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Natural radioactivity and human exposure by raw materials and end product from cement industry used as building materials
Radiation Measurements 45 (2010) 969e972
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Technical report
Natural radioactivity and human exposure by raw materials and end product from cement industry used as building materials Z. Stojanovska a, *, D. Nedelkovski a, M. Ristova b a b
Laboratory for Radioecology, Institute of Public Health, Skopje 1000, The Former Yugolav Republic of Macedonia Physics Department, Faculty of Natural Sciences and Mathematic, University in Skopje, The Former Yugolav Republic of Macedonia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 October 2008 Received in revised form 8 June 2010 Accepted 11 June 2010
During the manufacturing process in the cement industry, raw materials of different levels of natural radioactivity are utilized. In this study we present the radiological impact of cements as a building material and the different raw materials used in their manufacture. A total of 218 samples of raw materials and their end product cements were collected from the cement industry of Macedonia (The Former Yugoslav Republic) during the period 2005e2007. The specific activities, evaluated by gamma spectrometry analysis, showed the highest mean specific activity in fly ash (226Ra, 107 45 Bq kg1; 232 Th, 109 30 Bq kg1; 40K, 685 171 Bq kg1), which is used as a raw material. However, the final cement product usually has relatively lower activity compared with the activity of the raw material and the mean specific activity of the final cement products were lower (226Ra, 42 10 Bq kg1; 232Th, 28 6 Bq kg1; 40K, 264 50 Bq kg1). The radium equivalent activity and the hazard index were calculated for each sample to assess the radiation hazard. The mean annual effective dose originating from the cements was found to be 111 22 mSv y1, which is below the recommended EC limit of 300 mSv y1. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Natural radioactivity Building materials Raw materials Cements Gamma spectrometry
1. Introduction Cement is a widely used building material. Hence, it is of a great benefit for the entire society to examine the radioactivity of the raw materials used in its manufacture. Evaluation of the specific activity (Bq kg1) of these raw materials is an important issue, for they could be a source of considerable indoor dose rate. They consist mainly of the natural occurring uranium (238U) and thorium (232Th) series, and potassium (40K). In the 238U series, the contribution of the radionuclides in the first half of the series between 238U and 230Th is negligible relative to the second half comprising 226Ra to 210Pb. Consequently the measurement of the activities of 226Ra, 232Th and 40 K in all the component materials is relevant to a study of cement. Naturally radioactive materials, manufactured products and industrial residues are widely used in the cement industry as raw materials. Residues from industrial processes such as fly ash from coal-fired power plants produced in large quantities can be recycled and used as a supplement in cement production. This process could yield technological, economical and environmental benefits, but if not subject to regular control, can yield elevated indoor radioactivity exposure rates.
* Corresponding author. Tel.: þ389 2 3125044; fax: þ389 2 3223354. E-mail address: [email protected] (Z. Stojanovska). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.06.023
The safety requirements for building materials refer to the excess exposure rate caused by these materials in addition to terrestrial and cosmic radiation. In this study, safety requirements proposed by the European Commission (EC, 1999) have been examined. The basic concept in determination of the excess exposure rate consists of (1) determination of the total exposure resulting from the building material including the background and (2) background subtraction (Markkanen, 1995).
2. Materials and methods 2.1. Sampling and sample preparation The samples included the following: cement collected since 2005 on a monthly basis from the Cement Factory in Skopje; 218 samples (of which 49 were fly ash samples) from the deposits of two power plants, REK Bitola Fly ash I and REK Oslomej Fly ash II; 45 samples from Pozzolana (originating from Strmos-Pozzolana I and sinovo-Pozzolana II), 16 natural gypsum samples, 42 clinker Ce samples and 66 cement samples. The specifications of the cements under investigation are given in Table 1. The cement CEM I, well known as Portland cement, is produced by grinding clinker (96e97%) and natural gypsum (3e4%) and other two types of cement, CEM II/AeM and CEM II/BeM, containing additional
970
Z. Stojanovska et al. / Radiation Measurements 45 (2010) 969e972
Table 1 Specifications of the cements, subject of this study. Cement type
Raw materials
CEM I
Portland cement
CEM II/AeM
Portland composite cement Portland composite cement
CEM II/BeM
Table 3 Comparison of the activity concentrations of the Macedonian (FYR) (a) fly ash samples and (b) cement samples with those obtained from other international data (in Bq kg1).
