Introduction

There is no place on earth that is free from radioactivity. Radionuclides such as 238U, 232Th, and 40K emit gamma radiation and their activity concentrations vary from place to place. Soil that contains naturally occurring radionuclides above the maximum permitted exposure limit can be very dangerous and can affect people’s health living in that place. This can pose a serious hazard if they are present in high concentrations. Industrial processes such as cement production, mining, oil and gas exploration, and fertilizer production enhance the concentration of the radionuclides (Abbady 2004; Abdul Aziz and Khoo (2018). Consequently, it is crucial to measure the radioactivity levels in rock material to assess their radiological hazards. The knowledge of the amount of natural activity present in rocks used for any application is of prime importance in determining their appropriateness. Public concern led to the engagement of many research teams to measure the natural radioactivity in building materials, underground water, minerals etc. These studies include the works of Abdel Gawad et al. (2023), Taalab et al. (2023), Abed et al. (2022), Awad et al. (2022), Kammar et al. (2022), Agbalagba et al. (2014), Ravisankar et al. (2014), Merle and Enn (2012), Viruthagiri (2011), El-Taher et al. (2010), Prasong and Susaira (2008), Zalewski et al. (2001), among others.

In crystalline rocks, most of the uranium is incorporated into accessory minerals such as monazite, allanite, sphene and zircon so that uranium is not readily accessible for solution and available to secondary mineralization processes (Speer et al. 1981).

The occurrence of naturally occurring radionuclides in construction materials leads to radiation exposure both in outside environments and inner buildings. This is mainly due to gamma radiation of 40K and members of the U and Th decay series.

Igneous rocks have been extensively used in Egypt as building materials, with granites representing the majority of them. In general, granites are widely recognized to exhibit high levels of U and Th due to the characteristics of the genetic magma and associated tectonic environment.

Rocks generated in the crust are more enriched in radioelements than those formed in the mantle, as a consequence the magma’s partial melting and fractional crystallization concentrated them in the liquid phase enhanced in silica.

This paper aims to contribute to a better understanding of the radioactivity of some igneous rocks provided by distinct tectonic environments and commonly used as ornamental or building materials.

General geology

The Eastern Desert of Egypt is a part of the Arabian Nubian Shield. It was classified into three provinces (north, central and south) depending on the variation in lithology and tectonic environments (Stern and Hedge 1985; El Gaby et al. 1988). The border between the NED and CED is demarcated by an intrusive contact, while an extensive shear zone separates the CED from the SED (Stern and Hedge 1985; Fowler et al. 2006). The NED is characterized by ample granitic plutons (syntectonic granitoids) with different gneissic compositions (Windley 1977). This part is devoid of the ophiolitic ultramafics and pillowed tholeiite basalts (Abdel Meguid 1992; El Gaby et al. 1988; El Gaby et al. 1990; Ries et al. 1983; Stern 1981). Lithologically, the CED is composed of larger volumes of ophiolitic sequences and mélanges, ultramafic rocks and pillowed tholeiite basalts, as well as significant portions of arc‐type volcanic and volcanogenic sediments (Sims and James 1984). The pre-Pan-African medium‐grade gneisses characterized the SED territory. It includes continental shelf facies (meta-sedimentary rocks) which have been intruded by a series of calc‐alkaline granitoids (O’Conner et al. 1993).

Most of the southwest of Egypt is a cuesta (small to medium–high escarpment landscape) of Late Jurassic to Cretaceous clastics, with extensive sand and gravel sheets. The Precambrian basement is exposed in some places, covering an area of about 40,000 km2 (Klitzcsh and Schandlemier 1990). The basement separating the deep intra-cratonic Dakhla basin (Egyptian side) from the shallower basins of North Sudan is called “Oweinat- Bir Safsaf- Aswan Uplift”, this is the oldest tectonic event “Permo-Triassic” in age (Frantz et al. 1987; Schandlemier and Darbyshire 1984). The uplift is represented by four large enclaves and numerous smaller ones: (1) G. Uweinat (35,000 km2); (2) Bir Safsaf (2500 km2). (3) G. El Asr (900 km2). (4) G. Umm Shaghir (600 km2).

Geological settings

Our samples were collected from the younger granites of the Eastern and Western Deserts (Figs. 1, 3).The samples covered an area from latitude 27° 52′ 55.00″ N and longitude 33° 0′ 46.90″ E (north Eastern Desert NED) to latitude 24° 35′ 57.80″ N and longitude 34° 9′ 1.60″ E (south the Eastern Desert SED). In the Western Desert, the samples were collected from latitudes 23° 24′ 8.09″ N–23° 11′ 19.00″ N and longitudes 31° 23′ 29.10″ E–31° 49′ 52.20″ E. Accordingly, it is difficult to give detailed geological settings for the eighteen localities where the rock samples were collected. Therefore, only outlines of the geological settings and geochemical characteristics of the granitic samples collected will be presented here.

