Radiological Effectual and Mineral Salts Measurements of Sandstone Used in the Construction from Al Wajh, Al Ula and North Al Ula, Az Zabirah-Saudi Arabia

Safia H. Q. Hamidalddin

Physics Department, Faculty of Science, Jeddah University, Jeddah, Saudi Arabia.

DOI: 10.4236/gep.2022.109005                

Abstract

The activity concentrations of natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K, were measured in (16) sandstone samples collected from two regions of Saudi Arabia, Region 1 (Al Wajh on Red Sea coast and Al Ula north-East of Medina), Region 2 (North of Al Ula and Az Zabirah, North-West of Hail) by (HPGe gamma spectrometer). The activity concentration average values of the radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K in the sandstone samples (Region 1) ranged from 10.97 ± 0.43, 27.68 ± 0.37 and 64.56 ± 0.74 Bq/kg respectively. These values are less than the international values reported by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000), in (Region 2), average values ranged from 2465.49 ± 0.00, 2042.00 ± 0.00 and 2259.65 ± 0.64 Bq/kg respectively. These values are higher than the values reported by (UNSCEAR, 2000). Average values of radium equivalent activity Ra_eq (Bq/Kg), absorbed dose rate D (nGy/h), annual effective radiation dose D_eff (mSv/y), External index (H_ex) and Internal index (H_in) were in (region 1) 21.13, 27.22, 11.75, 0.07 and 0.10 respectively, in (region 2) 5775.19, 1787.78, 846.58, 11.57 and 15.64 respectively. These results are lower (except annual effective radiation dose) in (region 1) and higher in (region 2) than the world recommended values by (UNSCEAR, 2000). Also, samples were analyzed by Atomic Absorption spectrometer (AAS) for Al, Ca, Fe, K, Mg and Bi in % elements concentrations. Average value in (region 1) (Al Wajh and Al Ula) are 4.42, 0.41, 1.37, 0.04 and 0.03, (in region 2) (N. Al Ula and Az Zabirah) are 12.50, 10.05, 1.01, 1.19, 0.04 respectively. Classifications of sandstone depend on the content of these elements. These results are important for the safety of dwellers and user of sandstone in constructions.

Keywords

Gamma Spectrometer, AA Spectrometer, Natural Radioactivity, Chemical Elements

1. Introduction

Natural activity arises from radioactive elements in the earth crust and terrestrial radionuclides. Natural radioactive materials can be reach hazardous radiological levels. It is necessary to study the natural radioactivity levels in building matter such as sandstone (Baxter, 1993). Human exposure to ionizing radiation emitted from these natural radioactive sources is an ongoing and unavoidable fact of life on earth (UNSCEAR, 2008). The external exposure (indoor and outdoor) results from gamma-rays of radionuclides ²²⁶Ra, ²³²Th, and their radioactive series and ⁴⁰K are existing in all environmental media may vary depending on the geological and geochemical structure of the region (UNSCEAR, 2008). The sandstone is an important environmental material which is used for many purposes such as building materials concentrations. Sandstone has a wide variation from region to another on the crust of earth (Roger & Adams, 1969). Hence, the specific level of ambient background radiation in the crust varies from one region to another as the concentrations of these natural radioactive elements vary due to their non- uniform nature in sandstone and the types of rock from which they originate. Therefore, the terrestrial radiation depends on the geological conditions of the area (Roger & Adams, 1969; NCRP, 1975; Florou & Kritidis, 1992; Tzortzis et al., 2003). Sandstone is containing natural radionuclides that contribute to indoor and outdoor exposure. The measurement of natural radioactivity in sandstone concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K is very important to determine the amount of change of the natural background activity with time as a result of any radioactive release. The aim of this work is to measure the sandstone samples activities from two regions: (Al Wajh on Red Sea coast, Al Ula north-East of Medina) and (North of Al Ula, Az Zabirah, North-West of Hail) in Saudi Arabia and to estimate the potential health impact to the human in these areas under investigation. In addition, to calculate elements concentrations of Al, Ca, Fe, K, Mg and Bi in % in these areas, classifications of sandstone depend on the content of these elements. These results are important for the safety of dwellers and user of sandstone in constructions.

