Impacts of the calcinated clay on structure and gamma-ray shielding capacity of epoxy-based composites

2.1 Fabrication and characterization

The fired clay is a result of calcinated clay mineral at 1,000°C, to exclude the moisture and organic materials in the natural clay. Then, the fired clay was mixed with epoxy resin according to the mixing formula (100−x) (0.66 epoxy + 0.34 curing agent) + x fired clay; x is 0, 20, 40, and 60 wt% for samples EC0, EC20, EC40, and EC60, respectively. The SlabDOC (Ivanovo, Russia) produces the epoxy resin, and its curing agent with purities reach 98%. The required amount of fired clay, epoxy resin, and curing agent were weighted accurately using an electric balance and then mixed for 15 min using a vertical blender. After that, the mixture was molded in silicon rubber cubic molds with dimensions of 3 cm in length and 3 cm in width. For solidifying the molded sample, they were kept at +25°C overnight. For each sample, three different thicknesses were fabricated to be used in the gamma-ray attenuation experimental examination as shown in Figure 1.

Figure 1

Fabricated samples of composite-based epoxy doped with calcinated clay.

The density (ρ, g·cm⁻³) of the developed fired clay-based epoxy composites was determined with the MXBAOHENG MH 300A density meter (Guangdong, China). The uncertainty in the ρ measurements is ±0.001 g·cm⁻³. The Archimedes principle in Eq. 1 is the method used to determine ρ values for the developed composites, where W _L and W _a stand for the composite weight in immersing liquid and in dry air, respectively. In addition, ρ _L ≈ 1 for the immersing liquid, which is tap water (27–29).

The chemical concentration (wt%) of the developed calcinated clay-based epoxy composites was determined using an X-ray fluorescence analyzer (OLYMPUS X-5000 portable analyzer field EDXRF lab analysis capability, USA). The X-5000 combines the dependability and low cost of conventional benchtop EDXRF analysis with the safety and superior performance of field-proven handheld X-ray fluorescence (XRF) equipment. The Olympus X-5000 portable analyzer provides a high degree of performance because of its 50 keV/10 W X-ray tube, which offers a flawless detection limit (LOD) from light elements like magnesium (Mg) to heavy elements like uranium (U). In addition, different anode types, such as silver (Ag), tantalum (Ta), and rhodium (Rh), are used to differentiate it. The chemical composition and the density of the fabricated samples are listed in Table 1. In addition, for the Fourier transform infrared (FTIR) measurements spanning a wavenumber range of 4,500–500 cm⁻¹, a compact FTIR spectrometer, ALPHA II (Bruker Optics, USA), was used.

2.2 Gamma-ray attenuation parameters examination

A NaI(Tl) crystal gamma-ray spectrometer was employed to gauge the linear attenuation coefficient (LAC, in cm⁻¹) at fixed γ-ray energies emitted from the radioactive sources Cs-137, Co-60, Na-22, Ba-133, and Eu-152, as depicted in Figure 2. To prevent photon accumulation and mitigate the impact of the buildup factor, the narrow beam transmission technique was utilized. During the measurement, the NaI(Tl) detector captured the activity of the radioactive sources that reached the detector with the presence of the fabricated EC composites (I _t), as well as without their presence (I _o). To ensure precision, the thickness of the fabricated EC composites was precisely measured using a micrometer with an uncertainty of ±0.01 µm. The relationship between ln (I _o/I _t) and the thickness was modeled with a straight line, and the slope of this line yielded the LAC values, as demonstrated in Eq. 2 (30,31).

Figure 2

The experimental setup for the linear attenuation coefficient measurements.

The half-value layer (HVL), measured in centimeters, represents the thickness of the manufactured composite material that effectively reduces the intensity of photon radiation emitted by a radioactive source by half (see Eq. 3). Within this context, the HVL is directly influenced by the LAC, such that composites with higher LAC values exhibit correspondingly higher HVL values. Conversely, the transmission factor (TF; see Eq. 4), expressed as a percentage, quantifies the proportion of the radioactive source’s activity that successfully traverses the composite’s thickness (I _t) relative to the original activity of the source (I _o) (32,33).

The radiation protection efficiency (RPE), expressed as a percentage, quantifies the extent to which the fabricated EC composites absorb the radioactive source’s activity (I _a) in comparison to the original radioactive source activity (I _o). Eq. 5 is employed to calculate this vital parameter.

