Natural radioactivity of some Egyptian building materials
M.F. Eissa*, R.M. Mostafa and F. Shahin Physics Department Faculty of Science Beni-Suef University Beni-Suef, Egypt Fax: +2082–233–4551 E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] *Corresponding author
Abstract: The study of the radiation hazards from building materials is of interest in most countries. The measurements of natural radioactivity were verified for some Egyptian building materials to assess any possible radiological hazard due to their use. The measurements were performed by gamma-ray spectroscopy using a Hyper-Pure Germanium (HPGe) detector. A CR-39 track detector was used to measure the radon exhalation rates, and these were found to vary from 2.83 ± 0.86 to 41.57 ± 8.38 mBq m–2 h–1 for Egyptian alabaster. The absorbed dose rate in the air was lower than the international recommended value (55 nGy h–1) for all test samples.
Reference to this paper should be made as follows: Eissa, M.F., Mostafa, R.M., Shahin, F., Hassan, K.F. and Saleh, Z.A. (2008) ‘Natural radioactivity of some Egyptian building materials’, Int. J. Low Radiation, Vol. 5, No. 1, pp.1–8.
Biographical notes: Mostafa Fawzy Eissa is a Lecturer in the Physics Department of Beni-Suef University. He was awarded his PhD in Physics from Cairo University, Egypt, in 2002. His PhD was about fast neutron activation analysis. He has conducted research on radioactivity in the environment (radon measurements) and on positron annihilation spectroscopy for irradiated materials. He has published eight papers on radon and positron annihilation (Doppler-Broadening spectroscopy).
2 M.F. Eissa, R.M. Mostafa, F. Shahin, K.F. Hassan and Z.A. Saleh
Rafaat Mohamed Mostafa is a Lecturer in the Physics Department of Beni-Suef University. He was awarded his PhD in Physics from Beni-Suef University, Egypt, in 2006. His PhD was on radon measurements in the Wadi Sanuur cave, Egypt. He has conducted research on radioactivity in the environment (radon measurements).
Fayez Mohamed Shahin is a Professor of Physics in the Physics Department of Beni-Suef University. He was awarded his PhD in Nuclear Physics from Dresden University, Germany. He was head of the Physics Department from 1996 to 2004. His research area is in radioactivity, radon measurement and atomic physics. He has supervised several PhD and MSc candidates in radiation and atomic physics.
Khalid Forrag Hassan is a Researcher in the Cyclotron project of the Egyptian Atomic Energy Authority. He was awarded his PhD in Radiation Chemistry from Mansoura University in 2007. His research area is in isotope production and radiation chemistry in the Atomic Energy Authority.
Zeinab Abdo Saleh is a Professor of Physics in the Cyclotron project of the Egyptian Atomic Energy Authority. Her research area is in isotope production and radioactivity in the Cyclotron project. She has supervised several PhD and MSc candidates in radiation and neutron physics.
1 Introduction
The most abundant sources of external and internal radiation exposure in homes are gamma rays, emitted by members of the uranium and thorium decay chains and 40K, and also radon and its daughters, which are exhaled by building materials. Knowledge of the radioactivity present in building materials enables one to assess any possible radiological hazard caused by the use of such materials. This study has been satisfied in most countries (Sharma et al., 2003; Petropoulos et al., 2002; Keller et al., 2001; Khan et al., 1992). Few data are available about the natural radioactivity of Egyptian building materials (Arafa, 2004; Walley El-Dine et al., 2001; Sharaf et al., 1999; El-Arabi et al., 2004), particularly that of alabaster, building limestone and raw floor slabs, which represent the major components of public and residential buildings in Egypt. In the present work, measurements of the natural radioactivity and radon exhalation rates in Egyptian alabaster from the eastern desert of Beni-Suef, Egypt, building limestone, raw floor slabs and raw building bricks have been investigated. The measurements have been verified using a Hyper-Pure Germanium (HPGe) detector and an etch track detector of type CR-39.
2 Experimental technique
Five types of alabaster and raw samples (sand, sand clay, yellow clay and cement) were collected from different quarries and regions from the eastern desert of Beni-Suef, Egypt. Other samples were collected from different locations across the country. The black marble and Karara from outside the Egyptian country. The samples were dried at room temperature and crushed to 1 mm grain size.
Natural radioactivity of some Egyptian building materials 3
2.1 Activity concentration measurements
The prepared samples were weighed and sealed in plastic containers with a volume of 350 cm3. The samples were sealed tightly for four weeks to reach secular equilibrium between 226Ra and its daughters. The gamma-ray lines were measured directly using a HPGe detector. The detector has a Full Width at High Maximum (FWHM) of 1.85 keV for the 1332.5 keV 60Co gamma-ray line.
