Impact of Bulk and Nano Bismuth Oxide on the Attenuation Parameters of Bentonite Barite Composites

Abstract

Since bentonite can absorb neutrons and gamma rays without sacrificing structural integrity, it is frequently used as the main shielding material in many nuclear installations. Recently, there has been a trend toward enhancing the shielding qualities of bentonite by adding various chemicals. However, the majority of the added materials either require particular handling procedures or pose health risks. The availability of environmentally friendly additives would be wonderful. The addition of barite to bentonite composites greatly raises the density of the specimens. Additionally, the performance of bentonite–barite composites as radiation shielding materials is improved by adding various amounts of bulk and nano Bi₂O₃ as a filler (6%, 13%, and 20%). Energy dispersive X-ray analysis (EDX) was used to determine the chemical makeup of the produced specimens. The scanning electron microscopy (SEM) pictures showed the samples’ cross-sections’ porosity and homogeneity. ²⁴¹Am, ¹³³Ba, ¹³⁷Cs, and ⁶⁰Co are radioactive sources that emit energies of 59.53, 80.99, 356.01, 661.66, 1173.23, and 1332.5 keV, respectively, and the NaI (Tl) scintillation detector was used in this investigation. The area under the peak of the observed energy spectra was measured using the Genie 2000 program in both the specimen’s absence and presence. The coefficients for linear and mass attenuation were calculated. To determine the theoretical mass attenuation coefficients, the XCOM program was utilized and then compared to the corresponding experimental values. Various radiation shielding parameters dependent on the linear attenuation coefficient were computed for each studied composite. These parameters include the mean free path (MFP), half value layer (HVL), and tenth value layer (TVL). Also, the Z_eff and the EABF were determined for each specimen. According to the findings, bismuth oxide was added to bentonite–barite composites to reduce the transmitted flux through the specimens, which increased the LAC of the bentonite–barite composites. Furthermore, adding nanosized bismuth oxide particles increased the sample’s density and improved the material’s shielding properties. At a photon energy of 0.356 keV, the relative deviation (∆%) between the experimental nano- and micro values for Bi₂O₃ (20 wt%) was 12.1974, confirming that the nanoparticles increase attenuation efficiency.

1. Introduction

Gamma rays are a form of electromagnetic radiation that find extensive applications across various industries, including medicine, agriculture, industry, dentistry, and scientific research. Gamma photons have the remarkable capacity to penetrate deeply, travel at light speed, and possess no charge or mass. These unique characteristics pose significant challenges when it comes to defending against gamma rays. The utilization of gamma sources in hospitals and research facilities for diagnostic purposes has granted individuals access to potentially hazardous areas. Consequently, it becomes imperative to develop a suitable and effective shielding substance to safeguard against gamma rays. The effectiveness of shielding materials depends on several factors, including the thickness, type of medium, attenuation performance, and the presence of high atomic number (z) materials [1,2,3,4].

In order to create a shield that effectively mitigates gamma radiation, it is crucial to conduct comprehensive studies on the interaction between gamma rays and matter. These studies will provide valuable insights into the mechanisms through which gamma radiation interacts with different materials, enabling the development of robust shielding solutions [5]. Gamma radiation has been reduced by the use of lead because lead is a high-Z element. However, lead is poisonous, heavy, and chemically unstable. Due to these drawbacks, scientists are actively seeking lead-free materials that are not only non-toxic but also possess strong gamma-ray attenuation properties [6]. Bismuth oxide (Bi₂O₃) was chosen for this study due to its higher atomic number and non-toxic nature. Additionally, it is considered a high-density material that is suitable for radiation shielding. Bismuth oxide has been successfully applied to a wide range of materials, including glass, rubber, and building materials [7,8].

