Assessment of Radiological Hazards of Sedimentary, Igneous and Sediments Natural Rocks

Gamma-ray spectroscopy based on a 100% efficiency hyper-pure germanium detector was used to evaluate the activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K natural radionuclides in sedimentary, conglomerate, igneous and sedi-ments rock samples collected from four different locations in Eastern desert in Egypt. The obtained activity concentrations are used to evaluate the radi-ological hazards indices, absorbed dose rate, annual effective dose equivalent in air, radium equivalent, external and internal hazard index, radiation level index, annual gonadal dose equivalent, excess lifetime cancer risk and expo-sure rate. The results show that 1) the absorbed dose rate depends on the rock type, 2) the annual effective dose equivalent in air in 71% of sample below 20 mSvy ^-1 (permissible limit for workers), 3) the conglomerate rocks show low radioactivity level, 4) sedimentary rocks are rich in radium while igneous rocks are rich in thorium and the sediments rocks are rich in both radium and thorium.

• Gamma Spectrometry
• Radiological Hazard Indices
• NORM
• Sedimentary
• Conglomerate
• Igneous
• Sediments

1. Introduction

Naturally occurring radioactive elements like uranium (²³⁸U), thorium (²³²Th), and potassium (⁴⁰K), along with their decay by-products such as radium (²²⁶Ra) and radon (^220,222Rn), are examples of NORM. These elements have always been present in the Earth’s crust and atmosphere and their concentrations may vary from one place such as places near mining activities to another. The designation of NORM serves the purpose of delineating “natural radioactivity” from anthropogenic sources of radioactive material, such as those utilized in nuclear medicine and in industry [1] . These radionuclides have different sources, including the earth’s crust, rocks, soils, plants, water, sediments, minerals, and air [2] .

Uranium, thorium, and potassium-40 are significant sources of radiation, which can be found in various types of rocks, particularly in igneous and sedimentary rocks. All building materials are mostly composed of rock and soil containing ²³⁸U and ²³²Th decay series and ⁴⁰K. These natural radionuclides may cause both external exposure due to their direct gamma radiation and internal exposure from radon gas. If inhaled for an extended period, alpha particles can become trapped in the lungs, causing irritation to the cells of mucous membranes, and potentially leading to a high risk of lung cancer. There has been increased trend of public worldwide in using ceramic tile, stone, marble, granite, etc., due to their polished surface, decorative and different attractive colours, as building materials. The ceramic tiles are generally made of a mixture of different raw materials including clays, quartz materials and feldspar. The marble, on the other hand, is a metamorphic rock composed of recrystallized carbonate minerals. It is extracted from the mountains and after mining it is transported to marble factories in various cities. Granite is the best-known igneous rock. It is composed mainly of quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. A common opacifying constituent of glazes, applied to these materials, is zircon that may cause natural radioactivity concentration significantly higher than the average values for building materials. Hazard parameters, play a significant role to assess the potential radiation hazards posed by these building materials [3] .

Workers engaged in anthropogenic activities, particularly in mining, face a significant risk of radiation exposure from Naturally Occurring Radioactive Materials (NORM). These materials are often present in various geological formations and can be released into the environment during mining processes, leaving behind contamination that poses potential health hazards. Without proper monitoring and containment measures, the environment can become laden with substances that emit radiation, presenting remote but significant risks to both workers and surrounding communities. Effective management strategies are imperative to mitigate these risks and ensure the safety of those involved in anthropogenic activities [4] .

Radium (²²⁶Ra) nuclide is commonly chosen in studies due to its gamma rays emitted by its two main daughters, ²¹⁴Pb and ²¹⁴Bi. These gamma rays contribute to 98% of the external dose from all nuclides in the ²³⁸U series. It is crucial to determine the baseline of natural radiation and radioactivity so that man-made contamination can be contrasted with natural radioactivity. This makes it possible to detect contamination instantly, and thus appropriate measures against the risk to human health and the environment from radiation can be taken. For the above reasons, the worldwide interest in natural radiation exposure has received particular attention and has led to extensive surveys in many countries. This reflects the activity concentration of primordial radionuclides in the soil. Approximately 95% of the world’s population is assumed to live in areas of normal background radiation, with outdoor exposure ranging from 24 to 160 nGy∙h⁻¹ [5] . Thus, environmental studies to determine the levels of radiation from natural sources are very important. The external absorbed dose rate in air at 1 m above ground level and the annual effective dose are commonly used to estimate exposure to the population. Knowledge of radionuclide distribution is needed to understand natural environmental radioactivity and the associated external exposure resulting from gamma radiation, which varies based on geological and geographical conditions.