The counting time was about 18 000 s to obtain the gamma-ray spectrum with good statistics. The gamma-ray transitions of energies 351.9 keV (214Pb), 609.3 keV, 1120.3 keV and 1764 keV (214Bi) were used to determine the activity concentration of the 238U series. The gamma-ray transitions of energies 338.4 keV (228Ac), 583.3 keV (208Tl), 2614 keV (208Tl) and 911.1 keV (228Ac) were used to determine the activity concentration of the (232Th) series. The 1460 keV gamma-ray transition 40K was used to determine the concentration of 40K in different samples.
2.2 Surface exhalation rate measurements
A 100 g amount of each sample was placed at the base of a cylindrical glass cup. The cup was 6.5 cm in diameter and 11 cm in height. A CR-39 detector of area 1.5 × 1.0 cm2 was fixed at the top centre of the cup to register alpha particles from the decay of radon and its daughters. The cups were sealed for 60 days. The calibration factor of the can was 0.163 ± 0.028 tracks cm−2 (Bq m−3d)−1 (Eissa, 2006).
The surface exhalation rate ES (Bq m−2 h−1) of the rock sample was found from the following expression (Abu-Jarad et al., 1980):
( 1)S T
CVE
eA T
λ
λ
λ
−=
⎛ ⎞−+⎜ ⎟
⎝ ⎠
(1)
where C is the integrated radon concentration measured by the CR-39 detector (Bq m−3 h), V is the volume of the emanation container (m3), λ is the decay constant of radon (h−1), A is the surface area emanating the radon (m2) and T is the exposure time (days).
After exposure, the detectors were etched chemically in a 6.25 M NaOH solution at 70°C for 6 h. The tracks were counted with an optical microscope magnifying 400 times.
3 Results and discussion
Table 1 shows the radiation measurements (activity concentrations of 238U, 232Th and 40K, radium equivalent in Bq kg−1 and the absorbed dose rate in the air (D) in nGy h−1) measured by the HPGe detector beside CR-39 measurements for the radon exhalation rate (in mBq m−2 h−1) for Egyptian alabaster. The average activity concentrations of 238U, 232Th, 40K, radium equivalent and effective dose rate were found to be 15.47 ± 0.78, 7.00 ± 3.06, 62.41 ± 5.01, 30.21 ± 4.31 Bq kg−1 and 13.90 ± 2.02 nGy h−1, and the corresponding average radon exhalation rate is 18.76 ± 7.56 mBq m−2 h−1.
4 M.F. Eissa, R.M. Mostafa, F. Shahin, K.F. Hassan and Z.A. Saleh
Table 1 The activity concentrations of 238U, 232Th and 40K, radium equivalent, absorbed dose rate and the radon exhalation rate Es of Egyptian alabaster
The variation of the radon exhalation rate measured by the CR-39 track detector with the uranium concentration measured by the HPGe detector for alabaster samples is shown in Figure 1. A linear dependence between uranium concentration and the exhalation of radon with correlation factor of R2 = 0.67 is observed.
Figure 1 Dependence of the radon exhalation rate on the uranium concentration for alabaster samples
Rad
on e
xhal
atio
n ra
te (m
Bq
m–2
h–1
)
The above radiation measurements have been investigated for building limestone, raw floor slabs and raw building bricks (Tables 2 and 3). The raw building bricks have the highest average value of 238U concentration (22.18 ± 4.56 Bq kg−1). The lowest value was found for building limestone, 1.15 ± 0.33 mBq m−2 h−1.
Table 2 Radiation measurements for building limestone and raw floor slabs
A nonlinear relationship between the uranium concentration and the radon exhalation rate for raw floor slabs was revealed as in Figure 2. This behaviour is not apparent for raw building bricks as shown in Figure 3, owing to variations in the radium content of the sample and the porosity (Folkerts et al., 1984).
Figure 2 Dependence of the radon exhalation rate on the uranium concentration for raw floor slabs
Rad
on e
xhal
atio
n ra
te (m
Bq
m–2
h–1
)
To compare materials containing different 238U, 232Th and 40K, we used the radium equivalent activity, Raeq (Bq kg–1) formula (Beretka and Mathew, 1985), as follows:
1.43 0.077 .eq U Th kRa S S S= + + (2)
The average value of Raeq in the measured samples was found to be 34.56 ± 5.26 Bq kg−1. This value was lower than the recommended maximum value of 370 Bq kg−1 (Beretka and Mathew, 1985).
