Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip

M.O. El-Ghossain

International Journal of Physics

Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip

M.O. El-Ghossain

Department of Physics, The Islamic University of Gaza, Gaza, Palestine

Abstract

Building materials are one of the potential sources of indoor radioactivity because of the naturally occurring radionuclides in them. Radon exhalation rate is one of the most important factors for evaluation of the environmental radon level. Radon contributes more than half of the total ionizing radiation dose Indoor radon has been recognized as one of the health hazards for mankind because long-term exposure to radon increases the risk of developing lung cancer. This study aims at assessing the contribution of destroyed building materials in war 2014 towards the total indoor radon exposure to the inhabitants of in . 40 Samples have been collected from common destroyed building materials in Jabalia district. The closed-can technique has been employed in this study using solid state nuclear track detectors (CR-39). After 124 days of exposure to radon, CR-39 detectors were etched chemically by (6 N) NaOH solution at 75°C for three months and then counted under an optical microscope. Results obtained from the current study show that radon exhalation rates from concrete and asbestos have relatively high values as compared to other building materials while glass, marble and a red brick contribute less to radon exhalation rate. The average radon exhalation rate in term of area in the studied samples ranged from (86.506) mBq.m-2.h-1 for glass samples to (469.017) mBq.m-2.h-1 for Concrete samples. In general, the annual effective doses from the investigated building materials are low and under the global value (from 1 to 5 mSv/y) except for Concrete and asbestos samples with average values (9.464) and (9.3528) mSv/y, respectively.

Cite this article:

  • M.O. El-Ghossain. Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip. International Journal of Physics. Vol. 4, No. 6, 2016, pp 146-151. http://pubs.sciepub.com/ijp/4/6/1
  • El-Ghossain, M.O.. "Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip." International Journal of Physics 4.6 (2016): 146-151.
  • El-Ghossain, M. (2016). Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip. International Journal of Physics, 4(6), 146-151.
  • El-Ghossain, M.O.. "Measurement of Radon Exhalation Rate from Destroyed Building Material in the Gaza Strip." International Journal of Physics 4, no. 6 (2016): 146-151.

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1. Introduction

All building materials contain various amounts of main natural radionuclides of the uranium (238U) and thorium (232Th) series, and since those radionuclides are sources of Radon gas then the knowledge of the natural radioactivity of building materials is important for the determination of population exposure to radiations. For the aforementioned reasons we intend to study the concentration of Radon and the exhalation rate from destroyed building materials in the 2014 war used in the districts of Jabalia in the northern Gaza Strip [1, 2, 3, 4, 5]. It will then be compared to results obtained with the results of previous studies. Then we will study the health risks of radon gas.

In this study, we present our data concerning measurement of the radon exhalation rate from destroyed building material samples collected from Jabalia district in the Gaza strip in Palestine using close vessel technique. The location of this district is shown in Figure 1. Houses in this district are mainly constructed from soil, bricks, cement, sand, granite and marble. This district is located in the northern part of the Gaza strip of Palestine.

This study was done during the month of March to July 2015, which includes the following main stages, where the samples are collected from destroyed building materials.

The purpose of this study is to measure the Radon exhalation rates from destroyed building materials during 2014 war against Gaza, Palestine. Our study will include samples of a red brick, marble, ceramic, concrete, tiles, asbestos, glass and building stones from different origins used in the mentioned area of study.

Figure 1. The figure shows the map of the Gaza strip

In a previous studies, in Egypt, a study on 222Rn exhalation rate from Egyptian building materials was performed in 2009 and found that the radon exhalation rate in the studied samples ranged from (2.2 x 104 ± 7.2 x102) μBq m-2 s-1, for granite sample, to (3.4x101 ± 9.0x100) μBqm-2 s-1, for portland cement with an average value (1.8x103 ± 6.5x101) μBq m-2 s-1 [6]. In Nablus district, Palestine, They measured Radon exhalation rates from granite and marble have relatively high values as compared to other building materials followed- in order- by cement, ceramic, concrete, building stones, and porcelain, while gypsum, sand, gravel and bricks contribute less to radon exhalation rate which was found to range from (55.37 ± 15.01) mBq/m2h for gypsum samples to (589.54 ± 73.24) mBq/m2h for granite samples, with a total average value of (268.56 ± 166.21) mBq/m2h. The corresponding radon concentration, effective radium content, and annual effective dose average values were (148.49 ± 91.13) Bq/m3, (1.93 ± 1.20) Bq/Kg and (3.74 ± 2.30) mSv/y [7].