In recent years, there has been a significant focus on the capability of bentonite composites to block radiation, which was driven by the expanding nuclear sector worldwide. Bentonite composites are increasingly being utilized in nuclear technology and science, particularly for protection against gamma and X-rays. As a result of extensive research efforts, numerous papers on the usage of bentonite composites as radiation shields have been published globally [9]. This has positioned bentonite composites as a desirable technique for creating mixtures that can effectively attenuate high-energy gamma rays. Gallala et al. [10] have been dedicated to increasing the gamma-ray shielding capability of bentonite with aggregate additives of different mixtures of cement–barite–bismuth as bulk or nano materials. High-performance concrete, including barite aggregate and bismuth powder, increased the shielding properties of the concrete against gamma rays. Ouda et al. [11] show that concrete’s aggregate is crucial in influencing the material’s mechanical characteristics by using the coarse aggregates of barite, magnetite, goethite, and serpentine, which significantly affect its shielding properties. As a result, mixing magnetite as a fine aggregate with high-performance concrete improves its ability to shield γ-rays. Mcconn et al. [12] investigated that the attenuation of gamma rays is influenced by the additives of bentonite, the density, the thickness of the specimen, and the gamma-ray energy. Sallem et al. [13] demonstrated that ball-milled calcinated bentonite has a higher gamma-ray attenuation capacity than ordinary calcinated bentonite. Al-Ghamdi et al. [14] deduced that pure bentonite ceramic, granite, and marble all exhibit less radiation shielding compared to bentonite ceramic with CdO and Bi₂O₃. The densities of barite and bismuth are equal to 4.5 g/cm³ and 9.75 g/cm³, respectively, which are considered to be high densities. So, bismuth and barite additives are excellent absorbent materials for reducing gamma-ray radiation [15,16].

This study investigated the shielding capabilities, mechanical properties, and morphology of various mixes of bentonite–barite–bismuth oxide specimens. The aim was to enhance the quality of radiation protection. Furthermore, the influence of the particle size and weight percentage of Bi₂O₃ particles on the gamma radiation shielding capability of bentonite–barite–bismuth oxide composites was examined. The radiation shielding parameters of different composites with varying weight fractions were evaluated using a NaI scintillation detector, covering photon energies ranging from 59.53 keV to 1408.01 keV. Additionally, a comparative analysis was conducted to assess the radiation shielding abilities of nano Bi₂O₃ and micro Bi₂O₃ composites.

2. Materials and Method

2.1. Materials

In this study, the primary material used was bentonite, which was obtained from Suez, Egypt. The bentonite was crushed and then ground into a fine powder. Barite and bismuth oxide were also included as ingredients. To determine the composition of the bentonite and barite chemically, energy dispersive X-ray (EDX) analysis was conducted. The results, including the average mass percentage of each metal, can be found in Figure 1 and Figure 2. Furthermore, two different sizes of Bi₂O₃ particles were utilized in this research. The first type was Bi₂O₃ microparticles (bulk), which are high-purity powders with a purity level of 99.9%. These microparticles were obtained from Loba Chemie in Mumbai, India. The second type was Bi₂O₃ nanoparticles, which were synthesized chemically by the Nanotech firm in Giza, Egypt.

2.2. Samples Preparation

The specimens were created using a combination of finely ground bentonite powder, water, and additional substances, such as bismuth oxide (Bi₂O₃) and fine barite powder. To produce the samples, specific mass ratios of barite (20, 23.3, 27, and 30) were mixed with micro (bulk) and nano bismuth oxide (Bi₂O₃) in varying amounts of 0%, 6%, 13%, and 20%, respectively. The corresponding specimen codes and weight percentages (wt%) of bentonite, barite, and Bi₂O₃ are presented in

Table 1. Specimen codes and weight fraction in percentage (wt%) of bentonite, barite, and Bi₂O₃.

Sample Codes	Compositions (wt%)			Density (g/cm3)
	Main Matrix		Bismuth Oxide (Bi2O3)	Micro	Nano
	Bentonite	Barite
BB-0	67	33	0	2.338 ± 0.012
BB-1		27	6	2.584 ± 0.052	2.885 ± 0.013
BB-2		20	13	2.815 ± 0.064	2.955 ± 0.089
BB-3	61	33	6	2.911 ± 0.043	3.024 ± 0.054
BB-4	54		13	3.105 ± 0.023	3.291 ± 0.064
BB-5	56.7	23.3	20	3.2547 ± 0.081	3.312 ± 0.072

. A coin-shaped mold with a diameter of 3 cm and a thickness of 0.5 cm was utilized to shape the specimens. The mixture was poured into the mold and left to dry and solidify in the open air. Each specimen’s average density (g/cm³) was then determined using the Archimedes method with water serving as the immersion medium.

