Utilization of Waste Marble and Bi₂O₃-NPs as a Sustainable Replacement for Lead Materials for Radiation Shielding Applications

Abstract

In an attempt to reutilize marble waste, a new approach is presented in the current study to promote its use in the field of shielding against ionizing radiation. In this study, we aimed to develop a novel and sustainable/eco-friendly lead-free radiation shielding material by improving artificial marble (AM) produced from marble waste combined with polyester by reinforcing it with bismuth oxide (Bi₂O₃) nanoparticles. Six samples of AM samples doped with different concentrations ($0\%$,$5\%$,$10\%$,$15\%$, $20\%$, and $25\%$) of Bi₂O₃ nanoparticles were prepared. The linear attenuation coefficient ($LAC$) values were measured experimentally through the narrow beam method at different energies $(0.0595 \mathrm{M}\mathrm{e}\mathrm{V}$, $0.6617 \mathrm{M}\mathrm{e}\mathrm{V}$, $1.1730 \mathrm{M}\mathrm{e}\mathrm{V}$, and $1.330 \mathrm{M}\mathrm{e}\mathrm{V}$) for all samples with various concentrations of Bi₂O₃. Radiological shielding parameters such as half value layer ($HVL$), tenth-value layer ($TVL$), and radiation shielding efficiency ($RSE$) were estimated and compared for all the different samples. The results prove that increasing the concentration of Bi₂O₃ leads to the enhancement of the radiation shielding properties of the AM as a shielding material. It was observed that as the energy increases, the efficiency of the samples falls. High energy dependence was found when calculating the $HVL$ and $TVL$ values of the samples, which increased with increases in the energy of the incident photons. A comparison between the sample with the most efficient gamma radiation attenuation capability (AM-$25\%$), concrete, and lead was conducted, and a discussion regarding their radiation shielding properties is presented herein. The results show that the AM-$25\%$ sample is superior to the ordinary concrete over all the studied energy ranges, as evidenced by its significantly lower $HVLs$. On the contrary, lead is superior to the AM-$25\%$ sample over all the studied energy ranges owing to its unbeatable density as a shielding material. Overall, this new type of artificial marble has the potential to be used as a radiation shielding material at low- to medium-gamma energy regions, specifically in medical imaging and radiation therapy.

1. Introduction

The marble industry produces vast quantities of waste during the quarrying and subsequent processing of rocks [1]. By-product waste can be classified into three types of waste, fine powder waste (marble dust), coarse waste (various shapes and sizes of rock fragments), and slurry (mud) produced during the cutting process of marble slabs [1]. The disposal of marble waste is considered an economic and environmental problem [1]. Fine marble powders result in air and visual pollution. Moreover, marble slurry and residues could cause water pollution, soil pollution, and environmental deterioration through the air [2]. The reutilization of marble waste protects our environment from pollution and adds more economic value to the marble industry since more than $50\%$ of marble is converted to waste after mining and processing. As marble slurry generated from processing units dries, it leaves a surface residue that pollutes the air, and due to rain, this waste could contaminate surface water [3,4].

At the same time, developing a variety of radiation shielding materials is necessary to match the increasing ionizing radiation applications in the medicine, energy, industry, agriculture, and research sectors [5]. Exposure to high doses of ionizing radiation could lead to huge risks to human health, and the use of shielding materials is considered the most effective approach for shielding against radiation [6,7,8].

Many previous studies have been conducted to investigate the possibility, efficiency, and feasibility of using marble waste to develop radiation shielding materials, mostly in the form of concrete [9,10,11], aiming to increase the attenuation of ionizing radiation by raising the density of concrete. Using marble waste as a partial replacement for some components of the concrete mix has been proven to increase gamma attenuation power, improve some mechanical and physical properties like compressive strength, and decrease the water permeability of concrete [12]. Moreover, marble waste has been added to other materials like clays, bricks, cement pastes, and polymers [11,13,14]. Focusing on polymers in particular, lately, they have become popular to use in inventing upgraded materials to shield against radiation. Polyester, polypyrrole, polyvinyl chloride, isophthalic resin, ethylene vinyl acetate, methyl vinyl silicone rubber, styrene-butadiene rubber, and polydimethylsiloxane are the most frequently used polymers including several additives for the innovation of adequate radiation shielding materials thanks to their durability, light weight, flexibility, and good mechanical properties [15]. Having the lowest shrinkage quality, outstanding resistance against chemical deterioration, shape stability, and greater compression, fatigue, and tensile strength, polyester polymers are the most favorable among all polymers, and their properties can be further improved by introducing different metal oxides [16,17,18,19].

