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).

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 ⁶⁰Co. 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.

The concentration of ²²⁶Ra was determined from the average concentration of gamma-ray lines of energies 351.87 keV of ²¹⁴Pb and 609.31 keV of ²¹⁴Bi (since there is secular radioactivity equilibrium in²²⁶Ra series). Also, the concentration of ²³²Th, which it is in secular radioactivity equilibrium with its short half-life daughters, was determined from the average concentrations of ²²⁸Ac (with gamma-ray line 911.16 kev) and of ²⁰⁸Tl (with gamma-ray line 583.10 keV). The analysis of ⁴⁰K 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).

To assess the real activity level of ²²⁶Ra, ²³²Th and ⁴⁰K 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 ²²⁶Ra, 259 Bq/kg of ²³²Th and 4810 Bq/kg of ⁴⁰K 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 ²²⁶Ra, ²³²Th and ⁴⁰K, respectively.

The measured activity of ²²⁶Ra, ²³²Th and ⁴⁰K 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 ²²⁶Ra, ²³²Th and ⁴⁰K, 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] :

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 ²²⁶Ra,²³²Th and ⁴⁰K Respectively. The value of this index must be less than unity for the radiation hazard to be negligible.

The internal exposure to ²²²Rn 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 (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] :

where: C_Ra, C_Th and C_k are the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K 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 Figure 2(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 3 is a review of the chemical composition of each mineral and its description which reflects the con- dition of its formation [13] .

^*[14] .