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ARTICLE
Year : 2011  |  Volume : 34  |  Issue : 4  |  Page : 229-234  

Measurements of the natural radioactivity in building materials (raw and manufactured), other than granites in Kingdom of Saudi Arabia


Department of physics, University of Taif, Al-Haweiah, Taif, Saudi Arabia

Date of Web Publication17-Jan-2013

Correspondence Address:
M Eldaghmah
Department of physics, University of Taif, Al-Haweiah, Taif
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.106091

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  Abstract 

In this work, we have measured the natural radioactivity contents of the building materials (raw and manufactured) using HPGe detector. The intensities of γ-ray emitted by radioactive nuclides present in the samples were determined. Efficiencies of the detector at different energies were determined using standard sources, so that radioactivity content of the samples can be estimated. Samples from different areas in Kingdom of Saudi Arabia were collected. These samples were prepared in the form of fine powder suitable to be used by Marinelli beakers. Software equipped with the detector electronic system had been used to analyze the data; hence the results were recorded. The highest measured activity concentrations in the samples are: 48, 42, and 971 Bq/kg for 232 Th, 226 Ra, and 40 K, respectively, which are in the range of the corresponding typical worldwide values. The absorbed dose rates, effective dose rates, radium equivalent activities as well as the radiation hazard indices were estimated. The maximum radium equivalent activity (Ra eq ) was 186 Bq/kg, which is lower than the limit of 370 Bq/kg set by the Organisation for Economic Cooperation and Development.

Keywords: Building materials, gammy-ray spectrometry, natural radioactivity


How to cite this article:
Aydarous A, Zeghib S, Eldaghmah M. Measurements of the natural radioactivity in building materials (raw and manufactured), other than granites in Kingdom of Saudi Arabia. Radiat Prot Environ 2011;34:229-34

How to cite this URL:
Aydarous A, Zeghib S, Eldaghmah M. Measurements of the natural radioactivity in building materials (raw and manufactured), other than granites in Kingdom of Saudi Arabia. Radiat Prot Environ [serial online] 2011 [cited 2020 Jun 6];34:229-34. Available from: http://www.rpe.org.in/text.asp?2011/34/4/229/106091


  1. Introduction Top


All building materials contain various amounts of radioactive substances. Building materials originating from rock and soil contain mainly natural radio nuclides of uranium ( 238 U), thorium ( 232 Th) series and the radioisotope of potassium ( 40 K). In the uranium series, the decay chain starts by the most important radioisotope 226 Ra, therefore, reference is often made to radium instead of uranium. In addition to natural radioactive substances, some industrial by-products also contain radionuclides, Caesium ( 137 Cs) in particular, which are spread into the environment due to fallout from nuclear weapon tests and industrial nuclear accidents such as Chernobyl and recently Fukoshima in Japan. [1]

If such by-product is incorporated into building material; the final product will also contain these artificial radionuclides. [2] Ash, which is generated during combustion of peat, coal, wood, forest processed chips, field biomass, by-products of wood industry or other comparable materials, contains both natural radioactive substances and artificial radionuclides originating from fallout. Ash is used as landscaping, and as an additive in concrete. It is also used as bulk material under roads, taken to dumps, or mounded. [2] The world wide concentrations of radium, thorium, potassium and 137 Cs in earth crust ranging from 27-40 Bq/kg, 46-62 Bq/kg, 63-629 Bq/kg, and 3-5.15 Bq/kg, respectively, depending on the location on earth. [3] The reported values of radium, thorium and potassium concentrations in rocks were 26.6, 23.2 and 515.6 Bq/kg, respectively; while, these values in earth crust were: 50, 50 and 500 Bq/kg, respectively. [4] Typical activity concentrations in common building materials and industrial by-products used for building materials in European Union (EU) ranging from 10 up to 390 Bq/kg for 226 Ra, from 10 up to 100 Bq/kg for 232 Th and from 60 up to 670 Bq/kg for 40 K. [5] While maximum activity concentrations of these materials were ranging from 25 up to 2600 Bq/kg for 226 Ra, from 30 up to 340 Bq/kg for 232 Th and from 200 up to 4000 Bq/kg for 40 K. [5] Worldwide average annual effective doses of radiation at year 2000 from natural sources (2400 μ Sv) and Inhalation (mainly radon) 3600 μ Sv). [6]

