Radiation Shielding Enhancement of Polyester Adding Artificial Marble Materials and WO₃ Nanoparticles

Abstract

The radiation shielding abilities of waste marbles with different concentrations of WO₃ (tungsten oxide) nanoparticles were investigated. Four marbles were prepared with 0, 0.05, 0.1, and 0.2 WO₃ nanoparticles. The study aims to investigate the effect of the WO₃ concentration, the density, and the particle size of the waste marble samples. The linear attenuation coefficient (LAC) of the S1 sample, the sample with no WO₃, was determined theoretically and experimentally, and the results demonstrated that they were close enough together to adequately determine the LAC of the other samples. Additionally, the samples with nano-WO₃, rather than micro-WO₃, were found to have a greater LAC, showing that decreasing the particle size of the sample improves their shielding ability. Samples with greater WO₃ content also had higher LAC values. The LAC of the marbles was also evaluated at a wide energy range (0.015–15 MeV) to examine the shielding properties of the samples for a wide range of applications, and an inverse trend between LAC and energy was observed. The radiation protection efficiency (RPE) of the marbles demonstrated that the marbles absorb almost all incoming photons at low energies. As energy increases, the efficiency of the samples naturally drops, as the photons are able to penetrate through them with greater ease. High energy dependence was found when calculating the half-value layers (HVL) of the samples. When comparing the LAC and mean free paths (MFP) of the marbles, an inverse relationship was observed. Furthermore, the samples with nano-WO₃ had a smaller MFP than those with micro-WO₃, meaning that decreasing the particle size of the samples improves their radiation shielding ability. The Z_eff of the micro-WO₃ samples was also determined and the values followed three distinctive trends depending on the energy range of the incoming photons.

1. Introduction

For diagnostic imaging, radiotherapy, food sterilization, widespread scientific progress, and manufacturing purposes utilization of ionizing radiations has augmented day by day [1]. From the concept of radiation shielding, ‘shield’ stands as a meddlesome article interim the radiation source and the target object (living cells, sophisticated tools, and materials) to reduce the intensity of the incoming radiation [2]. Gamma rays of all energies have not been captivated and stopped entirely [3]. To minimize the possible hostile corporeity of radiation, the application of suitable radiation shielding materials has no options; consequently, the discovery of novel dependable materials has become a crucial interest to researchers [4]. Concrete, HC, compact soil, iron, lead, and water are conventional radiation shielding materials [5]. Whereas, among those shielding materials, lead has shown the greatest shielding efficiency due to its high density though it is toxic [6]. On the other hand, concrete also provides structural and functional properties with a few drawbacks, for instance, the creation of cracks for continued radiation exposure [7]. Therefore, a lot of studies have been ongoing to invent substitutes for those traditional radiation shielding materials [3].

Marble is a non-foliated metamorphic rock with a silky appearance, numerous colors, consistent texture, and smooth and shiny surface; and consists of carbonate minerals available in a natural material [8]. The addition of nanoparticles such as SiO₂ [9], TiO₂ [10], Fe₂O₃ [11], Al₂O₃ [12], Nano-CaCO₃ [13], Nano-MgO [14], and Nano-Silica [15] and nanofibers [16] have been investigated on concretes for the interest of reducing the porosity in concrete microstructure at the nanoscale and to improve the mechanical strength with the durability of concrete.

To obtain the preferable shape and size, 60% of marble blocks have to be reshaped through grinding and polishing with water which produced nearly 5–6 million metric tons of waste slurry marble yearly [17]. Groundwater refreshing percentage declined because of the contamination of marble slurry waste on the mud which also reduces the soil productiveness and rainwater’s purification level. Moreover, contaminated water through marble waste slurry rises the turbidity, suspended solids, calcium, and magnesium which worsted the equilibrium ecology state [17]. To reduce marble waste on the environmental consciousness, the investigators made an effort to invent a novel construction material conducted by recycling [18]. Marble waste added with lime/cement performs as a suitable construction material [19]. The alteration of cement by marble slurry deteriorates the air content as well as the flexibility of the concrete [20]. The serviceability of concrete integration with marble dust as a filler content material up to 200 kg/m³ did not make any change [21]. In the super plasticizing mixture contamination of marble powder in the substitute of sand boosted the compressive strength of the traditional mixture [22]. Waste marble on concrete paste instead of cement augmented the durability and dimensional stability of mortar [23]. Marble waste mix concrete showed greater strength than concrete made with cement [24]. By plummeting the yearly created carbon dioxide on the earth and minimizing the manufacturing prices waste marble dust containing concrete in place of natural sand enhanced the mechanical properties [25]. A total of 16% of the concrete’s hardness was improved by waste marble powder replacing the original normal cement in the mixture [26].