Pioneering researchers have conducted extensive investigations of the radiation shielding properties of materials produced by combining marble waste with polyester resin. Elhemily, H. and her colleagues [20] investigated the effect of introducing different concentrations and sizes (micro and nano) of tungsten oxide (WO₃) on the radiation shielding capabilities of crumbly waste marbles mixed with polyester. Their composites with higher WO₃ concentrations had higher linear attenuation coefficient ($LAC$) values. In terms of their results, the radiation shielding efficiency ($RSE$) of waste marble + polyester + WO₃ demonstrated that their marble composites absorb almost all incoming photons at low energies. Moreover, the effect of increasing the concentration of lead carbonate (PbCO₃) and cadmium oxide (CdO) contents on the physical properties and radiation attenuation factors of a newly developed radiation shielding absorber fabricated by Sayyed, M. and his team [21] was experimentally examined. The $LAC$ values for all the marble compositions were highest at the lowest energy ($0.06 \mathrm{M}\mathrm{e}\mathrm{V}$), while the $LAC$ decreased with increasing energy. The highest $LAC$ was found for Marb-$3$, with a composition of waste marble ($50$ $\mathrm{w}\mathrm{t}\%$), polyester ($25$ $\mathrm{w}\mathrm{t}\%$), PbCO₃ ($17.5$ $\mathrm{w}\mathrm{t}\%$), and CdO ($7.5$ $\mathrm{w}\mathrm{t}\%$). They also studied the impact of the addition of CdO to substitute PbCO₃, and they found that the half-value layer ($HVL$) decreases with increasing CdO content. On top of that, Almuqrin, A. and his fellow workers [22] have developed a new shielding material based on waste marble and polyester. It was made by the combination of polyester and fine waste marble, mixed along with lead oxide (PbO) and bismuth oxide (Bi₂O₃). Their newly prepared shield’s $HVL$ and mean free path ($MFP$) exhibited that the sample PWPBi-$10$—composed of polyester ($40$ $\mathrm{w}\mathrm{t}\%$), fine waste marble ($30$ $\mathrm{w}\mathrm{t}\%$), PbO ($20$ $\mathrm{w}\mathrm{t}\%$), and Bi₂O₃ ($10$ $\mathrm{w}\mathrm{t}\%$)—provides an excellent shielding capability compared to the other investigated polyester samples. The $MFP$ behavior reveals that the ratio of PbO and Bi₂O₃ on those novel polyesters has a direct effect on their radiation shielding characteristics. It is worth noting that the novel polyester sample, PWPBi-$10$, exhibited the lowest $MFP$ value compared to the rest of the tested samples.

As a continuation of earlier efforts, the aim of the research presented herein was to develop a novel lead-free radiation shielding material by utilizing artificial marble (AM) produced from marble waste and polyester resin while reinforcing it with nanoscale Bi₂O₃ particles. Bismuth is a heavy metal, and it has a higher atomic number than lead and a density close to lead, but it is not toxic to human beings and can be considered an eco-friendly chemical element, unlike lead, which has adverse harmful effects on the environment and humans during its production, usage, and disposal. Also, nano Bi₂O₃ could enhance gamma attenuation and some physical properties of the designed material [23,24]. For the novel designed mixture, six samples of AM with nano-sized Bi₂O₃ (as a filler) were prepared, and the radiation shielding properties of the fabricated composites (waste marble + polyester + nano-Bi₂O₃) were recorded. Experiments were conducted using a high-purity germanium detector (HPGe detector) and different radioactive point sources (²⁴¹Am, ¹³⁷Cs-, and ⁶⁰Co). The linear attenuation coefficients ($LAC$s) for the samples were determined experimentally at $0.06$, $0.662$, $1.173,$ and $1.333 \mathrm{M}\mathrm{e}\mathrm{V}$. Additional shielding parameters, such as half-value length ($HVL$), tenth-value length ($TVL$), and radiation shielding efficiency ($RSE$), were calculated for the novel designed marble formations.

