg−1 h−1 to a maximum of (2.70 ± 0.33) × 10−2Bq kg−1 h−1 for concrete and Thermostone, respectively. Surface exhalation rates varied from a minimum value of 0.71 ± 0.13 Bq m−2 h−1 for concrete to a maximum value of 2.00 ± 0.80 Bq m−2 h −1 for gravel. Mean values of exhalation rates in terms of mass and surface were (1.41 ± 0.19) × 10−2Bq kg−1 h −1 and 1.42 ± 0.20 Bq m−2 h −1, respectively. These values were within the limit of recommended values. Keywords: Building materials, SSNTDs, CR-39, Radon, Exhalation rate.

1. Introduction Radon is a naturally occurring radioactive gas that is formed by the decay of radium. Radon is found in all types of rocks, soils and building materials. Among all isotopes of radon, 222Rn, with a half-life of 3.8 days, is considered the predominant hazardous radionuclide. Prolonged exposure to radon may increase the risk of lung cancer (ICRP, 1970). The long half-life of the 222Rn isotope allows it to migrate from soil and construction materials and penetrate closed rooms, where it can sometimes reach levels that are harmful to human health. The assessment of radiological risk from inhalation of radon and its progeny is based mainly on integrated measurements of radon. Recommended radon values given by the International Commission on Radiological Protection (ICRP 1993) are between 200 and 600 Bq m−3. It is recommended to measure radon levels and find its sources, especially in houses (Ramola and Choubey, 2003). Radium concentration is one of the most important factors affecting radon exhalation from building materials. Other factors include material porosity, emanation power or fraction, surface preparation, and building material covering. Radium in building materials should be restricted to a level that does not exceed the ICRPrecommended design level for indoor radon (200 Bq m−3) or, ideally, an even lower level to allow for some contribution from other sources (especially underlying soil) (Hůlka et al., 2008). The aim of the present work is to assess indoor radon concentrations in construction material samples commonly used in Iraq. In addition, surface and mass radon exhalation rates were calculated for the surveyed area.

2. Materials and methods A total of 12 building material samples were analyzed using the sealed can technique with a CR-39 ————————————— *Corresponding author (e-mail: [email protected]) Received on January 2014; Published on August, 2015

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Measurements of radon exhalation rates in building materials used in Iraqi houses

solid-state nuclear track detector. Solid samples were crushed and milled to a fine powder with uniform particle size; powder samples were used in their natural forms. Twenty-four grams of each sample were placed at the bottom of a plastic can (height = 6.5 cm, diameter = 4 cm), together with two 1.5 × 1.5 cm2 pieces of CR-39 detector. One piece was placed directly atop the sample and the other atop the container, 4 cm above the sample (Figure 1). In this arrangement, the lower detector records α-particles emitted from radon, thoron and their progenies that are present in the samples. Alpha particles emitted from 222Rn are recorded in the upper detector. Thus, 220Rn and its progeny in the sample are represented by the difference in track densities of the two detectors. The dosimeters were left in place for 3 a period of 90 days. This long period of irradiation is necessary to accumulate a considerable number of tracks of α- particles emitted from radon, thoron and their progenies. After irradiation, CR-39 plastic detectors were developed in NaOH solution with chemical etching conditions 6.25 N at 80 °C for 5 h. The detectors were then examined for α- tracks using an optical microscope with 10×40 magnification.

Figure 1: Sealed can technique Equation (1) was used to calculate radon concentrations CRn (Bq m−3) in building materials (Najam et al., 2013):

The effective radium content CRa (Bq kg−1) was calculated by (Zubair et al., 2012)

Here, ρ is the measured α-track density (units track cm−2); h is the distance between the CR-39 detector and the sample (cm); A is the area of CR-39 (cm2); T is exposure time (h); M is sample mass (kg); CF (0.04891 Track cm−2 d−1 /Bq m−3) is the calibration factor, which is calculated using Equation (3) (Hussein et al., 2013):

Here, r is the radius of the container (cm), θc (35°) is the critical angle of CR-39, and Rα (4.15 cm) is the range of α particles emitted from 222Rn. The value of CRa should not exceed 200 Bq kg−1 , so that it does Sahar A. Amin Int. Journal of Applied Sciences and Engineering Research, Vol. 4, No. 4, 2015