Researchers have found the importance of using WO₃ nanoparticles on different materials due to some advantages. For an extensive range of temperatures, silicon rubber is thermally stable with the contamination of micro and nanoparticles of WO₃ particles [27]. The shielding possessions of epoxy resin are enhanced through the contamination of nano-WO₃ [28]. Nano-Bi₂O₃ particles displayed a more heightened photon absorption capability than micro-WO₃ particles as the filer on the epoxy resin [29]. Not only micro-WO₃ but also nano-Bi₂O₃ particles expand the shielding ability of concrete [30]. In a silicon resin, the addition of Bi₂O₃ or PbO nanoparticles showed better shielding ability than WO₃ nanoparticles [31]. Contamination of WO₃ on the epoxy/B₄C composite showed a noteworthy outcome in thermal neutron and gamma ray shielding properties [32].

In this work, we prepared artificial marble using polyester, and the radiation shielding abilities of waste marbles with different concentrations of WO₃ nanoparticles were investigated.

2. Materials and Methods

2.1. Materials

In this study, a fixed amount of polyester resin and waste marble was used in this innovative polyester whereas numerous ratios of lead carbonate (PbCO₃) and Tungsten oxide (WO₃) nanoparticles were been added. It is well known that Pb is conventional shielding material. However, it has a few drawbacks such as toxicity, weight, expensiveness, high elasticity as well as rigidity [33]. That is why our interest was to prepare an innovative polyester where the amount of Pb composition will be minimum, and it has to be replaced by WO₃ -nanoparticles. As there is no such high shielding element as lead hence a minimum amount has been used here to obtain better shielding ability.

In addition, according to the literature, it has been found that nano-WO₃ in epoxy resin has displayed better shielding ability than micro-WO₃ [34] as well as adding nano-ZnO (nZnO) particles to the absorber has enhanced the shielding ability comprising macro-ZnO [35]. For this reason, in this study WO₃ -nanoparticles have been used.

2.2. Methods

Artificial marble was prepared using polyester. The materials used in the preparation were liquid polyester, lead carbonate (PbCO₃) and some marble crumbly waste, and tungsten oxide. The characteristics of the polyester resin used in this study were tabulated in

Table 1. The characteristics of used polyester resin.

Density (g/cm3)	1.25
Yield modulus (GPa)	2–4
Compressive Strength (MPa)	140
Tensile Strength (MPa)	55
Tensile Elongation at Break (%)	2

. The waste marble was collected from one of the marble factories, with an average diameter of 5 mm “coarse marble”. EDX or “Energy Dispersive X-ray” analysis for waste marble was analyzed as shown in Figure 1. A fine powder PbCO₃ was used to help the material texture and strength in the manufacturing of the artificial marble, it is a white powder with a density of 6.6 g.cm³ and a melting point of 315 °C. Tungsten oxide (WO₃) nanoparticles were purchased from Nano-Tech Company, Cairo, Egypt, and added to the prepared samples to give an improvement in the attenuation of the incident photons.

The polyester resin was gradually mixed with PbCO₃ and stirred well, making sure that the mixture is free of agglomeration, then the percentages to be added of waste marble and WO₃ nanoparticles were added, and the hardener was also added at 0.5% with an amount of polyester added. The compound was stirred well, poured into molds and left for 24 h in the air until completely dry and hardened. Figure 2 shows the prepared samples used to measure the attenuation coefficients. The chemical compositions, densities, and codes of the prepared marbles were listed in

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

Code	Chemical Compositions wt (%)				Density (g/cm3)
	Polyester	PbCO3	Waste Marble	WO3-Nanoparticles
S1	25	25	50	—	2.321 ± 0.004
S2	25	20	50	5	2.329 ± 0.008
S3	25	15	50	10	2.333 ± 0.007
S4	25	5	50	20	2.339 ± 0.003

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

TEM or Transmission Electron Microscope of JEOL model, Japanese-made available at the Faculty of Science, Alexandria University in Egypt was used to photograph WO₃ powder nanoparticles before adding it to the marble formation to know its average size as shown in Figure 3a,b. From the TEM imaging, it was confirmed that the size of the used WO₃ particles is all less than 100 nm with an average of 40 nm, and on the other hand, the shape of the particles is spherical as shown in the figure.