Clinker in range of 96e97%; natural gypsum 3e4% Portland cement and max 15% of Pozzolana, limestone, and fly ash Portland cement and max 30% of Pozzolana, limestone, and fly ash
226
components of limestone, fly ash and Pozzolana (maximum 15% and 30%, respectively). Each sample was ground and dried at 105 C until the moisture was removed. The dried material was homogenised and transferred to 500 ml Marinelli beakers, for gamma spectrometry measurements. The spectra were first measured with empty containers (blank probes) and then with containers filled with weighed amounts of sample. The mean values of mass of the analyzed samples were gypsum (0.78 0.04 kg), fly ash (0.44 0.05 kg), Pozzolana (0.60 0.07 kg), clinker (0.85 0.07 kg) and cement (0.69 0.07 kg). The containers were sealed hermetically and stored for a month to achieve secular equilibrium between 226Ra and its short-lived daughters before gamma spectrometry measurements. 2.2. Gamma spectrometry measurements The gamma spectrometry measurements were carried out with a p-type HPGe detector (Canberra Inc.; 25% relative efficiency, resolution of 1.79 keV at 1.33 MeV, 8192 ch. digital analyser, and with 12 cm of lead shielding and internal lining of 2 mm high purity copper). The activity of 226Ra was determined from the gamma lines associated with the short-lived daughters of 214Bi (609.31 keV, 1120.29 keV, 1764.49 keV) and 214Pb (351.93 keV). The activity of 232 Th was determined by the 911.2 keV and 969.1 keV gamma lines from 228Ac, the 860.56 keV gamma lines from the 208Tl and the 238.6 keV line of 212Pb. The activity of 40K was determined from its 1460.8 keV gamma line. Depending on the activity of the sample, each spectrum was collected between 10 ks and 50 ks. The total combined uncertainty of each nuclide was less than 5% at the 95% level of confidence. Efficiency calibration was performed with mixed calibration standard sources MBSS2 from The Czech Metrological Institute. The analysis procedure included the subtraction of the background spectrum. 3. Results and discussion The specific activities (Bq kg1) of 226Ra, 232Th and 40K (minimum, maximum and mean values) of the raw materials and cements are given in Table 2. From the results of all the analyzed Table 2 Activity concentration of Sample
N
226
Ra,
232
Th and
16 20 29 17 28 42 19 28 19
Ra
232
40
Th
K
(a) Fly ash samples Hungary 760 Turkey 232 107 Greece 273e1377 Germany 210 Macedonia (FYR) 107 45
117 117 45 41e65 130 109 30
441 466 148 143e661 700 685 171
Somlai et al. (2008) Turhan (2007) Petropolos et al. (2002) UNSCEAR (1982) Present work
(b) Cement samples Greece 63 Turkey 41 27 Italy 38 Macedonia (FYR) 42 10
24 26 19 22 28 6
284 267 102 218 264 50
Papastefanou et al. (2005) Turhan (2007) Rizzo et al. (2001) Present work
materials it is evident that lowest activity mean values of Ra, 232Th and 40K were found for gypsum (5.9 1.1 Bq kg1, 1.44 0.44 Bq kg1 and 11 5.2 Bq kg1, respectively). On the other hand, the highest activity mean value for 226Ra (140 89 Bq kg1) was found in Fly ash I samples. Likewise, the highest values for the specific activities of 232Th (171 48 Bq kg1) and 40K (786 134 Bq kg1) were found for the Pozzolana II and Fly ash II samples, respectively. Hence, the highest mean values in the raw materials (fly ash and Pozzolana) are above the world mean values (50, 50 and 500 Bq kg1 for 226Ra, 232Th and 40K, respectively; UNSCEAR, 1993). The results obtained for fly ash were compared with the data from the literature (Table 3a). The mean activities of the analyzed cement samples were found to be: 226Ra (42 10 Bq kg1), 232Th (28 6 Bq kg1) and 40K (264 50 Bq kg1). The results for the activities of the cements, subject to this study, were compared to the results of similar published studies (Table 3b). It can be seen that the results are similar to those reported in the literature. 226
3.1. Radium equivalent activity (Raeq) As the distribution of 226Ra, 232Th and 40K in building materials is not uniform, exposure to radiation can be defined in terms of radium equivalent activity (Raeq) to compare the differences in specific activities (Beretka and Mathew, 1985). The radium equivalent activity can be defined as:
Raeq ¼ CRa þ 1:43 CTh þ 0:077 CK ;
(1)
where, CRa, CTh and CK are the specific activities of 40 K, respectively.
226
Ra,
232
Th and
K in raw materials and cements (in Bq kg1).
