A Comparison Study of Soil Samples from Sinai Province in Egypt by Using X-Ray Diffraction and Gamma-Ray Analysis

Ten soil samples from Jabal Al Qur, Wadi Baba, and Wadi Sieh in Sinai, Egypt, were analyzed by XRD spectroscopy. The XRD spectroscopy results indicate that the major, minor and trace constituents varied from one sample to another. Samples were also analyzed by HPGe gamma spectrometer to determine the activity concentration of U-238, Th-232 series and K-40. The concentrations for 238U ranged from 57.03 to 4220.41 Bq/kg with an average 1110.75 Bq/kg, for 232Th, ranged from 13.55 to130.46 Bq/kg with an average 71.85 Bq/Kg. The concentrations for 40K were in the range from 12.18 to 948.93 Bq/kg with an average value 457.09 Bq/kg. The average activity concentration values of 226Ra, 232Th, and 40K, in all the collected samples were higher than the world average. The radium equivalent (Req), absorbed dose rate (DR), the effective dose rate (Deff), and hazard indices resulted due to the natural radionuclides in soil are also calculated. The Results show that the study area is not safe for human and environments.


Introduction
Measurement of the concentrations of natural radionuclides in soil give information's on the natural radionuclide sources.Beck suggested that 50% -80% of the total gamma flux at the earth's surface arises from 40 K and 232 Th, 238 U series [1].Knowledge of the distribution of these radionuclides in the environment is essential in the sense of controlling radiation levels [2].Further, data on natural radiation are important for designing rules and regulations for radiation protection purposes [3].The variation in data for various locations is due to the differences in the geology of sampling sites [3].So several authors have studied the levels of natural background radiation by analysis of radionuclide concentration in soil samples, see e.g.: [4]- [9].These studies pointed out that the effective gamma radiation levels were generally in the range of 10 -200 nGyh −1 with a mean of 60 nGyh −1 [10].
X-Ray Diffraction (XRD) is a non-destructive analytical technique.When X-ray strikes on a crystal surface at an angle θ, a portion of the X-ray is scattered by a layer of atoms at the surface.Un-scattered X-ray penetrates to the second layer of atoms where again a fraction is scattered.The remaining X-ray passes to the third layer until the energy of the X-ray is dissipated completely.An X-ray detector measures the cumulative effect of the scattering beams.The X-ray appear to be reflected from the crystal only if the angle of incidence satisfies the condition of Bragg Equation, nλ = 2d hkl sinθ.The X-ray pattern shows the peaks at various angles of incidence [11].
The objectives of the present study are to determine some metal concentrations and measure the natural radioactivity levels of 226 Ra, 232 Th, and 40 K in the soil samples taken from selected places in Sinai region, Egypt, also to assess the radiological Hazard indices in air and to compare the results with international levels.Radionuclides 226 Ra, 232 Th and 40 K were measured with a well-type gamma-ray detector, and metal concentrations were determined by X-Ray diffraction, patterns were recorded using X'Pert PRO Powder X-Ray Diffraction with Cu Kα radiation (λ = 0.1542 nm), Ni-filter and general area detector.The data generated in this study provide baseline values of natural radioactivity in Sinai soils and may be useful for authorities in the implementation of radiation protection standards for the general population in the country as well as to plan and conduct further studies on this issue.

Study Area
Sinai can be divided into three areas: The northern region consists of sand dunes and fossil beaches formed by the changing levels of the Mediterranean Sea during the glacial periods two million years ago.The landscape is flat and uniform, interrupted by sand and limestone hills.The central area with limestone dating from the Tertiary Period is the highlands extend towards the south.The third area consists of granite and volcanic rocks.Limestone and sandstone sediments are replaced by granite and basalt.Both rocks are produced by volcanic activity on the bottom of the ocean.Ten soil samples were collected from different areas of Sinai; Jabal Al Qur (28˚49'46.06''N-33˚17'45.41''E) is located inland south-east of Sinai and consists of granite and volcanic rocks, Limestone and sandstone sediments.Wadi Baba (28˚58'30.80''N-33˚17'31.47''E) is a low altitude system located inland south-east of Wadi Gharandel.The system consists of several smaller interconnecting wadis with gravel beds and high rise sandstone cliffs either side.Wadi Sieh (29˚03'27.28''N-33˚26'14.84''E) is located further inland north-east of Wadi Baba; the wadi has a sandy bed with sandstone canyons rising either side, as shown in Figure 1, (www.bedawi.com/Sinai_EN.html).

Sample Collection, Preparation and Measuring Methods
Ten soil samples were collected from different areas of Sinai; Jabal Al Qur, Wadi Baba and Wadi Sieh.These collected samples have different Descriptions as shown in Table 1.Samples were grounded and passed through a 1 mm sieve and dried to 95˚C for 24 hours in order not to lose the volatile polonium or cesium.Ten gm of the dried samples were analyzed by XRD model X'Pert PRO powder diffract meter equipped with Cu anode, for the chemical and mineral composition.The X-ray source used in this research has a wavelength of 1.540562 Å.The diffract grams were recorded in the 2θ range of 0.5˚ -70˚ with step size of 0.02 Å and a step time of 0.60 s.For radiometric analysis, the dried fine grained samples were packed in polyethylene Marinelli beaker for gamma spectroscopy and then stored for four weeks to reach secular equilibrium between radium-226 and thorium-232 and their progenies.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 60 Co.Genie 2000 basic spectroscopic software was installed in the computer for data acquisition and analysis.The system was calibrated for energy and absolute efficiency.The measurements were done for a time period of 82,800 sec.An empty polyethylene Marinelli beaker was placed in the detection system for the same time period of measurement, in order to collect the background count rates.Then, each sample was measured during the same accumulating time.