Fig. 1
figure 1

Google Earth view for the samples’ location

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Granites are widely distributed in the Neoproterozoic rocks of Egypt. They constitute about 60% of its plutonic assemblage (Hussein and ElRamly 1982). The main granitic masses are exposed in the Eastern Desert of Egypt, where the granite plutons intruded into the pre-existing country rocks. Based on their composition, color, and relative age, the granitoid rocks of Egypt are classified into older (750–610 Ma) and younger (620–540 Ma) granites (Akaad and Noweir 1979). They were further classified (Hussein et al. 1982) to (1) subduction-related older granites; (2) suture-related or post-orogenic younger granites and (3) intraplate anorogenic younger granites. The older granites comprise mainly tonalites and granodiorites, with minor trondhjemite and quartz diorites. According to their geological setting (Akaad et al. 1979), the younger granites are classified into: phase (I) granodiorites with minor monzogranites, phase (II) monzogranites and syenogranites and phase (III) alkali feldspar granites. Recently, Liégeois and Stern (2010) classified the younger granites (phase III). A major tectonic transition for the younger granites was proposed by Stern and Hedge (1985) from a compressive to an extensional regime at 600 Ma. They concluded that the Egyptian granites belong to two main phases of the Pan-African Orogeny: (1) an older group (715–610 Ma) comprises syn- to late-tectonic granites forming batholithic masses with wide compositional variations (trondhjemites to granodiorites with minor granites), and (2) a younger group (600–540 Ma) includes post-tectonic pluton to stock-sized granitic bodies (rich in K-feldspars). Bentor (1985) classified the granites of the Arabian Nubian Shield into two groups: older syn- to late-orogenic granites (880–610 Ma), and younger post-orogenic to orogenic granite (600–475 Ma). Loizenbauer et al. (2001) identified three magmatic pulses in the Central Eastern Desert, dated at 680 Ma; 620 Ma; and 585 Ma.

Topographically, the collected younger granites in this study form high relief. They are intruded with sharp contacts and possess steep walls. They show oval or elongated shapes enclosing mafic xenoliths, enclaves and roof pendants of the country rocks. The granites are pink to red, and medium to coarse-grained (Fig. 1A–D). The younger granites studied are mainly alkali feldspar granite, followed by syenogranite, monzogranite and rare granodiorite. Mineralogically, they are composed of quartz, k-feldspar and plagioclase as essential minerals, with subordinate biotite, muscovite, hornblende (Fig. 2g), riebeckite and arfvedsonite (Fig. e). Allanite, zircon, apatite, sphene, monazite and opaques (iron oxides and pyrite) are the main accessory minerals. Quartz occurs as anhedral large crystals interstitial to other mineral constituents. The potash-feldspars are presented by tabular orthoclase and microcline perthite crystals. Primary K-feldspar minerals are usually altered to sericite and clay minerals (Fig. 2h). The former is corroded by quartz and plagioclase. Plagioclase forms subhedral tabular crystals with albite-lamellar twining to oligoclase composition. In the alkali feldspar granite, quartz is actively intergrown by feldspar leaving blebs of quartz inside the replacing alkali feldspar forming micrographic and myrmekitic textures. Biotite is subordinate (Fig. 2f) and occurs as platy crystals.

Fig. 2
figure 2

a–d Field photos and e–h photomicrographs for some of the studied rocks

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Experimental techniques

Samples collection and preparation

A total of 96 fresh samples were collected from eighteen localities in the Eastern and Western Deserts. Forty-eight out of the 96 samples were chemically analyzed, their sampling location is shown in Figs. 1, 3 and Table 1. Samples from the northern part of the Eastern Desert (NED) were gathered the (Gebel G.) G. Um Mongul (Mo), G.ELDib (D), G. El Dokhan (Do), G. Al Reddah (R), and G. Qatar (Q). The samples from the central part covered the areas: G. Missikat (M), G. Gidamy (Gd), El Dokhan Volcanics (Wadi ElQueh) (Dv), G. Abu El Tiyur (At), G. Sibai (Sb), G. Um Naggat (Un), G. Abu Dabbab (Ad), and G. El Bakreya (Bk). The rocks studied from the southern part were assembled from G. Hamash (H). In the Western Desert, the samples were chosen from the southern part where igneous rocks are outcropping: G. El Garra El Hamra (Gh), G. El Garra El Soda (Gs), G. Um Shagher (Us), and around Bir Safsaf (Sf).