40
Activity concentration (Bq kg1) 226
Gypsum Fly ash I Fly ash II Pozzolana I Pozzolana II Clinker CEM I CEMII/A-M CEMII/B-M
References
Activity concentration (Bq kg1)
232
Ra
40
Th
K
Min
Max
Mean SD
Min
Max
Mean SD
Min
Max
Mean SD
4.4 89 26 42 43 21 23 31 38
9.0 245 111 81 192 46 37 58 58
5.9 1.1 140 89 85 17 64 12 80 27 31 6 30 4 45 7 50 6
0.92 60 538 36 104 15 17 22 29
2.23 120 1131 101 298 29 27 36 40
1.44 0.44 80 15 129 18 69 15 171 48 20 3 20 3 29 3 34 4
3.2 383 538 40 158 176 174 177 238
21.5 733 1131 183 663 322 280 355 369
11.0 5.2 540 99 786 134 105 43 349 168 234 46 222 36 272 45 295 43
Z. Stojanovska et al. / Radiation Measurements 45 (2010) 969e972 Table 4 Estimated radium equivalent and annual dose. Sample
Gypsum Fly ash I Fly ash II Pozzolana I Pozzolana II Clinker CEM I CEM II/AeM CEM II/BeM
N
16 20 29 17 28 42 19 28 19
Raeq (Bq kg
1
Ia ¼ 1
DE (mSv y
)
)
Min
Max
Mean SD
Min
Max
Mean SD
7.3 232 232 111 266 64 69 93 115
12.7 468 444 239 555 119 100 138 148
9.1 1.5 314 74 357 54 178 31 372 74 85 13 82 10 116 13 130 9
Lower 687 629 202 774 9 31 128 213
than background 1665 1030 314 1489 1141 213 684 457 121 1837 1175 273 234 94 52 155 86 38 313 224 53 351 279 38
971
CRa ; 200
(3)
where, CRa, is the specific activity of 226Ra. The safe use of materials in building construction requires Ia to be less than 1. This limit corresponds to the action level specific activity for 222Rn which is 200 Bq kg1 for future building construction (EC, 1990). The distribution of Ig and Ia for the different samples in this study is shown in Fig. 1 where it can be seen that the calculated mean values of Ig (0.37) and Ia (0.21) for the cements are below the limits for safe use.
3.3. Indoor absorbed dose
This dependence is based on the estimation that 1 Bq kg1 of Ra, 1.43 Bq kg1 of 232Th and 0.077 Bq kg1 of 40K produce equal gamma dose rates. For safe use of building materials, the maximum value of the Raeq should be less than 370 Bq kg1 (UNSCEAR, 1993, 2000). The calculated Raeq values for raw materials and for cement samples are presented in Table 4. The mean value of Raeq for the cements studied (111 22 Bq kg1) is below the set limit of 370 Bq kg1 but higher for Pozzolana II (372 74 Bq kg1). The radium equivalent concentration in fly ash and Pozzolana was found to be about 3e4 times higher than those in Portland cement, which is in agreement with the ratios reported by Kovler et al. (2005).
The activity indexes presented above are used for assessing whether the safety requirements are being fulfilled for materials which might be of concern. Any actual decision for restriction of use of materials should be based on a separate dose assessment into a scenario for the materials to be used (EC, 1999). The European Commission has proposed a scenario (RP 112) for the calculation of the annual effective dose in a concrete room with dimensions: 4 m 5 m 2.8 m. The thickness and density of walls are 20 cm and 2350 kg m3, respectively. The conversion factor used for calculation of the absorbed gamma dose rate D (nGy h1) corresponds to 0.92 nGy h1 per Bq kg1 for 226Ra, 1.1 nGy h1 per 1 Bq kg1 for 232 Th and 0.08 nGy h1 per 1 Bq kg1 for 40K (Markkanen, 1995; EC, 1999),
3.2. Gamma index
D ¼ 0:92 CRa þ 1:1 CTh þ 0:08 CK ;
226
In order to assess whether the safety requirements for building materials are being fulfilled, a gamma index proposed by the European Commission (EC, 1999) was used. It is defined as,
Ig ¼
CRa C C þ Th þ K ; 300 200 3000
(2)
where, CRa, CTh and CK are the specific activities of 226Ra, 232Th and 40 K, respectively. The gamma index should also take into account typical ways and amounts in which the material is used in a building. The limit values depend on the dose criteria, the way and amount of the material and the manner in which it was used in a building and construction. For material used in bulk amounts Ig 1 corresponds to an absorbed gamma dose rate of 1 mSv y1 (EC, 1990). Assessment of the internal hazard, originating from the alpha activity of building materials, requires calculations of the alpha index or internal hazard index. In this study the alpha index was calculated by using the following equation, proposed by Righi and Bruzzi (2006),
DE ¼ D 0:7 7000:
(5)
The results obtained for annual effective doses from different raw materials and cements are presented in the Table 4. It can be seen that the maximum values of the annual effective dose are associated with the fly ash samples and Pozzolana, which is consistent with the
1,2
Gamma index Alpha index
1,1
Gamma/alpha index
1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 Gypsum
Fly ash I
232
where CRa, CTh and CK are the specific activities of Ra, Th and 40 K, respectively. To assess the excess gamma dose rate, originating from the building materials in the proposed scenario room, the gamma dose rate from sources of naturally occurring radioactivity should be subtracted. A background dose rate of 50 nGy h1 corresponding to an average outdoor value in Europe was used. For assessment of the annual effective doses DE (mSv y1), the conversion coefficient from absorbed dose in air to effective dose was taken to be 0.7 Sv Gy1, and the indoor occupancy time was taken to be 7000 h per year (EC, 1999; UNSCEAR, 1993, 2000). Hence, the annual effective dose was calculated using the following equation:
1,3
0
(4) 226
Fly ash II Pozzolana I Pozzolana II
Clinker
Cement I
Cement II
Fig. 1. Gamma and alpha index in raw materials and cements.