2. Materials and Methods

2.1. Preparation

Artificial marble (AM) was prepared using polyester resin in liquid form, crumbly waste marble, calcium carbonate (CaCO₃), and bismuth oxide (Bi₂O₃).

Table 1. Polyester resin characteristics.

Density ($\mathrm{g}$·${\mathrm{c}\mathrm{m}}^{-3}$)	$1.25$
Yield Modulus ($\mathrm{G}\mathrm{P}\mathrm{a}$)	$2–4$
Compressive Strength ($\mathrm{M}\mathrm{P}\mathrm{a}$)	$140$
Tensile Strength ($\mathrm{M}\mathrm{P}\mathrm{a}$)	$55$
Tensile Elongation at Break (%)	$2$

shows the characteristics of the liquid polyester resin used in this study. Waste marble (coarse marble) with an average diameter of $5 \mathrm{m}\mathrm{m}$ was collected from a marble factory. A fine powder of CaCO₃ was added to the mixture to improve the AM’s texture and strength. Bi₂O₃ nanoparticles, which were added to the AM to improve its capabilities to attenuate to the incident photons, were purchased from Nanotech company, Cairo, Egypt.

The polyester resin was gradually added to CaCO₃ with continuous stirring to make sure that the mixture was free of agglomeration; then, the required amount of waste marble was added with Bi₂O₃ nanoparticles. The compound was stirred well, poured into molds, and left for $24 \mathrm{h}$ until completely dry and hardened. The chemical composition, densities, and codes of the prepared AM samples are listed in

Table 2. Chemical compositions, densities, and the codes of the prepared samples.

Code	Chemical Composition wt (%)
	Polyester	CaCO3	Waste Marble	Bi2O3 Nanoparticles	$\mathbf{Density} (\mathbf{g}/{\mathbf{c}\mathbf{m}}^3$)
AM-$0\%$	25	25	50	0	2.07
AM-$5\%$	25	25	50	5	2.13
AM-$10\%$	25	25	50	10	2.19
AM-$15\%$	25	25	50	15	2.25
AM-$20\%$	25	25	50	20	2.32
AM-$25\%$	25	25	50	25	2.39

. The density of the samples was measured practically using the mass per volume law, where the mass was measured using a $0.0001$ digital balance, and the volume was measured by the ($x \pi r^2$) formula, where $x$ and $r$ represent the thickness and the radius of a sample.

A Scanning Electron Microscope (SEM) (JEOL model, Japanese-made and available at the Faculty of Science, Alexandria University in Egypt) was used to photograph the Bi₂O₃ powder nanoparticles before they were added to the marble formation to determine their average size. An SEM image of the Bi₂O₃ powder nanoparticles is shown in Figure 1. From the SEM imaging, it was confirmed that the size of the used Bi₂O₃ particles is less than $500 \mathrm{n}\mathrm{m}$, with an average of $80 \mathrm{n}\mathrm{m}$, and that the shape of the particles is spherical, as shown in the figure.

2.2. Radiation Shielding Measurements

The attenuation of the prepared AM samples (waste marble + polyester + nano-Bi₂O₃) was determined experimentally using an HPGe detector and different point sources, including ¹³⁷Cs, ⁶⁰Co, and ²⁴¹Am (the mechanism for our measurements is illustrated in Figure 2). These radioactive sources were used because they emit photons of different energies, where the ²⁴¹Am source emits energy in the low range (0.060 MeV); this energy plays an important role in X-ray imaging, while ⁶⁰Co-60 (1.173 and 1.333 MeV) and ¹³⁷Cs (0.622 MeV) play an important role in medical, industrial, and agricultural applications, as well as food preservation applications, and therefore, they are dealt with continuously. Therefore, we focused on the energies that come out of them and how to reduce their effect and hazards. Within a certain time, the peaks related to the incoming energy photons emitted from the source are formed. The area under these peaks can be calculated using Genie-2000 software, and the rate of this area (calculated area per measuring time) represents the intensity of the incoming photon. The intensity in the absence of an AM sample is represented by the initial intensity ($I_0$), while by placing each AM sample between the detector and the point source, the calculated intensity is represented by the transmitted intensity ($I$). From these values, the linear attenuation coefficient ($LAC$) for a sample of a thickness ($x$) can be calculated by the following equation [25,26]:

$$LAC=\frac{1}{x} ln\frac{I_0}{I}$$

(1)