The present study could serve as baseline data for populated areas near the studied locations, with the aim of assessing the risk caused to workers engaged in anthropogenic activities, particularly in mining by outdoor exposure to terrestrial radiation, in addition to guiding decision-makers in solving some natural environmental problems that may be found anywhere in the world. Therefore, data obtained from such studies may be used locally to establish whether and where controls are needed. Furthermore, the results would enrich the world’s data bank, which is important for evaluating the worldwide average values of radiometric and dosimetry quantities.

The goal of the current study is to measure the naturally occurring radioactivity levels of radium-226, thorium-232, and potassium-40 in rocks some (sedimentary, conglomerate, igneous, and sediments) samples collected from four various sites in Eastern desert in Egypt. The study was conducted by using an advanced gamma spectrometer using 100% HPGe detector. The obtained information might be valuable for environmental radiation protection studies and can be used to estimate population (workers) exposure to radiation. The study evaluate and compare the absorbed dose rates D (nGy∙h⁻¹) and associated radiological effect indices such as Annual Effective Dose Equivalent AEDE (mSv∙y⁻¹), Radium Equivalent Activity Ra_eq (Bq∙kg⁻¹), Internal and External Hazard Index (H_ex and H_in), Radiation Level Index (I_γ), Annual Gonad Dose Equivalent AGDE (μSv∙y⁻¹), Excess lifetime cancer risk ELCR (mSv∙y⁻¹) and Exposure rate ER (μRh⁻¹) with published average values and accepted limits to assess the level of natural radioactivity and the associated radiological hazards to human health. In this work only the hazards due external exposure will be considered since the occupancy of such remote area is limited to the workers who might be present.

2. Materials and Methods

2.1. Sample Collection and Preparation

Twenty-one samples were collected according to its type from four different locations in Eastern desert in Egypt. This study includes ten samples of sedimentary, two of conglomerate, seven of igneous and two of sediments rocks.

The collected samples were dried at 105˚C temperature for 24 hours to eliminate the moisture content. Then crushed and sieved through 200 mesh size. The samples were weighted and placed in polyethylene beaker of 250 cm³ volume. The beakers were completely sealed for one month to allow secular equilibrium between ²²²Rn and its daughters.

2.2. Sample Counting

In the present study, the used gamma-ray spectrometer consists of 100% relative efficiency n-type hyper pure germanium detector (HPGe) connected to X-cooler-III electric cooling system. The X-cooler cooling system is used to assure permanent cooling facility of the detector. The detector is surrounded by 10 cm thickness of reprocessed high-performance and low-background lead shield cylinder. A graded liner of copper and tin layers is provided for the suppression of lead x-rays. The detection range is between 10 keV and 10 MeV. The detector has a resolution (FWHM) of 1.9 at 1332 keV γ-ray line of ⁶⁰Co. The detector is connected to digital spectrometer DSPC-pro which has high voltage, advanced spectroscopy amplifier and 16 k multichannel analyser. The acquisition system and analysis of spectra are controlled by gamma-Vision software [6] . The energy and efficiency calibration were performed using standard soil matrix source [7] . Angle-3 software was used to generate efficiency curves corrected for volume and density which ranged between 0.6 and 2.6 g∙cm⁻³ [8] . The high activity samples were counted during a period of 6 hours (live time) while, the low activity samples were counted for 24 hours live time. The environmental gamma-rays background at the laboratory site has been determined using an empty container that is counted in the same condition as the samples. The analysis of the collected samples has been carried out using Gamma Vision software [6] . The obtained data have been corrected for density and self-absorption effect of gamma ray, which depends on the density of the sample [9] .