2.3. Morphology Test

In order to distinguish between micro- and nanosized Bi₂O₃ particles, we utilized the JEM-2100F transmission electron microscope, JEOL, Japan with a 200 kV acceleration voltage to conduct the TEM investigation. Figure 3a,b reveals that the average size of microparticles is 3 µm, while nanoparticles measure 12 nm. The cross-section shape and distribution of the Bi₂O₃ inside the samples could be studied using scanning electron microscopy (SEM; JEOL-JFC-1100E). Images of the scanned samples for bentonite–barite of 0, 6, 13, and 20 wt% bulk and nano of Bi₂O₃ are shown in Figure 4. The morphology of the composites under testing was revealed with the scanning electron microscope in Figure 4a where bentonite with fluffy platelets and a porous structure was combined with barite as the plate lumps formed. Figure 4b–d shows composites of bentonite and barite intercalated with spherical-shaped bulk Bi₂O₃ of 6, 13, and 20 wt%, while Figure 4e–g showed composites of bentonite and barite intercalated with spherical-shaped nano Bi₂O₃ of 6, 13, and 20 wt%. This demonstrates that the high nanofiller Bi₂O₃ composites reduced the bentonite pores, increased the composite’s density, and improved the attributes of these nanocomposites as gamma-ray shielding materials.

2.4. Mechanical Properties

The material’s mechanical behavior reflects the link between a material’s response and deformation caused by a force or load applied. Strength, ductility, toughness, hardness, and stiffness are important mechanical design characteristics. The type of applied load, its duration, and environmental conditions are all factors that should be taken into account when determining how the mechanical properties of materials will behave. The load may be constant in magnitude and classified as tensile, compressive, or shear throughout time or continuously fluctuate. With the help of the universal testing machine (see Figure 5), the most typical mechanical stress-strain tests were carried out in tension for all test specimens at room temperature. A steadily increasing tensile force applied uniaxially along one of the specimen’s lengths causes deformation, typically leading to fracture. The test subjects’ tensile specimens were made into cylindrical specimens with a 23 mm diameter and an area of 415 mm².

Comparing samples with similar Bi₂O₃ concentrations and adding or fixing barite (BB-1 and BB-3 or BB-2 and BB-4) for micro samples, it is obvious that the break distance decreases while the ultimate tension grows. When contrasting BB-5 (highest concentration of Bi₂O₃ 20 wt%) with BB-4 (lowest concentration of Bi₂O₃ (13 wt%) and descending barite concentration, data in

Table 2. The table shows the ultimate force and ultimate stress with the break distance for each sample.

Sample Code	Ultimate Force (Newton)	Ultimate Stress (MPa)	Break Distance (mm)
BB-0	2654.46	6.39	4.51
BB-1 Micro	3868.55	9.31	6.73
BB-1 Nano	3251.87	7.9	4.56
BB-2 Micro	4737.5	11.4	2.93
BB-2 Nano	1819.67	4.38	7.53
BB-3 Micro	4333.33	10.43	2.99
BB-3 Nano	4916.67	11.87	5
BB-4 Micro	5161	12.42	1.85
BB-4 Nano	4090.24	9.84	2.07
BB-5 Micro	3615.33	8.7	3.84
BB-5 Nano	3685.46	8.87	7.47

demonstrate that the break distance increased, and the ultimate tension decreased. When BB-1 and BB-3, which have the same concentration of Bi₂O₃ (6 wt%), or BB-2 and BB-4, which have the same concentration of Bi₂O₃ (13 wt%), are compared, it can be seen that the extra barite increases final stress while decreasing break distance. When BB-5 and BB-4 are compared, bentonite somewhat increases while barite slightly reduces, and by adding more Bi₂O₃ (20 wt%), the final stress is reduced, and the break distance is increased (see Table 2).

2.5. Radiation Measurements

An experiment was conducted to determine the shielding characteristics and quantity of γ-rays that penetrated the sample. The experiment involved a focused beam of gamma rays produced by a gamma source, which passed through the sample and reached the detector. In this experiment, a scintillation detector of the NaI (Tl) type was used. The setup arrangement of the source–detector system is illustrated in Figure 6. Four radioactive sources (Am-241, Ba-133, Cs-137, and Co-60) were utilized for this study. These sources emit a wide range of radiation energy from 0.0595 MeV to 1.332 MeV. The photons that exited the sample interacted with the detector crystal, converting them into signals. The Genie 2000 software, 9233652E V3.0 was employed to display these signals as peaks in a spectrum [17,18], Figure 7.