The experimental results of the AM-microcomposites were compared with the results obtained from using Phy-x software [27], which is an easy-to-use online program for calculating parameters relevant to radiation attenuation and dosimetry. The other essential attenuator factors, such as the half-value length ($HVL$), tenth-value length ($TVL$), and radiation shielding efficiency ($RSE$), for any AM sample can be expressed by the following equations:

$$HVL=\frac{Ln 2}{LAC}$$

(2)

$$TVL=\frac{Ln \left(10\right)}{LAC}$$

(3)

$$MFP=\frac{1}{LAC}$$

(4)

$$RSE\%=(1-\frac{I}{I_0})\times 100$$

(5)

3. Results and Discussion

Some marble rocks have high radioactivity, and some have radioactivity values that are below the detection limit. To be environmentally safe, the radioactivity concentration of the used marble waste was determined, as this waste was collected from a factory in which three types of marble (Breshia, Galala, and Trista) were used. We conducted a gamma spectrometry analysis (high-purity germanium with a relative efficiency of 24% and resolution of 1.96 keV at 1.333 MeV). The results showed that the activity concentrations of the used marble waste were below the detection limits, as shown in

Table 3. Marble-specific activities (Bq kg⁻¹).

Samples		Activity Concentrations of Studied Radionuclides
		CRa	CTh	CK
Marble types	Breshia	L.L.D	1.36 ± 0.11	L.L.D
	Galala	13.68 ± 5	2.60 ± 0.35	4.90 ± 1.45
	Trista	23.69 ± 2.8	5.59 ± 0.27	5.27 ± 0.51

. The largest concentration obtained for the Trista marble type belonged to the Rd-226 sample, with a concentration of 23.69 Bq kg⁻¹, which is a small concentration that does not affect human health, especially considering that the quantities used in sample preparation are not large.

C_Ra, C_Th, and C_k represent the activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K, respectively, and L.L.D represents lower-level detectability (the uncertainties are quoted for a coverage factor k = 2).

To evaluate the radiation shielding efficiency of the artificial marble (AM) samples (waste marble + polyester + nano-Bi₂O₃) enhanced by various concentrations of bismuth oxide (Bi₂O₃) nanoparticles, the accuracy of the experimental results were confirmed through a comparison between theoretical $LAC$ values from PHY-X and the experimental results of the AM samples prepared without nanoparticles of Bi₂O₃ [28]. The PHY-X and experimental results, along with their relative deviations, are illustrated in Figure 3. The theoretical and experimental values of the linear attenuation coefficients ($LACs$) match well together, with relative deviations below $5\%$, as reported in

Table 4. The experimental and theoretical LAC values of the presented microcomposite AM (AM-0%).

Code	Energy, MeV	Phy-X	EXP	DEV (%)
AM-0%	0.060	0.689	0.672 $\pm$ 0.009	2.52
	0.662	0.162	0.160 $\pm$ 0.003	1.58
	1.173	0.123	0.126 $\pm$ 0.005	−2.54
	1.333	0.115	0.111 $\pm$ 0.004	4.11

.

Figure 4 demonstrates that the increase in $LACs$ is proportional to the concentration of Bi₂O₃ nanoparticles because Bi₂O₃ is a heavy metal oxide (Bi atomic number $=83$), so it can increase the probability of the photoelectric interaction of the incident gamma rays with the samples. It is worth mentioning that the $LACs$ decrease with increasing photon energy for all Bi₂O₃ nanoparticle concentrations because the Compton scattering and pair production interaction are most likely to happen at medium ($0.661 \mathrm{M}\mathrm{e}\mathrm{V}$) and high ($1.173$ and $1.33 \mathrm{M}\mathrm{e}\mathrm{V}$) energies, and these interactions are less closely related to the atomic number [29].

Table 5. A comparison of the LAC values against the Bi₂O₃ nanoparticle concentrations for different energies.