2. Materials and Experimental Methods

Different samples of destroyed building materials after the 2014 war against Gaza were collected randomly from different destroyed buildings, like, houses, commercial companies, and factories, all around the area of study during the month of March to July. Samples were a red brick, marble, ceramic, concrete, tiles asbestos, glass and building stones, samples were from different origins, used in construction of building in Jabalia district, Gaza Strip, Palestine. Samples were then identified and given a number and an identifying symbol which identify the location of the samples, as in Table 1. 5 kg from each sample were collected and dried in a temperature controlled furnace (oven) at a temperature100°C for two hours to ensure that moisture was completely removed. And then the samples were crushed to a fine powder and sieved through a small mesh size to remove the larger grains size and render them more homogenous. The respective net weights of the samples ready for measurement were recorded.

Table 1. List of numbers and codes for samples studied in this research

The close vessel technique was used in this study “can technique” or we call them “Dosimeters”. Dosimeters are plastic cylindrical vessels of volume (7.93×10-4) m3 with cross sectional area of (5.02×10-3 m2) as shown in figure 2. The destroyed building material samples were put at the bottom of these vessels. About 200 g of each sample was placed in a plastic can of dimensions15.8 cm in height and in diameter.

The use of plastic solid-state nuclear track detectors, SSNTDs of type CR-39, which were cut into small pieces, 2cm×2cm and fixed on the top of inner surface of the can, in such a way that its sensitive surface always facing the sample. The can was sealed air tight with adhesive tape and kept for assessment of radon exhalation for exposure evaluation over four months. During the exposure period (one hundred and twenty four days), the detector was exposed freely to the emergent radon from the sample in the can so that it could record alpha particles resulting from the decay of radon in the remaining volume of the can [3, 4, 5, 6, 7, 8].

After the mentioned period, forty detectors were taken out of the dosimeters. The detectors were then chemically etched in 6 N-solution of Sodium Hydroxide (Na OH) at a temperature of 70 C for four hours and one third of an hour. The etching process was performed at chemistry Laboratories at using the setup. In addition, the function of the condenser is to keep the concentration of the Na OH solution constant, and the function of the thermometer is to make sure that the temperature is constant during the whole period of the etching process. After four hours and one third of an hour detectors were washed by running and distilled water and then dried to remove any remaining amount of the etchant from the surface of the detectors. By now alpha tracks formed on the detectors were ready for scanning and counting.

A digital optical microscope with 400 times magnification was used to count the number of tracks per field of view; about ten fields of view were scanned randomly for each detector. Tracks of alpha particles emitted by radon in a CR-39 detector were scanned by the microscope as shown in Figure 3. The area of the field of view was calculated by the digital microscope and found to be equal about 5.3×10-3 cm2 ; the average number of tracks per field of view was used to calculate the track density. The calculated track density was converted into radon concentrations in Bq/m3 using the calibration factor (k) obtained by the standard manufacturer, where every track per cm2 per day on the CR-39 detectors corresponds to an exposure of 12.5 Bq/m3 for the activity of radon gas and its daughters and we use previous calibrations [6, 7, 8].

Figure 3. Tracks of alpha particles emitted by radon in a CR-39 detector. One viewing field from the microscope has the area of about 0.53 mm2

Calculations:

The radon concentrations, radon exhalation rate were calculated using the experimental measured average track densities according to the following relations from previous studies [7, 8, 9, 10].

