|Year : 2011 | Volume
| Issue : 3 | Page : 172-177
Measurement of natural radioactivity in common building materials used in Tiruvannamalai, Tamilnadu, India
R Ravisankar1, M Suganya1, K Vanasundari1, S Sivakumar2, G Senthilkumar3, J Chandramohan4, P Vijayagopal5, B Venkatraman5
1 Department of Physics, Government Arts College, Tiruvannamalai, India
2 Department of Physics, Arunai Engineering College, Tiruvannamalai, India
3 Department of Physics, University College of Engineering Arni, Arni, India
4 Department of Physics, Mahabarathi Engineering College, Chinasalem, India
5 Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu, India
|Date of Web Publication||27-Sep-2012|
Department of Physics, Government Arts College, Tiruvannamalai
Source of Support: None, Conflict of Interest: None
The radioactivity of some building materials used in Tiruvannamali City has been measured using a NaI (Tl) detector based gamma ray spectrometer. The distribution of natural occurring radionuclides ( 226 Ra, 232 Th and 40 K) in the building materials was studied. The radium equivalent activity (Ra eq ), the activity utilization index (I), external hazard index (H ex ) and internal radiation hazard index (H in ) associated with the natural radionuclide are calculated to assess the radiation hazard of the natural radioactivity in the building materials. The present work shows that the natural radioactivity levels in the building construction materials used in Tiruvannmalai City is well below the acceptable limits. From the analysis, it was found that these materials may be safely used as construction materials and do not pose significant radiation hazards.
Keywords: Building materials, gamma-ray spectrometry, natural radioactivity, radiological hazards
|How to cite this article:|
Ravisankar R, Suganya M, Vanasundari K, Sivakumar S, Senthilkumar G, Chandramohan J, Vijayagopal P, Venkatraman B. Measurement of natural radioactivity in common building materials used in Tiruvannamalai, Tamilnadu, India. Radiat Prot Environ 2011;34:172-7
|How to cite this URL:|
Ravisankar R, Suganya M, Vanasundari K, Sivakumar S, Senthilkumar G, Chandramohan J, Vijayagopal P, Venkatraman B. Measurement of natural radioactivity in common building materials used in Tiruvannamalai, Tamilnadu, India. Radiat Prot Environ [serial online] 2011 [cited 2020 Sep 21];34:172-7. Available from: http://www.rpe.org.in/text.asp?2011/34/3/172/101710
| 1. Introduction|| |
The values of specific radio activities of soil and building materials are required in setting the standard and guidelines for their safe usage and in assessing the radiation hazards associated with them. All building materials such as concrete, cement, brick, sand, aggregate, marble, granite, limestone, gypsum etc contain mainly natural radionuclides mainly, including uranium ( 238 U) and thorium ( 232 Th) and their decay products and the radioactive isotope of potassium ( 40 K). In the 238 U series, the decay chain segment starting from radium ( 226 Ra) is radiologically the most important and, therefore, reference is often made to 226 Ra instead of 238 U. The naturally occurring radionuclides in the building materials contribute to radiation exposure, which can be divided into external and internal exposure. External exposure is caused by direct gamma radiation while internal exposure is caused by the inhalation of the radioactive inert gas radon ( 222 Rn, a daughter product of 226 Ra) and its short lived secondary decay products. Knowledge of the level of natural radioactivity in building materials is then important to assess the possible radiological hazards to human health and to develop standards and guidelines for the use and management of these materials. The natural radioactivity of building materials in many countries have been reported [Beretka and Mathew,  El-Tahaway and Higgy,  Amrani and Tahtat,  Stoulous,  Anjos,  El-Arabi,  Righi and Bruzzi,  El-Gammal,  and Tufail et al.  ]. Natural radioactivity in some Indian building materials have also been reported by some authors [Nageswara et al,  Vireshkumar et al,  Ajaykumar et al,  and Ravisankar et al,  ]. However detailed information of each state is scanty. The data regarding the concentration of 226 Ra, 232 Th and 40 K in building materials belonging to Tiruvannamalai, Tamilnadu state of India is not available in literature.
In this paper, we present the results for the measured activities, radium equivalent activity, activity utilization index and radiation hazards of five kinds of building materials collected from Tiruvannamalai, Tamilnadu.
| 2. Materials and Methods|| |
2.1 Sample collection and preparation
Samples representing five kinds of commonly used structural building materials (clay, soil, brick, sand and cement) were collected randomly from sites where housing and other buildings were under construction and from building material suppliers in Tiruvannamalai for the measurement of the specific radioactivity of 226 Ra, 232 Th and 40 K. These materials were used in bulk amounts. The materials are studied in their natural form as such. The samples were properly catalogued, marked and coded according to the origin and location of the sampling site. After crushing, powdering, coning and quartering, representative samples of maximum grain size 1mm were dried in an oven at about 110°C until the sample weight became constant. These samples were sealed in radon-impermeable plastic containers. The samples were then stored for more than 40 days to bring 222 Rn and its short-lived daughter products into equilibrium with 226 Ra (Ravisankar et al.). 