Cement III Cement IV
972
Z. Stojanovska et al. / Radiation Measurements 45 (2010) 969e972
other results in this study. According to this scenario the mean annual effective dose in the concrete room, where cement is used as a raw material is 200 89 mSv y1. According to the EC recommendation, this value is below the limit of 300 mSv y1 for safe use.
4. Conclusions In this study we have found that the highest values for the mean activity concentrations are in fly ash (226Ra, 107 45 Bq kg1, 232Th, 109 30 Bq kg1; 40K, 685 171 Bq kg1), the specific activities of which are above the world mean values for building materials (50, 50 and 500 Bq kg1 for 226Ra, 232Th and 40K, respectively; UNSCEAR, 1993). However, the mean specific activities of the cement products (226Ra, 42 10 Bq kg1; 232Th, 28 6 Bq kg1; 40K, 264 50 Bq kg1) are similar to those reported by other investigators (Papastefanou et al., 2005; Rizzo et al., 2001; Turhan, 2007). The main contributors to the overall specific activities in the materials examined in this study are attributed to fly ash and Pozzolana and if these raw materials are used as additives in cement production, their activity concentration should be carefully monitored. However, the mean value of Raeq for cements (111 22 Bq kg1) is below the recommended level of 370 Bq kg1. The mean values of Ig and Ia for cements were found to be 0.37 and 0.21, respectively, which is below the limit for safe use. Although the mean values of the annual effective dose for Pozzolana and fly ash are estimated to be higher than the acceptable level their diluted concentration (< 30%) in the cements gives rise to an annual effective dose that does not exceed the recommended limits. Finally, the mean annual effective dose from the cements was estimated to be 200 89 mSv y1, which is below the limit of 300 mSv y1 for safe use. Taking into account the EC recommendation, the results from this research have shown that there is no significant radiation risk from the use of the cements investigated in this study.
References Beretka, I., Mathew, P.I., 1985. Natural radioactivity of Australian building materials, wastes and by-products. Health Physics 48, 87e95. EC (European Commission), March 27, 1990. Commission recommendation 90/143/ Euraatom of 21 February on the protection of the public against indoor exposure to radon. Official Journal of European Commission L-80 Brussels. EC (European Commission), 1999. Radiation Protection 122-Radiological Protection Principles Concerning the Natural Radioactivity of Building Materials. Directorate e General Environment, Nuclear Safety and Civil Protection. Kovler, K., Perevalov, A., Steiner, V., Metzger, L.A., 2005. Radon exhalation of cementitious materials made with coal fly ash: part 1 e scientific background and testing of the cement and fly ash emanation. Journal of Environmental Radioactivity 82, 321e334. Markkanen, M., 1995. Radiation Dose Assessments for Materials with Elevated Natural Radioactivity. Report STUK-B-STO 32. Radiation and Nuclear Safety Authority-STUK. Petropolos, N.P., Anagnostakis, M.J., Simopoulos, S.E., 2002. Photon attenuation, natural radioactivity content and radon exhalation rate of building materials. Journal of Environmental Radioactivity 61, 257e269. Papastefanou, C., Stoulos, S., Manolopoulou, M., 2005. The radioactivity of building materials. Journal of Radioanalytical and Nuclear Chemistry 266 (3), 367e372. Righi, S., Bruzzi, L., 2006. Natural radioactivity and radon exhalation in building materials used in Italian dwellings. Journal of Environmental Radioactivity 88, 158e170. Rizzo, S., Brai, M., Basile, S., Bellia, S., Hauser, S., 2001. Gamma activity and geochemical features of building materials: estimation of gamma dose rate and indoor radon levels in Sicily. Applied Radiation and Isotopes 55, 259e265. Somlai, J., Jobbágy, V., Kovács, J., Tarján, S., Kovács, T., 2008. Radiological aspects of the usability of red mud as building material additive. Journal of Hazardous Materials 150, 541e545. Turhan, S¸., 2007. Assessment of the natural radioactivity and radiological hazards in Turkish cement and its raw materials. Journal of Environmental Radioactivity 99, 404e414. UNSCEAR, 1982. Ionizing Radiation Sources and Biological Effect. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 1993. Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Technical report
Natural radioactivity and human exposure by raw materials and end product from cement industry used as building materials Z. Stojanovska a, *, D. Nedelkovski a, M. Ristova b a b
