Comprehensive study of the radiation shielding feature of polyester polymers impregnated with iron ﬁ lings

: Radiation and nuclear technologies have side e ﬀ ects in addition to their important applications, so appropriate shields must be used to protect users and the public from high doses as a result of exposure to this radiation. In this work, the attenuation coe ﬃ cients for polyester composites doped with waste iron ﬁ lings (IFs) were studied. Six samples of di ﬀ erent IF concentrations were manufactured, namely, Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60 (where Poly-IF60 represents 40% polyester and 60% IF). We measured the attenuation factors using high purity germanium (HPGe)-detector along with three radioactive sources 241 Am (emitting energy of 0.06 MeV), 137 Cs (emitting energy of 0.662 MeV), and Co-60 (emitting energy of 1.173 and 1.333 MeV). We compared the linear attenuation coe ﬃ - cient (LAC) obtained by theoretical (i.e., XCOM software) and experimental (i.e., HPGe-detector) approaches for the prepared polyester composites at various photon energies (0.060, 0.662, 1.173, and 1.333 MeV). The greatest di ﬀ erence between the LAC values of the samples occurs at 0.060 MeV, where the Poly-IF60 sample has a much greater LAC than the other shields, followed by the Poly-IF50 sample, Poly-IF40 sample, and so on until the pure polyester shield. Speci ﬁ cally, their values are equal to 0.245, 0.622, 0.873, 1.187, 1.591, and 2.129 cm − 1 for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively. We calculated the transmission factor (TF) and the radiation shielding e ﬃ ciency (RSE), and found that the TF for Poly-IF30 is equal to 28.82%, 77.94%, 82.75%, and 83.75% at 0.060, 0.662, 1.173, and 1.333, respectively, while its RSE is equal to 82.57%, 24.00%, 18.80%, and 17.72%, respectively. The fast neutron removal cross-section (FNRC) of the polyester samples was calculated and the values increase when more Ifs are added to the samples. More speci ﬁ cally, the FNRC values are equal to 0.095, 0.100, 0.103, 0.107, 0.110, and 0.113 cm − 1 for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively.


Introduction
Shielding is considered one of the most important requirements for radiation protection along with the duration of exposure and the distance between the person and the radiation source.Radiation shielding is necessary in medical and industrial places such as medical radiotherapy devices and X-ray generating devices, and in some facilities such as accelerators and nuclear reactors (1)(2)(3)(4).Lead is considered the basic material as a shield against ionizing radiation, but at the present time, studies tend to use materials that are less costly and environmentally friendly and have good efficiency as shielding materials that serve the community, whether they are flexible or non-flexible materials (5)(6)(7).
Among the recent studies in the field of shielding is the use of polymers as basic materials, such as polyethylene, polypropylene, polyester, and epoxy resins.Polymer materials have the characteristics of flexibility and ease of formation, which expands their use and susceptibility against photons and neutrons (8-10).Polyester resin is relatively high-density polymer and therefore plays an important role in attenuating neutrons and photons.Yazdani-Darki et al. (8) investigated the radiation shielding properties of polyester with PbO nanoparticles.The authors found that the superior radiation attenuation sample is the sample with 60 wt% nanocomposite.Moradgholi and Mortazavi (9) studied the radiation shielding parameters for polyester doped with CdO.The authors reported an enhancement in the neutron attenuation due to the addition of CdO.The linear attenuation coefficient for the undoped sample was 0.187 cm −1 , and it decreased to 0.224 and 0.231 cm −1 due to the addition of 1% and 5% of CdO.Yulianti et al. (11), investigated a polyester composite reinforced by lead against X-rays photons.The authors found that as the lead content increased, the optical density increased, and X-ray transmission decreased.Hemily et al. (12) designed new marble composites based on polyester resins for use as protective shields from gamma radiation.The authors found that the samples with WO 3 nanoparticles have higher linear attenuation coefficient than the samples with micro WO 3 .As reported by the authors, decreasing the particle size of WO 3 causes an improvement in the radiation shielding properties of the prepared samples.Sayyed et al. (13) studied the attenuation properties of polymeric materials, the matrix materials in the fabrication process were polyester resin and the fillers were some oxides such as B 2 O 3 and TeO 2 .The authors measured the radiation shielding factors using high purity germanium (HPGe) detector and different point sources.The linear attenuation coefficient (LAC) increased due to the addition of TeO 2 , while the half value layer (HVL) decreased.
The waste is used in many applications, such as recycling, or added to some matrixes as auxiliary materials in the formation of the compound.From these waste iron filings (IFs), it is possible to grind IFs and add them as fine aggregate to concrete or mortar to improve its shielding and mechanical properties.One of the recent applications is the use of polymeric materials as basic materials to which quantities of IF waste are added (14)(15)(16)(17).Satyaprakash et al. (18) studied the mechanical properties of concrete in case of sand replacement with filings and found that it improves compressive and tensile strengths.
In this study, the attenuation coefficients of photons and neutrons were determined for six polyester composites developed by adding different proportions of IF experimentally using narrow beam method and compared by XCOM software.This work introduces novel polyester composites doped with waste IF as radiation protection materials.The significance of this study lies in its contribution for developing ecofriendly, cheap, and non-toxic materials for use as radiation shielding materials.