HPGe with a relative efficiency of 24% and energy resolution of 1.92 at 1.333 MeV, and three different radioactive point sources Cs-137, Co-60, and Am-241 were used to experimentally measure the attenuation coefficients of the prepared samples as shown in Figure 4. These radioactive sources were used because they emit photons of different energies, where Am-241 source emits energy in the low range (0.060 MeV), this energy plays an important role in X-ray imaging while Co-60 (emits 1.173 and 1.333 MeV) and Cs-137 (emits 0.622 MeV) play an important role in medical, industrial and agricultural applications as well as food preservation, 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.

Genie 2000 software was used to analyze the area under the peak resulting from the detector reading of the incident photon. The measurement was carried out for a sufficient period until we reached the lowest error in the calculated area (less than 1%), and then the area was calculated in the presence (A) and absence (A₀) of the artificial marble sample at the same time. Given these areas, the linear attenuation coefficient was calculated from the following equation [36,37].

$$LAC=\frac{1}{x} ln\frac{A_0}{A}$$

(1)

The experimental results were compared with results calculated theoretically by Phy-X software [38], an online program used to calculate the attenuation coefficients of radiation shielding and dosimetry. Attenuation parameters that depend on LAC calculation such as half-value layer (HVL) and mean free path (MFP) were calculated by the following equations [39,40,41,42,43,44,45,46].

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

(2)

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

(3)

The Radiation Protection Efficiency (RPE) measures the ability of the material to absorb the incident photons and was calculated according to the following equation [47,48].

$$RPE \left(\%\right)=\left[1-\frac{A}{A_0}\right]\times 100$$

(4)

3. Results and Discussion

Figure 5 illustrates the experimental and theoretical LAC values (obtained using the Phy-X software) for the S1 sample. By comparing the two results, we aim to validate the experimental setup, as if the values are close together, then the experimental results can be trusted with a high degree of accuracy to properly determine the LAC of the other samples. The figure reveals that the two methods indeed do return values that are very close together. For example, at 0.662 MeV, the experimental LAC for S1 is equal to 0.1911 cm⁻¹, while its theoretical LAC is equal to 0.197 cm⁻¹. Meanwhile, at 1.17 MeV, the experimental and theoretical LAC is equal to 0.1389 cm⁻¹ and 0.140 cm⁻¹, respectively. From these results, we can adequately use the experimental results to assess the shielding ability of the samples S2–S4.

Figure 6 plots the relationship between the LAC of the prepared marble samples with WO₃ nano- and microparticles. The aim of this figure is to examine the influence of particle size on the LAC of the shielding materials. For all three samples, the LAC of the samples with WO₃ nanoparticles was slightly higher than the LAC of the microparticle WO₃. For example, at 0.0595 MeV, for the S2 marble sample, its LAC with micro-WO₃ is equal to 2.771 cm⁻¹, while its LAC with nano-WO₃ is equal to 2.8715 cm⁻¹. Additionally, S3′s LAC values at 0.662 MeV are equal to 0.195 cm⁻¹ and 0.1998 cm⁻¹ with micro- and nano-WO₃, respectively. These results show that reducing the size of the WO₃ particle enhances the radiation protection ability of the prepared samples and this is also found in previously published papers on epoxy and concrete [49,50]. The distribution of small particle size (nanoparticle) is better than large particle size (microparticles) because of large distribution surfaces; hence, the absorption rate has been found better, and that is why contamination of nanoparticles on the shielding material enhances the efficiency of the material. The effect of the nano-WO₃ concentration on the LAC values is graphed in Figure 7 to determine their relationship. The figure shows that S4 has a higher LAC than S1, and since the S4 sample contains 0.2 WO₃ while S1 contains no WO₃, the addition of the heavy compound WO₃ leads to an increase in the LAC values. Therefore, adding heavy compounds such as WO₃ improves the attenuation performance of the prepared waste artificial marbles.