2.3. Calculation of Radionuclides Concentration

The activity concentration (A) in Bq∙kg⁻¹ of each radionuclide in the samples was determined by using Equation (1).

A = C P S W ∗ I ∗ ε (1)

where CPS is the net gamma counts per second corrected for background, W is the dry mass of the sample (kg), I is the absolute transition probability of gamma-ray and e is the detector efficiency at energy E [10] .

2.4. Radiological Hazard Indices

2.4.1. Absorbed Dose Rate D

A direct connection between radioactivity concentrations of natural radionuclides and their exposure is known as the absorbed dose rate in the air at 1 meter above the ground surface. The mean activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K (Bq∙kg⁻¹) in the studied samples are used to calculate the absorbed dose rate using Equation (2)

D ( nGy ⋅ h − 1 ) = 0.462 A R a + 0.604 A T h + 0.0417 A K (2)

where D is the absorbed dose rate in nGy∙h⁻¹, A_Ra, A_Th and A_K are the activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K, respectively [11] [12] .

2.4.2. Annual Effective Dose Equivalent (AEDE)

The absorbed dose rate in air at 1 meter above the ground surface does not directly provide the radiological risk to which an individual is exposed. The absorbed dose can be considered in terms of the annual effective dose equivalent from indoor terrestrial gamma radiation which is converted from the absorbed dose by considering two factors, namely the conversion coefficient from absorbed dose in air to effective dose (0.7 Sv∙Gy⁻¹) and the outdoor occupancy factor (0.2). The annual effective dose equivalent can be estimated using the following equation.

A E D E ( mSv ⋅ y − 1 ) = D ( nGy ⋅ h − 1 ) × 0.2 × 0.7 ( Sv ⋅ Gy − 1 ) × 10 − 6 (3)

2.4.3. Radium Equivalent Activity (Ra eq )

A common radiological index referred to radium equivalent was used in this study to evaluate the actual activity level of ²²⁶Ra, ²³²Th and ⁴⁰K in the samples and the radiation hazards associated with these radionuclides. This is as results of the fact that distribution of natural radionuclide in the samples under investigation is not uniform and is assumed that 370 Bq∙kg⁻¹ of Ra, 259 Bq∙kg⁻¹ of Th and 4810 Bq∙kg⁻¹ of K produce an equal gamma-ray dose. This index is usually known as radium equivalent activity [13] and given by Equation (4).

R a e q = A R a + 1.34 A T h + 0.077 A T h (4)

2.4.4. Internal and External Hazard Index (H ex and H in )

The existence of natural radionuclides causes the emission of γ-ray in the environment. The internal hazard index (H_in) and the external hazard index (H_ex) are used to estimate the biological hazard of the natural gamma radiation [14] . Internal radiation explained as the radiation which occurs if a human consuming something that emits radiation, and then the radiation entered and radiated to the human’s body directly and resulted in radiological hazards. The internal hazard index, H_in is given by Equation (5).

H i n = A R a 185 + A T h 259 + A K 4810 (5)

where A_Ra, A_Th and A_K are defined in Equation (2). For the safe use as building materials H_in should be less than unity [15] .

External radiation exposure due to ²²⁶Ra, ²³²Th and ⁴⁰K is external assessed by external hazard index, H_ex [16] . Its level is calculated by the Equation (6)

H e x = A R a 370 + A T h 259 + A K 4810 (6)

For the safe use of samples, Hex should be less than unity [17] .

2.4.5. Radiation Level Index (𝚰 𝛾 )

This index can be used to estimate the level of γ-radiation hazard associated with the natural radionuclides is given by Equation (7).

I γ = A R a 150 + A T h 100 + A K 1500 (7)

For the safe use of samples, I_γshould be less than unity [18] .

2.4.6. Annual Gonadal Dose Equivalent

The bone marrow and bone surface cells are considered as organs of interest therefore, the Annual Gonadal Dose Equivalent (AGDE) was introduced to take care of the specific activities arising from ²²⁶Ra, ²³²Th and ⁴⁰K. The AGDE was calculated using Equation (8) [1] .