Parameter	Energy, MeV	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
LAC, cm−1	0.060	1.178 $\pm$ 0.005	1.695 $\pm$ 0.003	2.242 $\pm$ 0.003	2.821 $\pm$ 0.004	3.436 $\pm$ 0.004
	0.662	0.170 $\pm$ 0.007	0.178 $\pm$ 0.005	0.187 $\pm$ 0.004	0.196 $\pm$ 0.006	0.206 $\pm$ 0.004
	1.173	0.127 $\pm$ 0.002	0.131$\pm$ 0.001	0.135 $\pm$ 0.005	0.139$\pm$ 0.003	0.144 $\pm$ 0.002
	1.333	0.119 $\pm$ 0.009	0.122 $\pm$ 0.004	0.126 $\pm$ 0.002	0.130 $\pm$ 0.002	0.134 $\pm$ 0.005

compares the LAC values against the Bi₂O₃ nanoparticle concentrations for different energies.

The half-value length ($HVL$) and tenth-value length ($TVL$) are related to the $LAC$ of each sample. They decreased with an increase in the content of the nano-sized Bi₂O₃ particles and increased as the photon energy was raised. The $HVLs$ have their maxima at zero Bi₂O₃ content (AM-$0\%$), with the highest being a value of $6.0 \mathrm{cm}$ at a photon energy of $1.33 \mathrm{M}\mathrm{e}\mathrm{V}$, while its minima is at the highest concentration of Bi₂O₃ (AM-$25\%$), with a value of $0.2 \mathrm{c}\mathrm{m}$ at a gamma energy value of $0.06 \mathrm{M}\mathrm{e}\mathrm{V}$. A similar behavior can be observed for the $TVLs$. (see Figure 5 and Figure 6).

Table 6. A comparison of the HVLs and TVLs against the Bi₂O₃ nanoparticle concentrations for different energies.

Parameter	Energy, MeV	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
HVL, cm	0.060	0.588 $\pm$ 0.005	0.409 $\pm$ 0.002	0.309 $\pm$ 0.004	0.246 $\pm$ 0.007	0.202 $\pm$ 0.002
	0.662	4.080 $\pm$ 0.002	3.892 $\pm$ 0.007	3.711 $\pm$ 0.005	3.537 $\pm$ 0.004	3.369 $\pm$ 0.004
	1.173	5.459 $\pm$ 0.002	5.295 0.004	5.132 $\pm$ 0.007	4.971 $\pm$ 0.002	4.810 $\pm$ 0.006
	1.333	5.836 $\pm$ 0.005	5.669 $\pm$ 0.007	5.503 $\pm$ 0.006	5.337 $\pm$ 0.006	5.171 $\pm$ 0.005
Parameter	Energy, MeV	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
TVL, cm	0.060	1.954 $\pm$ 0.004	1.358 $\pm$ 0.006	1.027 $\pm$ 0.002	0.816 $\pm$ 0.003	0.670 $\pm$ 0.006
	0.662	13.554 $\pm$ 0.005	12.929 $\pm$ 0.007	12.329 $\pm$ 0.002	11.750 $\pm$ 0.001	11.193 $\pm$ 0.003
	1.173	18.134 $\pm$ 0.002	17.591 $\pm$ 0.003	17.050 $\pm$ 0.005	16.512 $\pm$ 0.004	15.977 $\pm$ 0.005
	1.333	19.387 $\pm$ 0.002	18.833 $\pm$ 0.003	18.280 $\pm$ 0.002	17.728 $\pm$ 0.008	17.178 $\pm$ 0.006

presents a comparison of the HVL and TVL values against the Bi₂O₃ nanoparticle concentrations for different energies.

The mean free path ($MFP$) is also related to the $LAC$ of each sample. The $MFP$ values decreased with an increase in the content of the nano-sized Bi₂O₃ particles and increased as the photon energy was raised. The $MFP$ was highest at zero Bi₂O₃ content (AM-$0\%$), with a value of $8.661 \mathrm{c}\mathrm{m}$ at a photon energy of $1.333 \mathrm{M}\mathrm{e}\mathrm{V}$, while the $MFP$ was lowest at the highest concentration of Bi₂O₃ (AM-$25\%$), with a value of $0.291 \mathrm{c}\mathrm{m}$ at a gamma energy value of $0.060 \mathrm{M}\mathrm{e}\mathrm{V}$. A comparison of the MFP values against the Bi₂O₃ nanoparticle concentrations for different energies is presented in

Table 7. A comparison of the MFP values against the Bi₂O₃ nanoparticle concentrations for different energies.