Many studies have been done to measure the concentrations and the doses resulting from the natural radioisotopes present in the building materials, all over the world. Samples of cement and ceramic bricks used as building materials in Poland have been analyzed for 226 Ra, 232 Th and 40 K using a high resolution HPGe gamma ray spectrometer shows a dose rate ranging from 99 to 102 nGy/h. [7] The radioactivity concentration of 226 Ra, 232 Th, and 40 K (Bq/kg) in soil samples taken from different locations in State of Qatar ranging from 65-301, 11-25 to 160-296, respectively [8], while the reported values in other countries were as follows: [8] Algeria: 2-127, 2-144, 35-1405, respectively, Egypt: 5-24, 10-20, 293-660 respectively, Jordan: 15-60, 4-29, 99-379, respectively, India: 5-71, 15-76, 20-854, respectively, Bangladesh: 13-43, 3-81, 402-750, respectively, China: 40-443, 33-68, 442-913, respectively and Worldwide: 40, 40, and 580, respectively.

The radioactivity concentrations of 226 Ra, 232 Th and 40 K (Bq/kg) were also measured for various cement samples used for building materials in the State of Qatar, the reported values ranging from 27-32, 8-14 to 54-98, respectively. [9] The activity concentrations of natural radionuclides in various building materials in Vietnam were found to be ranging from 5-170, 20-190 to 20-1980 (Bq/m 3 ) for 226 Ra, 232 Th and 40 K, respectively. [10] An investigation on the natural radioactivity of building materials in central Turkey, show that the average values resulting from 226 Ra, 232 Th and 40 K were: 632.2 Bq/kg for fly-ash, 4.4 Bq/kg for brick, 73.3 Bq/kg for soil, 306.6 Bq/kg for cement, 302 Bq/kg for gypsum and 83.6 Bq/kg for solvent-based paint. [11]

The investigation on the natural radioactivity of bricks in India, show that the average values resulting from 226 Ra, 232 Th and 40 K vary from 9.89-23.48 Bq/kg, 25.35-62.02 Bq/kg to 342.48-405.24 Bq/kg, respectively. [12] In Ghana, the calculated average activity concentrations of 226 Ra, 232 Th and 40 K in the cement samples were 35.9 Bq/kg, 25.4 Bq/kg and 233.3 Bq/kg, respectively. [13] The activity concentrations of 226 Ra, 232 Th and 40 K in Bq/kg of different Egyptian building materials were as follows: Sand (9.2, 2.9, 54.5), cement (22.5, 3.9, 68.7), limestone (13.4, 3.3, 61.6), yellow clay (27.2, 19.3, 188.7), respectively. [14] The concentrations of 226 Ra and 232 Th in building materials used in Saudi Arabia were found to be less than those reported in different countries, while the concentrations of 40 K were higher than those reported from other countries. [15]

Measurements of the concentrations of naturally occurring radionuclide ( 226 Ra, 232 Th and 40 K) in rocks and sand samples taken from Taif province in Saudi Arabia using Gamma ray spectrometer-2000 and portable gamma ratemeter gave lower values than the acceptable value of 1 mSv/y, [16] thus they concluded that accurate measurements on the collected samples using HPGe detector are highly recommended. [16] Saudi Arabia is considered a large market for local and foreign building materials. The aim of this present work is to measure the radiation doses resulting from these radionuclides. These doses can be hazardous to those who live in houses and buildings constructed from these building materials. Radioactive Radon ( 222 Rn) gas is generated from Uranium decay series and can be accumulated in houses and can result in increased risk of lung cancer. Thus certain precautions can be taken to protect humans from radiation, by using selected building materials having lowered concentrations of radioactivity. Several countries have adopted their own policies for limiting the radioactivity concentrations of building materials. If these materials have high concentration of radioactive nuclides, they can be used in other constructions, like roads instead houses. Even though this work cannot cover all samples of building materials used in the kingdom, it can be a pointer for similar studies if the findings are significant. It may also help to adopt policies with respect to regulating the use of building materials that might be hazardous to public. Authorities in areas such as Minister of Commerce and Industry and the Saudi Arabian Standards Organization (SSO) can benefit from the outcome of this work. High resolution γ-ray spectroscopy employing a HPGe detector was adopted in this work. The radioactivity concentrations of 226 Ra, 232 Th and 40 K in all the building material samples were determined. A comparative study of our data with different results in other areas of the world has been done. Thus, some conclusions can be derived, so that certain policies can be adopted to minimize the hazards of radiation to the public.