Fig. 3
figure 3

a–d Google Earth views for samples’ location for Qattar (NED), Abu El Tiyur (CED), Hamash (SED) and ElGara ElSouda (SWD)

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Table 1 The coordinates of the collected samples from the Eastern and Western Deserts
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For the chemical analysis, the representative collected samples were crushed into a fine powder using a jaw crusher and then sieved to pass a 75 μm mesh screen. All samples were dried at a temperature of 110 °C. For gamma measurement, the samples were sieved by a 200 µm mesh screen. Each sample was weighted and transferred into an airtight cylindrical plastic container (47.6 mm radius, 82 mm height and 0.5 mm thickness). The samples were saved for 4 weeks to attain a secular equilibrium between parents and their short-lived progenies in natural decay chains.

Geochemical analysis

Chemical analysis for the studied rocks was carried out at the commercial laboratories OMAC (Loughrea, Ireland).The major, minor and trace elements were analyzed using Induced Coupled Plasma Mass Spectrometry (ICP-MS). Below the detailed analytical technique is given.

The samples were digested with a concentrated mixture of HNO3, HF, HClO4 and HCl. The digestion was carried out in two steps. In the first step, the concentrated mixture of HNO3 (3 mL), HF (2 mL) and HClO4 (0.5 mL) was used. In the second step, the mixture of HNO3 (3 mL) and HF (1 mL) was added. This is followed by digestion using Aqua Regia (HCl (3 mL): HNO3 (1 mL) at 200 °C for 2 h in a fume hood. After complete evaporation, the residue was dissolved in 10 mL of 6 M HCl and then dried. The sample solution was prepared in 20 mL of 3% HNO3. A blank solution was prepared in the same way. An internal standard was spiked into each diluted sample for signal attenuation correction, due to the presence of various elements in the samples as well as for possible changes during ICP-MS measurement. The instrument was operated in a gas mode with He (flowing at 5 mL/min) to remove ion interferences. The ICP-MS detection limit was calculated as three times the standard deviation of the calibration blank measurements (n = 5). The detection limits varied from 5 to 0.03 ppm for all elements.

For the gamma-ray spectrometry, each sample was weighted and transferred into an airtight cylindrical plastic container. The samples were saved for 4 weeks towards a secular equilibrium action between parents and their short‐lived progenies in natural decay chains.

Gamma ray spectrometer

Measurements of the activity concentrations of 238U, 232Th and 40K in Bq.kg−1 for the studied samples were performed using gamma-ray spectrometry. The spectrometer employed for this analysis was a 3 × 3 inch (NaI (Tl) Model 802 with a 2048 multichannel analyzer (MCA). Its assembly were sealed tight, including a high-resolution NaI (Tl) crystal, a photomultiplier tube, an internal magnetic/light shield, an aluminum housing, a 14-pin connector, a preamplifier, a main amplifier, and an analogue-to-digital converter with Genie 2000 software. The detector used had the following specifications: a resolution of 7.5% as specified at the 662 keV peaks of 137Cs, and an aluminum window (thickness 0.5 mm, density 147 mg/cm3). The oxide reflector (thickness 1.6 mm, density 88 mg/cm3). The magnetic/light shield is composed of concentric lined steel. The gamma-ray photo peaks corresponded to 1.46 MeV (40 K), 1.76 MeV (214Bi) and 2.614 MeV (208Tl) for the activities of 40K, 238U and232Th, respectively. The sample measuring time (counting spectrum) was approximately in the range between 8 and 24 h. The gamma‐ray photopeaks corresponding to 1.4608 MeV (40K) were taken into account to compute 40K activity in the samples. These gamma‐ray photopeaks 0.6093, 0.1120, and 1.7645 MeV (214Bi) and 0.2952 and 0.3519 MeV (214Pb) were considered in reaching the 238U activity in the samples. 232Th activity was reached through the gamma‐ray photopeaks corresponding to 0.3383, 0.9112 and 0.9689 MeV (228Ac) and 0.5832 and 2.6145 MeV (208Tl) and 0.2386 MeV (212Pb). The detection limit of the detector for 40K, 238U and 232Th was 8.50, 2.21 and 2.11 Bq.kg−1, respectively. The overall uncertainty of the radiation levels was calculated using the propagation law of systematic and random measurement errors. Systematic errors of 0.5–2% existed in the efficiency calibration, and random errors of up to 5% existed in the radioactivity readings (Papadopoulos et al. 2017).