2.6. Gamma-Ray Attenuation Characteristics

The LAC describes how easily a beam of gamma ray can enter the body of material. The values of the linear attenuation coefficients were computed using Beer–Lambert’s law [19]:

I = Io e−µx

(1)

where µ (cm⁻¹) is the linear attenuation coefficient (LAC), x is the material’s thickness, I is the intensity of an attenuated photon, and I_o is the intensity of an input photon.

The average distance between two consecutive photon collisions is known as the mean free path, and it is determined using Equation (2) [20,21,22,23]:

MFP = 1/µ

(2)

The half value layer (HVL) was calculated to determine the specimen’s gamma shielding penetration strength. HVL is described as the thickness that reduces the incident photon’s intensity to 50% of its original intensity. Below, Formula (3) was used to calculate the HVL for the current specimens. [24,25]:

HVL = ln2/µ

(3)

The following formula was used to calculate the tenth value layer (TVL), which is the thickness of material needed to attenuate incident radiation to 90% of its original intensity [26,27,28]:

TVL = ln10/µ

(4)

The most crucial shielding metric, the mass attenuation coefficient (μ_m), is utilized to compare the shielding effects of various materials. The mass attenuation coefficient (µ/$\mathsf{\rho }$), is the division of the LAC by the composite density $\left(\mathsf{\rho }\right)$ of unit (cm² g⁻¹) as shown in the following equation:

$$\mathrm{MAC} (\mathsf{\mu }/\mathsf{\rho })={\sum }_i{{\mathrm{W}}_i\left(\mathrm{\mu }/\mathsf{\rho }\right)}_i$$

(5)

where W_i is a weight fraction of i-th constituent element in the shielding material sample, and (µ/$\mathsf{\rho }$)_I is the total mass attenuation coefficient of that element at certain photon energy.

The effective atomic number Z_eff is a crucial radiation interaction metric used to describe how radiation attenuation in composite materials varies depending on the specimen’s composition and photon energy. Formula (6) given below can be used to calculate the Z_eff values [29]:

$$\mathrm{Z}{\mathrm{eff}}_{ }=\frac{{\mathsf{\Sigma }}_{\mathrm{I}}{\mathrm{f}}_{\mathrm{I}}{\mathrm{A}}_{\mathrm{I}}{\left(\mathrm{M}\mathrm{A}\mathrm{C}\right)}_{\mathrm{i}}}{{\mathsf{\Sigma }}_{\mathrm{I}}\frac{{\mathrm{A}}_{\mathrm{i}}}{{\mathrm{z}}_{\mathrm{I}}}{\left(\mathrm{M}\mathrm{A}\mathrm{C}\right)}_{\mathrm{i}}}$$

(6)

where ${\mathrm{f}}_{\mathrm{I}}$, A_i, and Z_i are weight fraction, atomic weight, and the atomic number of each constituent element in each specimen, respectively.

The correction factor is the buildup factor that takes into consideration the increased radiation transmission through shielding. The buildup factor is affected by the energy of the primary radiation, the composition, and the thickness of the shielding substance.

For each sample, the equivalent atomic number (Z_eq), which represents the attributes of the composite material in terms of an equivalent element, must be computed in order to derive the energy absorption accumulation factor. The following formula can be used to calculate the values of Z_eq, which are affected by the photon energy values [30,31,32]:

$${\mathrm{z}}_{\mathrm{e}\mathrm{q}}=\frac{{\mathrm{z}}_1(\log {\mathrm{R}}_2-\log \mathrm{R})+{\mathrm{z}}_2(\log \mathrm{R}-\log {\mathrm{R}}_1)}{(\log {\mathrm{R}}_2-\log {\mathrm{R}}_1)}$$

(7)

where Z₁ and Z₂ are the atomic numbers of elements corresponding to the ratios R₁ and R₂, respectively, and R is the ratio of Compton partial mass attenuation coefficients (µ_Compton) to the total mass attenuation coefficients (µ_total) for the selected composite at specific values of energies.

Then, the five G-P fitting parameters (b, c, a, X_k, and d) for the selected composite must be determined using the same logarithmic interpolation as well as Z_eq (8) [33]:

$$\mathrm{h}=\frac{{\mathrm{h}}_1(\log {\mathrm{z}}_2-\log \mathrm{z})+{\mathrm{h}}_2(\log \mathrm{z}-\log {\mathrm{z}}_1)}{(\log {\mathrm{z}}_2-\log {\mathrm{z}}_1)}$$

(8)

where h represents the G-P fitting coefficient function, which corresponds to the obtained Z_eq, and h₁ and h₂ represent the values of G-P fitting parameters that correspond to the atomic numbers Z₁ and Z₂, respectively, within the range of energy between 0.015 and 15 MeV for penetration depth MFP up to 40.