2. Geological Setting

2.1. Study Area

Sixteen sandstone samples were collected from two regions of Saudi Arabia (Al Wajh on Red Sea coast and Al Ula north-East of Medina) (SS: 1 to 7), (North of Al Ula and Az Zabirah, North-West of Hail) (SS: 8 to 16) Table 1, Figure 1.

Table 1. Name and location of sandstone samples.

Figure 1. Al Wajh, a city on Red Sea coast, Al Ula and North Al Ula, north-East of Medina Az Zabirah, North-West of Hail.

2.2. Samples Preparation

The samples were dried in oven of one hundred ˚C to remove the moisture completely, crushed in an agate mortar, sieved in 2 mm to be homogenized in size. Each weighted sample (550 gm) was transferred to cylindrical plastic-container (Marinelli Beaker) then labelled and taped up tightly. The samples were stored for two months before counting to reach secular equilibrium between ²³⁸U and ²³²Th with their daughter nuclides.

3. Experimental Measurements

3.1. Gamma Spectroscopic and the Activity Concentration Calculations

The samples were analysed non-destructively, using gamma-ray spectrometry with Canberra (Model number GC2520) high purity coaxial germanium (HPGe) detector with efficiency of 25% and energy resolution of 2 keV FWHM for the 1332 keV line of ⁶⁰Co, and (16 k) MCA card with software Gamma (Gennie 2000) was used for Gamma acquisition and data analysis in our nuclear lab Jeddah university. The detector is boarded inside a thick lead shield (100 mm) with a fixed bottom and movable cover to reduce gamma ray background. The lead shield contained an inner concentric cylinder of copper (0.3 mm thick) to absorb X-ray generated in the lead. In order to determine the background distribution in the environment around the detector, an empty sealed beaker was counted in the same manner and in the same geometry as the samples. Each sample was counted for 28,800 s. The background was measured many times at the same conditions of the measurement. The system was calibrated for energy and efficiency (IAEA, 2018). 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. ²²⁶Ra activity concentrations were evaluated using gamma-ray lines of its related isotopes, ²¹⁴Pb (352 keV) and ²¹⁴Bi (609.31, 1120.27, 1764.49 keV). For ²³²Th, gamma ray lines of ²¹²Pb (238.6), Tl (583) KeV and ²²⁸Ac (338.42, 911.16, 964.6, 968.97 KeV) were used to measure the activity concentrations. The activity concentrations of ⁴⁰K were determined by using 1460.8 keV gamma ray line.

3.2. Atomic Absorption Spectroscopy (AAS)

(AAS) is a method often used in environmental studies (Haswell, 1991). The application of (AAS) to soil analysis has been discussed by (Ure, 1991). For this study, the samples were analysed by Atomic Absorption spectrometer model OPTIMA 4000 DV Series Perkin Elmer for Al, Ca, Fe, K, Mg and Bi % for the concentrations.

4. Calculations

4.1. Activity Concentrations

Determination of activity concentrations in Bq/kg dry weight was calculated from the following equation (Amrani & Tahtat, 2001).

$A=\frac{C}{m\beta \epsilon }$ (1)

where: C is the net peak area of specific gamma ray energy (count per second), m is the ass of the samples in (kg), β is the transition probability of gamma-decay, ε is the detector absolute efficiency at the specific gamma-ray energy. The measured dry weight activity concentrations of the gamma emitting radionuclides of the ²²⁶Ra series, ²³²Th series and ⁴⁰K in 16 sandstone samples are reported in Table 2 and Figure 2.

In region 1 (SS: 1 - 7), the measured activity concentration averages of ²²⁶Ra, ²³²Th and ⁴⁰K Bq/kg were 10.97 ± 0.43, 27.68 ± 0.37 and 64.56 ± 0.74 Bq/kg respectively. These values are less than the recommended reference Levels (50, 50 and 500) (UNSCEAR, 2000). In region 2 (SS 8 - 16), the average of measured activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K Bq/kg were 2465.49 ± 0.01, 2042.02 ± 0.10 and 2259.65 ± 0.64 Bq/kg respectively. These values are higher than the recommended reference Levels (50, 50 and 500) (UNSCEAR, 2000), the variations in the concentrations of the radioactivity in region 1 and region 2 depend upon the geological and geochemical conditions of the areas. These results are given in Table 2 and shown in Figure 2.