Analytical method

Activity concentration

The activity concentration (A) of the rock samples, measured in Becquerel per kilogram (Bq.kg−1) was determined using the following equation:

$$A = \frac{Np \times 100}{{\eta \times T \times m \times I_{\gamma } }}$$
(1)

Np represents the peak counts of the sample minus the peak counts of the background (BG), Iγ denotes the emitted gamma ray intensity, T is the counting time, η the measured efficiency for each gamma line, and m the sample mass in kilograms (Uosif and El-Taher 2008).

Radiological hazard

The radium equivalent activity (Raeq)

To assess the radiation hazard associated with the building materials used, the Raeq was estimated, where all the decay products of 238U and 232Th are in radioactive equilibrium with their precursors. Raeq is calculated according to the formula (EC 1999):

$$Ra_{eq} = A_{U} + \, 1.43A_{Th} + 0.0077A_{K}$$
(2)

where AU, ATh, and AK speak for the radium equivalent activity of 238U, 232Th, and 40K in Bq.kg−1, respectively.

This formula is based on: 1 Bq.kg−1 of 238U, 0.7 Bq.kg−1 of 232Th and 13 Bq.kg−1 of 40K, producing the same gamma-ray dose rate. This index (Raeq) is related to both internal (due to the radon) and external gamma doses, it should have the value of 370 Bq.kg−1 for the safe use of the building materials.


The absorbed dose rates (D) resulting from gamma radiation in the air at a height of 1 m above the ground surface (UNSCEAR 2000) to fulfil the uniform distribution of the naturally occurring radionuclides 238U, 232Th, and 40K. Conversion factors were applied to compute the absorbed gamma dose rate (D) in air per unit activity concentration in Bq.kg−1 which is 0.462 nGy.h−1 for 238U, 0.604 nGy.h−1 for 232Th, and 0.042 nGy.h−1 for 40K. The calculation of D can be carried out using the Eq. (Knežević, et al. 2020).

$$D = \, 0.462A_{U} + 0.604A_{Th} + 0.0417A_{K}$$
(3)

where AU, ATh, and AK represent the concentration of 238U, 232Th, and 40K in Bq.kg−1, respectively.

The world average (UNSCEAR 2000) value of Dis reported as 57 nGy.h.−1

The internal hazard index (Hin) quantifies the exposure to radon and its daughter products. It is determined from the equation (EC 1999).

$$H_{in} = \frac{{A_{U} }}{185} + \frac{{A_{Th} }}{259} + \frac{{A_{K} }}{4810}$$
(4)

The External Hazard Index (Hex) assesses exposure to external gamma radiation. It is calculated using the Eq.

$$H_{ex} = \frac{{A_{U} }}{370} + \frac{{A_{Th} }}{259} + \frac{{A_{K} }}{4810}$$
(5)

where AU, ATh, AK represent the concentration of 238U, 232Th, and 40K in Bq.kg−1, respectively (Beretka and Matthew 1985).

The Gamma Activity Concentration Index (Iγ) is used to evaluate radiation hazards (European Commission).It is computed according to the Eq.

$$I_{\gamma } = \frac{{A_{U} }}{300} + \frac{{A_{Th} }}{200} + \frac{{A_{K} }}{4000}$$
(6)

where AU, ATh, and AK stand for the concentration of 238U, 232Th, and 40K in Bq.kg−1, respectively. The Iγ value is correlated with the annual dose rate resulting from the excess external gamma radiation caused by surface materials. Iγ values ≤ 2 correspond to a dose rate criterion of 0.3 mSv.y−1, while Iγ values ≤ 6 correlated with a criterion of 1 mSv.y−1. Iγ should be used as a screening tool to identify materials of concern for construction purposes. Materials with Iγ > 6 should be avoided as it is associated with a dose rate exceeding 1 mSv.y−1, which is the maximum recommended for human exposure (El-Taher et al. 2022).


Annual effective dose (AEDE) This parameter examines the conversion coefficient from the absorbed dose in the air to the effective dose and the indoor and outdoor occupancy factors. A conversion coefficient of 0.7 SvG.y−1 was utilized for the absorbed dose in air to the effective dose conversion received by adults. The indoor occupancy factor was set at 0.8, to indicate that 20% of the time was spent outdoors and 80% indoors on average worldwide. This parameter is calculated using Eqs. (7) and (8):

$$AEDE_{out} \left( {\mu Svy^{ - 1} } \right) = D\left( {nGyh^{ - 1} } \right) \times 8760h \times 0.7SvGy^{ - 1} \times 0.2 \times 10^{ - 3}$$
(7)
$$AEDE_{in} \left( {\mu Svy^{ - 1} } \right) = D\left( {nGyh^{ - 1} } \right) \times 8760h \times 0.7SvGy^{ - 1} \times 0.8 \times 10^{ - 3}$$
(8)

where D and AEDE express the absorbed dose rate and annual effective dose, respectively. The World average values (UNCEAR 2000) for indoor and outdoor AEDE are reported as 450 μSv.y−1 and 70 μSv.y−1, respectively.