Materials and methods
The matrix used in this work is polyester, which is one of the most important liquid polymers with good mechanical properties, ability to resist heat, and crystal transparency during use.Therefore, many industries depend on it, such as the manufacture of PET bottles, insulating films for wires, floors, and insulating surfaces, but in this work, polyester resins were used as matrix (19,20).The properties of the polyester resins used in this work are tabulated in Table 1.
In the blacksmithing, filings are produced as a result of cutting, scraping, and polishing raw iron materials.So, a quantity of fine IF was collected from a Blacksmithing factory in Egypt, then it was further ground and sieved with a 60 μm diameter sieve.The chemical compositions were tested using EDX analysis (21) as shown in Figure 1, while the shape and structure of the molecule were tested using SEM image (22) as shown in Figure 1.These IFs were added in different proportions to polyester to obtain compounds to be used as protective shields against radiation.
In the experimental measurements, a HPGe detector was used for attenuation coefficients determination at different gamma-ray energies emitted from 60 Co, 137 Cs, and 241 Am radioactive sources.The mechanism of measurements was graphed in Figure 2 (23)(24)(25)(26).
The intensities in the absence and the presence of the Poly-IF composite (I I and 0 ) can be calculated by the determination of the peak area using Genie-2000 software.From these intensities (at the same line energy), we can determine the LAC of Poly-IF sample of thickness (x) using Lambert-Beer expression as follows (27-29): XCOM is a widely used program to theoretically calculate gamma-ray attenuation coefficients, as well as interaction mechanisms for gamma-rays with an energy range from 1 keV to 100 GeV (30).
Attenuator coefficients such as mean free path (MFP), HVL, and tenth value layer (TVL) are calculated as an inverse function of the linear attenuation coefficient of the shield material as follows (31)(32)(33): The radiation shielding efficiency (RSE) of Poly-IF composite which is used as a radiation shield is determined by using the initial (I 0 ) and transmitted (I) gamma line intensities obtained from peak area calculation (34).
The lead equivalent thickness (LE th ) corresponding to the Polyester-IF thicknesses used in this work was evaluated by the following formula (35): The possibility of a neutron passing through glass without interacting is described by the fast neutron removal cross-section (FNRC).Every composite's FNRC can be evaluated using (36)   Comprehensive study of the radiation shielding feature of polyester polymers  3 ( ) where (Σ R /ρ) i is the removal cross-section of the ith composite