A G D E ( mSv ⋅ y − 1 ) = 3.09 A R a + 4.18 A T h + 0.31 A K (8)

2.4.7. Excess Lifetime Cancer Risk (ELCR)

The excess lifetime cancer risk (ELCR) for outdoor exposure, gives the probability for an individual to develop cancer over a lifetime at a given exposure. This was calculated using Equation (9).

E L C R ( mSv ⋅ y − 1 ) = A E D E × L E × R F (9)

where AGDE is the annual effective dose equivalent, LE life expectancy (66 years) and RF is risk factor (Sv⁻¹), which is 0.05 [19]

2.4.8. Exposure Rate (ER)

The exposure rate was calculated using Equation (10) [20]

E R ( μ Rh − 1 ) = 1.9 A R a + 2.28 A T h + 0.314 A K (10)

3. Results and Discussion

Activity Concentrations

Table 1 presents the activity concentration of natural radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K in samples collected from various locations under investigation. Additionally, it includes the mean values of these radionuclides' activity concentrations in samples categorized into Sedimentary, Conglomerate, Igneous, and Sediments groups of rocks. Previous studies conducted in Egypt and from the international literature are also included in this table for comparison purpose. Such comparisons offer valuable insights into variations and similarities in natural radioactivity levels across various geological formations and geographical regions, contributing to a comprehensive understanding of radiation exposure risks associated with specific rock types and locations.

However, the concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K obtained in the present work are comparable to those published by [21] in pegmatites rocks in other locations in the Egyptian desert. Nevertheless, they are significantly higher compared to the activity concentration of some commercial Egyptian granite samples used as a building material and published by reference [22] .

The mean activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K in sedimentary, igneous, and sediment samples obtained in the present work, as well as the mean activity concentration of pegmatite rock samples [21] from Egyptian deserts, are significantly higher compared to the activity concentrations for the investigated radionuclides reported in the literature from various countries around the world as shown in Table 1.

The analysis of Table 1 shows that the mean activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in all studied samples are found to be 18508.49 ± 148.93, 9614.53 ± 27.94 and 2469.35 ± 75.72 Bq∙kg⁻¹, respectively. These values are higher than world average radioactivity levels for building materials which are 35, 30 and 400 Bq∙kg⁻¹, respectively [23] .

In the sedimentary rock samples, the activity concentrations of ²²⁶Ra ranged between 194.03 ± 3.32 (10H) and 142245.40 ± 1982.97 (9H) Bq∙kg⁻¹ with mean value of 31790.01 ± 247.60 Bq∙kg⁻¹, while the concentration of ²³²Th ranged between 10.33 ± 0.85 (2H) and 1842.86 ± 143.86 (9H) Bq∙kg⁻¹ with mean value of 225.73 ± 17.34 Bq∙kg⁻¹. Finally, activity concentrations of ⁴⁰K varied between 100.15 ± 4.38 (7H) and 21733.77 ± 916.25 (9H) Bq∙kg⁻¹ with mean value of 2482.65 ± 108.79 Bq∙kg⁻¹.

In the igneous rock samples in the one found that ²²⁶Ra activity concentrations varied between 140.06 ± 2.82 (13H) and 22263.65 ± 38.99 (16H) Bq∙kg⁻¹ with mean value of 5125.7 ± 15.72 Bq∙kg⁻¹. The highest value of ²³²Th is 9278.23 ± 10.6 (18H) Bq∙kg⁻¹ and the lowest value found to be 106.08 ± 1.08 (13H) Bq∙kg⁻¹ and the mean value is 4041.04 ± 5.88 Bq∙kg⁻¹. As for ⁴⁰K the activity concentrations ranged between 298.35 ± 4.26 (17H) and 2052.18 ± 18.31 (18H) Bq∙kg⁻¹ with mean value of 1447.87 ± 11.87 Bq∙kg⁻¹.