Excess lifetime cancer risk (ELCR) This index is computed using the Eq.

$${\text{ELCR}} = {\text{AEDE}} \times {\text{DL}} \times {\text{RF}}$$
(9)

where AEDE substitutes for the annual effective dose, DL speaks for the duration of life (70 years), and RF serves as the risk factor for fatal cancer risk per Sievert. A value of 0.05 is commonly used (ICRP 1991) by the public to account for the probabilistic effects that occur by chance.

The annual gonadal dose equivalent (AGDE) This parameter results from the specific activities of 238U, 232Th, and 40 K. It is computed using Eq. (10)

$$AGDE \, \left( {\mu Sv.y^{ - 1} } \right) \, = \, 3.09 \, A_{U} + \, 4.18 \, A_{Th} + \, 0.314 \, A_{K}$$
(10)

where, AU, ATh and AK, are the concentrations in (Bq.kg−1) for 238U, 232Th and 40K respectively.

Results and discussion

Geochemical characteristics of the studied rocks

The chemical composition of representative samples from the studied localities is given in Table 11. They are highly evolved rocks, judging from the elevated SiO2 contents. They show an enrichment in Al2O3. The rocks’ nomenclature was carried out using the TAS plot (NaO2 + KO2/SiO2) (Middlemost 1994) (Fig. 4a) as well as the Streckeisen diagram (1979) based on the normative amounts of potash feldspar, quartz and plagioclase. As shown in Fig. 4a that the rocks are mainly granite. The rocks plotted in the diorite and gabbroic diorite fields are actually the volcanic rocks of Dokhan and Hamash. They are andesite and basaltic andesite. The rocks magma is mainly ferroan in composition, while the volcanics plot in the magnesian field (Fig. 4b). The rocks are peraluminous in composition (Fig. 4c). The majority of the rocks plot in the high K calc-alkaline field (Fig. 4d). On the Ga/Al versus Na2O + KO diagram, the rocks occupied the A-type granites. Some rock samples were plotted within the I-type granites (Dokhan volcanic and Hamashvolcanics) (Fig. 4e). On the tectonic setting diagram, they plot mainly within a plate and few points occupy the volcanic arc field (Fig. 4f).

Fig. 4
figure 4

a Classification of the studied rocks (Middlemost 1994) b Kind of magma for the studied rocks c Variation diagram of K2O vs. SiO2 (fields after Rickwood (1989) d A/CNK vs. A/NK diagram (Maniar et al. (1989) e Tectonic discrimination diagram, Rb versus (Nb + Y) diagram (Pearce 1984). f Ga/Al versus Na2O + K2O discrimination diagram (Whalen et al. 1987)

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The activity concentrations of the studied radionuclides

Tables 2, 3, 4, 5 list the results and mean values of the activity concentrations of 238U, 232Th, and 40K for the rock samples collected from the northeastern, central, southeastern and southwestern deserts, respectively.

Table 2 Activity concentrations of 238U, 232Th and 40K (in Bq.kg−1) in the Northeastern desert rock samples
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Table 3 Activity concentrations of 238U, 232Th and 40K (in Bq.kg−1) in the rock samples from the Central Eastern Desert
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Table 4 Activity concentrations of 238U, 232Th and 40K (in Bq.kg−1) in the rock samples from the Southeastern Desert
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Table 5 Activity concentrations of 238U, 232Th and 40K (in Bq.kg−1) in the rock samples from the Southwestern Desert
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In the North Eastern Desert, G. Qatar (sample Q10) exhibited the highest activity concentrations of 238U, 232Th, and 40K measured at 4148.79 ± 256.38, 192.08 ± 13.68, and 2314.01 ± 478.67 Bq.kg−1, respectively (Table 2).

Moving to the Central Eastern Desert, the highest activity concentration for 232Th was noted in G. El-Gidamy (sample Gd1) measured at 58.93 ± 5.8779 Bq.kg−1G. Um Naggat, (sample Un7) showed the highest activity concentrations for 238U and 40K, measured at 89.64 ± 8.79 and 1305.07 ± 270.16 Bq.kg−1, respectively (Table 3).

