assessment of radiation hazards due to natural

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Comparison of activities and Rav in Egyptian building products with those for ..... 279. El Afifi et al.(28). 65. 60. 920. 221. This work. RADIATION HAZARDS IN ...
Radiation Protection Dosimetry (2009), Vol. 133, No. 3, pp. 177–185 Advance Access publication 23 March 2009

doi:10.1093/rpd/ncp032

SCIENTIFIC NOTE

ASSESSMENT OF RADIATION HAZARDS DUE TO NATURAL RADIOACTIVITY IN SOME BUILDING MATERIALS USED IN EGYPTIAN DWELLINGS M. E. Medhat* Experimental Nuclear Physics Department, Nuclear Research Center, Cairo, PO Box 13759, Egypt

Received October 3 2008, revised February 10 2009, accepted February 19 2009

INTRODUCTION Knowledge of radioactivity present in building materials enables one to assess any possible radiological hazard to mankind, as most people spend about 80% of their life inside houses and office buildings. Furthermore, it is useful in setting the standards and national guidelines with regard to the international recommendations(1,2). All building materials are mainly derived from rock and soil and contain different concentrations of natural isotopes of the radium (226Ra) and thorium (232Th) series, and potassium (40K). These radioactive elements can be found in almost all types of rocks and soils from which building materials are produced(3). Radiation exposure due to building materials can be divided into external and internal exposure. The external exposure is caused by direct gamma radiation. The internal exposure is mainly caused by the inhalation of the inert gas radon, 222Rn and its short-lived decay products. The worldwide average concentrations in the soil are given as follows: 226Ra (32 Bq kg21), 232Th (45 Bq kg21) and 40K (420 Bq kg21), and in building materials 226Ra (50 Bq kg21), 232 Th (50 Bq kg21) and 40K (500 Bq kg21)(4,5). The growing worldwide interest in natural radiation exposure has led to extensive surveys to control ionised radiation in building materials in European, American, Asian and some African countries. The results are available in worldwide publications(6 – 25). Several studies have been made on the measurement of natural radioactivity of building materials and radon in Egypt (26 – 34). *Corresponding author: [email protected]

There is a wide variation of building designs in Egypt. This depends on the financial situation of the people in the area considered. In the most popular design, foundations are made of concrete, walls of clay bricks covered with a cement layer on one side for the outer walls and on two sides for the inner walls, and ceilings are made of concrete covered from inside with two layers of cement and gypsum. At the present time, Egypt does not have standards and guidelines with regard to acceptable levels of radioactivity in building materials. There is no complete collected data available about natural radioactivity of Egyptian building materials. The main object of this study was to determine the concentrations of the naturally occurring isotopes 226Ra, 232 Th and 40K in the most commonly used building materials in Egypt and to estimate the radiological hazards associated with the natural radioactivity levels of these materials. MATERIALS AND METHODS For natural radioactivity measurements, samples of different groups of building materials commonly used in Egypt have been collected randomly from different sites in Cairo and its suburbs and tested for their natural radioactivity content. Ten to 30 samples from each type of building material were used. The samples of building products and coarse aggregates were broken into small parts using a manual hammer and then crushed into homogenised material of particle size ,1 mm using a grinder machine. The powder was dried at 1058C in an oven for the complete removal of moisture(35). Weighed samples were stored in sealed polythene containers for 1 month to achieve secular equilibrium.

# The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]

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Different types of Egyptian building materials from various locations in Cairo and its suburbs have been analysed for natural radioactivity using gamma ray spectrometry. Concentrations of 226Ra, 232Th and 40K were in the ranges of (12 + 2.8–65 + 6.5), (5 + 1.8–60 + 6.7) and (159 + 3.8– 920 + 12.7 Bq kg21), respectively. The minimum concentration of 226Ra, 232Th and 40K was found in gravel samples, whereas the maximum in granite samples. The results are compared with the published data of other countries and with the world average limits. The radiological hazard parameters: radium equivalent activity, gamma index, alpha index, absorbed dose rate and the annual exposure rate, were determined to assess the radiation hazards associated with Egyptian buildings. All studied samples are lower than world average limits.