6 M.F. Eissa, R.M. Mostafa, F. Shahin, K.F. Hassan and Z.A. Saleh
Figure 3 Dependence of the radon exhalation rate on the uranium concentration for raw building bricks
Rad
on e
xhal
atio
n ra
te (m
Bq
m–2
h–1
)
The absorbed dose rate in the air (D) in nGy h−1, resulting from the activity concentration of 238U, 232Th and 40K in Bq kg–1 at a height of 1 m above the ground, was calculated using the following formula (UNSCEAR, 1988):
0.427 0.662 0.0432 .U Th KD S S= + + S (3)
Figure 4 shows the variations of D values for all investigated samples. The maximum value was found for the sand clay sample. This value is lower than the international recommended value (55 nGy h–1) (UNSCEAR, 1988).
Figure 4 The variations of absorbed dose rate in air (D) in nGy h–1 for alabaster, raw floor slabs, bricks and building limestone (see online version for colours)
The activity concentrations for some Egyptian building materials and their comparison with previously reported data are listed in Table 4. It is obvious from this table that there is an agreement between the present data and the reported data.
Natural radioactivity of some Egyptian building materials 7
Table 4 Comparison of Activity concentrations in Bq kg–1 of different Egyptian building
material with the corresponding values reported previously
Activity concentrations (Bq kg–1) Type of building material 226Ra 232Th 40K Reference
Sand 9.2 ± 2.5
9.26 ± 3.28
3.3 ± 1.3
2.91 ± 0.1
47.3 ± 9.0
54.52 ± 6.64
Sharaf et al. (1999)
Present
Cement 37.6 ± 6.0
31.3 ± 3.6
22.51 ± 3.23
11.8 ± 3.0
11.1 ± 1.1
3.99 ± 1.02
178.6 ± 15
48.6 ± 4.0
68.76 ± 8.29
El-Arabi et al. (2004)
Sharaf et al. (1999)
Present
Limestone 13.4 ± 4.05
31.5 ± 5.0
20.4 ± 2.8
3.29 ± 0.62
10.0 ± 2.0
4.4 ± 0.8
61 ± 6.79
–
19.3 ± 2.0
Present
El-Arabi et al. (2004)
Sharaf et al. (1999)
Yellow clay 27.22 ± 5.60
25.6 ± 2.4
19.36 ± 2.48
23.5 ± 3.5
188.71 ± 12.62
282 ± 15
Present
Sharaf et al. (1999)
6 Conclusions
From the present study, it can be concluded that:
• the radon exhalation rate is considered to be an indicator of the uranium present in the building material samples investigated
• Egyptian alabaster as a building material is very safe from radiation hazards of gamma rays and exhalation of radon gas
• the absorbed dose rate in the air at a height of 1 m above the ground is lower than the international recommended value (55 nGy h−1) for all test samples.
References Abu-Jarad, F., Fremlin, J.H. and Bull, R. (1980) Phys. Med. Biol., Vol. 25, p.683.
Arafa, W. (2004) J. Environ. Radioactivity, Vol. 75, p.315.
Beretka, J. and Mathew, P.J. (1985) Health Phys., Vol. 48, p.87.
Eissa, M.F. (2006) International Journal of Pure and Applied Physics, Vol. 2, No. 2, p.127.
El-Arabi, A.M., Abbady, A., El-kamel, A.H., Nosier, A. and Moustafa, A. (2004) VII Radiation Physics & Protection Conference, Ismailia-Egypt, 27–30 November.
Folkerts, K.H., Keller, G. and Muth, R. (1984) Radiat. Prot. Dosim., Vol. 9, p.27.
Keller, G., Hoffmann, B. and Feigenspan, T. (2001) The Science of the Total Environment, Vol. 272, p.85.
8 M.F. Eissa, R.M. Mostafa, F. Shahin, K.F. Hassan and Z.A. Saleh
Khan, A.J., Prasad, R. and Tyagi, R.K. (1992) Nucl. Tracks Radiat. Meas., Vol. 20, No. 4, p.609.
Petropoulos, N.P., Anagnostakis, M.J. and Simopoulos, S.E. (2002) J. Environ. Radioactivity, Vol. 61, p.257.
Sharaf, M., Mansy, M., El Sayed, A. and Abbas, E. (1999) Radiation Measurements, Vol. 31, p.491.
Sharma, D.K., Kumar, A., Kumar, M. and Singh, S. (2003) Radiation Measurements, Vol. 36, p.363.
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (1988) Sources Effects and Risk of Ionizing Radiation, United Nations, New York.
Walley El-Dine, N., El-Shershabya, A., Ahmed, F. and Abdel-Haleem, A.S. (2001) Applied Radiation and Isotopes, Vol. 55, p.853.
