Radiation Protection Dosimetry (2005) Vol. 114, No. 4, pp. 527–532
doi:10.1093/rpd/nch471
RADIOACTIVITY IN BUILDING MATERIALS USED IN AND AROUND DHAKA CITY S. Roy1,, M. S. Alam2,3, M. Begum1 and B. Alam2 1 Health Physics Division, Atomic Energy Centre, P.O. Box No. 164, Dhaka-1000, Bangladesh 2 Department of Physics, University of Dhaka, Dhaka-1000, Bangladesh 3 Physikalisches Institut III, Universitact Erlangen-Nuernberg, Erwin-Rommel Strasse 1, D-91058 Erlangen, Germany Received October 15 2004, amended January 27 2005, accepted February 7 2005 The activity levels of 226Ra, 232Th and 40K were determined using gamma-ray spectroscopy in different commercial brands of cement, sand and hollow concrete bricks, which were collected from the building material suppliers of Dhaka City. The activity concentrations in the samples were found to be somewhat higher than in other countries. An effort has been made to assess the radiation hazard associated with these materials by determining the gamma activity concentration index I. It was found that the value of I for all the samples was 2, which indicates that the gamma dose contribution was not more than 0.3 mSv y 1. The samples considered were safe for use in the construction of urban dwellings in Bangladesh and do not pose any significant source of radiation hazard.
INTRODUCTION It has been established that human exposure to radioactivity comes mainly from natural sources. The natural radiation to which the general public is exposed consists mainly of two distinct components, namely, internal exposure and external exposure. Internal exposure is due to the inhalation of radon gas in the air and the intake of traces of radionuclides in food and drinking water. External exposure originates from terrestrial gamma rays and cosmic radiation incident on the earth’s surface. The other source of external exposure is from man-made radiation. Building material is one such source of man-made radiation responsible for external exposure. There are few data available on the radioactivity of building materials in Bangladesh. A study was performed in Bangladesh(1) and found a somewhat higher level of activity in building materials than in other countries. An extensive study was carried out later(2) on the radioactivity in various types of brick samples fabricated and used in Dhaka City and its suburbs. The activity levels in brick samples were found to be consistent with the values quoted elsewhere(3,4). The determination of activity levels in building materials is also important in view of the living environment in Bangladesh. High-rise apartments are growing up to house the large population in Dhaka city (12 million). Many of these apartments provide office space for work. The rooms in these apartments are mostly small in size with low ceilings,
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and thus the residents and the workers are surrounded by a considerable amount of building materials. Consequently, the indoor exposure of these people may be significant. Equally, those people who remain outside the rooms where they work and live are still surrounded by building structures and exposed to external radiation. The main contributors to the external exposure in dwellings are the members of the 238U and 232Th decay chains and 40K. Building products can vary considerably according to the geological origin of the raw materials procured at the fabrication sites. External radiation exposure from naturally occurring radionuclides give rise to, on average, around one-half of the annual dose to the human body from radiation sources(5). The radioactivity levels of 226Ra, 232Th and 40K were measured using gamma-ray spectroscopy in different commercial brands of cement, sand and hollow concrete bricks, which were collected from the building material suppliers of Dhaka City. An effort has been made to assess the possible radiation hazard associated with these materials by computing the gamma activity concentration indices. The values of the activity concentration have been compared with those of other countries. This work is a continuation of our previously reported measurements on other building materials such as brick samples(2).
