Ceramics are one of the most important types of the industrial materials. Ceramic is made of a mixture of clay, feldspar, silica, talc kaolin minerals together with zirconium silicates (ZrSiO4). The ceramic raw materials contain naturally occurring radionuclide 238U and, 232Th series, and 40K (Abbady, 2004). Ceramic causes a potential radiation risk due to these radiation exposures and their chemical composition, controls should be restricted (Almayahi et al., 2012). Measurements of the radio activities from houseware, due to their composition contain radionuclides of 238U, 232Th and 40 K and their radioactive series are important. Such activities would provide the useful data of doses and hazard indices to make them safe in houseware product (Ahmad et al., 2015; Papadopoulos et al., 2013). There are many numbers of work worldwide measured the natural radioactivity of ceramic and porcelain by gamma rays spectroscopy and used their values to determine the doses and the hazard indices, these data are important to human health and compare the results with the recommended limits (Aksoy et al., 2010; Tufail et al., 2010; Janković et al., 2013). The objectives of this study are: 1) Use X-Ray Diffraction and Atomic Absorption techniques to study the Chemical, Mineral, Compositions and Concentrations (of Some Metals) in fifteen local and imported Ceramic and Porcelain dinner wares samples. 2) Measure the Natural Radioactivity of 226Ra, 232Th and 40K by gamma-ray spectroscopy having a high-purity germanium (HPGe) detector in these samples, and to determine their specific radioactivity concentrations. 3) Calculate the radium equivalent activity concentrations Raeq (Bq/kg), gamma dose rate D (nGy/h), annual effective dose Deff (mSv/year) and external hazard Hix values, and compare the results with worldwide values to control the causes of potential radiation risk.
2. Materials and Methods
2.1. Sample Collection and Preparation
Fifteen different types and different origins of food wares were collected from commercial suppliers as shown in Table 1. These samples were crushed, grounded, sieved by 1 mm × 1 mm, and dried to 105˚C for 24 hr. not to lose the volatile 137Cs or the natural polonium and to remove moisture. Twenty gm of the dried samples were kept for analyzed by XRD and Atomic Absorption spectroscopy. For radiometric analysis, each dried sample was weighed and transferred to 640 cc poly-ethylene Marinelli beakers then sealed and stored for 2 - 4 months to stop the escape of Radon gas and to get the radioactive secular equilibrium between 238U, 232Th and their progenies.
Table 1. Origin, type, and description of the 15 samples.
2.2. Experimental Techniques
Ten gm of the dried samples were analyzed by XRD spectrometer model Burker XR-D D8 Advance for the chemical and mineral compositions. Ten gm of the samples were used for the analysis by Atomic Absorption spectrometer model OPTIMA 4000 DV Series Perkin Elmer for the Al, Bi, Pb, U, Th, and K concentrations. The samples were analyzed non-destructively, using gamma-ray spectrometry with Canberra high purity germanium (HPGe) coaxial detector with relative efficiency of 25% and FWHM 2.0 keV at 1332 keV, of 60Co. Genie 2000 basic spectroscopic software was installed in the computer for data acquisition and analysis. The system was calibrated for energy using standard gamma-ray sources and absolute efficiency. The lowest detection limits (DL) of HPGe detector system were 0.33, 0.27, and 2.31 for 226Ra, 232Th, and 40K respectively for a counting time of 82,800 seconds. An empty polyethylene Marinelli beaker was placed in the detection system for this time period in order to collect the background count rates. Then, each sample was measured during a same accumulating time.
The concentrations of 226Ra, 232Th-232 and 40K were determined from the average concentrations of gamma ray lines of energies tabulated in Table 2. There is secular equilibrium between the 226Ra and its daughters 214Pb, 214Bi. For 232Th, the secular equilibrium is between the 232Th and its daughters 228Ac, 212Bi and 208Tl. The concentration of 40K is determined.
Table 2. Gamma lines used for spectrometry determinations.
Determination of activity concentrations in Bq/kg dry weight was calculated using the equation (Younis et al., 2018):
where: Nc is the net count area of the gamma line for the measured sample (counts/second), m is mass of the sample, ϵ is the absolute efficiency of the spectrometer at the photo-peak energy and β is the probability of emission of the gamma ray. Exposure to radiation has been defined in terms of the radium equivalent Raeq Bq/kg which is calculated from equation (UNSCEAR, 1993).
where: CRa, CTh and CK are the concentrations in Bq/kg dry weight for radium, thorium and potassium respectively. The total air absorbed dose rate (nGy/h) in the outdoor air at 1 m above the ground due to the activity concentrations of 226Ra, 232Th and 40K (Bq/kg) dry weight was calculated using the equation (UNSCEAR, 2000; Veiga et al., 2006).