Activity Concentrations
The concentration of 226 Ra was determined from the average concentration of gamma-ray lines of energies 351.87 keV of 214 Pb and 609.31 keV of 214 Bi (since there is secular radioactivity equilibrium in 226 Ra series).Also, the concentration of 232 Th, which it is in secular radioactivity equilibrium with its short half-life daughters, was determined from the average concentrations of 228 Ac (with gamma-ray line 911.16kev) and of 208 Tl (with gamma-ray line 583.10 keV).The analysis of 40 K concentrations was based on its single peak in the spectrum at energy 1460.80 kev.The activity concentrations "As" of the natural radionuclides in the measured samples were computed using the following relation [12]: ( ) where: Ca is the net gamma counting rate (counts per second), ε the detector efficiency of the specific γ-ray, Pr the absolute transition probability of Gamma-decay and Ms the mass of the sample (kg).

Radiological Hazard Indices Radium Equivalent Activity Raeq (Bq/kg)
To assess the real activity level of 226 Ra, 232 Th and 40 K in soil, a common radiological index has been defined in terms of radium equivalent activity (Ra eq ) in Bq/kg can be used, provides a very useful guideline in regulating the safety standards in radiation protection for a human population.The index was calculated through the following formula is based on the assumption that 370 Bq/kg of 226 Ra, 259 Bq/kg of 232 Th and 4810 Bq/kg of 40 K produce the same gamma-ray dose rate [10]: ( ) where: C Ra , C Th and C K are the specific activities (Bq/kg dry weight) of 226 Ra, 232 Th and 40 K, respectively.

Absorbed Dose Rate and Annual Effective Dose
The measured activity of 226 Ra, 232 Th and 40 K were converted into doses by applying the factors 0.4551, 0.5835 and 0.0429(nGyh −1 /Bqkg −1 ) for radium, thorium and potassium, respectively.These factors were used to calculate the total absorbed gamma dose rate in air at 1 m above the ground level using the following equation [10]: where: C Ra , C Th and C K are the activity concentrations (Bq/kg) of 226 Ra, 232 Th and 40 K, respectively.Annual estimated average effective dose equivalent received by a member is calculated using a conversion factor of 0.7 Sv/Gy, which is used to convert the absorbed dose rate to annual effective dose with an outdoor occupancy of 20% [10]: D mSv y D nGy h 8760 h y 0.7 Sv Gy 0.

External Hazard Index and Internal Hazard Index
In the literature a number of criterion formulae have been derived over the years to assess the radiation dose rate due to exposure to gamma radiation from the natural radionuclides contained in soil.To limit the annual external gamma-ray dose to 1.5 Gy for the samples under investigation [10], the external hazard index (H ex ) is given by the equation: where: C Ra , C Th and C K are the activity concentrations in Bq/kg of 226 Ra, 232 Th and 40 K Respectively.The value of this index must be less than unity for the radiation hazard to be negligible.The internal exposure to 222 Rn and its radioactive progeny is controlled by the internal hazard index (H in ) [10], which is given by the equation: where: C denotes the respective specific activity in Bq/kg, for the safety, H in should be less than unity.

Representative Level Index (Iγr)
Representative level index (I γr ) is used to estimate the level of γ-radiation hazard associated with the natural radionuclides in specific building materials, is defined as [4] [10]:   3 is a review of the chemical composition of each mineral and its description which reflects the condition of its formation [13].
Thorium(V) sulfide-Th2S5 An inorganic chemical compound composed of two thorium atom ionically bonded to five atoms of sulfur.
Thorium-Th Chemical element and radioactive actinide metal.
Sodium Beryllium Thorium Fluoride-NaBeTh3F15 An inorganic chemical compound with one Na, and Be , three Th atom ionically bonded to fifteen F.
Uranium Fluorid-UF4 UF4 is a solid composed of particles with a texture and soluble in water.
Uranium-U Uranium is heavy metal.In nature, uranium is found as an xide.dices values are much higher than the corresponding world average.• Precautions and recommendations should be taken into consideration for high levels of radioactivity concentrations in these samples especially when people may inhabit in these areas.I recommend that this study to be taken as a base line for any future studies in this area.

Figure 1 .
Figure 1.Location map of the collected samples.
Ra , C Th and C k are the activity concentrations of 226 Ra, 232 Th and 40 K in Bq/k, respectively.

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.In the present study, the XRD results indicate that the main major, minor and trace constituents varied from one sample to another, as shown in Figure2(a), Figure 2(b), and in Table 2.The major element defines the samples and has the highest concentrations.In sample soil1, Calcium Thorium Phosphate is the major in XRD spectrum Figure 2(a), Figure 2(b).While, trace elements occur in small concentrations (usually measured in ppm).They do not change the essence of what a material is and minor elements are in between major and trace elements.XRD spectrum Figure 2(a), Figure 2(b), shows that Thorium (V) sulfide and Thorium are minor and trace elements in sample 1 respectively.Table

Table 1 .
Description of collected samples.
Description Sample CodeSandy dolostone, medium hard to hard, grey.Soil 1 Siltstone with ferruginous Shale, mainly red and grey.

Table 2 .
The compound Name of mineral constituents of 10 samples analyzed by XRD spectrometer. [14]].

Table 3 .
The Compound name/Chemical composition and description.

Table 4 .
The specific radioactive concentrations in Bq/kg, dry weight for Sinai samples.

Table 5 .
The radium equivalent Ra eq (Bq/kg), Dose rate D R outdoor (nGy/h), annual effective Dose (mSv/y and hazard indices for the samples.