M. E. MEDHAT



S ; 1ðEÞGðEÞW

ð1Þ

where S is the net count rate of the sample subtracted from the background, 1(E) is the photo-peak efficiency Table 1. Isotopes used for measuring 226Ra, 232Th and 40K. Natural isotope

Energy (keV)

Intensity (%)

226

351.9 609.3 1764.5 238.6 583.3 911.1 1460.8

35.1 44.6 15.1 43.5 30.6 26.6 10.7

232

40

Ra Th

K

Detected nuclide 214

Pb Bi 214 Bi 212 Pb 208 Tl 228 Ac 40 K 214

at energy E, G(E) is the gamma ray yield per disintegration of the specific nuclide for a transition at energy E and W is the dried sample weight expressed in kg. Depending on the peak background and the counting time of each measured spectrum, the calculated minimum detectable activity varies within the range of 4.1–6.2 Bq kg21 for both 226Ra and 232Th and within the range of 8.2–9.3 Bq kg21 for 40K.

RESULTS AND DISCUSSION Natural activity concentration Activity concentrations of 226Ra, 232Th and 40K have been measured for different Egyptian building materials. The measured activities with their standard deviations are presented in Table 2. From these results, it can be seen that the lowest mean value of the 226Ra concentration is 12 + 2.8 Bq kg21 measured in gravel, whereas the highest mean value for the same radionuclide is 65 + 6.5 Bq kg21 measured in granite. The lowest mean value of 232Th is 5 + 1.8 Bq kg21 recorded in gravel and the highest mean value is 60 + 6.7 Bq kg21 measured in granite. The lowest mean value for 40K is 159 + 3.8 Bq kg21 recorded in gravel and the highest mean value is 920 + 12.7 Bq kg21 measured in granite. It is clear that the activity of 226Ra for ceramics and granite are higher than that of the world average (50 Bq kg21). The activity of 232Th in granite samples is higher than the world average (50 Bq kg21). The activity of 40K in all samples except granite is lower than the world average (500 Bq kg21)(4,5). It can be seen that the isotope 40K contributes the most activity, compared with other isotopes. The thorium activity concentrations for all samples are lesser than the uranium activity

Table 2. Activity concentration of some Egyptian building materials. Material

Activity concentrations (Bq kg21)

N 226

Cement Sand Gravel Bricks Gypsum Limestone Ceramics Granite Marble Floor tiles

13 15 18 30 21 16 29 16 25 30

232

Ra

40

Th

K

Range

Mean + SD

Range

Mean + SD

Range

Mean + SD

45–51 30–44 10–15 25–37 26–41 15–21 49–58 55–79 28–37 29–37

48 + 5.8 33 + 3.7 10–15 30 + 4.5 39 + 3.2 17 + 5.0 52 + 7.8 65 + 6.5 32 + 6.5 35 + 7.8

20–26 24–32 3– 8 17–26 19–28 8 –12 30–38 58–66 25–31 18–27

22 + 3.9 27 + 4.2 5 + 1.8 21 + 2.4 25 + 1.4 10 + 3.1 33 + 7.9 60 + 6.7 25 + 5.2 23 + 1.8

118–126 355–398 145–162 275–295 191–238 271–293 421–487 885–955 460–471 372–398

220 + 8.9 385 + 8.9 159 + 3.8 289 + 10.5 226 + 2.9 280 + 12.2 450 + 5.7 920 + 12.7 466 + 7.9 377 + 5.8

N, number of samples; SD, standard deviations.

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This step was necessary in order to ensure that radon was confined within the volume and the daughters also remained in the samples. Gamma ray measurements were carried out using a high-pure germanium detector with relative efficiency of 70%. The energy resolution of the used detector is 2.46 keV at 1332.5 keV gamma energy of 60Co. The detector was coupled to a personal computer analyser with Genie 2000 for data acquisition and analysis. The detector used was housed in a lead shield of 5 cm thickness to reduce the effect of the background radiation. The measuring time ranged from 12 to 24 h depending upon the activity levels present in the samples. The energies and intensities of the measured isotopes used for the concentration determination of 226 Ra, 232Th and 40K are shown in Table 1(36). The activity concentration (Bq kg21) for a peak at energy E, is given by:

RADIATION HAZARDS IN SOME BUILDING MATERIALS

232

Th and 40K in some building materials.