Parameter	Energy, MeV	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
HVL, cm	0.060	0.849 $\pm$ 0.004	0.590 $\pm$ 0.002	0.446 $\pm$ 0.005	0.354 $\pm$ 0.001	0.291 $\pm$ 0.002
	0.662	5.886 $\pm$ 0.002	5.615 $\pm$ 0.003	5.354 $\pm$ 0.007	5.103 $\pm$ 0.004	4.861 $\pm$ 0.007
	1.173	7.876 $\pm$ 0.001	7.639 $\pm$ 0.002	7.405 $\pm$ 0.004	7.171 $\pm$ 0.007	6.939 $\pm$ 0.004
	1.333	8.420 $\pm$ 0.006	8.179 $\pm$ 0.007	7.939 $\pm$ 0.008	7.699 $\pm$ 0.003	7.460 $\pm$ 0.002

.

The most important factor is the radiation shielding efficiency ($RPE$). At a practical and operational thickness of $2 \mathrm{c}\mathrm{m}$, it manifests the radiation shielding properties of the investigated samples. From Figure 7, it can be deduced that the AM-$25\%$ sample ($25\%$ Bi₂O₃ NPs) had the maximum $RPE$ over all the energy ranges, with approximately $100\%$ radiation absorption efficiency at $0.06 \mathrm{M}\mathrm{e}\mathrm{V}$ photon energy. When this energy range is exceeded, the efficiency is decreased to about $46.06\%$ at a radiation energy of $0.661 \mathrm{M}\mathrm{e}\mathrm{V}$. The lowest $RPE$ value for the samples with $25\%$ Bi₂O₃ NPs was $33.11\%$ at $1.33 \mathrm{M}\mathrm{e}\mathrm{V}$. The RSE values at different thicknesses (2, 5, and 8 cm) are presented in

Table 8. The RSE values at different thicknesses (2, 5, and 8 cm) and different energies.

	Energy, MeV	AM-0%	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
RSE, % (2 cm)	0.060	74.773	90.522	96.629	98.871	99.645	99.896
	0.662	27.692	28.807	29.965	31.170	32.425	33.730
	1.173	21.848	22.427	23.033	23.670	24.339	25.042
	1.333	20.619	21.143	21.693	22.270	22.877	23.516
	Energy, MeV	AM-0%	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
RSE, % (5 cm)	0.060	96.804	99.723	99.979	99.999	100.000	100.000
	0.662	55.540	57.234	58.953	60.696	62.462	64.249
	1.173	46.005	46.999	48.030	49.097	50.205	51.354
	1.333	43.858	44.780	45.737	46.731	47.765	48.840
	Energy, MeV	AM-0%	AM-5%	AM-10%	AM-15%	AM-20%	AM-25%
RSE, % (8 cm)	0.060	99.595	99.992	100.000	100.000	100.000	100.000
	0.662	72.663	74.311	75.943	77.556	79.148	80.713
	1.173	62.695	63.788	64.908	66.054	67.228	68.430
	1.333	60.294	61.332	62.399	63.495	64.621	65.779

.

To determine whether the newly designed and manufactured samples of AM reinforced with Bi₂O₃ NPs are practically efficient in terms of radiation attenuation, they were compared with the most commonly used building material (ordinary concrete) and the most efficient and commonly used radiation shielding material (lead). It was concluded that the AM sample with the highest concentration of $25\%$ of Bi₂O₃ NPs (AM-$25\%$) has efficient gamma radiation attenuation capabilities, so a comparison between AM-$25\%$, concrete, and lead regarding their radiation shielding properties was carried out. The $HVLs$ will be the measure for this comparison (Figure 8). From the figure below, it can be observed that at 0.662 MeV, the thickness needed to attenuate or absorb most of the incoming radiation was nearly 30 cm for AM-25%, while for ordinary concrete, it was around 37 cm, as calculated based on Equations (1) and (5).