2.1. Determination Radon Concentration:
(1)

CRn: is the radon concentration (Bq/m3)

K: is the calibration factor = 12.5 Bqm-3/tracks cm-2h-1.

: Is the track density (tracks/ cm2)

Teff: effective time = [t + (e-λt - 1)/λ]

t: exposure time

2.2. Determination Radon Exhalation Rate in Area

The radon exhalation rate (Ex) of any sample is defined as the flux of radon released from the surface of material. The surface exhalation rate in the building material samples was calculated using equation (2), the radon exhalation rate in terms of area (surface exhalation rate) in units of Bq∙m−2∙h-1 can be obtained by as [8, 9, 10, 11, 12].

(2)

Where:

C: is the integrated radon exposure (Bq∙m−3∙h);

V: is the volume of air in the cup (m3) = 7.942×10-4m3

λ: is the decay constant for Rn222 (h−1) = 7.56×10-3h-1

A: is the surface area of the sample (m2) = 5.0265×10-3m2

t: is the exposure time (h) = 124 days = 2976h

2.3. Determination Radon Exhalation Rate in Mass

The mass exhalation rate (Bqkg−1∙h−1) in the building material samples is calculated using the following formula 3:

(3)

Where EM is the mass exhalation rate in (Bqkg−1∙h−1) and M is the mass of sample (kg) [8-15][8].

2.4. Determination the Annual Effective Dose

The following equation was used to calculate the annual effective dose as in equation 4:

(4)

Where:

fRn: is the conversion factor = 9 nSv / (Bq h m-3).

Ty: is the time spent indoors per year = 7000 hours

ϵ: is the equilibrium factor (= 0.4)

CRn : is the radon concentration.

Substituting the previous parameters in equation (4) we can evaluate the annual effective dose simply according to the following relation 5 [16, 17, 18].

(5)

3. Results and Discussion

Results and discussion for radon concentrations, radon exhalation rate in terms of area Ex, and radon exhalation rate in term of mass Em for destroyed building material samples used in Jabalia city are given in this chapter. Equations 1, 2, 3 and 5 respectively were used for calculating radon concentrations, radon exhalation rate in term of area, Ex, radon exhalation rate in terms of mass, Em, and Annual Dose for destroyed building material samples used in this study which include a red brick, marble, ceramic, concrete, tiles, asbestos, glass, and building stones. The results of Radon concentration only is shown in Table 2 for all building materials.

But radon exhalation rate in terms of area Ex, and radon exhalation rate in term of mass Em, and annual effective dose for Ceramic is shown in Table 3.

The radon exhalation rate in terms of area Ex, and radon exhalation rate in term of mass Em, and annual effective dose for each individual sample collected from Jabalia area are summarized in Table 3.

Table 2. Radon concentration only is shown in Table 2 for all building materials

Table 3. Summary of results of the average radon exhalation rate in terms of area Ex, radon concentration, radon exhalation rate in terms of mass Em and the annual effective dose from all destroyed building materials used in Jabalia district using standard calibration [6,7,8,9,10]

The data listed in Table 1 clearly show that concrete, tiles, building stones and asbestos are have high radon exhalation rate in terms of area Ex, radon concentration, radon exhalation rate in terms of mass Em and the annual effective dose. But the glass have low radon exhalation rate in terms of area Ex, radon concentration, radon exhalation rate in terms of mass Em and the annual effective dose.

The Figure 4 shows the comparison between destroyed building materials in terms of the average radon exhalation rates in term of area where the concrete have the highest value with 469.017 mBq.m-2.h-1 then asbestos with 463.895 mBq.m-2.h-1 then (tiles, building stones, ceramic, a red brick, marble and glass) with (204.087, 190.025, 133.92, 105.945, 105.130 and 86.506) mBq.m-2.h-1 respectively. Note that the glass have the lowest value of the materials studied.