Table 3. Comparison of activities and Rav in Egyptian building products with those for other countries. Material

Activity (Bq kg21)

Country 226

Ra

Clay bricks

Floor tiles

Ceramics

Marble

Granite

Algeria Australia Bangladesh Brazil Cameroon China Greece India Malaysia Pakistan Kuwait Sri Lanka Zambia Egypt Cameroon Serbia Zambia Egypt Algeria India Israel Serbia Egypt Algeria Cameroon Kuwait Pakistan Egypt Greece Egypt

65 41 29 47 50 59 35 18 241 23 12 35 32 30 16 38 52 35 55 28 46 66 52 23 8 4 29 32 67 65

232

Th

51 89 53 120 91 50 45 33 51 35 7 72 81 21 14 52 96 23 41 64 48 53 33 18 0.35 0.22 32 25 95 60

179

40

Rav

Reference

190 220 127 248 193 178 154 69 895 106 42 183 180 82 36 168 — 97 145 121 174 201 134 73 10 4 82 104 295 221

Amrani and Tahtat (20) Beretka and Mathew(25) Mantazul et al. (44) Malanca et al. (45) Ngachin et al. (10) Xinwei (14) Stoulos et al. (1) Kumar et al. (18) Ibrahim(44) Faheem et al. (8) Bou-Rabee and Bem(47) Hewamanna et al. (21) Hayumbu et al. (24) This work Ngachin et al. (10) Krsticˆ et al. (11) Hayumbu et al. (24) This work Amrani and Tahtat (20) Kumar et al. (18) Kovler et al. (19) Krsticˆ et al. (11) This work Amrani and Tahtat (20) Ngachin et al. (1) Bou-Rabee and Bem(47) Faheem et al. (8) This work Pavlidou et al. (12) This work

K

675 681 292 322 172 714 710 45 7541 431 332 585 412 289 — 720 — 377 410 24 776 776 450 310 19 4 98 466 1200 920

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Figure 1. Mean activity of 226Ra,

M. E. MEDHAT Table 4. Comparison of activities and Rav in Egyptian building binders and aggregates compared with those for other countries. Material

Activity (Bq kg21)

Country 226

Cement

Sand

Gravel

Limestone

Kuwait Turkey Zambia Egypt Israel India Lebanon Egypt Algeria Australia Bangladesh Brazil Cameroon China Greece India Lebanon Malaysia Pakistan Kuwait Zambia Egypt Algeria Bangladesh Brazil Cameroon China Greece Israel Lebanon Pakistan Egypt Algeria Australia Austria Brazil China Israel India Egypt

41 52 61 27 68 66 63 46 38 73 25 26 13 41 23 48 10 8 7.2 39 12 52 15 10 14 41 18 9 — 60 20 8 24 33 24 25 10 24 19 29 11 15 28 33 12 16 — 9 7 20 18 74 17

Rav

Reference

112 129 262 70 163 133 117 109 92 92 69 88 45 98 79 96 23 10 8 92 28 129 88 34 104 96 71 84 23 136 91 45 117 101 58 21 82 31 80 83 39 23 28 83 31 37 16 16 50 47 35 79 53

Amrani and Tahtat (20) Beretka and Mathew(25) Roy et al. (13) Ngachin et al. (10) Xinwei (14) Kovler et al. (19) Papaefthymiou and Gouseti(7) Kumar et al. (18) Rizzo et al. (22) Kobeissi et al. (9) Faheem et al. (8) Khan and Khan(37) Bou-Rabee and Bem(47) Turhan(3) Hayumbu et al. (24) This work Kovler et al. (19) Kumar et al. (18) Kobeissi et al. (9) This work Amrani and Tahtat (20) Beretka and Mathew(25) Mantazul et al. (44) Malanca et al. (45) Ngachin et al. (1) Xinwei (14) Stoulos et al. (1) Kumar et al. (18) Kobeissi et al. (9) Ibrahim(46) Faheem et al. (8) Bou-Rabee and Bem(47) Hayumbu et al. (24) This work Amrani and Tahtat (20) Mantazul et al. (44) Malanca et al. (45) Ngachin et al. (10)