Figure 8 plots the LAC of the four artificial marbles with WO₃ at a wide energy range. Since only a limited number of radioisotopes are available at our lab, the energy values that we can analyze are also limited. In order to obtain a wider range of LAC values, at both low and high energies, the LAC of the samples with micro-WO₃ was plotted between 0.015 and 15 MeV. The experimental results were obtained using three radioisotopes included in the same figure. All four of the investigated samples have their greatest LAC values at 0.015 MeV, decreasing as the energy increases. For example, S2’s LAC at 0.015 MeV is equal to 68.885 cm⁻¹, and then drops to 15.390 cm⁻¹ at 0.03 MeV, 2.771 cm⁻¹ at 0.0595 MeV, and 1.144 cm⁻¹ at 0.150 MeV. The LAC value continues decreasing at all energies, but a small peak occurs at 0.1 MeV, which is due to the K-absorption edge of Pb (the samples contain PbCO₃). At higher energies, the LAC of the samples is very high, and the difference between the LAC of the samples also gets much smaller. For instance, the LAC of the samples at 1.33 MeV are all roughly equal to 1.30 cm⁻¹ ± 0.01 cm, while at 15 MeV they are equal to 0.064 cm⁻¹ ± 0.01 cm. This trend can be explained by the Compton scattering interaction, which has low dependence on the atomic number of the materials.

Figure 9 demonstrates the radiation protection efficiency (RPE) of the four waste artificial marble samples with WO₃ nanoparticles. At 0.0595 MeV, the RPE is extremely high, almost at 100%, which means the samples can absorb almost all incoming photons at low energies. This makes artificial marble effective material for low-energy applications. As the energy increases to 0.662 MeV, the RPE values decrease to almost half, around 43–46%, which means that the samples can block half of the photons with this energy, while the other half can penetrate through the marbles. As the incoming photon energy increases further to 1.33 MeV, RPE drops to 32–33%, which means that most of the photons (around 66%), can penetrate through the samples. In other words, the prepared samples can block 33% of the incoming photons, which makes them less effective radiation shields at energies greater than 1 MeV.

The half-value layer (HVL) of the samples was calculated and graphed in Figure 10. At 0.0595 MeV, the HVL values are at their minimum, which means that a thickness of about 0.23 cm is enough to absorb 50% of the incoming photons at 0.0595 MeV. As the energy of the incoming radiation increases, so does the penetrating power of the photons. Thus, a shield with a thickness of about 3 cm is needed to shield 50% of photons with an energy of 0.662 MeV. From these results, it is clear that the HVL values are highly dependent on the energy, as HVL drastically changes from 0.2 to 3 cm as the energy increases from 0.0595 to 0.662 MeV. Continuing, the thickness of the marbles reaches around 5 cm when the energy increases to 1.33 MeV. More specifically, to shield 50% of incoming radiation with an energy of 1.33 MeV, a 5.35 cm thick sample of S1 is needed, or a 5.19 cm thick sample of S4 is needed.

Figure 11 shows the relationship between the LAC and MFP of S4. The figure demonstrates an inverse relationship between LAC and MFP, meaning that MFP increases as the energy increases from 0.0595 to 1.33 MeV, while LAC decreases as energy increases. As an illustration, it can be shown that the smallest MFP value occurs at 0.0595 MeV is equal to 0.334 cm (for S4), but quickly decreases to 4.73 cm at 0.662 MeV. While at energy 0.0595 MeV, the value of LAC is 2.86 cm⁻¹ (for S4) and a sharp decline has been found at energy 0.662 MeV with the value of LAC (0.191 cm⁻¹).