where: CRa, CTh, and CK are the specific activities (concentrations) of 226Ra, 232Th and 40K in Bq/kg dry weight respectively. The annual effective dose equivalent Deff (mSv/y) in air was calculated using the values of the absorbed dose rate by applying the dose conversion factor of 0.7 Sv/Gy and the outdoor occupancy factor of 0.2 (people spend about 20% of their life outdoor) the Annual Effective Dose (in mSv/y) received by population can be calculated using equation (UNSCEAR, 2000):
where: D (nG/h) is the total air absorbed dose rate in the outdoor. 8766 h is the number of hours in 1 year. 10−6 is conversion factor of nano and milli. To limit the annual external gamma-ray dose to 1.5 Gy for the samples under investigation, the external hazard index (Hex) is given by the equation (El Aassy Ibrahim et al., 2011):
3. Results and Discussion
3.1. XRD Analysis
X-ray diffraction is a non-destructive analytical technique, which provides detailed information about the atomic structure of crystalline substances, chemical composition, and physical properties of materials. It is a powerful tool in the identification of minerals in rocks and soils (Harris & White, 2008). The minerals of 15 samples analyzed by XRD spectrometer are shown in Table 2. The results show that the major mineral constituent of all samples (except P4) is quartz (SiO2). As expected, most common type of clay (ceramic products are clay-based) consists of kaolinite, mica, quartz (SiO2), and feldspar (a group of rock-forming tectosilicate minerals). While Porcelain is mostly kaolinite (Al2Si2O5(OH)4) and is defined as glazed or unglazed glassy ceramic. Minor element in porcelain samples is mullite (Al6Si2O13) except sample 7, its minor element is Albite (NaAlSi3O8). In ceramic samples minor elements vary from sample to sample as well as trace elements in all samples. Table 3 represents the mineral chemical composition and its description (Don Leet et al., 1982).
Table 3. The mineral constituents analyzed by XRD spec.
3.2. Atomic Absorption Spectroscopy
Table 4 lists the results of the concentrations for 15 porcelain and ceramic samples for sex elements (Al. Pb, Bi, U, Th, K) are measured by atomic absorption spectroscopy. Ceramic and porcelain include Aluminum (Al) in the form of aluminum oxide (Al2O3), Aluminum is considered to be a non-essential element and is known to be toxic to different species, the toxicity depends on its form in solution. Results show that the concentrations (ppm) of Al ranged from 4.56 (P2) to 15.97 (C10), with mean 10.3 (ppm) (10%) which is less than the acceptable value (11%) (Lehman, 2002). Lead (lead oxide (PbO)) glazes used on many kind of porcelain and ceramic food wares. Lead is high toxicity element when absorbed into the body, depending on the size and shape of the wares. It is harmful to human health at high concentrations, the allowed limit is 0.2 ppm (European Community, EC, 2005). Lead concentration mean value is 1.65 ppm. Bi concentrations for all samples were lower than (DL < 10). For U, concentrations were lower than (DL < 5) except samples C9 and C11 (7.67 and 11.84) respectively, these values are much less than values measured by gamma spectroscopy (C9: 93.8, C11: 144.8). Thorium is found almost everywhere, and it can be absorbed through food, drinking water, and in air. Thorium has no known biological function. Th concentrations ranged from LDL (<1) (P2) to
Table 4. Concentrations of Al, Bi, Pb, U, Th and K measured by Atomic Absorption spectrometer.
52.88 ppm (P3), Th concentrations for all samples (accept P1, P2, P4) were much greater than the acceptable value 7.24 ppm (Rudnick et al., 2004). Potassium is the eighth most abundant element in the Earth’s crust (2.1%) (Emsley, 2001), it is found in almost all solids on Earth It is not found in pure form in nature, but in from of compounds. Potassium is an essential element for all organisms. Potassium toxicity, a condition called hyperkalemia, is very rare the potassium concentrations in ppm range from 2079.09 (P1) to 48205.50 (P5), where the mean is 24974.54 ppm (2.5%), which is greater than the acceptable value (1.92%) (Heiserman, 1992).
Figure 1 shows a comparison between samples activity concentration values for 232Th, and 40K were measured by Gamma-Ray Spectrometry and samples concentration values for Th, and K measured by Atomic Absorption Spectrometer. Both analysis results are in a good agreement and this means that the geochemical analysis (Atomic Absorption Spectrometer) can determine the concentrations of elements in the minerals with reasonable values.
3.3. Gamma Spectroscopy
Porcelain and ceramic samples were measured using the gamma spectrometer. The results in Table 6 show that: There is secular equilibrium between the 226Ra and its daughters 214Pb, their activities were used to calculate the concentrations of 226Ra in Bq/kg dry weight. Their ranged were from 11.51 (P2) to 192.67 (P7). Samples show high radium in samples P3 (184.68) and P7 (192.67). The decay of short half-life daughters 228Ac, 212Bi, and 208Tl were used to determine the activity concentrations of 232Th, since there is secular radioactivity equilibrium in 232Th series. The activity concentrations in Bq/.kg dry weight of 232Th were varied form 13.01 (P4) to 184.04 (C10). Activity concentration values in Bq/.kg dry weight for 40K were from low value 67.10 (P1) to high value 1736.30 (P3). The 226Ra, 232Th and 40K activity concentrations were varied, this is due to the mineral constituents (Table 3), of the studied samples. The high value of 226Ra was in porcelain sample (P7), 232Th highest concentration was in ceramic sample (C10), for 40K, the highest concentration was in porcelain sample (P3), this is due to the chemical composition of these sample (Table 5).