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not cause indoor radon levels greater than 200 Bq m−3 (OECD, 1979). Equation (4) was used to calculate the surface exhalation rate of the sample for radon emission EA, in Bq m−2 h−1 (ICRP, 1993 and Zubair et al., 2012):

Here, C is the integrated radon exposure (Bq m−3 h), V is volume of the container (cm3), and is the decay constant of radon (h−1). The mass exhalation rate EM of the sample for radon emission (Bq kg−1 h−1) was calculated by (Zubair et al., 2012)

3. Results and discussion Results of the present work are summarized in Table 1. The calculated radon concentrations ranged from 316.3 ± 58.1 Bq m−3 for concrete to 894.6 ± 56.1 Bq m−3 for gravel, with an average of 636.3 ± 65.6 Bq m−3. Thoron concentrations were from 63.3 ± 1.6 Bq m−3 for white cement to 2015.1 ± 21.7 Bq m−3 for ceramic, with an average of 430.7 Bq m−3. The histogram shown in Figure 2 illustrates that radon levels in all samples were higher than the permissible limit of exposure to radon for the population (200 Bq m−3). Thoron levels in brick, Jumhoori brick, ceramic, kashi, black sand Karbala, and cement samples were higher than the permissible limit; levels in the remaining samples were lower than this limit (ICRP, 1993). Radium content for the studied building materials in Iraqi houses is shown in Figure 3. Radium content ranged from a minimum of 0.62 ± 0.11 Bq kg−1 in the concrete sample to a maximum of 1.74 ± 0.69 Bq kg−1 in the gravel sample. The variation in radium content may be attributable to differing radioactive contents, emanation factors and the diffusion coefficient of radon, as well as the porosity and density of the materials (Hassan, 2009). Acceptable values of radium activity for safe use in soil should not exceed 370 Bq kg−1(Nordic, 2000). Thus, as far as health hazards are concerned, our results reveal that the investigated building materials are unsafe for use. Figures (4 and 5) show that the surface exhalation rates varied from 0.86 ± 0.16 Bq m−2 h −1 in concrete to 2.42 ± 0.96 Bq m−2 h−1 in gravel, with mean value of 1.72 ± 0.25 andmass exhalation rates ranged from (0.8 ± 0.1) ×10−2Bq kg− 1 h−1 in concrete to (2.3 ± 0.9) ×10−2Bq kg−1 h−1 in gravel, with a mean of (1.6 ± 0.2) ×10−2Bq kg−1 h−1, respectively.

Figure 2: Average radon and thoron concentrations in different building material samples Sahar A. Amin Int. Journal of Applied Sciences and Engineering Research, Vol. 4, No. 4, 2015

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Table 1: Radon and Thoron levels, Radium content and Exhalation rates in the studied building materials.