Finally, the calculated G-P parameters were used to compute the EABF from the following G-P fitting formula [34]:

$$\mathrm{B} (\mathrm{E},\mathrm{x})=1+\frac{\mathrm{b}-1}{\mathrm{K}-1}({\mathrm{K}}^{\mathrm{x}}-1) \mathrm{f}\mathrm{o}\mathrm{r} \mathrm{K}\ne 1$$

(9)

B (E, x) = 1+ (b – 1) x for K = 1

(10)

$$\mathrm{K}\left(\mathrm{E},\mathrm{x}\right)=\mathrm{c}{\mathrm{x}}^{\mathrm{a}}+\mathrm{d}\frac{\tanh \left(\frac{\mathrm{x}}{{\mathrm{X}}_{\mathrm{k}}}-2\right)-\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{h}(-2)}{1-\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{h}(-2)} \mathrm{f}\mathrm{o}\mathrm{r} \mathrm{x}\le 40 \mathrm{m}\mathrm{f}\mathrm{p}$$

(11)

where x is the depth of penetration in mfp, K is the photon dose multiplicative factor and represents the spectrum shape change, E is the incident photon energy, and (b, c, a, X_k, d) are the calculated G-P fitting parameters in the previous step.

3. Results and Discussion

Without a doubt, the linear attenuation coefficient (μ) is the most basic parameter employed in experiments to gauge a substance’s capacity to absorb input gamma radiation. It shows the likelihood of a photon interacting with any material for a given travel path length. The LAC (μ) of the absorbing substance is proportional to how the photons interact predominantly with atomic electrons. The linear attenuation coefficient of the specimen increases with the increase in the wt% of the reinforcement materials (Bi₂O₃—Barite) due to the rise in density ($\mathsf{\rho })$ of the samples while decreasing with the rise in photon energy. Therefore, at a photon energy of around 0.05953 MeV, the LAC shows larger values in Figure 8. The graph clearly shows that for the same concentrations and photon energy, the LAC values of the nano Bi₂O₃ particles are greater than those of the micro Bi₂O₃ particles. More barite concentrations also result in higher sample densities, which raise the linear attenuation coefficient (LAC) values for constant bismuth oxide (Bi₂O₃) concentrations at the same photon energy.

When barite and bismuth oxide are added to the bentonite matrix, they do not suffer any chemical reactions and instead choose to occupy the matrix’s interstitial spaces.

Table 3. The mass attenuation coefficient values at different photon energies for bentonite–bismuth oxide and barite in different concentrations.

Sample Code/ Bi2O3wt%	Energy (keV)	Mass Attenuation Coefficient (cm2 g−1)
		XCOM	Micro Bi2O3/ (Bentonite and Barite)	Δ%
BB-0 0 wt%	59.53	1.7310	1.7694	2.22
	80.99	0.8142	0.7943	−2.44
	356.01	0.1054	0.1060	0.61
	661.66	0.0760	0.0778	2.36
	1173.23	0.0570	0.0579	1.69
	1332.5	0.0534	0.0536	0.35
BB-1 6 wt%	59.53	1.7180	1.7391	1.23
	80.99	0.8086	0.8277	2.37
	356.01	0.1136	0.1113	−2.06
	661.66	0.0776	0.0772	−0.59
	1173.23	0.0573	0.0588	2.58
	1332.5	0.0536	0.0535	−0.28
BB-2 13 wt%	59.53	1.7030	1.6933	−0.57
	80.99	0.8021	0.7867	−1.92
	356.01	0.1233	0.1206	−2.20
	661.66	0.0795	0.0782	−1.64
	1173.23	0.0577	0.0564	−2.27
	1332.5	0.0539	0.0542	0.54
BB-3 6 wt%	59.53	1.9720	2.0176	2.31
	80.99	0.9171	0.9179	0.09
	356.01	0.1148	0.1181	2.90
	661.66	0.0776	0.0777	0.16
	1173.23	0.0571	0.0581	1.78
	1332.5	0.0534	0.0537	0.49
BB-4 13 wt%	59.53	2.2560	2.3008	1.99
	80.99	1.0370	1.0153	−2.10
	356.01	0.1258	0.1255	−0.25
	661.66	0.0794	0.0795	0.06
	1173.23	0.0573	0.0580	1.34
	1332.5	0.0535	0.0524	−1.90
BB-5 20 wt%	59.53	2.1270	2.1972	3.30
	80.99	0.9816	0.9703	−1.15
	356.01	0.1349	0.1351	0.18
	661.66	0.0814	0.0801	−1.58
	1173.23	0.0577	0.0587	1.65
	1332.5	0.0538	0.0528	−1.80