Table 2. The specific activity concentrations in Bq/kg in sand stone samples measured by Gamma spectroscopy.

Figure 2. The specific activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰ K in Bq/kg for sandstone samples in (Al Wajh, Al Ula) and (N. Al Ula, AzZabira) Sa. Arabia.

The variations in the concentrations of the radioactivity in sandstone samples depend upon the geological and geographical conditions of the area (UNSCEAR, 2000).

4.2. The Radiological Hazard Indices

Exposure to radiation has been defined in terms of the radium equivalent Ra_eq Bq/kg which is calculated from equation (Jose, Jorge, Cleomacio, Sueldo, & Romilton, 2005).

${\text{Ra}}_{\text{eq}}={\text{C}}_{\text{Ra}}+\left({\text{C}}_{\text{Th}}\times \text{1}.\text{43}\right)+\left({\text{C}}_{\text{K}}\times 0.0\text{77}\right)$ (2)

where: C_Ra, C_Th and C_K 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 The concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K were determined from the average concentrations of gamma ray lines of energies tabulated in Table 2.

⁴⁰K (Bq/kg) dry weight was calculated using the equation (Jose, Jorge, Cleomacio, Sueldo, & Romilton, 2005).

$\text{D}\left(\text{nGy}/\text{h}\right)=0.{\text{462C}}_{\text{Ra}}+0.\text{6}0{\text{4C}}_{\text{Th}}+0.0{\text{417C}}_{\text{K}}$ (3)

where: C_Ra, C_Th, and C_K are the specific activities (concentrations) of ²²⁶Ra, ²³²Th and ⁴⁰K in Bq/kg dry weight respectively. The annual effective dose equivalent D eff (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 (Krieger, 1981).

${\text{D}}_{\text{eff}}\left(\text{mSv}/\text{y}\right)=\text{D}\left(\text{nGy}/\text{h}\right)\times \text{8766h}\times 0.\text{7}\left(\text{Sv}/\text{Gy}\right)\times 0.\text{2}\times \text{1}{0}^{-\text{6}}$ (4)

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 (H_ex) is given by the equation (Krieger, 1981).

${\text{H}}_{\text{ex}}={\text{C}}_{\text{Ra}}/\text{37}0+{\text{C}}_{\text{Th}}/\text{259}+{\text{C}}_{\text{K}}/\text{481}0$ (5)

Internal exposure to radon and its progeny can be quantified using the index H_in, which was estimated by the following expression (Krieger, 1981). Results are given in Table 3 and Figure 3.

${\text{H}}_{\text{in}}={\text{C}}_{\text{Ra}}/\text{185}+{\text{C}}_{\text{Th}}/\text{259}+{\text{C}}_{\text{K}}/\text{481}0$ (6)

4.3. Results and Discussion

In region 1, (Al Wajh, Al Ula). Radium equivalent (Ra_eq Bq/Kg) average value in sandstone samples) is 121.13 Bq/Kg. This value of Ra_eq is lower than the limit of

Table 3. The radiation hazards, D (nGy/h), D_eff (mSv/y), H_ex and H_in for sandstone samples in sand stone samples.

Figure 3. D (nGy/h), D_eff (mSv/y), H_ex and H_in for sandstone samples.