The results show that the AM-$25\%$ sample outperforms ordinary concrete over all the studied energy ranges, as evidenced by its significantly lower $HVLs$ at the low energy range ($0.059 \mathrm{M}\mathrm{e}\mathrm{V}$) due to the influenced of the atomic number-dependent photoelectric effect interaction over this energy region. The composition of AM-$25\%$ has Ca and Bi ($Z$ $=20$ and $Z$ $=83$) as the main elements, while ordinary concrete is predominantly composed of silica, i.e., Si ($Z=14$), which has a lower atomic number. On the contrary, lead outperforms AM-$25\%$ over all the studied energy ranges due to its higher density and atomic number, which makes its shielding performance unconquerable despite its environmental issues. After all, it can be settled that these designed AM samples are very efficient at low energy to medium ($0.4 \mathrm{M}\mathrm{e}\mathrm{V}$ to $0.661 \mathrm{M}\mathrm{e}\mathrm{V}$) gamma energy regions as radiation shielding materials. Hence, they could be used as convenient gamma radiation shielding materials in medical diagnosis X-rays (conventional X-ray and CT imaging) because the utilized energy range of medical X-ray imaging is from $0.01 \mathrm{M}\mathrm{e}\mathrm{V}$ to $0.15 \mathrm{M}\mathrm{e}\mathrm{V}$ [30].

Finally, the attenuation results of the current work were compared with related works, and as shown in tabulated form in

Table 9. A comparison of the marbles from the present work with materials from other published works.

Reference	Sample Code	LAC, cm−1				TVL, cm
		0.060 MeV	0.662 MeV	1.173 MeV	1.333 MeV	0.060 MeV	0.662 MeV	1.173 MeV	1.333 MeV
AM-WO3 [21]	S1	2.862	0.191	0.139	0.129	0.805	12.049	16.577	17.794
	S2	2.872	0.197	0.140	0.130	0.802	11.694	16.459	17.699
	S3	2.886	0.200	0.142	0.132	0.798	11.524	16.238	17.457
	S4	2.991	0.211	0.144	0.134	0.770	10.908	16.035	17.248
PWPBi-composites [22]	PWPBi-5	3.505	0.190	0.131	0.122	0.657	12.111	17.530	18.874
	PWPBi-10	3.506	0.190	0.131	0.122	0.657	12.114	17.537	18.882
	PWPBi-20	3.510	0.190	0.131	0.122	0.656	12.116	17.542	18.887
	PWPBi-30	3.512	0.190	0.131	0.122	0.656	12.123	17.555	18.902
Present Work	AM-10%	1.695	0.178	0.131	0.122	1.358	12.929	17.591	18.833
	AM-15%	2.242	0.187	0.135	0.126	1.027	12.329	17.050	18.280
	AM-20%	2.821	0.196	0.139	0.130	0.816	11.750	16.512	17.728
	AM-25%	3.436	0.206	0.144	0.134	0.670	11.193	15.977	17.178

. The data in the table show that the manufactured marble samples studied in this work provide suitable results as a shield against gamma rays, especially at low energies, as at 0.060 MeV, AM25% performs slightly better than AM-WO3 and similar PWPBi-composites, while at higher energies, there are no significant differences.

4. Conclusions

The present study was performed to estimate the radiation shielding characteristics of innovative fabricated artificial marble (AM) composites made of waste marble with polyester resin embedded with nano-sized bismuth oxide (Bi₂O₃) in different concentrations. An experimental approach was employed to find out the linear attenuation coefficient ($LAC$) for each of the prepared AM samples and then calculate other shielding parameters using the determined $LAC$ values. The $LAC$ values obtained from the pure AM (without nanoparticles of Bi₂O₃) using the Phy-X software were consistent with the experimental values measured using an HPGe (high-purity germanium) detector, which is considered an indication of the accuracy of the results. The uniform distribution of the Bi₂O₃ nanoparticles, through the AM samples’ matrices, was proven to enhance the attenuation capabilities of the samples. Increasing the Bi₂O₃ content enhanced the shielding performance of the AM composites in terms of the $LAC$. The proportionality relation between the $LACs$ and the concentration of Bi₂O₃ nanoparticles in the composites was highly distinguished in the low-energy radiation zone; on the other hand, it was not as noticeable in the high-energy zone. Regarding the other shielding parameters of the composites under study, such as the half-value layer ($HVL$) and tenth-value layer ($TVL$), they decreased with increasing Bi₂O₃ NP concentrations. To comprehensively understand more of the characteristics of waste marble composites with potential as shielding materials against ionizing radiation, future studies should investigate incorporating additional types of polymers with the waste marble, such as epoxy resin, polydimethylsiloxane, polyvinyl chloride, etc.