Results discussion
Figure 3 shows the calculated and experimental LAC determined for the polyester radiation shields at various photon energies.The aim of this figure is to ensure that the experimental LAC values closely align with the theoretical calculated values, so that further parameters which rely upon these results will also be accurate.Focusing on the pure polyester sample first, its theoretical LAC values range between 0.245 −1 at 0.060 MeV and 0.075 cm −1 at 1.333 MeV.Comparing these results (30) with the experimental values, a percent deviation between 0.91% and 2.13% is observed, which is well within the acceptable range for accurate determination of the shields' attenuation capability.Looking at some of the other samples, all the values remain in the same range.For example, Poly-IF30's percent deviation lies between 0.25% and 2.72%, while Poly-IF50's percent deviation lies between 0.72% and 2.16%.For all the samples at the four tested energies, the deviation never goes past 2.72%, which means that the experimental LAC values are very close to the theoretical ones and will accurately predict the overall shielding ability of the prepared polyester samples.Figure 4 shows the LAC values of the polyester shields as a function of photon energy to compare the shielding ability of the materials against each other.The greatest difference between the LAC values of the samples occurs at 0.060 MeV, where the Poly-IF60 sample has a much greater LAC than the other shields, followed by the Poly-IF50 sample, Poly-IF40 sample, and so on until the pure polyester shield.This is due to the domination of photoelectric effect (37).Specifically, their values are equal to 0.245, 0.622, 0.873, 1.187, 1.591, and 2.129 cm −1 for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively.At 0.662 MeV and onward, however, the difference between the LAC values of the polyester shields is much smaller, but the same relative order is maintained.For example, the pure polyester sample's LAC is equal to 0.106, 0.081, and 0.075 cm −1 at 0.662, 1.173, and 1.333 MeV, respectively, while Poly-IF60's LAC is equal to 0.200, 0.151, and 0.142 cm −1 at the same respective energies.In other words, the Poly-IF60 sample has the greatest LAC at all energies, while the pure polyester sample has the least LAC.This means that the addition of IFs can improve the LAC and thus the radiation shielding properties of the prepared composites since iron has relatively high density.
Figure 5 shows the HVL, MFP, and TVL of the six tested samples against photon energy.Looking at all the parameters together, all three increase with the increase in the photon energy for all the samples (38).This suggests that the penetrating ability of the photons increases with the increase in the energy of the radiation.For example, Poly-IF20's HVL is equal to 1.114, 5.563, 7.320, and 7.816 cm at 0.060, 0.662, 1.173, and 1.333 MeV, respectively, while Poly-IF50's HVL is equal to 0.436, 4.003, 5.287, and 5.644 cm at the same energies.Meanwhile, their MFP values are equal to 1.607, 8.025, 10.561, and 11.276 cm for Poly-IF20 at the same respective energies and 0.629, 5.775, 7.628, and 8.142, respectively, for Poly-IF50.These upward trends occur because as higher energy photons gain more penetrating power, the sample's thickness must be increased to stop the same number of photons, and at the same time the distance between subsequent collisions, which is the definition of MFP, also increases (39).Focusing on only one parameter at a time, the values at any energy are inversely related to the quantity of IF in the sample.For instance, at 0.662 MeV, the TVL values are equal to 21.778, 18.479, 16.781, 15.058, 13.298, and 11.508 cm for Poly through Poly-IF60, respectively, while at 1.333 MeV they are 30.530, 25.963, 23.604, 21.205, 18.748, and 16.244 cm for the same respective samples.Thus, increasing the IF content in the samples lowers the HVL, MFP, and TVL of the shields, leading to greater shielding efficiency.
Figure 6 shows the transmission factor (TF) and radiation shielding efficiency (RSE) of the samples with a Comprehensive study of the radiation shielding feature of polyester polymers  5 thickness of 2 cm at the four tested energies.The TF and RSE values show two opposite trends with energy, where the TF values increase with greater energy, while the RSE values drop when facing higher energy (40,41).For instance, Poly-IF30's TF is equal to 28.82%, 77.94%, 82.75%, and 83.75% at 0.060, 0.662, 1.173, and 1.333, respectively, while its RSE is equal to 82.57%, 24.00%, 18.80%, and 17.72%, respectively.Thus, higher energy photons can transmit or pass through the polyester samples easily than lower energy photons, or likewise the shielding efficiency of the materials drops when facing higher energy radiation.For this reason, we must increase the thickness of the shielding materials in order to block the high energy radiation (42).Furthermore, the TF values decrease at all energies when introducing more IFs to the polyester and the RSE values increase.For example, at 1.173 MeV, the TF values decrease from 85.12% to 82.75%, 81.20%, 79.31%, 76.94%, and 73.89% for Poly to Poly-IF60, respectively, while the RSE values increase from 14.88% to 17.25%, 18.80%, 20.69%, 23.06%, and 26.11% respectively.Therefore, it can again be concluded that the Poly-IF60 sample, the shield with the greatest IF concentration, has the most desirable attenuation capability.Figure 7 shows the LE th of the polyester samples as a function of the energy of the radiation.At the smallest tested energy, 0.060 MeV, the values are at their lowest, between 0.019 cm for Poly and 0.162 cm for Poly-IF60.As the photon energy increases, so does the LE th for the  samples.At 0.662 MeV, the values are between 0.360 and 0.681 cm for Poly and Poly-IF60, respectively, at 1.173 MeV they are between 0.476 and 0.894 cm, and at 1.333 MeV they are between 0.488 and 0.917 cm, respectively.Additionally, these values also show that the Poly sample has the lowest LE th at all energies, while the Poly-IF60 sample has the greatest LE th at all energies, following the order of the IF concentration in the samples.For example, at 0.662 MeV, the values are equal to 0.360, 0.424, 0.467, 0.520, 0.589, and 0.681 cm for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively, while at 1.333 MeV they are equal to 0.488, 0.574, 0.631, 0.702, 0.794, and 0.917 cm, respectively.
Figure 8 shows the effective atomic number (Z eff ) of the polyester samples as a function of the energy of the radiation.At 0.060 MeV, the Z eff values are at their lowest, ranging from 4.52 for Poly to 18.08 cm for Poly-IF60.As the photon energy increases, the Z eff decreases for all composites except for Poly, where the Z eff for this sample is almost constant.The constant Z eff for Poly can be explained according to the chemical composition of this sample, since it does not contain IF, and the atomic number of the consistent elements for this sample is close together, so we found that the Z eff is almost constant (varied between 4.39 and 4.52).It is also clear from Figure 8 that the addition of IF causes an increase in the Z eff .This is due to the increase in the proportion of the relatively high atomic number (i.e., Fe), so adding more IF to the prepared   Finally, we compared the results of the highest LAC values with other related polyester-dependent composites (13,43,44) as shown in Figure 10.The results showed good efficiency against gamma rays for Poly-IF60 compared with other composites which indicated that it can be used as attenuators against incoming photons and neutrons.