3.1 Based on the measured LAC

The demeanor can be explained in relation to the photoelectric effect (σ _PE), which denotes the interaction between particles and their environment, particularly at low photon energies. In the photoelectric effect, cross-sectional mechanism is proportional with the ratio of Z ^4–5 and E ^3.5, which is determined by the atomic number (Z) and energy of the material (E), which are also represented by their respective values. Above 100 keV, the LAC values decreased within the range of medium gamma photon energy. The energy (E) and atomic number (Z) are directly related to the Compton scattering cross sections (CS) in the formula given (σ _CS ∝ Z/E) (39,40). At energies above 1,000 keV, the pair production mechanism becomes more important, resulting in a slight decrease in both the LAC values. The cross-section for pair production, denoted as σ _pp, increases with the square of the atomic number (Z ²).

ρ values for the fabricated samples and the mass attenuation coefficient (MAC, cm²·g⁻¹) were calculated at gamma-ray energy of 662 keV and compared to some polymetric composites (µm) as recently reported in publications, as illustrated in Table 2. The MAC values for the fabricated samples at 662 keV are 0.1263, 0.1258, 0.1329, and 0.1299 cm²·g⁻¹ for samples EC0, EC20, EC40, and EC60, respectively. The fabricated calcinated clay-based-epoxy composites have high shielding capacity compared to other reported polymetric composites, as illustrated in Table 2.

Figure 6 shows how the HVL of EC composites changes with photon energy for different concentrations of clay. At low photon energies, the HVL increases rapidly due to the photoelectric effect. At medium photon energies, the HVL increases more slowly due to compton scattering. At high photon energies, the HVL continues to increase, but more slowly, because some photons can penetrate the EC composites without interacting with them. The figure also shows that the HVL of EC composites increases with the concentration of clay from 0 to 60 wt%. During the evolution of gamma photon energy from 33 to 1,408 keV, the HVL values were observed to increase with the increasing gamma photon energy. HVL values at 33 keV ranged from 2.8 to 0.6 cm for compositions containing 0 and 60 wt% clay, respectively. When gamma energies are increased to 1,407 keV, HVL values are expected to be 7.6 cm for compositions with 0% clay and 5.2 cm for compositions with 60% clay.

Figure 6

The fabricated composites half-value layer (HVL, cm) at various γ-ray energies.

The TF of synthetic EC composites has been computed and is presented in Figure 7. The figure demonstrates the variations in TF as the incoming gamma photon energies span from 33 to 1,408 keV. The increase in the gamma-photon energy decreases the PE and CS interaction CS, leading to a reduction in the photon–electron interaction and an increase in the I t photon number. Then, the increase in I t photon increases the I t I o ratio and TF values. For example, the increase in applied photon energy between 33 and 1,408 keV is followed by an increase in the TF values between 78.13–91.32% (for the EC sample), 64.28–88.28% (for the EC20 sample), 53.16–87.95% (for the EC40 samples), and 43.57–87/58% (for the EC60 sample), as presented in Figure 7. In contrast, the increase in the I t photons decreases the photons absorbed within the fabricated sample thickness and decreases the RPE values. Figure 8 shows a reduction in the RPE values when the photon energy increases. In this regard, the fabricated samples’ RPE decreased between 21.87–8.68% (for the EC0 sample), 35.72–10.28% (for the EC20 sample), 46.84–12.05% (for the EC40 sample), and 56.43–12.42% (for the EC60 sample) with increasing the gamma-photon energy between 33 and 1,408 keV, respectively.

Figure 7

The fabricated composite transmission factor (TF, %) at various γ-ray energies.

Figure 8

The fabricated composite radiation protection efficiency (RPE, %) at various γ-ray energies.

Figure 9 illustrates how EC composite materials with thicknesses between 0.5 and 10 cm exhibit an impact on the mutation of TF and RPE data. A fixed gamma energy of 122 keV was used to observe the variation in composites of EC, containing clay concentrations of 0%, 20%, 40%, and 60%. TF and RPE values of EC composites are influenced significantly by their thickness. As the composite material thickness reduced to 0.5 cm, gamma photons are easily able to traverse it with low impulse, resulting in a reduction in TF values from 91% to 87% and an increase in RPE from 8% to 12%. However, with an increase in thickness, the gamma photons encounter more interactions, resulting in a decrease in their transmission (TF) and a simultaneous increase in impulse (RPE) for the EC composite material. The reduction of TF and the increase in RPE values are attributed to the track length of gamma-photons with increasing thickness of the fabricated samples. The increase in the sample thickness increases the path length of gamma-photons as well as increases the interactions between applied photons and the material electrons. As a result, I t , I t I o , and TF values were reduced accompanied by an increase in the RPE values, as illustrated in Figure 9(a) and (b).