370 Bq/kg recommend by (UNSCEAR, 2000). The Absorbed dose D (nGy/h), External hazard index (H_ex) and Internal index (H_in) average values are 27.22, 0.07 and 0.10, these values are lower than the limit 65, ≤1, ≤1 recommend by (UNSCEAR, 2000). For the Annual effective dose D_eff (mSv/y) average value is 11.75 (mSv/y) this value is higher than the limit 1 (mSv/y) recommend by (UNSCEAR, 2000). As shown in Table 3. In region 2, (N. Al Ula, AzZbira-wasia). Radium equivalent (Ra_eq Bq/Kg), the absorbed dose D (nGy/h), the Annual effective dose D_eff (mSv/y) and External hazard index (H_ex) and Internal index (H_in) average values are 5775.19 Bq/Kg, 1787.78 D (nGy/h), 846.58 D_eff (mSv/y), 11.57 (H_ex) and 15.64 (H_in), these values for all samples are higher than the limit 370, 65, 1, ≤1 and ≤1 recommend by (UNSCEAR, 2000). As shown in Table 3. In region 2, (N. Al Ula, AzZbira-wasia). Radium equivalent (Ra_eq Bq/Kg), the absorbed dose D (nGy/h), the Annual effective dose D_eff (mSv/y) and External hazard index (H_ex) and Internal index (H_in) average values are 5775.19 Bq/Kg, 1787.78 D (nGy/h), 846.58 D_eff (mSv/y), 11.57(H_ex) and 15.64 (H_in), these values for all samples are higher than the limit 370, 65, 1, ≤1 and ≤1 recommend by (UNSCEAR, 2000). As shown in Table 3. In region 1, the results of the radiological hazard, the values of Radium equivalent (Ra_eq), absorbed dose (D), the annual effective dose (D_eff), external (H_ex) and internal hazard of sandstone samples show that there is no health hazard. It is less threat to the environment and to the human health. In region 2, these values of sandstone samples are higher than the limit 370, 65, 1, ≤1, ≤1 recommend by (UNSCEAR, 2000). These calculated dose rates in sandstone samples put the users, dwellers and people around the area on radiological hazard. This study has refers to background guideline on the natural radioactivity levels in region 2 which will be database to the population.

4.4. Elements Concentrations (%) of Sandstones Measured by AAS

Sandstone is sedimentary rock that is mainly composed of quartz or feldspar (both silicates-SiO₂). Sandstones are resistant to weathering and are very much easy to work. This makes sandstone commonly used as building and tiling material (Mubiayi, 2013). Sex elements (Al, Ca, Fe, K, Mg, Bi) of (16) sandstone samples in two regions were measured by atomic absorption spectroscopy (AAS).

Sandstone may be any colour due to impurities within the minerals. Sandstone that contains more than 90% Silicon (Si) is called Quartz sandstone. When the sandstone contains more than 25% Silicon (Si), it is feldspar sandstone. If sandstone contains 5.0% Iron (Fe), it is Hematite and sandstone with 2.9% Aluminium (Al), it is Kaolinite Clay, when there is a significant with 11% others, it is Impurities (Mundra et al., 2020). Elemental analysis of Al, Ca, Fe, K, Mg %. detection limit lies in %. In region 1, the averages concentrations of Al, Ca, Fe, K, Mg, Bi % are 4.42, 0.41, 1.37, 0.04, 0.03 and ND % respectively. In region 2, the averages concentrations of Al, Ca, Fe, K, Mg % are 12.50%, 10.05%, 1.01%, 1.19% and 0.04% respectively. The colour of sandstone varies, depending on its (elemental composition). The results are listed in Table 4 and Table 5.

Table 4. Elements concentrations of Al, Ca, Fe, K, Mg, Bi (%) for Sandstone samples using AAS.

ND: Not Detected.

Table 5. Shows the measured concentrations of Al, Ca, Fe, K, Mg, (%), Elemental Composition and Sandstone and description for the samples.

The obtained results show that, in region 1 (Al Wajh and Al Ula), the major element in sandstone samples (except SS2 and SS5) is Aluminium (Al) with content more than 2.9%, the sandstones are Kaolinite-clay. SS2 content is more than (2.9%) and (5.9%) the sandstone is Kaolinite-clay and Hematite. SS5 contents are minor and trace elements. Sandstone description of sample 5 is impurities. In region 2 (North Al Ula and Az Zabira Wasis), the major element in all sandstone samples is Aluminium (Al) with content more than 2.9%, the sandstones are Kaolinite-clay, with elements are dominantly controlled by clay minerals and/or by minerals associated with clays during sedimentation (Boggs, 2006).