In the Southern Eastern Desert, among the rock samples of G. Hamash, the highest values were recorded in sample (H2) 20.30 ± 2.88, 20.30 ± 2.88 and 266.51 ± 55.25 Bq.kg−1 for 238U, 232Th, and 40K, respectively (Table 4).

In the Southern Western Desert, G. El Garra El Souda (sample Gs1) showed the highest activity concentrations for 238U, 232Th, and 40K, noted at 183.52 ± 15.15, 159.95 ± 11.13, and 2128.61 ± 441.54 Bq.kg−1, respectively (Table 5).

In the following, we compare the activity concentrations of 238U, 232Th, and 40 K, individually, in the studied rock samples.

The average activity concentrations of 238U (Tables 2, 3, 4, 5) in the North Eastern Desert rocks (NED) measured at Um Mongul, ElDib, G. El Dokhan, El Reddah and Qatar) were 144.86 ± 11.55 Bq.kg−1. The rocks collected at Missikat, Al-Gidamy, Volcanics (Wadi ElQueh), Abu El Tiyur, El Sibai Um Naggat, Abu Dabbab and El Bakreya in the Central Eastern Desert (CED) showed average values of 49.48 ± 5.43 Bq.kg−1. In the Southeastern Desert (SED), the average measured values for Hamash (H) were 12.68 ± 2.59 Bq.kg−1, whereas in the Southwestern Desert (SWD) rocks El Gara El Hamra, El Gara El Soda, Um Shagher and Bir Safsaf measured 69.46 ± 7.08 Bq.kg−1. 238U showed the highest activity concentration in the rocks from the north, southwest, and central-eastern desert and the least activity was in the SED. Thus the rock samples studied from the NED, CED and SWD exceeded the World average value of 238U (35 Bq.kg−1).

232Th average activity concentrations of the rock samples from the North Eastern Desert (NED) was 61.95 ± 5.83 Bq.kg−1, while the rock samples showed an average of 28.49 ± 2.88 Bq.kg−1in the rocks of the Central Eastern Desert (CED). The average values for the rocks Southeastern Desert were 6.93 ± 1.15 Bq.kg−1. Whereas, in the Southwestern Desert (SWD), the average values measured were 58.02 n ± 5.06 Bq.kg−1. The concentration of 232Th in the rocks studied is like that of 238U where they are enriched in the north and impoverished in the southeastern desert. The mean value of 232Th reported in the rocks of the northeastern desert NED (Missikat, Al-Gidamy, Volcanics (Wadi El Queh), Abu El Tiyur, El Sibai Um Naggat, Abu Dabbab and El Bakreya) and southwestern desert SWD El Gara El Hamra, El Gara ElSoda, Um Shagher and Bir Safsaf surpass the value of the World Reference Standard (50 Bq.kg−1) (UNCEAR 2008).

The average activity concentrations of 40K in the rocks of the North Eastern Desert (NED) were 1099.88 ± 227.69 Bq.kg−1, while in the Central Eastern Desert (CED) rocks, the average values were 877.85 ± 182.27 Bq.kg−1. In the Southeastern Desert (SED), the measured values for the rocks showed an average of 108.87 ± 23.48 Bq.kg−1, while in the South Western Desert (SWD), the computed values were 1144.37 ± 237.49 Bq.kg−1. The values of 40K in the rocks under investigation exceeded the Worldwide average (UNCEAR 2008) of 40K (400 Bq.kg−1) except for the volcanic rocks of Hamash in the SED.

Table 6 and Fig. 5 show the results of the natural radioactivity levels of the investigated granites versus the previously studied granites compared to those from Egypt and other countries.

Table 6 The average activity concentrations of the investigated rock samples from the Eastern and Southern deserts compared with other countries and world average values
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Fig. 5
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Comparison between the mean activity concentrations of the studied radioisotopes from the rocks from the four parts of both Deserts compared with the World average

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As shown in Table 6, the comparison revealed distinct patterns of radionuclide concentrations among the rocks studied. Specifically, the concentration of 238U exceeded the global average in all regions except in the rocks from SED, due to the enrichment of uranium-rich accessory minerals like monazite, zircon, and xenotime in these rocks. On the other hand, 232Th concentrations are higher than the global average in the rocks of the NED and SWD, but lower in the CED and SED rocks, suggesting enrichment of the accessory minerals allanite, and monazite minerals in the rock samples of both parts. Furthermore, 40K concentrations are exceled in all studied parts of both desserts, due to the high concentration of potash feldspars in rocks.

Radiological hazard parameters

The activity concentrations of naturally occurring radionuclides in building materials have been reported in several publications, which can vary according to the type and origin of the building material.