Conclusion
Different polyester-IF composites were investigated for photons and neutrons shielding applications.The photon attenuation parameters were determined by experimental and theoretical methods such as LAC, MFP, and RSE.LAC determined for the polyester radiation shields at various photon energies (0.060, 0.662, 1.173, and 1.333 MeV).The greatest difference between the LAC values of the samples occurs at 0.060 MeV, where the Poly-IF60 sample has a much greater LAC than the other shields, followed by the Poly-IF50 sample, Poly-IF40 sample, and so on until the pure polyester shield.Specifically, their values are equal to 0.245, 0.622, 0.873, 1.187, 1.591, and 2.129 cm −1 for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively.The HVL, MFP, and TVL of the six tested samples against photon energy have been calculated.Looking at all the parameters together, all three increase with the increase in the photon energy for all the samples.The FNRC of the polyester samples was calculated and the values increase when more Ifs were added to the samples.More specifically, the FNRC values are equal to 0.095, 0.100, 0.103, 0.107, 0.110, and 0.113 cm −1 for Poly, Poly-IF20, Poly-IF30, Poly-IF40, Poly-IF50, and Poly-IF60, respectively.The outcome from this work opens up the opportunities for the improvement of the current radiation shielding materials and development of new materials for radiation protection with practical applications in different industries and medical facilities.

Figure 1 :
Figure 1: The morphological characteristics of waste IF.

Figure 2 :
Figure 2: Schematic diagram of the experimental technique.

Figure 4 :
Photon Energy (MeV)Figure4: The linear attenuation coefficient determined for the polyester samples as a function of the energy.

Figure 5 :
Figure 5: The HVL, MFP, and TVL for the prepared composites.

Figure 6 :
Figure 6: The TF and the RSE of the samples with a thickness of 2 cm.

Figure 7 :
Figure 7: The LE th of the polyester samples as a function of the energy of the radiation.

Figure 8 :
Figure 8: The Z eff of the polyester samples as a function of the energy of the radiation.

Figure 9 :
Figure 9: The FNRC of the polyester samples.

Table 1 :
Physical properties of the polyester resin

Table 2 :
Compositions of fabricated polyester resin-IF samples