Sample code

Country of origin

Radon level Bq.m-3

Thoron level Bq.m-3

Radium content Bq/kg

EA Bq.m-2.h1

EM Bq.kg-1.h-1

Bricks, Ordinary

S1

Iraq

822.3±96 .1

460.9

1.60±0.1 9

2.22±0.2 6

0.021±0.0 02

Concrete

S2

Iraq

316.3±58 .1

198.8

0.62±0.1 1

0.86±0.1 6

0.008±0.0 01

Bricks, Jumhoori

S3

Iraq

433.7±59 .7

587.4

0.85±0.1 2

1.17±0.1 6

0.011±0.0 02

gravel

S4

Iraq

894.6±56 .1

90.4

1.74±0.6 9

2.42±0.9 6

0.023±0.0 09

Ceramic

S5

Spain

713.9±67 .1

2015.1

1.39±0.1 3

1.93±0.1 8

0.018±0.0 02

Thermostone

S6

Iraq

686.8±85 .3

207.8

1.34±0.1 7

1.86±0.2 3

0.017±0.0 02

Kashi

S7

Iran

469.9±65 .3

307.2

0.94±0.1 3

1.27±0.1 8

0.012±0.0 02

Sand Al-Ekhader

S8

Iraq

759.1±63 .7

117.5

1.48±0.1 2

2.05±0.1 7

0.019±0.0 02

Sand Karbala

S9

Iraq

822.3±76 .7

144.6

1.60±0.1 5

2.22±0.2 1

0.021±0.0 02

Black Sand Karbala

S10

Iraq

840.4±74 .5

216.9

1.64±0.1 5

2.27±0.2 0

0.021±0.0 02

White Cement

S11

Iraq

397.6±36 .5

63.3

0.78±0.0 7

1.08±0.1 0

0.010±0.0 01

Cement

S12

Iraq

478.9±48 .6

759.1

0.93±0.0 9

1.30±0.1 3

0.012±0.0 01

636.3±65 .6

430.7

1.24±0.1 8

1.72±0.2 5

Building material

Average

0.016±0.0 02

Figure3: Effective radium content (Bq/kg) for building material samples Sahar A. Amin Int. Journal of Applied Sciences and Engineering Research, Vol. 4, No. 4, 2015

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Figure 4: Surface exhalation rate (Bq.m-2.h-1) for building material samples

Figure 5: Mass exhalation rate (Bq.kg-1.h-1) for building material samples

4. Conclusions The aim of this work was to assess the contribution of sampled building materials to total indoor radon exposure of the population in Iraq. We concluded that the sampled building materials are major sources of radon. However, it should be kept in mind that radon concentrations were measured by the sealed can technique, in which air during the entire exposure time was confined in the container. With good building ventilation conditions, people would be exposed to lower doses. In general, our results indicate that radon exhalation rates from the investigated building materials are low and less than the value recommended by the ICRP. Therefore, the studied materials are safe for use in construction, especially with good indoor ventilation rates. Finally, the obtained data can be useful as a reference database.

Acknowledgement The author would like to thank Mr. Adel Jassim for his assistance in preparing the samples.

5. References 1. Hassan, N. M., Hosoda, M., Ishikawa, T., Sorimachi, A., Sahoo, S. K., Tokonami, S. and Fukushi, M., 2009. Radon Migration Process and Its Influence Factors.Review, Jpn. J. Health Phys., 44 (2), 218 – 231. 2. Hůlka, J., Vlček J., & Thomas, J., 2008. Natural radioactivity in building materials - Czech experience and European legislation.Proceedings of the American Association of radon scientists and technologists, International Symposium (Las Vegas, Nevada, USA, 14–17. Sahar A. Amin Int. Journal of Applied Sciences and Engineering Research, Vol. 4, No. 4, 2015

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3. Hussein, Z. A., Jaafar, M. S., & Ismail, A. H., 2013. Measurement of radium content and radon exhalation rates in building material samples using passive and active detecting techniques.International Journal of Scientific and Engineering Research, 4(9), 1827–1831. 4. ICRP, 1970. Lung cancer risks from indoor exposure to radon daughters. International Commission on Radiological Protection, Report 50, 17(1). 5. ICRP, 1993. Protection against Rn222 at home and at work. International Commission on Radiological Protection, Annals of the ICRP,Oxford: Pergamon, 65, 35–242. 6. Najam, L.A., Tawfiq, N. F. &Mahmood, R. H., 2013. Radon Concentration in Some Building Materials in Iraq Using CR-39 Track Detector. International Journal of Physics, 1(3), 73-76. 7. Nordic, 2000. Naturally occurring radiation in the Nordic Countries–Recommendations. In The Flag-Book series, the radiation protection authorities in Denmark, Finland, Iceland, Norway and Sweden, Reykjavik. 8. OECD, 1979. Exposure to radiation from the natural radioactivity in building materials. Report by a group of experts of the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (Paris, France, 1979). 9. Ramola, R. C., &Choubey, V. M., 2003. Measurement of radon exhalation rate from soil samples of Garhwal Himalaya India. Journal of Radioanalytical and Nuclear Chemistry, 256(2), 219–223. 10. Zubair, M., Shakir Khan, M., &Verma, D., 2012. Measurement of radium concentration and radon exhalation rates of soil samples collected from some areas of Bulandshahr district, Uttar Pradesh, India using plastic track detectors. Iranian Journal of Radiation Research, 10(2), 83-87.

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