40

Th

K

27 48 80 15 52 39 24 42 22 9 37 29 9 26 32 22 6 — — 25 7 48 34 12 31 22 17 52 — 13 29 7 26 27 10 55 — 139 26 20 12 3 0.4 32 5 13 11 3 24 13 7 — 10

422 115 1133 277 173 138 284 36 218 80 245 273 240 267 134 220 51 27 7 226 74 115 3033 51 586 302 367 66 — 750 383 360 714 385 259 228 933 1161 304 287 140 50 5 57 159 36 — 34 205 63 77 65 280

180

Xinwei (14) Stoulos et al. (1) Kovler et al. (19) Kobeissi et al. (9) Iqbal et al. (23) This work Amrani and Tahtat (20) Beretka and Mathew(25) Sorantin and Teger(38) Malanca et al. (45) Xinwei (14) Kovler et al. (19) Kumar et al. (18) This work

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Gypsum

Algeria Australia Bangladesh Cameroon China Israel Greece India Italy Lebanon Pakistan

Ra

232

RADIATION HAZARDS IN SOME BUILDING MATERIALS Table 5. Comparison of activities and Rav in Egyptian building products compared with those in other Egyptian researches. Activity (Bq kg21)

Material 226

Ra

Cement

Gypsum Clay bricks

Gravel Limestone Floor tiles Ceramics

Marble

Granite

187 59 65

Rav

Reference

42 51 292 151 96 208 60 92 78 77 91 125 82 17 18 101 20 31 25 53 28 97 213 252 266 134 20 436 71 104 421 279 221

El-Tahawy and Higgy(34) Sharaf et al. (33) Ahmed(29) El Afifi et al. (28) This work Ahmed(29) El Afifi et al. (28) This work El-Tahawy and Higgy(34) Sharaf et al. (33) Higgy et al. (32) Ahmed(29) This work Sharaf et al. (33) El-Tahawy and Higgy(34) This work Sharaf et al. (33) This work Sharaf et al. (33) This work Higgy et al. (32) This work Higgy et al. (32) Ahmed(29) El Afifi et al. (28) This work Higgy et al. (32) Ahmed(29) El Afifi et al. (28) This work Ahmed(29) El Afifi et al. (28) This work

40

Th

K

10 11 88 33 22 45 28 25 24 24 26 37 21 3 4 27 4 5 4 10 6 23 64 72 75 33 6 115 20 25 118 70 60

40 49 416 337 220 500 129 226 258 227 298 511 289 47 75 385 62 159 19 280 47 377 569 300 900 450 19 865 157 466 852 1560 920

concentrations. The means of the three isotopes in all samples under investigation are shown in Figure 1. Columns 3–5 of Tables 3 and 4 present the average radionuclide concentrations from other countries for comparison. It is clear that the activities varied from one country to another. A comparison of the results of other Egyptian researchers is presented in Table 5. There is a variation with the published data. This depends on the nature of the region from which samples are collected.

Assessment of radiation hazards In the present study, radiological hazard parameters, such as the radium equivalent activity, the gamma index, the alpha index, the absorbed dose rate and the annual exposure rate were determined in Egyptian building material samples.