Figure 9

Impacts of the samples’ thickness on (a) transmission factor (TF, %) and (b) radiation protection efficiency (RPE, %).

The LAC of gamma-rays in a composite made of clay and epoxy resin is determined by various factors like the density, the atomic number of the clay particles, and the volume fraction of the clay particles in the composite. One of these factors is the density of EC composites. The density of the EC composite has a direct impact on the LAC. This is because a denser material contains more atoms per unit volume, which means that there are more opportunities for the gamma-rays to interact with the EC material. In the case of EC composites made of clay and epoxy resin, the LAC will increase with increasing density and increasing volume fraction of clay particles. This is because clay has a higher atomic number than epoxy resin and therefore interacts more strongly with gamma-rays. As shown in Figure 10(a), at the selected gamma energies (33, 662, and 1,408 keV), the LAC increases with the increasing density. For example, the LAC of Composite EC60 is 3.5 and 1.4 times higher than the LAC of Composite EC 0% at gamma energies, 33 and 1,408 keV, respectively. This is because Composite EC60 has a higher density and a higher volume fraction of clay particles. The volume fraction of the clay particles in the composite also has an impact on the LAC. This is because the LAC is a weighted average of the LACs of the individual components of the composite. The weight of each component is determined by its volume fraction. This means that the LAC of the composite can be controlled by adjusting the volume fractions of the clay particles and the epoxy resin. As depicted in Figure 10(b), it is evident that the LAC values increase with the variation of Fe₂O₃ concentrations from 1.93% to 10.8% in the EC composites. The LAC values increase from 0.24 to 0.83 cm⁻¹ and from 0.09 to 0.13 cm⁻¹ at gamma energies 33 and 1,408 keV, respectively. It is clear that the highest values of LAC with the variation of Fe₂O₃ concentrations are detected at the low gamma energy, 33 keV. This is because Fe₂O₃ has a higher atomic number than the other constituents of the EC composition. As a result, the EC composite doped with clay the higher probability of interacting with photons through the photoelectric effect.

Figure 10

Variation of the linear attenuation coefficient for the fabricated composites as a function of (a) sample density (ρ, g·cm⁻³) and (b) Fe₂O₃ concentration.

The addition of Fe₂O₃ to composites made of clay and epoxy resin has a significant impact on the HVL values. The Fe₂O₃ is a dense material with a high atomic number, which makes it a good absorber of gamma-rays. The HVL is the thickness of material required to reduce the intensity of a gamma beam by half. As the concentration of Fe₂O₃ in the composite increases, the HVL increases. This is because the Fe₂O₃ atoms in the composite interact more strongly with the gamma-rays and therefore absorb more of them. The evidence depicted in Figure 11(a) undeniably portrays the conclusive fact that the maximum (2.8, 4.8, and 7.9 cm at 33, 662, and 1,408 keV, respectively) and minimum (0.8, 3.8, and 5.2 cm at 33, 662, and 1,408 keV, respectively) HVL values are detected at the lowest (1.93%) and highest (10.8%) concentrations of Fe₂O₃ across all the specified gamma energies.

Figure 11

The impact of Fe₂O₃ concentrations on (a) half-value layer (HVL, cm), (b) transmission factor (TF, %), and (c) radiation protection efficiency (RPE, %) of the fabricated composites.

The addition of Fe₂O₃ to composites made of clay and epoxy resin has a significant impact on both the TF and the RPE. The TF is the fraction of incident radiation that is transmitted through a material. RPE is a measure of how well a material shields against radiation. As the concentration of Fe₂O₃ in the composite increases, the TF decreases and the RPE increases. This is because the Fe₂O₃ atoms in the composite interact more strongly with the radiation and therefore absorb more of it. As shown in Figure 11(b) and (c), the TF decreases and the RPE increases with the increasing Fe₂O₃ concentration. This means that composites with higher concentrations of Fe₂O₃ are more effective at shielding against radiation. As the amount of Fe₂O₃ in EC composites rises, the TF values drop by a large amount, going from 78% and 91% to 43% and 88% at gamma energies of 33 and 1,408 keV, respectively. In addition, the RPE values increased from 21% and 8.7% to 56% and 12.4% at gamma energies of 33 and 1,408 keV, respectively. This reduction in TF and rise in RPE values highlights the critical role of Fe₂O₃ in mediating the attenuation of gamma-rays.