Tables 7, 8, 9, and 10 exhibit the radiation hazards associated with the rock samples collected from the North, Central, Southeastern, and Southwestern Deserts. The calculation intends to provide a comprehensive assessment of the potential radiation risks posed by the investigated rocks.

Table 7 Radiological hazard parameters of the Northeastern Desert rock samples
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Table 8 Radiological hazard parameters of the Central Eastern Desert rock samples
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Table 9 Radiological hazard parameters of the Southeastern Desert rock samples
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Table 10 Radiological Hazard parameters of the studied rock samples from the Southwestern Desert
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The radium equivalent (Raeq) values for the samples under consideration were carefully examined following the recommended safety limit of 370 Bq.kg−1 (UNSCEAR 2000). The majority of the samples demonstrated activity Raeq values below the safety threshold, indicating an acceptable level of radiation. However, several exceptions were observed, as the samples from G. El Dib (D1, D8, and D11) were estimated at 472.50, 390.88 and 459.44 Bq.kg−1) and G. Qatar (Q8 and Q10) (609.69 and 4601.65 Bq.kg−1) from the Northeastern Desert exceeding the safe limit. In contrast, the rock samples studied from the Central and Southeastern Desert did not surpass the limit. The rocks of G. El Garra El Souda (sample Gs1) (576.16 Bq.kg−1) in the Southwestern Desert showed an elevated activity of Raeq which is attributed to the higher concentrations of 238U in rocks.

The absorbed dose rates (D) nGy·h−1. It is important to note that the mean D values for all measured rocks exceeded the global average soil value of 59 nGy·h−1 reported by UNSCEAR (2000), except those of Dokhan volcanics (Wadi El Queh) and G. Abu Dabbab (27.40 and 41.51 nGy·h−1) in the Central Eastern Desert, as well as the rocks of G. Hamash (14.51 nGy·h−1) in the Southeastern Desert. This indicates a significant radiological risk associated with these particular types of rocks.


The Outdoor Annual Effective Dose Equivalent (AEDE out) (μSv·y−1). All the examined rocks surpassed the World average value of outdoor AEDE (70 μSv·y−1) reported by UNSCEAR (2000). Except those rocks of Dokhan Volcanics (Wadi ElQueh) and G. Abu Dabbab (33.63 and 50.94 μSv·y−1) in the Central East Desert, as well as the volcanics of G. Hamash (17.81 μSv·y−1) in the Southeastern Desert.


Concerning the indoor annual effective dose equivalent (AEDEin) (μSv·y−1). This parameter showed that many samples in different localities in the Northeastern Desert and Southwestern Deserts manifested higher AEDE values compared to the World average value of indoor AEDE (450 μSv·y−1), except for the rocks of G. El Gara El Hamra (427.33μSv·y−1) in the Southwestern Desert. Conversely, in the Central and Southeastern Desert, all localities displayed values lower than the World average, except G. El-Gidamy and G. El Sibai (557.31 and 535.03 μSv·y−1) respectively, in the Central Eastern Desert.


The excess lifetime cancer risks (ELCR) utilized the calculated annual effective dose equivalent (AEDE) results for the estimation of the risk associated with the studied rock samples. Remarkably, the mean ELCR values for most examined rocks exceeded the World average value of outdoor ELCR (1450) (Qureshi et al. 2014) except Dokhan volcanics (Wadi ElQueh), G. Abu Dabbab and G. Abu Eltiyur (588.46, 891.44 and 1414.28 μSv·y−1) in the Central Eastern Desert, as well as the rock samples from G. Hamash (311.61 μSv·y−1) in the Southeastern Desert.


Internal and External Hazard Indices (Hin) (Hex). The average values for the studied rocks (Tables 7, 8, 9, 10) were below unity, which is the recommended safe limit. However, the rocks of G. Qatar exhibited mean Hin and Hex values of 2.79 and 1.63, respectively, indicating a higher level of internal and external radiological hazards.

Moreover, the Iγ values for the rock samples under investigation are found to be less than 2, suggesting that the gamma dose originating from these rocks does not exceed 0.3 mSv·y−1.


Annual gonadal dose equivalent (AGDE) (mSv·y−1) mean values exceeded the Global average soil value of 0.3 mSv·y−1 (Xinwei et al. 2006), except for the Dokhan Volcanics (Wadi El Queh) (0.20) in the Central Eastern Desert and the volcanics of G. Hamash (0.10) in the Southeastern Desert (Tables 11, 12).