In sediments samples, the ²²⁶Ra activity concentration ranges between 6143.89 ± 155.16 (21H) and 10163.53 ± 210.93 (20H) Bq∙kg⁻¹ with mean value of 8153.71 ± 183.05 Bq∙kg⁻¹ while, the activity concentration of ²³²Th ranges between 41878.96 ± 97.31 (21H) and 115234.3 ± 203.11 (20H) Bq∙kg⁻¹ with mean value of 78556.68 ± 150.21 Bq∙kg⁻¹ and ⁴⁰K activity concentration ranges between 3698.3 ± 112.41 (21H) and 9582.31 ± 175.88 (20H) Bq∙kg⁻¹ with mean value of 6640.31 ± 144.15 Bq∙kg⁻¹.

The activity concentration of ²²⁶Ra in conglomerate rock samples, is below the detection limit in sample (12H) and 82.39 ± 17.15 Bq∙kg⁻¹ in sample (11H), while ²³²Th activity concentration ranges between 4037.15 ± 39.56 and 4632.68 ± 43.86 with mean value of 4334.92 ± 41.71 Bq∙kg⁻¹. ⁴⁰K activity concentration ranges between 874.94 ± 47.46 and 1144.82 ± 55.17 Bq∙kg⁻¹ with mean value of 1009.88 ± 51.32 Bq∙kg⁻¹. The highest value of ²²⁶Ra activity concentrations was found in the sedimentary rock samples (9H) while the lowest activity concentrations of ²²⁶Ra was found in the conglomerate rock samples (12H). These results show that the location where sedimentary rocks had been collected are characterized by high concentration of ²³⁸U and low concentration of ²³²Th as concluded by [24] .

Table 1

The specific activities (Bq∙kg −1 ) of 226 Ra, 232 Th and 40 K for the studied samples

Sample	Sample type	226Ra (Bq∙kg −1)	232Th (Bq∙kg −1)		40K (Bq∙kg −1)
1H 2H 3H 4H 5H 6H 7H 8H 9H 10H		63634.66 ± 117.03 5462.52 ± 13.74 41226.26 ± 115.78 247.32 ± 2.74 204.52 ± 2.66 39478.03 ± 139.65 6455.06 ± 14.68 18752.33 ± 83.43 142245.40 ± 1982.97 194.03 ± 3.32	67.26 ± 6.92 10.33 ± 0.85 58.31 ± 7.97 59.46 ± 0.73 47.43 ± 0.66 102.39 ± 7.34 16.35 ± 1.36 18.10 ± 3.00 1842.86 ± 143.86 34.76 ± 0.71	560.33 ± 34.83 118.83 ± 6.69 334.52 ± 32.72 348.02 ± 3.75 293.01 ± 3.41 882.00 ± 59.25 100.15 ± 4.38 142.43 ± 22.16 21733.77 ± 916.25 313.47 ± 4.41
Mean	Sedimentary	31790.01 ± 247.60	225.73 ± 17.34		2482.65 ± 108.79
11H 12H		82.39 ± 17.15** ---**	4632.68 ± 43.86 4037.15 ± 39.56		1144.82 ± 55.17 874.94 ± 47.46
Mean	Conglomerate	82.39 ± 17.15	4334.92 ± 41.71		1009.88 ± 51.32
13H 14H 15H 16H 17H 18H 19H		140.06 ± 2.82 1498.50 ± 13.71 1679.59 ± 11.52 22263.65 ± 38.99 698.70 ± 5.77 7761.36 ± 25.36 1838.03 ± 11.88	106.08 ± 1.08 8740.40 ± 8.37 5668.61 ± 6.80 1753.61 ± 6.72 587.54 ± 2.09 9278.23 ± 10.60 2152.81 ± 5.48		1501.88 ± 8.23 1880.67 ± 12.20 1724.92 ± 10.94 2003.49 ± 19.74 298.35 ± 4.26 2052.18 ± 18.31 673.61 ± 9.38
mean	Igneous	5125.7 ± 15.72	4041.04 ± 5.88		1447.87 ± 11.87
20H 21H		10163.53 ± 210.93 6143.89 ± 155.16	115234.39 ± 203.11 41878.96 ± 97.31		9582.31 ± 175.88 3698.30 ± 112.41
Mean	Sediments	8153.71 ± 183.05	78556.68 ± 150.21		6640.31 ± 144.15
Previous works	Greek [25]	74	85		881
	India [26]	25.88	42.82		560.6
	Iran [27]	77.4	44.5		1017.2
	Jordan [28]	41.5	58.4		897
	Nigeria [29]	63.29	226.6		832.5
	Palestine [30]	71	82		780
	Spain [31]	84	42		1138
	S. Arbia [32]	28.8	34.8		665.08
	Turkey [33]	80	101		974
	Egypt [22]	137	82		1082
	Egypt [21]	13176.00	11883.00		1573.00
	Present study	18508.49 ± 148.93	9614.53 ± 27.94		2469.35 ± 75.72