Radium-equivalent activity index The distribution of radioactivity in natural samples is not uniform. Therefore, a common index has been introduced to represent the radioactivity levels of radium, thorium and potassium in the samples, which takes into account the radiation hazards associated with them. This index is usually known as radium equivalent activity (Rav). It is based on the assumption that 370 Bq kg21 of 26Ra, 259 Bq kg21 of 232Th and 4810 Bq kg21 of 40 K produce the same gamma ray dose rate equivalent. Thus, the radium equivalent activities may be calculated using the formula(25):   ARa ATh AK þ þ ; ð2Þ Rav ¼ 370 370 259 4810 where ARa, ATh and AK are the activity concentrations in Bq kg21 for 226Ra, 232 Th and 40 K, respectively. Figure 2 summarises the Rav results for

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Sand

25 31 134 78 48 105 10 39 24 25 32 33 30 9 7 33 10 12 20 17 15 35 77 126 90 52 205 30 32

232

M. E. MEDHAT

all the studied samples. These values, ranging from 31 Bq kg21 in gravel to 222 Bq kg21 in granite, are less than the maximum admissible value of 370 Bq kg21(25). Thus, all materials would not present a significant radiological hazard when used in constructions. However, from the results, we notice variations of the Rav values in all building materials and in the same type of material studied by other Egyptian researchers; for example cement: Rav ¼ 96 Bq kg21 in our work, 151 Bq kg21 in the work of El Afifi et al. (28), 292 Bq kg21 in the work of Ahmed(29), 51 Bq kg21 in the work of Sharaf et al. (33) and 42 Bq kg21 in the work of El-Tahawy and Higgy(34). This depends on the nature of the region from which samples are collected. Column 6 of Tables 3 and 4 present the Rav from other investigations in different countries for comparison. It is clear that these activities varied from one country to another.

Table 6. Gamma-index values suggested by the EC (1999) taking into account the amounts and typical ways in which the material is used in a building. Dose criterion Materials used in bulk, e.g. bricks Superficial materials with restricted use: tiles, boards

0.3 mSv y21

1 mSv y21

Ig  0.5

Ig  1

Ig  2

Ig  6

materials are shown in Figure 3. It ranged from 0.11 to 0.82 in all building materials. The recommended upper limit is not exceeded. The average relative contributions to the gamma index due to 226Ra, 232Th and 40K were 33, 32 and 35%, respectively. This means that generally 226Ra and 232Th contributed similarly to the external exposure, but lower than the 40 K contributions.

Gamma index The gamma index proposed by the European Commission (EC) is calculated using the following formula(39): Ig ¼

ARa ATh AK þ þ 300 200 3000

ð3Þ

The EC recommends that gamma doses due to building materials should be in the range of 0.3 –1 mSv y21. Most of the European countries apply their controls based on the upper end of the dose scale (1.0 mSv y21). The index shall not exceed the values given in Table 6, depending on the dose criterion and the amount and manner in which the material is used in the building. Gamma index values according to the EC for the investigated

Alpha index A number of indices dealing with the assessment of the excess alpha radiation due to radon inhalation originating from building materials (called ‘alpha index’ or “internal index”) have been proposed by Krieger(40) and Stoulos et al. (1). The alpha index is determined through the following formula: Ia ¼

ARa 200 Bqkg1

ð4Þ

The recommended exemption level and recommended upper level for 226Ra activity concentration are 100 and 200 Bq kg21, respectively, in building materials as suggested by the Radiation Protection

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Figure 2. Radium equivalent activity (Bq kg21) for building materials.

RADIATION HAZARDS IN SOME BUILDING MATERIALS

Authorities in Denmark, Finland, Iceland, Norway and Sweden(41). It is important to point out that there is no distinction between materials used in bulk amounts and materials with restricted use in the determination of Ia. There is evidence that in some cases, 200 Bq kg21 of 226Ra in building materials is a very conservative value. Studies of Bruzzi et al. suggest that values exceeding 200 Bq kg21 of 226Ra in ceramic tiles could be accepted because the structure of the tile is highly condensed and gives little possibility for radon to escape; moreover, the external surface of a tile is vitreous representing an efficient barrier against the radon release(42). Alpha index (Ia) values for investigated materials are shown in Figure 3. It ranged from 0.06 to 0.325 in the samples. All the samples measured showed values below the recommended level (0.5, 1). Estimation of the absorbed gamma dose rate The absorbed dose rate dˆ in air inside a room is due to gamma ray emission from the isotopes 226Ra 232 Th and 40K inside the building materials. It can be defined if the radionuclide concentrations are known. The absorbed dose rate can be obtained in units of nGy h21 using the following formula: X R  Ai ; ð5Þ d^ ¼ i i where Ai (Bq kg21) are the mean activities of 226Ra, 232 Th and 40K, and Ri (nGy h21 per Bq kg21) their corresponding dose conversion factors. According to an EC report, the dose conversion coefficients were calculated using the standard room model. Dimensions of the room are 4  5  2.8 m. The thickness of walls and density of the structures are