5. Conclusion

The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K and some chemical elements (Al, Ca, Fe, K, Mg) are measured in 16 sandstone samples used for construction purpose taken from two regions (Al Wajh, Al Ula) and (North Al Ula, Az Zabira Wasis), Saudi Arabia. Region 1, the activity concentrations of the three radionuclides in the samples are less than the worldwide values. The average values of Ra_eq Bq/Kg, Absorbed dose, D (nGy/h), External hazard index (H_ex) and Internal index (H_in) are lower than the worldwide values. The Annual effective dose D_eff (mSv/y) average value is higher than the worldwide value. This area is within normal radiation level, which leaves the sandstone radioactivity less of a threat to the environment and the human health. The obtained results for chemical elements show that, the major element content in samples (1, 3, 4, 6, 7) is Aluminium (Al), the sandstones are Kaolinite-clay. Sample 2 content major is (Al) and (Fe), the sandstone is Kaolinite-clay and Hematite. Sample 5 content is minor and trace elements. Sandstone description is impurities. Region 2, for all samples the measured activity concentrations and radiation hazards are higher than the worldwide values. The major element content in all samples is Aluminium (Al), the sandstones descriptions are Kaolinite-clay. The obtained data can provide general background levels of the natural radionuclides and chemical metals exposure to the population in the construction materials to evaluate the risks associated with the use of these materials.

Acknowledgements

The author is indebted to the Saudi Geological Survey (SGS) for supplying the geological samples, also thanks for their help during the measurements by Atomic Absorption Technique.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

[1]	Amrani, D., & Tahtat, M. (2001). Natural Radioactivity in Algerian Building Materials. Applied Radiation and Isotopes, 54, 687-689. https://doi.org/10.1016/S0969-8043(00)00304-3
[2]	Baxter, M. S. (1993). Environment Radioactivity: A Perspective on Industrial Contributions. Journal of Environmental Radioactivity, 2, 33-38.
[3]	Boggs, S. (2006). Principles of Sedimentology and Stratigraphy (4th ed., pp. 119-135). Pearson Prentice Hall.
[4]	Florou, H., & Kritidis, P. (1992). Gamma Radiation Measurements and Dose Rate in the Coastal Areas of a Volcanic Island, Aegean Sea, Greece. Radiation Report Dosimetry, 45, 277-279. https://doi.org/10.1093/rpd/45.1-4.277
[5]	Haswell, S. J. (1991). Atomic Absorption Spectrometry, Theory, Design and Applications. Analytical Spectroscopy Library.
[6]	IAEA, International Atomic Energy Agency (2018). IAEA Safety Glossary, Vienna.
[7]	Jose, A., Jorge, J., Cleomacio, M., Sueldo, V., & Romilton, S. (2005). Brazilian Archives of Biology and Technology Journal, 221-228.
[8]	Krieger, R. (1981). Radioactivity of Construction Materials. Betonwerk Fertigteil-Technik, 47, 468.
[9]	Mubiayi, M. P. (2013). Characterisation of Sandstones: Mineralogy and Physical Properties. In Proceedings of the World Congress on Engineering 2013. London.
[10]	Mundra, S., Agrawal, V., & Nagar, R. (2020). Sandstone Cutting Waste as Partial Replacement of Fine Aggregates in Concrete: A Mechanical Strength Perspective. Journal of Building Engineering, 32, 101534.
[11]	NCRP (1975). Background Radiation in the USA Recommendation of the National Council of Radiation and Measurements. Report No. 45.
[12]	Roger, J. J. W., & Adams, J. A. S. (1969). Uranium. In K. H. Wedephol (Ed.), Handbook of Geochemistry (Vol. 4). Springer.
[13]	Tzortzis, M. et al. (2003). Gamma-Ray Measurements of Naturally Occurring Radioactive Samples from Cyprus Characteristic Geological Rocks. Radiation Means, 37, 221-229. https://doi.org/10.1016/S1350-4487(03)00028-3
[14]	UNSCEAR (2000). United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly. Annex B: Exposures from Natural Radiation Sources, New York.
[15]	UNSCEAR (2008). Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation Report, New York.
[16]	Ure, A. M. (1991). Atomic Absorption and Flame Emission Spectrometry Analysis Modern Instrumental Techniques (2nd ed., pp. 20-21). Marcel Dekker.