Laboratory for Radioecology, Institute of Public Health, Skopje 1000, The Former Yugolav Republic of Macedonia Physics Department, Faculty of Natural Sciences and Mathematic, University in Skopje, The Former Yugolav Republic of Macedonia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 October 2008 Received in revised form 8 June 2010 Accepted 11 June 2010
During the manufacturing process in the cement industry, raw materials of different levels of natural radioactivity are utilized. In this study we present the radiological impact of cements as a building material and the different raw materials used in their manufacture. A total of 218 samples of raw materials and their end product cements were collected from the cement industry of Macedonia (The Former Yugoslav Republic) during the period 2005e2007. The specific activities, evaluated by gamma spectrometry analysis, showed the highest mean specific activity in fly ash (226Ra, 107 45 Bq kg1; 232 Th, 109 30 Bq kg1; 40K, 685 171 Bq kg1), which is used as a raw material. However, the final cement product usually has relatively lower activity compared with the activity of the raw material and the mean specific activity of the final cement products were lower (226Ra, 42 10 Bq kg1; 232Th, 28 6 Bq kg1; 40K, 264 50 Bq kg1). The radium equivalent activity and the hazard index were calculated for each sample to assess the radiation hazard. The mean annual effective dose originating from the cements was found to be 111 22 mSv y1, which is below the recommended EC limit of 300 mSv y1. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Natural radioactivity Building materials Raw materials Cements Gamma spectrometry
1. Introduction Cement is a widely used building material. Hence, it is of a great benefit for the entire society to examine the radioactivity of the raw materials used in its manufacture. Evaluation of the specific activity (Bq kg1) of these raw materials is an important issue, for they could be a source of considerable indoor dose rate. They consist mainly of the natural occurring uranium (238U) and thorium (232Th) series, and potassium (40K). In the 238U series, the contribution of the radionuclides in the first half of the series between 238U and 230Th is negligible relative to the second half comprising 226Ra to 210Pb. Consequently the measurement of the activities of 226Ra, 232Th and 40 K in all the component materials is relevant to a study of cement. Naturally radioactive materials, manufactured products and industrial residues are widely used in the cement industry as raw materials. Residues from industrial processes such as fly ash from coal-fired power plants produced in large quantities can be recycled and used as a supplement in cement production. This process could yield technological, economical and environmental benefits, but if not subject to regular control, can yield elevated indoor radioactivity exposure rates.
* Corresponding author. Tel.: þ389 2 3125044; fax: þ389 2 3223354. E-mail address: [email protected] (Z. Stojanovska). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.06.023
The safety requirements for building materials refer to the excess exposure rate caused by these materials in addition to terrestrial and cosmic radiation. In this study, safety requirements proposed by the European Commission (EC, 1999) have been examined. The basic concept in determination of the excess exposure rate consists of (1) determination of the total exposure resulting from the building material including the background and (2) background subtraction (Markkanen, 1995).
2. Materials and methods 2.1. Sampling and sample preparation The samples included the following: cement collected since 2005 on a monthly basis from the Cement Factory in Skopje; 218 samples (of which 49 were fly ash samples) from the deposits of two power plants, REK Bitola Fly ash I and REK Oslomej Fly ash II; 45 samples from Pozzolana (originating from Strmos-Pozzolana I and sinovo-Pozzolana II), 16 natural gypsum samples, 42 clinker Ce samples and 66 cement samples. The specifications of the cements under investigation are given in Table 1. The cement CEM I, well known as Portland cement, is produced by grinding clinker (96e97%) and natural gypsum (3e4%) and other two types of cement, CEM II/AeM and CEM II/BeM, containing additional
970
Z. Stojanovska et al. / Radiation Measurements 45 (2010) 969e972
Table 1 Specifications of the cements, subject of this study. Cement type
Raw materials
CEM I
Portland cement
CEM II/AeM
Portland composite cement Portland composite cement
CEM II/BeM
Table 3 Comparison of the activity concentrations of the Macedonian (FYR) (a) fly ash samples and (b) cement samples with those obtained from other international data (in Bq kg1).