MATERIALS AND METHODS A total of 34 samples of different commercial brands of cement, white sand, red sand and hollow concrete bricks were collected for the measurements of activity
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S. ROY ET AL. Table 1. Activity concentrations and gamma activity concentration indices in some building materials used in and around Dhaka City. Code
Activity concentration (Bq kg1)
Material(a) 226
232
Ra
SC01 CE01 CE02 RU01 RU02 RU03 TG01 TG02 TG03 RY01 RY02 CD01 CD02 IE01 IE02 KG01 KG02 SH01 SH02 EL01 EL02 HC01 HC02 NL01 BH01 SR01 SR02 SD01 SD02 SD03 RS01 RS02 HB01 HB02
Cement (Scan) Cement (Cemex 1) Cement (Cemex 2) Cement (Ruby 1) Cement (Ruby 2) Cement (Ruby 3) Cement (Tiger 1) Cement (Tiger 2) Cement (Tiger 3) Cement (Raymond 1) Cement (Raymond 2) Cement (Confidence 1) Cement (Confidence 2) Cement (Indoenergy 1) Cement (Indoenergy 2) Cement (King Brand 1) Cement (King Brand 2) Cement (Seven Horse 1) Cement (Seven Horse 2) Cement (Elephant 1) Cement (Elephant 2) Cement (Holcim 1) Cement (Holcim 2) Cement (Niloy 1) Cement (Bull Head 1) Cement (Seven Rings 1) Cement (Seven Rings 2) White sand 1 White sand 2 White sand 3 Red sand 1 Red sand 2 Hollow concrete brick 1 Hollow concrete brick 2
Th
48.2 3.0 78.5 4.5 73.9 4.3 96.5 5.4 96.1 5.4 106.3 5.9 47.5 3.9 62.7 3.9 67.4 3.8 115.3 6.3 118.1 6.5 62.8 3.7 59.0 3.5 44.6 3.1 51.6 3.1 40.8 2.6 41.2 2.7 40.8 2.6 45.5 2.8 59.8 3.5 59.8 3.3 52.1 2.9 50.8 3.1 69.0 4.1 64.5 3.8 44.4 2.8 42.5 2.7 39.0 2.5 44.6 2.8 50.4 3.1 72.2 4.2 50.4 3.1 43.4 2.7 45.9 2.8
84.7 6.0 68.7 5.2 81.7 5.8 84.1 6.0 79.7 5.8 100.2 6.9 64.6 4.9 69.9 5.2 70.5 5.3 101.0 6.9 113.0 7.5 102.1 7.0 93.6 6.5 83.3 5.9 81.9 5.9 68.7 5.3 72.7 5.4 67.5 5.1 63.0 4.9 82.8 5.9 90.2 6.3 69.2 4.8 70.1 5.2 64.5 4.9 66.8 5.1 77.9 5.7 85.5 6.1 110.6 7.4 107.6 7.3 90.2 6.3 243.2 14.0 123.6 8.1 97.1 6.7 105.6 7.2
40
Gamma activity concentration index (I )
K
1223.3 95.8 1102.9 87.2 1062.8 84.4 1069.5 84.8 1069.5 84.8 955.9 76.7 1042.8 82.9 1069.5 84.8 1016.0 81.0 1129.7 89.1 1169.7 92.0 1290.1 100.6 1350.3 104.9 1230.0 96.3 1243.3 97.3 1109.6 87.7 1096.3 86.7 1176.5 92.5 1049.5 83.4 1216.6 95.3 1096.3 86.7 1169.8 92.0 1169.5 94.0 1009.4 80.6 1102.9 87.2 1169.5 94.0 1189.8 93.4 1604.3 123.0 1597.5 122.5 1577.5 121.1 1624.3 124.4 1557.5 119.6 1564.2 120.1 1550.8 119.2
0.67 0.05 0.97 0.04 1.01 0.04 1.10 0.05 1.08 0.04 1.17 0.05 0.83 0.04 0.92 0.04 0.92 0.04 1.27 0.04 1.35 0.05 1.15 0.05 1.11 0.05 0.98 0.05 1.00 0.05 0.85 0.04 0.87 0.04 0.87 0.04 0.82 0.04 1.02 0.05 1.02 0.04 0.91 0.04 0.91 0.04 0.89 0.04 0.92 0.04 0.93 0.04 0.97 0.05 1.22 0.06 1.22 0.06 1.15 0.05 2.00 0.08 1.31 0.06 1.15 0.05 1.20 0.05
(a)
The commercial brand names of the cement are given within parentheses. Numbers in the sample names indicate that they were collected from different suppliers
concentrations. These samples were collected directly from the local building material suppliers and manufacturers. Of the samples listed in Table 1, the white sand samples SD01 to SD03 were reported to have been procured from the River Brahmaputra, Mymenshingh, which is 120 km north of Dhaka. The red sand samples RS01 and RS02, which are granular sands used in casting, were obtained from the rivers Surma and Kushiyara, Sylhet, which is 250 km northeast of Dhaka city (shown in Figure 1). The use of hollow concrete bricks as a construction material in Bangladesh is new. Environmentalists believe that these materials hold promise because their fabrication is free from pollution. However, the materials are not yet popular because
they are expensive compared with conventional bricks. Solid samples were crushed and pulverised in a large mortar and pestle made of cast iron, dried in an oven at 105 C and sieved with a laboratory test sieve of aperture 425 mm (Mesh No. 40 and Serial No. 238523; supplied by the Endecotts Ltd, London, UK), homogenised, ground and then screened(6). The prepared samples were transferred to radonimpermeable plastic containers of almost uniform size (8 cm diameter 7 cm height), weighed and sealed for 45 days to allow a growth period to establish secular equilibrium between 226Ra (of 238 U) and 232Th and their daughter products. The natural radioactivity of building materials is usually
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RADIOACTIVITY IN BUILDING MATERIALS
Figure 1. Map of Bangladesh. The locations where white sand was collected from Mymensingh and red sand from Sylhet are shown, along with other major cities and rivers of the country.
