Fabrication of Lead Free Borate Glasses Modified by Bismuth Oxide for Gamma Ray Protection Applications

In the present work, bismuth borate glass samples with the composition of (99-x) B2O3 + 1Cr2O3 + (x) Bi2O3 (x = 0, 5, 10, 15, 20, and 25 wt %) were prepared using the melt quenching technique. The mass attenuation coefficient (MAC) of the prepared glass samples was measured through a narrow beam technique using a NaI(Tl) scintillation detector. Four point sources were used (241Am, 133Ba, 152Eu, and 137Cs) to measure the MAC for the prepared glasses. The experimental data were compared with the theoretical results obtained from the XCOM, and it was shown that for all samples at all tested energies, the relative deviation between the samples is less than 3%. This finding signifies that the experimental data can adequately be used to evaluate the shielding ability of the glasses. The MAC of the sample with x = 25 wt % was compared with different lead borate glasses and the results indicated that the present sample has high attenuation which is very close to commercial lead borate glasses. We determined the transmission factor (TF), and found that it is small at low energies and increases as the energy increases. The addition of Bi2O3 leads to reduction in the TF values, which improves the shielding performance of the glass system. The half value layer (HVL) of the BCrBi-10 sample was 0.400 cm at 0.595 MeV, 1.619 cm at 0.2447 MeV, and 4.946 cm at 1.4080 MeV. Meanwhile, the HVL of the BCrBi-20 sample is equal to 0.171 and 4.334 cm at 0.0595 and 1.4080 MeV, respectively. The HVL data emphasize that higher energy photons tend to penetrate through the glasses with greater ease than lower energy photons. Furthermore, the fast neutron removable cross section (FNRC) was determined for the present samples and compared with lead borate glass and concrete, and the results showed a remarkable superiority of the bismuth borate glass samples.


Introduction
The ionizing radiation in the human environment that results from normal background radioactivity, mining, milling, use of synthetic radioactive isotopes in nuclear power, nuclear research, space research, etc., all cause human exposure to the hazards of ionizing radiation. The scientific trend towards replacing fossil fuels by generating energy from nuclear reactors, and the accompanying possibilities of radioactive leakage and dangerous radioactive waste, which pose great risks to humans, requires serious research and effective Furthermore, borate glasses that contain Bi 2 O 3 acquired special interest due to their long infrared cutoff and high third order nonlinear optical susceptibility. These special characteristics make them excellent materials for several applications, particularly for developing internal transmission components, ultrafast switches for femtosecond lasers, and high-speed optical data processing systems [16][17][18].
In this work, we aimed to use a melt quenching technique to prepare glass samples of compositions (99−x)B 2 O 3 + 1Cr 2 O 3 + (x)Bi 2 O 3 (x = 0, 5, 10, 15, 20 and 25 wt %). The mass attenuation coefficient (MAC) of the prepared glass samples was measured through a narrow beam technique using a NaI(Tl) scintillation detector.

Materials and Method
In this work, glass samples with composition (99-x)B 2 O 3 + 1Cr 2 O 3 + (x)Bi 2 O 3 (x = 0, 5, 10, 15, 20, and 25 wt %) were prepared using the melt quenching technique. Equivalent quantities of high purity chemicals (99.8%) B 2 O 3 , Cr 2 O 3, and Bi2O3 were taken as chemical intermediates to manufacture this glass system. They were purchased from the Elgamhoria Chemical Company in Egypt. The reason for choosing this glass system is that the boron oxide (B 2 O 3 ) is an excellent absorber for neutrons, and Cr 2 O 3 improves the mechanical, thermal, and optical properties, as well as giving a transparent light green color which adds to the applications in the radiological field. Additionally, Bi 2 O 3 increases the density of the sample to use as a shield for photons. To reach homogeneity, chemicals were mixed with agate slurry. The mixture was taken into a crucible (made of German refractory bricks) and placed in a 1000 • C electric furnace. The molten mixture was placed in another electronic furnace for annealing at 400 • C for 2 h, with the temperature slowly lowered to remove cracks and thermal strain for the selected glass samples. The steps of manufacturing this glass are summarized in Figure 1. Due to the potential for bremsstrahlung X-ray produced from the interaction of beta particles with high Z eff materials, samples that do not exceed 25 weight% Bi 2 O 3 were prepared in the glass system. Furthermore, borate glasses that contain Bi2O3 acquired special interest due to their long infrared cutoff and high third order nonlinear optical susceptibility. These special characteristics make them excellent materials for several applications, particularly for developing internal transmission components, ultrafast switches for femtosecond lasers, and high-speed optical data processing systems [16][17][18].
In this work, we aimed to use a melt quenching technique to prepare glass samples of compositions (99−x)B2O3 + 1Cr2O3 + (x)Bi2O3 (x = 0, 5, 10, 15, 20 and 25 wt %). The mass attenuation coefficient (MAC) of the prepared glass samples was measured through a narrow beam technique using a NaI(Tl) scintillation detector.