displays the improvement in the μ_m values due to the energy of the photons and the chemical makeup of the system composed of bentonite, Bi₂O₃, and barite. Table 3 shows that the μ_m values decrease as the photon energy and the amount of bismuth oxide–barite in the samples rise. At energies below 356.01 keV, the μ_m values drop off due to the photoelectric absorption process. This behavior is linked to the energy of the associated photon [35]. Due to the Compton scattering effect phenomenon, the values of μ_m also drop, although with minor deviations, as the energy level increases for the energy range of 661.66 to 1.332.5 keV [36].

The MFP exhibits high values at higher photon energies and decreases at lower photon energies, which is a straightforward observation. Moreover, the inclusion of bismuth/barite in the samples affects the MFP trend, resulting in decreased MFP values as the bismuth/barite content increases. These results imply that as the bismuth/barite level rises, the MFP values decline. This relationship is illustrated in Figure 9 where the BB-0 sample with no bismuth oxide content displays the highest MFP values, while the BB-5 sample with the highest concentration of bismuth oxide exhibits the lowest MFP values. Additionally, the MFP values of the nanoparticles are lower than the microparticles.

Another parameter for assessing the shielding capacity of gamma photons is the half value layer (HVL), which provides specific information about the samples. A lower HVL indicates more effective radiation shielding. Figure 10 illustrates the HVL trend for the sample composition at photon energies of 59.53, 661.66, and 1332.5 keV. It is evident that the values of HVL for BB-0 containing 0 wt% of bulk and NPs Bi₂O₃ are higher than those of the BB-1, BB-2, BB-3, BB-4, and BB-5 composites at the same values of photon energy. As the concentration of bismuth oxide increases, the HVL decreases. Furthermore, nanosized bismuth oxide particles in the bentonite–barite composites significantly reduce the HVL compared to microsized particles of the same concentration and photon energy. This indicates that nanocomposites outperform micro composites of the same concentration in shielding against gamma radiation at the same values of photon energy. Additionally, it was observed that higher barite concentrations lead to lower HVL levels at the same photon energies when comparing samples.

Similarly, the values of the tenth value layer (TVL), which show a greater reduction in the incident photon intensity to a tenth of its initial intensity value when the shielding material thickness grows to particular levels, have a direct link with photon energy. Additionally, it is noted that the composite without Bi₂O₃ has a larger TVL. When Bi₂O₃ is added to the composites in varying amounts (6, 13, or 20 wt%), the tenth value layer decreases with the increase in photon energy.

Additionally, the impact of the particle sizes on the tenth value layer values is demonstrated in samples of nano Bi₂O₃–bentonite–barite with substantially lower TVL values than samples of micro Bi₂O₃–bentonite–barite at the same photon energy. Accordingly, increasing the amount of barite in samples while maintaining the same photon energy levels results in a drop in TVL, as seen in Figure 11.

Figure 12 shows the relationship between the effective atomic number, the photon energy, and the density of each sample. It was noticed that the photon energy and sample composition generally affect the effective atomic number (Z_eff) values. By increasing the energy of the photon, the values of Z_eff decrease. The examined composites have Z_eff values ranging from 12.65 to 64.32. When comparing the Z_eff values for samples BB-1 and BB-3 with the same Bi₂O₃ concentration (6 wt%), it is obvious that Z_eff is higher for BB-3 than BB-1. Similar to this, comparing BB-2 and BB-4 with the same amount of Bi₂O₃ (13 wt%), it is noticed that BB-4’s Z_eff values are greater than that of BB-2’s. This is due to the samples BB-3 and BB-4 containing more barite than the samples BB-1 and BB-2, respectively. Additionally, it was discovered that the bentonite–barite sample BB-5, which contains the highest amount of Bi₂O₃ (20 wt%), has the highest Z_eff, whereas the BB-0 (0 wt% Bi₂O₃) bentonite–barite sample has the lowest Z_eff. Consequently, the shielding material efficiency against the incident gamma ray increases with the increase in the gamma rays’ interaction with the samples that have a more effective atomic number. It is evident that the higher the Z_eff, the better the shielding material performance.