Clinker in range of 96e97%; natural gypsum 3e4% Portland cement and max 15% of Pozzolana, limestone, and fly ash Portland cement and max 30% of Pozzolana, limestone, and fly ash
226
components of limestone, fly ash and Pozzolana (maximum 15% and 30%, respectively). Each sample was ground and dried at 105 C until the moisture was removed. The dried material was homogenised and transferred to 500 ml Marinelli beakers, for gamma spectrometry measurements. The spectra were first measured with empty containers (blank probes) and then with containers filled with weighed amounts of sample. The mean values of mass of the analyzed samples were gypsum (0.78 0.04 kg), fly ash (0.44 0.05 kg), Pozzolana (0.60 0.07 kg), clinker (0.85 0.07 kg) and cement (0.69 0.07 kg). The containers were sealed hermetically and stored for a month to achieve secular equilibrium between 226Ra and its short-lived daughters before gamma spectrometry measurements. 2.2. Gamma spectrometry measurements The gamma spectrometry measurements were carried out with a p-type HPGe detector (Canberra Inc.; 25% relative efficiency, resolution of 1.79 keV at 1.33 MeV, 8192 ch. digital analyser, and with 12 cm of lead shielding and internal lining of 2 mm high purity copper). The activity of 226Ra was determined from the gamma lines associated with the short-lived daughters of 214Bi (609.31 keV, 1120.29 keV, 1764.49 keV) and 214Pb (351.93 keV). The activity of 232 Th was determined by the 911.2 keV and 969.1 keV gamma lines from 228Ac, the 860.56 keV gamma lines from the 208Tl and the 238.6 keV line of 212Pb. The activity of 40K was determined from its 1460.8 keV gamma line. Depending on the activity of the sample, each spectrum was collected between 10 ks and 50 ks. The total combined uncertainty of each nuclide was less than 5% at the 95% level of confidence. Efficiency calibration was performed with mixed calibration standard sources MBSS2 from The Czech Metrological Institute. The analysis procedure included the subtraction of the background spectrum. 3. Results and discussion The specific activities (Bq kg1) of 226Ra, 232Th and 40K (minimum, maximum and mean values) of the raw materials and cements are given in Table 2. From the results of all the analyzed Table 2 Activity concentration of Sample
N
226
Ra,
232
Th and
16 20 29 17 28 42 19 28 19
Ra
232
40
Th
K
(a) Fly ash samples Hungary 760 Turkey 232 107 Greece 273e1377 Germany 210 Macedonia (FYR) 107 45
117 117 45 41e65 130 109 30
441 466 148 143e661 700 685 171
Somlai et al. (2008) Turhan (2007) Petropolos et al. (2002) UNSCEAR (1982) Present work
(b) Cement samples Greece 63 Turkey 41 27 Italy 38 Macedonia (FYR) 42 10
24 26 19 22 28 6
284 267 102 218 264 50
Papastefanou et al. (2005) Turhan (2007) Rizzo et al. (2001) Present work
materials it is evident that lowest activity mean values of Ra, 232Th and 40K were found for gypsum (5.9 1.1 Bq kg1, 1.44 0.44 Bq kg1 and 11 5.2 Bq kg1, respectively). On the other hand, the highest activity mean value for 226Ra (140 89 Bq kg1) was found in Fly ash I samples. Likewise, the highest values for the specific activities of 232Th (171 48 Bq kg1) and 40K (786 134 Bq kg1) were found for the Pozzolana II and Fly ash II samples, respectively. Hence, the highest mean values in the raw materials (fly ash and Pozzolana) are above the world mean values (50, 50 and 500 Bq kg1 for 226Ra, 232Th and 40K, respectively; UNSCEAR, 1993). The results obtained for fly ash were compared with the data from the literature (Table 3a). The mean activities of the analyzed cement samples were found to be: 226Ra (42 10 Bq kg1), 232Th (28 6 Bq kg1) and 40K (264 50 Bq kg1). The results for the activities of the cements, subject to this study, were compared to the results of similar published studies (Table 3b). It can be seen that the results are similar to those reported in the literature. 226
3.1. Radium equivalent activity (Raeq) As the distribution of 226Ra, 232Th and 40K in building materials is not uniform, exposure to radiation can be defined in terms of radium equivalent activity (Raeq) to compare the differences in specific activities (Beretka and Mathew, 1985). The radium equivalent activity can be defined as:
Raeq ¼ CRa þ 1:43 CTh þ 0:077 CK ;
(1)
where, CRa, CTh and CK are the specific activities of 40 K, respectively.
226
Ra,
232
Th and
K in raw materials and cements (in Bq kg1).