**Below the detection limits.

The obtained activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K are used to calculate different hazards indices using Equations (2)-(10). The deduced values of D (nGy∙h⁻¹), AEDE in air (mSv∙y⁻¹), Ra_eq (Bq Kg⁻¹), H_ex, H_in, I_γ, AGDE (mSv∙y⁻¹), ELCR (mSv∙y⁻¹) and ER (mR∙h⁻¹) hazards indices are given in Table 2 compared to worldwide limits for building materials (WL).

In Figure 1 the absorbed dose rate (D) is plotted alongside the radium equivalent (Ra_eq) and exposure rate (ER) calculated for each sample. The results obtained reveal that the Ra_eq values for all samples exceed the permissible maximum value of 370 Bq∙kg⁻¹, except for samples 4H, 5H, and 10H, which are sedimentary rocks. However, Table 3 presents the minimum, maximum, and mean values of (D), (Ra_eq), and (ER) for sedimentary, igneous, conglomerate, and sediments rock samples. It is evident from the table that the mean absorbed dose rate in sediments rocks is approximately three times greater than that in sedimentary

Table 2

The radiation hazards indices calculated for different samples

Sample No.	D (nGy∙h‑1)	AEDE in air (mSv∙y‑1)	Raeq (Bq∙kg−1)	Hex	Hin	Iγ	AGDE (mSv∙y−1)	ELCR (mSv∙y−1)	ER (mR/h)
1H	29463.20	36.13	63773.84	172.36	344.35	425.28	197.09	119.24	121.25
2H	2534.88	3.11	5486.42	14.83	29.59	36.60	16.96	10.26	10.44
3H	19095.70	23.42	41335.29	111.72	223.14	275.65	127.74	77.28	78.57
4H	164.69	0.20	359.03	0.97	1.64	2.48	1.12	0.67	0.71
5H	135.36	0.17	294.82	0.80	1.35	2.03	0.92	0.55	0.59
6H	18337.47	22.49	39692.14	107.28	213.97	264.80	122.69	74.21	75.52
7H	2996.29	3.67	6486.12	17.53	34.98	43.26	20.05	12.13	12.33
8H	8680.45	10.65	18789.14	50.78	101.46	125.29	58.07	35.13	35.72
9H	67736.76	83.07	146549.89	396.08	780.53	981.22	454.07	274.14	281.29
10H	123.71	0.15	267.80	0.72	1.25	1.85	0.84	0.50	0.54
11H	2883.94	3.54	6788.57	18.35	18.57	47.64	19.98	11.67	11.08
12H	2474.92	3.04	5834.66	15.77	15.77	40.95	17.15	10.02	9.48
13H	191.41	0.23	407.13	1.10	1.48	3.00	1.35	0.77	0.98
14H	6049.93	7.42	14129.45	38.19	42.24	98.65	41.76	24.48	23.37
15H	4271.74	5.24	9910.29	26.78	31.32	69.03	29.43	17.29	16.66
16H	11428.53	14.02	24922.92	67.36	127.53	167.30	76.76	46.25	46.93
17H	690.12	0.85	1561.00	4.22	6.11	10.73	4.71	2.79	2.76
18H	9275.38	11.38	21173.84	57.23	78.20	145.89	63.41	37.54	36.55
19H	2177.55	2.67	4965.28	13.42	18.39	34.23	14.89	8.81	8.61
20H	74696.71	91.61	175521.19	474.38	501.85	1226.49	516.10	302.31	285.05
21H	28287.59	34.69	66255.46	179.07	195.67	462.21	195.2	114.48	108.32
(WL)	59	20	370	1	1	1	0.298	2.9E-4	0.600