Table 7. Dose conversion factors (nGy h 21 per Bq kg 21). Dose criterion Bulk materials Superficial materials

226

Ra

0.92 0.12

232

Th

1.10 0.14

40

K

0.08 0.009

0.2 m and 2.35 g cm23, respectively. The values of the dose conversion factors according to the EC (1999) are listed in Table 7. The worldwide average value of the absorbed gamma dose rate is 55 nGy h21(43). The estimated indoor gamma dose rate values for all samples are shown in Table 8. It ranges from 11 to 91 nGy h21 in all building materials. Cement, sand, brick and gypsum samples exceed the recommended upper limit. Estimation of the annual effective dose In order to estimate the annual effective dose rate, Eˆ, the conversion coefficient from the absorbed dose in air to the effective dose (0.7 Sv Gy21) and the annual exposure time factor were used. Eˆ was calculated using the following formula: ^ ¼ d^  Aexp  Cf ; E

ð6Þ

where dˆ must be taken in mGy h21, Aexp is the annual exposure time factor (0.8  365 d 24 h  7000 h yr21 and Cf is the conversion factor. The estimation annual effective dose values for all samples are shown in Table 8. The recommended upper limit of 1 mSv y21is not exceeded.

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Figure 3. External and internal radiological hazard indices in some building materials.

M. E. MEDHAT Table 8. Radiation hazard parameters associated with Egyptian building material samples. Material Cement Sand Gravel Bricks Gypsum Limestone Ceramics Granite Marble Floor tiles

Ig

Ia

dˆ(nGy h21)

Eˆ(mSv y21)

0.34 0.37 0.12 0.30 0.33 0.20 0.49 0.82 0.39 0.36

0.24 0.17 0.06 0.15 0.19 0.08 0.26 0.32 0.16 0.17

85.96 90.86 29.26 73.82 81.46 49.04 15.18 25.03 11.81 11.03

0.42 0.44 0.14 0.36 0.39 0.24 0.07 0.12 0.06 0.05

The natural radioactivity and radiological hazard parameters of some building materials commonly used in Egyptian dwellings were assessed by gamma ray spectrometry. The concentration values for 226Ra, 232 Th and 40K have been found to lie within the ranges of 12 + 2.8–65 + 6.5, 5 + 1.8 –60 + 6.7 and 159 + 3.8-920 + 12.7 Bq kg21, respectively. The lowest 226Ra concentration was found in gravel and the highest in granite. The lowest 232Th was found in gravel and the highest in granite. The lowest 40K concentration was found in gravel and the highest in granite. The average concentrations for 226Ra (36 Bq kg21), 232Th (25 Bq kg21 and 40K (377 Bq kg21) in these samples of building materials are lower than the corresponding typical world averages of 50, 50 and 500 Bq kg21, respectively. The radium equivalent activities ranging from 31 to 103 Bq kg21 are lower than the maximum admissible value of 370 Bq kg21. Calculations of the Ig, Ia indices, absorbed and annual effective doses was not in excess of the recommended admissible level for all samples for external and internal radiation exposure. There is no distinction between materials used in bulk amount and restricted use in the results of Ia. Therefore, it is hoped that, for the gamma index, the EC will set limit values for the alpha index also taking into account typical amounts and the ways in which the material is used in a building. The absorbed dose rate in air was found to vary from 11.03 to 90.86 nGy h21 and the effective dose ranged from 0.05 to 0.44 mSv y21

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CONCLUSION

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