40
Activity concentration (Bq kg1) 226
Gypsum Fly ash I Fly ash II Pozzolana I Pozzolana II Clinker CEM I CEMII/A-M CEMII/B-M
References
Activity concentration (Bq kg1)
232
Ra
40
Th
K
Min
Max
Mean SD
Min
Max
Mean SD
Min
Max
Mean SD
4.4 89 26 42 43 21 23 31 38
9.0 245 111 81 192 46 37 58 58
5.9 1.1 140 89 85 17 64 12 80 27 31 6 30 4 45 7 50 6
0.92 60 538 36 104 15 17 22 29
2.23 120 1131 101 298 29 27 36 40
1.44 0.44 80 15 129 18 69 15 171 48 20 3 20 3 29 3 34 4
3.2 383 538 40 158 176 174 177 238
21.5 733 1131 183 663 322 280 355 369
11.0 5.2 540 99 786 134 105 43 349 168 234 46 222 36 272 45 295 43
Z. Stojanovska et al. / Radiation Measurements 45 (2010) 969e972 Table 4 Estimated radium equivalent and annual dose. Sample
Gypsum Fly ash I Fly ash II Pozzolana I Pozzolana II Clinker CEM I CEM II/AeM CEM II/BeM
N
16 20 29 17 28 42 19 28 19
Raeq (Bq kg
1
Ia ¼ 1
DE (mSv y
)
)
Min
Max
Mean SD
Min
Max
Mean SD
7.3 232 232 111 266 64 69 93 115
12.7 468 444 239 555 119 100 138 148
9.1 1.5 314 74 357 54 178 31 372 74 85 13 82 10 116 13 130 9
Lower 687 629 202 774 9 31 128 213
than background 1665 1030 314 1489 1141 213 684 457 121 1837 1175 273 234 94 52 155 86 38 313 224 53 351 279 38
971
CRa ; 200
(3)
where, CRa, is the specific activity of 226Ra. The safe use of materials in building construction requires Ia to be less than 1. This limit corresponds to the action level specific activity for 222Rn which is 200 Bq kg1 for future building construction (EC, 1990). The distribution of Ig and Ia for the different samples in this study is shown in Fig. 1 where it can be seen that the calculated mean values of Ig (0.37) and Ia (0.21) for the cements are below the limits for safe use.
3.3. Indoor absorbed dose
This dependence is based on the estimation that 1 Bq kg1 of Ra, 1.43 Bq kg1 of 232Th and 0.077 Bq kg1 of 40K produce equal gamma dose rates. For safe use of building materials, the maximum value of the Raeq should be less than 370 Bq kg1 (UNSCEAR, 1993, 2000). The calculated Raeq values for raw materials and for cement samples are presented in Table 4. The mean value of Raeq for the cements studied (111 22 Bq kg1) is below the set limit of 370 Bq kg1 but higher for Pozzolana II (372 74 Bq kg1). The radium equivalent concentration in fly ash and Pozzolana was found to be about 3e4 times higher than those in Portland cement, which is in agreement with the ratios reported by Kovler et al. (2005).
The activity indexes presented above are used for assessing whether the safety requirements are being fulfilled for materials which might be of concern. Any actual decision for restriction of use of materials should be based on a separate dose assessment into a scenario for the materials to be used (EC, 1999). The European Commission has proposed a scenario (RP 112) for the calculation of the annual effective dose in a concrete room with dimensions: 4 m 5 m 2.8 m. The thickness and density of walls are 20 cm and 2350 kg m3, respectively. The conversion factor used for calculation of the absorbed gamma dose rate D (nGy h1) corresponds to 0.92 nGy h1 per Bq kg1 for 226Ra, 1.1 nGy h1 per 1 Bq kg1 for 232 Th and 0.08 nGy h1 per 1 Bq kg1 for 40K (Markkanen, 1995; EC, 1999),
3.2. Gamma index
D ¼ 0:92 CRa þ 1:1 CTh þ 0:08 CK ;
226
In order to assess whether the safety requirements for building materials are being fulfilled, a gamma index proposed by the European Commission (EC, 1999) was used. It is defined as,
Ig ¼
CRa C C þ Th þ K ; 300 200 3000
(2)
where, CRa, CTh and CK are the specific activities of 226Ra, 232Th and 40 K, respectively. The gamma index should also take into account typical ways and amounts in which the material is used in a building. The limit values depend on the dose criteria, the way and amount of the material and the manner in which it was used in a building and construction. For material used in bulk amounts Ig 1 corresponds to an absorbed gamma dose rate of 1 mSv y1 (EC, 1990). Assessment of the internal hazard, originating from the alpha activity of building materials, requires calculations of the alpha index or internal hazard index. In this study the alpha index was calculated by using the following equation, proposed by Righi and Bruzzi (2006),
DE ¼ D 0:7 7000:
(5)
The results obtained for annual effective doses from different raw materials and cements are presented in the Table 4. It can be seen that the maximum values of the annual effective dose are associated with the fly ash samples and Pozzolana, which is consistent with the
1,2
Gamma index Alpha index
1,1
Gamma/alpha index
1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 Gypsum
Fly ash I
232
where CRa, CTh and CK are the specific activities of Ra, Th and 40 K, respectively. To assess the excess gamma dose rate, originating from the building materials in the proposed scenario room, the gamma dose rate from sources of naturally occurring radioactivity should be subtracted. A background dose rate of 50 nGy h1 corresponding to an average outdoor value in Europe was used. For assessment of the annual effective doses DE (mSv y1), the conversion coefficient from absorbed dose in air to effective dose was taken to be 0.7 Sv Gy1, and the indoor occupancy time was taken to be 7000 h per year (EC, 1999; UNSCEAR, 1993, 2000). Hence, the annual effective dose was calculated using the following equation:
1,3
0
(4) 226
Fly ash II Pozzolana I Pozzolana II
Clinker
Cement I
Cement II
Fig. 1. Gamma and alpha index in raw materials and cements.