  2. Materials and Methods Top


2.1. Collection of samples

Local and imported samples of different building materials were collected from different areas in the kingdom. We focus on the widely and mostly used materials in various constructions and buildings. Each sample was classified by its origin (local or imported) and the place of origin.

2.2. Processing of samples

Brick and tiles samples were crushed in the laboratory in two stages in sequence to convert them into fine powder. The first grinder breaks the hard samples to small pieces. The second grinder crushes the samples to dust. The samples were then sieved through 40 mesh sieve and then heated at 110 o C in an oven for 24 h to get rid of moisture, if any. The samples were then cooled and transferred to plastic Marinelli beakers of volume 500 cc each and then sealed by epoxy. The net mass of each sample was recorded. Also vinyl tapes were wrapped along the edges of the lids of the beakers. This kind of sealing by epoxy and tapes is expected to keep the radon gas that emanates from the crushed samples to be confined to the beaker, as much as possible. These sealed Marinelli beakers were then kept for a period of about 1 month in order to allow the daughters of 238 U and 232 Th to reach secular equilibrium with each other.

2.3. Energy calibration

The multichannel analyzer of our electronic system was calibrated for energy using standard radioactive source of 152 Eu. 152 Eu being a multi-peak gamma emitter provides a reasonable coverage of the gamma spectrum, the lowest energy is 121.78 keV and the highest is 1408.11 keV.

To have the same geometry as the samples, standard 152 Eu sources should be prepared in Marinelli beaker. 152 Eu in a liquid form with known activity was the standard radioactive source used for the preparation of such an extended source. For this purpose, clean Marinelli beaker was weighed empty and then was filled with selected sample. The sample was then counted for the background time (about 7000 s). The region of interests (ROIs) in the MCA spectrum corresponding to the 152 Eu energies were marked previously, and the counts for all ROIs for this time period were noted. The sample was now emptied to a clean glass bowl. Using pipette, 0.2 ml of 152 Eu solution was put drop by drop to the sample. This was mixed thoroughly and carefully to ensure homogeneity of the radioactivity in the sample. The radioactive standard was then transferred to the Marinelli beaker and counted for 7000 s.

2.4. Efficiency calibration

The detector efficiency is known as: The ability of the detector for recording interactions within its effective volume. If spectral quantitative analysis is required, the detector efficiency must be determined over the range of energies of interest. The general method is to collect a spectrum from a known source and determine the ratio of the number of events counted to the number of actual events. This was done for several peaks in the spectrum to allow the plotting of the efficiency curve. In this work, we will use the so called absolute efficiency. The absolute efficiency is defined as the ratio of the number of pulses recorded by the detection system to the number of radiation quanta emitted by the source; it depends on the geometry of the experiment and the detector properties. The absolute efficiency (ε) is given by the following equation: [17]



Where cp is the total net counts per second, representing the number of photons detected under the photopeak. A is the activity of the standard source in Bq Iγ is the intensity of gamma line (relative abundance)

The error can be calculated using the relation:



2.5. Gamma-ray spectrometer

The high-resolution gamma spectrometry system used for analyzing the samples consisted of Canberra high-purity germanium HPGe detector, of 50% relative efficiency coupled to Canberra Digital Spectrum Analyzer DSA 2000 (GENIE-2000) with an FWHM of 2 keV for the 1.332 MeV gamma ray of 60 Co.

The HPGe' detector is equipped with model 747 Canberra lead shield system (composed of 10-cm thick low-background lead, and 1-mm tin and 1.6-mm copper graded liner to prevent interference by lead X-rays).

The radionuclides under focuses were 226 Ra, 232 Th and 40 K. The 226 Ra activities were estimated from the gamma rays of 214 Pb (295.2, 351.9 keV) and 214 Bi (609.3 and 1120.3 keV). The 232 Th activities were estimated from the gamma rays of 212 Pb (238.6 keV), 228 Ac (338.4, 911 keV) and 208 Tl (583.2 keV).

Several peaks from 226 Ra and 232 Th daughters were also monitored. The 40 K-activities was determined from its own gamma ray (1460.8 keV).

Once the absolute efficiency curve is plotted, the efficiency of the detector at any value of gamma energy can be determined; hence the activity concentrations (Ap in Bq/kg) for the natural radionuclide in the given sample can be calculated using the relation:



Where Cp is the net peak counting rate of gamma ray (counts per second), ε is the detector efficiency of the specific gamma ray, and Ms is the mass of the sample (kg). Pr represents the absolute transition probability of the specific gamma decay. When the activity concentration is evaluated from several gamma peaks, the weighted average is considered after taking into account all necessary corrections as previously indicated.