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S. ROY ET AL. 226
232
40
determined from the Ra, Th and K contents(7) since 98.5% of the radiological hazard of the uranium series is produced by radium and its daughter products, and the contribution from 238U and other 226Ra precursors are generally ignored(8). Measurements were made with a HPGe detector with 62.7 cm3 effective volume (Model No. IGC 1018 and Serial No. P2760; PGT, Germany) and energy resolution 2.10 keV FWHM for the 1.332 MeV gamma line of 60Co. The counting time for the samples weighing 380–500 g was 10,000 s. The gamma-ray spectra of the samples were analysed using an MCA card 9308/A containing commercial software, Emcaplus version 1.102 (Silena, Germany). The 226Ra concentration was determined from the photopeaks of 214Pb (352 keV) and 214Bi (609.4 keV). The activity concentration of 232Th was found from the photopeaks of 228Ac (911.1 and 968.9 keV). For the activity concentration of 40K, the 1460 keV gamma line was analysed. The only fission product, 137Cs, was found at trace level in a single white sand sample and its concentration was obtained from the 662 keV gamma line. The method of efficiency calibration of the detector has been described in our previous work(2). The activity concentration Ai in Bq kg1 of a radionuclide of energy Ei in any sample is given by Ai ¼
C ðEi Þ BðEi Þ , 2 wft
ð1Þ
where C(Ei) is the counts under the photopeak of energy Ei, B(Ei) is the background counts under the energy peak Ei, 2 is the detector efficiency at energy Ei, w is the quantity of the sample in kilograms, f is the fraction of gamma-ray emission at energy Ei and t is the measuring live time in seconds. The restriction on building materials for gamma radiation is based(9) on a dose range of 0.3–1 mSv y1. In order to examine whether a building material meets these limits of dose criteria, the gamma activity concentration index I of the samples is found from the following Equation(9): I¼
ARa ATh AK þ þ , 300 200 3000
ð2Þ
where ARa, ATh and AK are the concentrations of 226 Ra, 232Th and 40K, respectively, in Bq kg1. The numerical quantities in the denominator of Equation 2 are also in units of Bq kg1, so that the gamma activity concentration index I is a dimensionless quantity. For the activity concentration index, I 2 corresponds to a dose criterion of 0.3 mSv y1, while I 6 corresponds to 1 mSv y1 in the report of the European Commission in 1999, as mentioned by Tzortzis et al.(9).
RESULTS AND DISCUSSION The activity concentrations ARa, ATh and AK (in Bq kg1) of 226Ra, 232Th and 40K were determined in 14 commercial brands of cement samples, 2 categories of sand samples (white and red) and 1 category of hollow concrete brick sample. The activity concentration level in those samples and the gamma activity concentration index I are presented in Table 1. The activity levels for 226Ra, 232Th and 40K in cement samples were found to range from 40.8 2.6 to 118.1 6.5 Bq kg1, 63.0 4.9 to 113.0 7.5 Bq kg1 and 955.9 76.7 to 1350.3 104.9 Bq kg1 respectively, and the values of the gamma activity concentration index of these samples varied from 0.82 0.04 to 1.35 0.05. The activity levels for 226Ra, 232Th and 40K in sand samples ranged from 39.0 2.5 to 72.2 4.2 Bq kg1, 90.2 6.3 to 243.2 14.0 Bq kg1 and 1557.5 119.6 to 1624.3 124.4 Bq kg1, respectively, and the values of the gamma activity concentration index of these samples were found to vary from 1.15 0.05 to 2.00 0.08. The radioactivity levels in two hollow concrete bricks were found to be 43.4 2.7 and 45.9 2.8 Bq kg1 for 226Ra, 97.1 6.7 and 105.6 7.2 Bq kg1 for 232Th and 1550.8 119.2 and 1564.2 120.1 Bq kg1 for 40K. The gamma activity concentration indices for these two concrete brick samples were determined to be 1.15 0.05 and 1.20 0.05. In fact, the values of the activity concentrations and the gamma activity concentration indices in these two hollow concrete bricks were found to be statistically the same. It is observed in Table 1 that the values of the gamma activity concentration index I for all but one sample under study were