Cement III Cement IV
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other results in this study. According to this scenario the mean annual effective dose in the concrete room, where cement is used as a raw material is 200 89 mSv y1. According to the EC recommendation, this value is below the limit of 300 mSv y1 for safe use.
4. Conclusions In this study we have found that the highest values for the mean activity concentrations are in fly ash (226Ra, 107 45 Bq kg1, 232Th, 109 30 Bq kg1; 40K, 685 171 Bq kg1), the specific activities of which are above the world mean values for building materials (50, 50 and 500 Bq kg1 for 226Ra, 232Th and 40K, respectively; UNSCEAR, 1993). However, the mean specific activities of the cement products (226Ra, 42 10 Bq kg1; 232Th, 28 6 Bq kg1; 40K, 264 50 Bq kg1) are similar to those reported by other investigators (Papastefanou et al., 2005; Rizzo et al., 2001; Turhan, 2007). The main contributors to the overall specific activities in the materials examined in this study are attributed to fly ash and Pozzolana and if these raw materials are used as additives in cement production, their activity concentration should be carefully monitored. However, the mean value of Raeq for cements (111 22 Bq kg1) is below the recommended level of 370 Bq kg1. The mean values of Ig and Ia for cements were found to be 0.37 and 0.21, respectively, which is below the limit for safe use. Although the mean values of the annual effective dose for Pozzolana and fly ash are estimated to be higher than the acceptable level their diluted concentration (< 30%) in the cements gives rise to an annual effective dose that does not exceed the recommended limits. Finally, the mean annual effective dose from the cements was estimated to be 200 89 mSv y1, which is below the limit of 300 mSv y1 for safe use. Taking into account the EC recommendation, the results from this research have shown that there is no significant radiation risk from the use of the cements investigated in this study.
References Beretka, I., Mathew, P.I., 1985. Natural radioactivity of Australian building materials, wastes and by-products. Health Physics 48, 87e95. EC (European Commission), March 27, 1990. Commission recommendation 90/143/ Euraatom of 21 February on the protection of the public against indoor exposure to radon. Official Journal of European Commission L-80 Brussels. EC (European Commission), 1999. Radiation Protection 122-Radiological Protection Principles Concerning the Natural Radioactivity of Building Materials. Directorate e General Environment, Nuclear Safety and Civil Protection. Kovler, K., Perevalov, A., Steiner, V., Metzger, L.A., 2005. Radon exhalation of cementitious materials made with coal fly ash: part 1 e scientific background and testing of the cement and fly ash emanation. Journal of Environmental Radioactivity 82, 321e334. Markkanen, M., 1995. Radiation Dose Assessments for Materials with Elevated Natural Radioactivity. Report STUK-B-STO 32. Radiation and Nuclear Safety Authority-STUK. Petropolos, N.P., Anagnostakis, M.J., Simopoulos, S.E., 2002. Photon attenuation, natural radioactivity content and radon exhalation rate of building materials. Journal of Environmental Radioactivity 61, 257e269. Papastefanou, C., Stoulos, S., Manolopoulou, M., 2005. The radioactivity of building materials. Journal of Radioanalytical and Nuclear Chemistry 266 (3), 367e372. Righi, S., Bruzzi, L., 2006. Natural radioactivity and radon exhalation in building materials used in Italian dwellings. Journal of Environmental Radioactivity 88, 158e170. Rizzo, S., Brai, M., Basile, S., Bellia, S., Hauser, S., 2001. Gamma activity and geochemical features of building materials: estimation of gamma dose rate and indoor radon levels in Sicily. Applied Radiation and Isotopes 55, 259e265. Somlai, J., Jobbágy, V., Kovács, J., Tarján, S., Kovács, T., 2008. Radiological aspects of the usability of red mud as building material additive. Journal of Hazardous Materials 150, 541e545. Turhan, S¸., 2007. Assessment of the natural radioactivity and radiological hazards in Turkish cement and its raw materials. Journal of Environmental Radioactivity 99, 404e414. UNSCEAR, 1982. Ionizing Radiation Sources and Biological Effect. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 1993. Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York.