2.6. Assessment of radiological risk

In order to assess the radiation hazard associated with the building materials used, the Ra eq and the absorbed dose rate (D.) have been evaluated, where it is assumed that all the decay products of 226 Ra and 232 Th are in radioactive equilibrium with their precursors. The Ra eq is calculated according to the following formula: [18],[19]



Where, ARa , ATh and AK are the specific activities (Bq/kg) of 226 Ra, 232 Th and 40 K, respectively. This formula is based on the estimation that 1 Bq/kg of 238 U, 0.7 Bq/kg of 232 Th and 13 Bq/kg of 40 K produce the same gamma-ray dose rates.

The outdoor absorbed dose rate (nGy/h) in air from terrestrial gamma radiation at 1 m above the ground is calculated after applying the conversion factors (in nGy/h per Bq/kg) to transform specific activities ARa , ATh and AK into absorbed dose rate according to the following formula: [20],[21]



In addition, the annual effective dose rate indoors (É) (measured in mSv/y) was calculated, assuming a value of 0.7 Sv/Gy for the conversion factor from absorbed dose in air to annual effective dose received by adults and a 0.8 factor for the indoor occupancy. [22],[23] The formula used is:



To estimate the gamma-radiation dose expected to be delivered externally from building materials, a model was suggested by various researchers to limit the radiation dose from building materials to 1.5 mSv/y. In this model the external hazard index has been defined as: [18]



The radiation risk is negligible when the maximum value of the external hazard index is less than unity (Hex ≤1), which is equivalent to a maximum value of the Ra eq activity <370 Bq/kg. In terms of dose equivalent, this index must be less than unity so that the annual effective dose due to radioactivity in the material will be ≤1.5 mSv/h.

Internal exposures arise from the inhalation of radon ( 222 Rn) gas and its short-lived decay products as well as from the inhalation or ingestion of other radionuclides. Radon is part of the radioactive series of 238 U, which is present in building materials. To assess the internal exposure to 222 Rn gas, the internal hazard index has been defined as: [18]



The use of a material in the construction of dwellings is considered safe when the maximum value of the internal hazard index is less than unity (Hin ≤1).


  3. Results and Discussion Top


The activity concentrations of most commonly used building materials in the kingdom of Saudi Arabia were measured, employing the high-resolution gamma ray spectrometry. In [Table 1] we show the various 232 Th, 226 Ra and 40 K activity concentrations (Bq/kg) for the building materials' samples under investigation.
Table 1: 232Th, 226Ra and 40K activity concentrations (Bq/kg) for the building materials samples under investigation

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In [Table 2], we show the Absorbed Dose rate (nGy/h), Ra eq (Bq/kg) and the indoors effective dose rate (mSv/y) for all samples.
Table 2: The absorbed dose rate (nGy/h), Raeq(Bq/kg) and the indoors effective dose rate (mSv/y) for all samples

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In [Table 3], we show the calculated values in this work of both Hex and Hin indices for all samples; it is seen clearly that their values are less than unity, which indicate that the radiation doses are below the hazardous limits.
Table 3: Values of both Hex and Hin calculated for all investigated samples in this work

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Thus, one can conclude that:

  1. The highest radiation content was detected for each of: Kishani China, Ceramices China and Saudi Ceramics samples.
  2. The lowest radiation content was detected for each of: Sand samples, gypsum and cement samples. For sand samples, we can see that the Tayma sand has the lowest radiation content. The Yanbu gypsum gave the lowest radiation content. Egyption white cement containd the lowest radiation level.
  3. The effective dose rates from all the samples are all at the acceptable level with maximum value of 450 μ Sv/y.
  4. It is recommended here the use of Tyma sand, the Yanbu gypsum and the Egyption white cement from among other building materials and recommend little use of Kishani China and Ceramics in building materials, because of their relatively higher radiation content.

  4. Acknowledgements Top


Thanks to ALLAH most gracious, most merciful, first and last who enables us to do this work. The investigators would like to acknowledge the financial support provided by Taif University, Saudi Arabia, Project number 1-432-1058. The acknowledgements would be also extended to all those unknowns who helped to bring this work to light.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3]


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