Table 11 Major oxides (wt%), trace and rare earth elements (ppm) concentration for some of the studied rock samples
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Table 12 Pearson correlation between rare earth elements, trace elements and major oxides
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The contribution of 238U, 232Th and 40 K in the studied rock samples

Figures 6a–d illustrate the average contribution of 238U, 232Th, and 40K for the rock samples from the North, Central, Southeastern, and Southwestern Deserts, respectively. The analysis revealed that the input of 238U, 232Th, and 40K were 7.65%, 4.81%, and 87.54%, respectively in the rock samples from the Northeastern Desert. In comparison, they supplied 5.90%, 2.82%, and 91.28%, respectively to the rock samples from the Central Eastern Desert. For the Southeastern Desert, the additions were 31.54%, 8.95%, and 59.51% respectively and for the Southwestern Desert 5.29%, 4.29%, and 90.42%, respectively. As shown in (Fig. 6) that the highest contribution originated from 40K. This isotope occurs in the potash feldspars in all studied rocks, followed by 238U (Fig. 6c), which is the most common isotope of uranium found in nature, with a relative abundance of 99%. Zircon mineral (ZrSiO4) contains ppb amounts of 235U and 238U. This accessory mineral is the most predominant one in all igneous rocks, especially granitic rocks. The contribution of 232Th (Fig. 6) was relatively small due to the relative depletion of the accessory minerals bearing thorium in the studied rock samples.

Fig. 6
figure 6

a–d The average values for the relative contribution to 238U, 232Th and 40K of the studied radioisotopes for the studied rocks of both Deserts compared to the World average

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Pearson correlation between the natural radionuclides

Pearson correlation for the natural radionuclides (238U, 232Th, and 40K) are illustrated in Figures A, B, C, and D for the rocks under investigation. These correlations were performed to determine the interrelation between the natural radionuclides and the calculated radiological hazard parameters (Fig. 7).

Fig. 7
figure 7

Pearson correlation between the natural radionuclides (238U, 232Th and 40K) in the rock samples from NED, CED, SED and SWD

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The correlation coefficients between (U, Th), (U, K), and (Th, K) were found to be 0.622, 0.628, and 0.589 in the rocks from the North Eastern Desert (NED), while they calculated 0.761, 0.610, and 0.663 in the Central Eastern Desert (CED) samples. The correlations between the radioactive elements in the samples of the Southeastern Desert (SED) were 0.988, 0.558, and 0.600 and 0.918, 0.817, and 0.677 in the Southwestern Desert (SWD) samples, respectively. It is reported (Bashir et al. 2019) that 238U and 232Th are usually found together in nature, and a good correlation between them is indicative of common sources, i.e. associated in the same mineralogical phase. 238U and 232Th are positively correlated with all calculated radiological parameters. This is due to the enrichment of 238Uand 232Th, as both play important roles in determining the hazards associated with the building materials. The poor correlation between 232Th and 40Kfrom one side and 238U and 40K from the other were attributed to the presence of minerals that greatly affect the mobility of the radionuclides (Stockdale and Bryan 2013). 40K is the most common radionuclide in continental rocks (such as granitic rock) and dominant in many light and non-carbonate minerals (Ergül et al. 2013; Wang et al. 2020). The concentration of 40K showed significant variability, indicating that there are notable differences in 40K levels among the rock samples, due to variations in mineral composition and geochemical characteristics.

Conclusions

The 226Ra, 232Th and 40K activity concentrations in 96 samples of igneous rocks collected at eighteen areas in Egypt allowed estimation of the radium equivalent activity (Raeq), the absorbed dose rates (D), outdoor annual effective dose equivalent (AEDEout), the excess lifetime cancer risks (ELCR), internal and external hazard indices (Hin) (Hex), annual gonadal dose equivalent (AGDE). Some rocks (samples Q8, Q10, D1, D8, D11 and Gs11) from the Qatar, El Dib, El Garra El Souda areas exhibited values of Raeq˃ 370 Bq/kg and Hex ˃1, which are the threshold limits recommended globally, corresponding mainly to high K calc-alkaline granites. The index of gamma radiation has been related to the effective dose rate, indicating that the radioactivity emitted in all studied samples did not exceed the guideline value of 1 mSv/yr. The exhalation rate of Rn and daughters varied between < 1, except for one sample from Qatar (Q10).

The results reported here suggest that most of the studied igneous rocks can be utilized in closed indoor environments. In contrast, those exhibiting values of Raeq ˃370 Bq/kg and Hex ˃1 could be used in outdoor environments and indoors with ample ventilation to avoid any risk of human exposure to 222Rn and daughters due to their radiotoxicity.