Table 3

Minimum, maximum, and mean value of the absorbed dose, radium equivalent and exposure rate in sedimentary (I), igneous (II), conglomerate (III) and sediments (IV) rocks

Sample type	D (μGy/h)			Raeq (k Bq∙kg −1)			ER (mR/h)
	min	max	mean	min	max	mean	min	max	mean
I	0.16	67.74	16.57	0.27	146.55	32.30	0.55	281.29	61.69
II	0.19	11.43	4.87	1.56	24.92	12.78	2.76	46.93	22.48
III	2.47	2.88	2.68	5.83	6.79	6.31	9.48	11.08	10.28
IV	28.29	74.69	51.49	66.23	175.52	120.89	108.32	285.05	196.69

rocks, surpassing that in igneous rocks by a factor of 10.6, and exceeding that in conglomerate rocks by 19.2 times. The variation of the mean value of Ra_eq and exposure rate for each group of sample’s number is shown in Figure 2.

One can conclude that sediments rocks contain high concentration of Th and U causes much more hazards effect than the igneous rocks which is trich in Th and sedimentary rocks which is rich in U. However, the conglomerate rock samples show the lowest hazards effect among all the tested samples.

In Table 4, the mean values of H_in, H_ex, and AEDE are provided for each category of rocks while, Figure 3 illustrates the variation of the mean values of H_in, H_ex and AEDE for sedimentary, igneous, conglomerate and sediments groups of rock’s type. Analysis of the data reveals that the values of H_ex for samples 4H, 5H, and 10H (sedimentary rock), as well as sample 13H (igneous rock), fall within the permissible value of 1. However, it is noteworthy that H_ex exceeds the permissible limit for all other samples, indicating significant variations in radiation levels across the different rock categories.

In Figure 4, a linear relationship is depicted between the annual gonadal dose equivalent, excess lifetime cancer risk, radiation level index, and annual effective dose. The linearity coefficients corresponding to these relationships are determined to be 5.555, 12.651, and 3.3, respectively. From Equation 9, the risk factor (RF) can be inferred from the slope of the excess lifetime cancer risk (ELCR) line, yielding a value of 0.05, assuming a lifespan (LF) of 66 years, which is consistent with previous findings [19] .

Table 4

Minimum, maximum, and mean value of the internal, external hazard index and annual effective dose equivalent for sedimentary (I), igneous (II), conglomerate (III) and sediments (IV) rocks

Sample Type	Hin			Hex			AEDE (mSv/y)
	min	max	mean	min	max	mean	min	max	mean
I	1.25	780.52	173.22	0.73	396.08	87.31	0.15	83.07	18.30
II	1.47	127.53	43.61	1.10	67.36	29.75	0.23	14.01	5.97
III	15.75	18.65	17.17	15.77	18.34	17.06	3.04	3.53	3.28
IV	195.67	501.85	348.76	179.07	474.38	326.73	34.69	91.60	63.14

4. Conclusion

Twenty-one rock samples, including sedimentary, igneous, conglomerate, and sediments were collected from four distinct locations in Egypt’s Eastern desert. Utilizing a high-performance gamma spectrometer equipped with a 100% efficiency hyper pure germanium detector, electric cooling, digital electronic systems, and a 16 k channels Multi-Channel Analyzer (MCA), specific activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were measured. Results revealed heightened levels of ²²⁶Ra in regions where sedimentary samples were obtained, whereas igneous samples exhibited a relatively higher concentration of ²³²Th compared to ²²⁶Ra. Sediments rock samples displayed elevated concentrations of both ²³²Th and ²²⁶Ra. Conversely, conglomerate rocks demonstrated low levels of radioactivity, particularly in ²²⁶Ra. These findings align with previously published data on pegmatite rocks in Egypt. Comparative analyses were conducted with previously published international literature, providing valuable insights into the natural radioactivity variations across diverse geological formations and geographical regions. The comparisons contribute to a comprehensive understanding of radiation exposure risks pertinent to specific rock types and locations. Furthermore, hazard indices associated with most rock samples exceeded international safety standards, highlighting the significant radiation hazards inherent in the studied regions.

Conflicts of Interest

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

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