Figure 4. This figure shows the Comparing histogram for the average radon exhalation rates in term of area.
Figure 5. This figure shows the Comparing histogram for the average radon concentration rates

The Figure 5 shows the comparison between destroyed building materials in terms of the average radon concentration rates where the concrete have the highest value with 375.580 By/m3 then asbestos with 371.140 By/m3 then (tiles, building stones, ceramic, a red brick, marble and glass) with( 163.280, 152.030, 107.650, 84.630, 84.110 and 69.210) respectively. Note that the glass has the lowest value of the materials studied.

The Figure 6 shows the comparison between destroyed building materials in terms of the average radon exhalation rates in term of mass where the concrete have the highest value with 11.799 mBq.kg-1.h-1 then asbestos with 11.659 mBq.kg-1.h-1 then (tiles, building stones, ceramic, a red brick, marble and glass) with (5.129, 4.776, 3.570, 2.658, 2.642 and 2.174) mBq.kg-1.h-1 respectively. Note that the glass has the lowest value of the materials studied.

Figure 6. This figure shows the Comparing histogram for the average radon exhalation rates in term of mass

The Figure 7 shows the comparison between destroyed building materials in terms of the average annual effective dose for radon gas where the concrete have the highest value with 9.464 msv.y-1 then asbestos with 9.352 msv.y-1 then (tiles, building stones, ceramic, a red brick, marble and Glass) with ( 4.114, 3.831, 2.712, 2.132, 2.119 and 1.744) msv.y-1 respectively. Note that the glass has the lowest value of the materials studied.

Figure 7. This figure shows the Comparing histogram for the average annual effective dose for radon gas
Figure 8. This figure shows the Comparing histogram for the average radon concentrations (CRn Ave.) and exhalation rates () from building materials used in Jabalia district

In Figure 8 We notice that, the concrete have the highest value of the average radon concentration and the average radon exhalation rate in term of area Ex, then (asbestos, tiles, building stones, ceramic, a red brick, marble and glass ) respectively.

4. Conclusion

Using the closed can technique and the solid state nuclear track detectors (CR-39), we measured the radon exhalation rate from building material samples used in Jabalia in order to assess the contribution of individual material (e.g. red brick, marble, ceramic, concrete, tiles, asbestos, glass, and building stones) to the total indoor radon exposure of the inhabitants of Jabalia district. The corresponding radon concentration, and the annual effective dose were determined and compared with the effective dose limit values recommended by the National Council on Radiation Protection which (from 1 to 5 mSv/y). Results obtained from the current study show that the radon exhalation rates from asbestos and concrete have relatively high values as compared to other building material samples followed red brick, marble, ceramic, tiles, glass, and building stones contribute less to the indoor radon. From the results of our study we can conclude that the Concrete have the maximum values of radon concentrations 375.58Bq/m3, radon exhalation rate in term of area469.017mBq.m-2.h-1, radon exhalation in term of mass 11.799 mBq.Kg-1.h-1 and the annual effective dose 9.464 mSv.y-1,also asbestos have maximum values of radon concentrations 371.14 Bq/m3, radon exhalation rate in term of area 463.895 mBq.m-2.h-1, radon exhalation rate in term of mass 11.659 mBq.Kg-1.h-1 and the annual effective dose 9.3528 mSv.y-1. But the glass have the minimum values radon concentrations 69.21 Bq/m3, radon exhalation rate in term of area 86.506 mBq.m-2.h-1, radon exhalation rate in term of mass 2.174 mBq.Kg-1.h-1and the annual effective dose 1.744 mSv.y-1. In comparison with the annual effective dose of Radon by NCRP, we found that concrete and asbestos are 9.46 and 9.35 mSv/y, are much higher than the proposed limit which is 1 to 5 mSv/y, and all other material are below the limit. There are many researchers studied radon gas for building materials, comparison with previous studies will be shown in following tables, the results obtained in Sudan are in Table 4 [19]:

The results obtained in Palestine are in Table 5 [7]:

Table 5. Results from Palestine (Shoqwara) [7]

All these results are close to the values we have for the building materials we studied.

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