2.2 Gamma ray spectroscopic technique
All the selected samples were subjected to gamma spectral analysis using a 7.62 × 7.62cm NaI (Tl) detector. The energy resolution of NaI (Tl) detector measured in terms of full-width at half maximum (FWHM) is 50 keV at 662 keV of 137 Cs gamma energy at 25cm from the top of the detector. The detector is shielded with 15cm thick lead on all sides including top to reduce the background contribution of the surroundings. The inner sides of the lead shielding are lined by 2mm thick Cadmium and 1mm thick copper to cut off lead X-rays and cadmium X-rays respectively. The certified reference materials IAEA RGU, RGTh and RGK were used for the energy and efficiency calibration of the system in the energy range from 186.21 to 2614.53 keV. The activity contents of the IAEA reference materials in 250ml bottle geometry are known within ± 3% accuracy. The efficiency percentage for 40 K (1.461 MeV), 214 Bi (1.764 MeV) and 208 Tl (2.615 MeV) were found to be 0.154, 0.357 and 0.301 cps Bq -1 . The samples were sealed in radon-impermeable plastic containers. The samples were then stored for more than 30 days to bring 222 Rn and its short-lived daughter products into equilibrium with 226 Ra. The samples were then counted in the same source-to-detector geometry as used for the establishment of the efficiency calibration. The spectra were acquired for 20,000 sec and the photo peaks were evaluated by using the PCA software. The gamma- ray photo peaks corresponding to 1.461 MeV ( 40 K), 1.764 MeV ( 214 Bi) and 2.615 MeV ( 208 Tl) were considered in arriving at the activity of 40 K, 226 Ra and 232 Th in the samples. The detection limit of NaI (Tl) detector system with 95% confidence limit for 40 K, 226 Ra and 232 Th are 8.50, 2.21 and 2.11 Bq kg -1 , respectively, for a counting time of 20, 000 sec. The results of the activity concentration of the samples have been reported with 2σ error.
| Results and Discussion|| |
3.1 Specific radioactivity
The distribution of natural radionuclides in building materials and also the calculated radium equivalent activity (Ra eq ), activity utilization index (I) and radiation hazards are presented in [Table 1]. [Figure 1] shows the activity concentration of radionuclides and different kind of building materials. It can be seen from the [Table 1], the highest value for the specific activity of 226 Ra, 232 Th and 40 K are 54.09 (Cement 1), 198.58 (Sand-5) and 724.46Bq kg -1 (Soil-4) respectively while the lowest value of the specific activity of the same radionuclides are BDL and 149.76 (Cement-1) Bq kg -1 respectively. It may be seen from the [Table 1], that the activity of 226 Ra varies from <2.21 to 54.09 Bq kg -1 and the geometric mean is 4.97 Bq kg -1 . The activity concentration of 232 Th varies from <2.11 to 198.58 Bq kg -1 and the geometric mean is 30.38 Bq kg -1 . The activity concentration of 40 K varies from 149.76 to724.46 Bq kg -1 and the geometric mean is 339.98 Bq kg -1 . The mean values are lower than the corresponding world-wide average values which are 35, 30 and 400 Bq kg -1 for 226 Ra , 232 Th and 40 K respectively UNESCAR (2000).  If one compares the activity of radionuclides of the present study with world average values, 226 Ra is lower by a factor of 0.14 while the activity of 232 Th was found to be equal to that of world average and 40 K activity is lower by a factor of 0.85.
|Figure 1: Different kinds of Building materials Vs Activity Concentration (Bq/kg)|
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|Table 1: Activity Concentration of Primordial radionuclides in building materials used in Tiruvannamalai, Calculated Radium equivalent (Raeq) activity, Activity utilization index, and Radiation hazards|
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3.2 Radium equivalent activity (Ra eq )
The distribution of natural radionuclides in the samples under investigation is not uniform. Therefore, a common radiological index has been introduced to evaluate the actual activity level 226 Ra, 232 Th and 40 K in the samples and the radiation hazards associated with these radionuclides [Beretka and Mathew (1985)].  This index is usually known as radium equivalent activity.
Where A Ra , A Th and A K are the specific activities of 226 Ra, 232 Th and 40 K respectively in Bq/kg. In the definition of radium equivalent, it is assumed that 10 Bq kg -1 of 226 Ra, 7 Bq kg -1 of 232 Th and 130 Bq kg -1 of 40 K produce an equal gamma ray dose rate [Krisuk et al (1971).  Stranden (1976)].  The values of calculated Ra eq for building materials are shown in the fifth column of the [Table 1]. [Figure 2] shows different kind of building materials and radium equivalent activity. The calculated Ra eq values range from 25.95 (Brick-5) to 325.26 (sand-5) Bq kg -1 with an average of 86.60 Bq kg -1 . All the values of the Ra eq in the studied samples are found to be lower than the criterion limit of 370 Bq kg -1 (NEA-OECD (1979).  The results of this study show that the average value of Ra eq obtained for the building materials is 86.60 Bq kg -1 which is less than the recommended value (370Bq kg -1 ) and as such does not pose any radiological hazard when used for construction of buildings.