Figure 1. Activity concentrations (Bq/Kg) of 226Ra, 232Th and 40K.
The mean concentrations of 226Ra, 232Th and 40K are greater than the mean values reported by UNSCEAR (Table 6). So, there is necessary need for more specific rules for buy and sale these local and imported housewares. Figure 1 shows the Activity concentrations (Bq/kg) of 226Ra, 232Th and 40K.
A comparison between the results of activity concentrations for 232Th, and 40 measured by γ -Ray spectrometer and concentrations values for Th, and K measured by A. A. Spectrometer. Both analysis results are in a good agreement and this means that the geochemical analysis (Atomic Absorption Spectrometer) can determine the concentrations of elements in the minerals with reasonable values, shown in Figure 2.
Figure 2. A comparison between activity concentrations for 232Th, and 40 measured by γ-Ray Spectrometer and concentrations values for Th, and K measured by A. A. Spectrometer.
Table 6. The specific activity concentrations in Bq/kg for 15 samples.
3.4. Radiation Hazard Indices
The distribution of natural radionuclides in the samples is not the same. Therefore, radiological index has been used to estimate the actual activity values of 226Ra, 232Th and 40K in the samples and the radiation hazards accompanied with these radionuclides (the radium equivalent activity Raeq, absorbed dose rate D, the annual effective dose rate Deff, and external hazard index Hex. The results were presented in (Table 7).
The values of the radium equivalent activities range in Porcelain from (58.83 to 551.25 Bq/kg). For Ceramic, the values of the radium equivalent activity range from (195.66 to 401.87 Bq/kg), its mean value for all samples is (302.61 Bq/kg), which is lower than the worldwide value (370 Bq/kg). The radium equivalent activities for samples (P: 3, 5, 6, 7 and C: 8, 10) are higher than the maximum admissible limit of 370 Bq/kg. The analysis of the data in Table 7 shows the variation of area for the same type of material. This is due to the place of origin, varied origin sources, different additives. More indices are useful to be found: gamma dose rate D (nGy/h), annual effective dose Deff (mSv/year), and external hazard Hix for analyzed samples. The mean value of D (nGy/h) is 140.15 is higher than the maximum admissible limit of 60 (nGy/h), D (nGy/h) exceeding should be taken into account in terms of radiation protection. It is therefore recommended that controls should be based on a dose range. Deff (mSv/year) and Hix are below the published admissible limit ≤ 1 and the risk is negligible (UNSCEAR, 2000).
Table 7. Raeq (Bq/kg), D (nGy/h), Deff (mSv/year), Hix.
Fifteen samples of ceramic and porcelain items commonly were found in everyday living in Jeddah Saudi Arabia were examined by three techniques. *X-ray diffraction provides detailed information about the atomic structure of crystalline substances, chemical composition and physical properties of materials. The major mineral constituent of all samples in ceramic (except P4) is quartz (SiO2). Ceramic samples minor and trace elements vary from sample to sample. Porcelain is mostly kaolinite (Al2Si2O5(OH)4), and minor element is mullite (Al6Si2O13) (except P7), its minor element is Albite (NaAlSi3O8). This is due to the geological origin for the samples. Atomic absorption spectroscopy is used to measure the concentration values in ppm for sex elements (Al, Pb, Bi, U, Th, K). In this study, ceramic and porcelain include Aluminum (Al) which is known to be toxic to different species, the mean concentration (ppm) of Al is 10.3 ppm which is less than the acceptable value. Toxicity lead oxide (PbO) glazes are used on many kinds of porcelain and ceramic food wares. The allowed limit is 0.2 ppm (EC, 2005), the mean concentration value is 1.65 ppm. Bi concentrations for all samples were lower than (DL < 10). For U, concentrations were lower than (DL < 5) except two samples, Thorium is chemotoxic, radiotoxic and a carcinogen element. The mean concentration value is 27.16 ppm, which is much greater than the acceptable value 7.24 ppm. Potassium is the eighth most abundant element in the Earth’s crust (2.1%), Potassium mean concentration is 24974.54 ppm (2.5%), which is greater than the acceptable value (1.92%). *Porcelain and ceramic samples were measured using the gamma spectrometer. The results show that: their activities were used to calculate the concentrations of 226Ra, Th and 40K. The mean concentrations of 226Ra, 232Th and 40K are greater than the mean values reported by UNSCEAR. So, there is necessary need for more specific rules for buy and sale these local and imported housewares. The mean value of the radium equivalent activities for all samples is (302.61 Bq/kg), which is lower than the worldwide value (370 Bq/kg). This is due to the place of origin, varied origin sources, different additives. Indices mean values of D (nGy/h), Deff (mSv/year) and Hix are useful to be found in terms of radiation protection. The mean value of D (nGy/h) is higher than the maximum admissible limit. It is therefore recommended that controls should be based on a dose range. Deff (mSv/year) and Hix are below the published admissible limit ≤ 1 and the risk is negligible.
The author is appreciated to the Saudi Geological Survey (SGS) for their technical help.
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