The MFP for the waste artificial marble samples with nano- and micro-WO₃ are graphed in Figure 12. to determine the effect of particle size on the MFP values. By observing S2’s results, it can be seen that the MFP for nanoparticle-WO₃ is lower than the MFP for S2 with micro-WO₃. Thus, using nanoparticle WO₃ is preferable for radiation shielding applications since a lower thickness is required to obtain the same attenuation capability, which improves space efficiency in comparison with micro WO₃. The same results can be concluded for S3 and S4; namely, the MFP of the nanoparticle samples was lower than the microparticle counterparts.

In Figure 13, the Z_eff for the samples with micro-WO₃ were graphed against energy. The Z_eff values can be divided into three regions: before 0.1 MeV, between 0.1 and 0.8 MeV, and after 0.8 MeV. In the first region, the Z_eff is very high. As can be seen by the subfigure highlighting the results at 0.015 MeV, the values are around 42. In the second energy region, Z_eff greatly decreases and approaches its minimum value. Lastly, in the third energy region, the Z_eff values are almost constant up to 8 MeV, after which they slightly increase. At 8 MeV, the Z_eff values are small and are around 10. The comparison table on the performance efficiency of the reported literature has been added to confirm the advantage of the prepared materials, shown in

Table 3. Comparison table on the efficiency of literature performance.

Name of Samples	LAC (cm−1)				HVL (cm)				Refs.
	0.06 MeV	0.66 MeV	1.17 MeV	1.33 MeV	0.06 MeV	0.66 MeV	1.17 MeV	1.33 MeV
Marble	1.06	0.22	0.17	0.16	2.94	4.52	4.79	4.86	[48]
Granite	0.77	0.22	0.16	0.15	3.25	4.53	4.80	4.87	[49]
Bentonite Clay	0.78	0.16	0.12	0.11	3.24	4.82	5.10	5.16	[44]
Ball Clay	0.57	0.15	0.12	0.11	3.56	4.88	5.15	5.21
Kaolin clay + Bi2O3 nanoparticles (KBi-10)	1.54	0.17	0.13	0.12	2.56	4.76	5.06	5.13	[50]
Kaolin clay + Bi2O3 nanoparticles (KBi-20)	2.74	0.20	0.14	0.13	1.99	4.63	4.97	5.04
S1	2.86	0.19	0.14	0.13	1.94	4.65	4.97	5.04
S2	2.87	0.20	0.14	0.13	1.94	4.62	4.96	5.04
S3	2.89	0.20	0.14	0.13	1.94	4.61	4.95	5.02
S4	2.99	0.21	0.14	0.13	1.90	4.55	4.94	5.01

.

4. Conclusions

We successfully prepared waste artificial marble samples with WO₃ nanoparticles and investigated the radiation shielding parameters for the prepared samples to understand the influence of the amount of WO₃ and the size of this compound on the attenuation competence of the new samples. Firstly, we validated the experimental setup by comparing the experimental and Phy-X LAC values for the S1 sample, and we found that the two methods indeed do return values that are very close together, which suggests that we can adequately use the experimental results to assess the shielding ability of the S2–S4 samples. When we examined the LAC for the prepared waste artificial marble samples, we found that the LAC values of the samples with WO₃ nanoparticles are slightly higher than the LAC of the microparticle WO₃, which demonstrated that decreasing the particle size of WO₃ enhances the radiation shielding ability of the prepared samples. In addition to the particle size, we examined the influence of the amount of WO₃ on the samples on the LAC values and other parameters. We noticed that adding heavy compounds (i.e., WO₃) improves the attenuation performance of the prepared waste artificial marbles. We also reported the RPE for the four waste artificial marble samples with WO₃ nanoparticles, and we found that at 0.0595 MeV, the RPE is extremely high, almost at 100%, which means the samples can absorb almost all incoming photons at low energies, while as the energy increases to 0.662 MeV, the RPE values decrease to almost half, around 43–46%. The RPE results showed that the artificial marbles are effective materials for low-energy applications, while they are less effective radiation shields at energies greater than 1 MeV. From the HVL results, a thickness of about 0.23 cm is enough to absorb 50% of the incoming photons at 0.0595 MeV, whereas a shield with a thickness of about 3 cm is needed to shield 50% of photons with an energy of 0.662 MeV. In conclusion, from the different parameters, using nanoparticle WO₃ is preferable for radiation shielding applications since a lower thickness is required to obtain the same attenuation capability.