The primary radiation’s energy, the shielding material’s makeup, and the shielding material’s thickness all affect buildup factors. Figure 13 shows the relation between the EABF and the photon energy at 1, 15, 25, and 40 mfp. It is observed that the EABF in the lower and higher energies has a lower level according to the photoelectric absorption that predominates in regions of lower photon energy and the pair production that predominates in regions of higher photon energy. At moderate photon energies where the buildup factor rises, Compton scattering predominates. The multiple Compton scattering increases the buildup factors’ values to their maximum. A result of the K-edge of barium (37.44 keV) and bismuth (90.5 keV), there is a dramatic change in the buildup factor’s behavior at lower photon energies. The abrupt rise in the energy is due to the fact that the incident photon energy must exceed the electron’s binding energy in the K shell of the atom with which it interacts. At energy levels exceeding 10 MeV, the values exhibited a consistent trend of gradual increase with the incident energy. Moreover, the material’s penetration depth increases, resulting in an augmented thickness of the interacting material. Consequently, this leads to an increase in scattering events within the interacting medium, especially for the material that has the highest equivalent atomic number. As a result, significant values of EABF are observed.

In a comparison between this study, which used the bentonite–barite matrix and Bi₂O₃ bulk and Np’s (filler), and the study of Abbas et al. [34], which used bulk and nanoscale Bi₂O₃ as filler in the bentonite matrix, at the same Bi₂O₃ microparticle concentrations and photon energies (59.53, 80.99, 356.01 keV) and the bentonite–barite composites of the current work for (6 wt% and 20 wt%), the Bi₂O₃ microparticles have a higher linear attenuation coefficient than that of the bentonite–gypsum composite of Abbas et al. [34], as seen in

Table 4. The comparison in the linear attenuation coefficient at photon energies 59.53, 80.99, and 356.01 keV and at the same concentrations of bismuth oxide (6 wt% and 20 wt%) between bentonite–gypsum composites and bentonite–barite composites.

Bi2O3 wt%	Energy (keV)	Linear Attenuation Coefficient (cm−1)
		Bentonite–Gypsum/Bi2O [34]	Bentonite–Barite/Bi2O3
6 wt% Bi2O3	59.53	1.3473	4.4937
	80.99	0.7537	2.1389
	356.01	0.2705	0.2874
20 wt% Bi2O3	59.53	3.1821	7.1512
	80.99	1.5177	3.1581
	356.01	0.3767	0.4398

. This means that the presence of barite in the bentonite composites increases the linear attenuation coefficient, which confirms the higher shielding performance of the bentonite in the nano Bi₂O₃ composites.

4. Conclusions

Due to their good radiation-shielding qualities, bentonite and barite were chosen as the primary matrix in this investigation. Bismuth oxide, both in bulk and in nanoscale form, was employed as a filler with varying weight percentages. The comparison that was carried out between the determined experimental and theoretical (XCOM) mass attenuation coefficients produced positive findings. The composites with higher concentrations of bismuth oxide were found to have higher mass attenuation coefficient values. Composites with a higher barite content had greater mass attenuation coefficient values as well due to their high density value. Moreover, the mass attenuation coefficients of the nanosized particles were substantially higher when compared to bulk samples of the same Bi₂O₃ weight percentages and at the same values of photon energies, which ranged from 0.0595 MeV to 1.3325 MeV. When compared to bulk samples of the same Bi₂O₃ oxide weight percentages and at a range of γ-ray photon energies from 0.0595 MeV to 1.3325 MeV, the nanosized particles exhibited significantly better mass attenuation coefficients. The determination of the HVL, TVL, MFP, and the effective atomic number for all samples at variant gamma energies confirmed the obtained results that were calculated using the mass attenuation coefficient. Moreover, the estimation of the values for the EABF for all composites grew at low photon energies and showed the maximum at middle photon energies. Furthermore, composites with higher bismuth oxide content had lower absorption build-up factors. Additionally, at deeper penetration depths, the energy absorption build-up factor values were higher. Finally, barite-containing bentonite composites improved attenuation efficiency, especially when nanofiller Bi₂O₃ was present in high concentrations.