|Figure 2: Different kinds of Building Materials Vs Radium equivalent activity (Bq/kg)|
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3.3 Activity utlization index (I)
The building materials act as sources of radiation and also as shields against outdoor radiation (UNSCEAR, 1993).  In massive houses made of different building materials such as stone, bricks, concrete or granite, the factor that mainly affects the indoor absorbed dose is the activity concentrations of natural radionuclides in those materials, while radiation emitted by sources outdoors is efficiently absorbed by the walls. Consequently, dose rates in air indoors will be elevated according to the concentrations of naturally occurring radionuclides used in construction materials. In order to facilitate the calculation of dose rates in air from different combinations of the three radionuclides in building materials and by applying the appropriate conversion factors, an activity utilization index (I) is constructed that is given by the following expression:
where CTh , C Ra and CK are actual values of the activities per unit mass (Bq kg -1 ) of 232 Th, 226 Ra, and 40 K in the building materials considered; fTh , fRa and fK are the fractional contributions to the total dose rate in air due to gamma radiation from the actual concentrations of these radionuclides. In the NEA-OECD (1979)  Report, typical activities per unit mass of 232 Th, 226 Ra, and 40 K in building materials CTh , C Ra and CK are referred to be 50, 50 and 500 Bq kg -1 , respectively. The activity utilization index is, finally, weighted for the mass proportion of the building materials in a house by being multiplied by a factor wm that represents the fractional usage of those materials in the dwelling with the characteristic activity. To be more specific, full mass utilization (wm = 1) of a given material implies that all building materials used in a model masonry house are composed of this specific material. Half mass utilization (wm = 0.5) means that 50% of the masonry mass is composed of the material considered, and so on. For full mass utilization of a model masonry house (CTh = CRa = 50 Bq kg -1 and CK = 500 Bq kg -1 ), the activity utilization index is unity by definition and is deemed to imply a dose rate of 80 nGyh -1 (UNSCEAR, 1993). 
The studied building materials are examined whether they are used as building construction or not by calculating the activity utilization index. The activity utilization of the building materials are calculated using the equation (2). The calculated values vary from 0.03 to 2.51 with an average of 0.48. Except 4 samples (Sand-3, Sand-5, Sand-6 and Sand-7), the activity utilization index exhibit I <2 which corresponds to an annual effective dose <0.3 mSv/y (El-Gamal et al.  ). This indicates that these materials can be used for safe construction of buildings. [Figure 3] shows the different kinds of building materials with activity utilization index.
|Figure 3: Different kinds of Building materials Vs Activity Utilization Index (I)|
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3.4 Radiation hazard indices
In order to measure the hazards one can define radiation hazard indices (Beretka and Mathew (1985)  (i) the external radiation hazard, H ex and (ii) internal radiation hazard, H in , as follows:
3.4.1 External radiation hazard (H ex)
The external hazard index is another criterion to assess the radiological suitability of a material. It is defined as follows:
where A Ra , A Th and A K are the activities of 226 Ra, 232 Th and 40 K in Bq Kg -1. The values of these indices should be <1. It is observed from [Table 1] that the mean value 0.23 of H ex is below the criterion value (<1). [Figure 4] shows different kind of building materials with H ex .
3.4.2 Internal radiation hazard (H in )
The internal hazard index is a criterion for index radiation hazard. In addition to gamma rays, 222 Rn plays an important role for internal exposure in a room. Effectively, the radio toxicity of 238 U is increased by a factor of two to allow for the contribution from 222 Rn and its short lived progeny. The internal exposure due to radon and its daughter products is quantified by the internal hazard index H in , which has been defined as shown below:
The internal hazard index is defined so as to reduce the acceptable maximum concentration of 226 Ra to half the value appropriate to external exposures alone. For the safe use of materials in the construction of dwellings the following criterion was proposed by Krieger H in ≤1. The mean value of H in is determined to be 0.25 which is less than one which indicates that the internal hazards are less than the critical value. [Figure 5] shows the different kinds of building materials with internal hazards.
| 4. Conclusion|| |
The specific radioactivity values of 226 Ra, 232 Th and 40 K measured in commonly used building materials used for the construction purposes in Tiruvannamalai have been determined by gamma ray spectrometer. For each sample in this study, the specific activity, radium equivalent activity, and radiation hazard indices have been determined to assess the radiological hazards from the building materials. The calculated mean radium equivalent activity (Ra eq ) values for the entire building materials examined are lower than the recommended maximum level of radium equivalent value of 370 Bq kg - 1 . The average value of activity utilization index (I) is less than the permissible limit. Moreover, the calculated values of external (H ex ) and internal (H in ) hazard indices are lower than unity.
The values obtained in the study are within the recommended safety limits, showing that these building materials do not pose any significant radiation hazard and hence the use of these materials in the construction for dwelling purpose can be considered to be safe for the inhabitants. This study can be used as a reference for more extensive studies of the same subject in future.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]