Materials and Method
In this work, glass samples with composition (99-x)B2O3 + 1Cr2O3 + (x)Bi2O3 (x = 0, 5, 10, 15, 20, and 25 wt %) were prepared using the melt quenching technique. Equivalent quantities of high purity chemicals (99.8%) B2O3, Cr2O3, and Bi2O3 were taken as chemical intermediates to manufacture this glass system. They were purchased from the Elgamhoria Chemical Company in Egypt. The reason for choosing this glass system is that the boron oxide (B2O3) is an excellent absorber for neutrons, and Cr2O3 improves the mechanical, thermal, and optical properties, as well as giving a transparent light green color which adds to the applications in the radiological field. Additionally, Bi2O3 increases the density of the sample to use as a shield for photons. To reach homogeneity, chemicals were mixed with agate slurry. The mixture was taken into a crucible (made of German refractory bricks) and placed in a 1000 °C electric furnace. The molten mixture was placed in another electronic furnace for annealing at 400 °C for 2 h, with the temperature slowly lowered to remove cracks and thermal strain for the selected glass samples. The steps of manufacturing this glass are summarized in Figure 1. Due to the potential for bremsstrahlung X-ray produced from the interaction of beta particles with high Zeff materials, samples that do not exceed 25 weight% Bi2O3 were prepared in the glass system. The chemical compositions of the selected glass system were tabulated in Table 1. To ensure the correct compositions after preparation, the samples were analyzed by EDXor, Energy Dispersive X-ray analysis of the analytical scanning electron microscope (JSM-5300, JEOL) as shown in Figure 2-for example the BCrBi-15 sample, which gives the proportion of each element in the sample [19,20]. The analyses were performed for the sample more than once at different points and then the average was taken for the required percentage. The density was measured, as listed in Table 1, using the Archimedes' rule. Some of the attenuating properties of photons and neutrons were experimentally studied and compared theoretically with the XCOM program [21,22]. The use of this glass as a protector and a transparent shield for neutrons and photons was examined at the same time. The chemical compositions of the selected glass system were tabulated in Table 1. To ensure the correct compositions after preparation, the samples were analyzed by EDXor, Energy Dispersive X-ray analysis of the analytical scanning electron microscope (JSM-5300, JEOL) as shown in Figure 2-for example the BCrBi-15 sample, which gives the proportion of each element in the sample [19,20]. The analyses were performed for the sample more than once at different points and then the average was taken for the required percentage. The density was measured, as listed in Table 1, using the Archimedes' rule. Some of the attenuating properties of photons and neutrons were experimentally studied and compared theoretically with the XCOM program [21,22]. The use of this glass as a protector and a transparent shield for neutrons and photons was examined at the same time.   The mass attenuation coefficient (MAC) of the present glass samples was measur through a narrow beam technique. The NaI(Tl) scintillation detector was used  The illustration of this detector is shown in Figure 3. The Genie 2000 software was us to analyze the output spectrum, which is a comprehensive set of capabilities for acquiri and analyzing spectra. First, the detector was calibrated using two point sources ( 137 and 60 Co). Before any measurement, the calibration process of the detector (energy a efficiency calibration) is carried out, and then a substance with a known attenuation co ficient, such as lead, was measured, which was followed by validating the experimen results. Four point sources were used for the measurements to cover the required ener ( 241 Am, 133 Ba, 152 Eu, and 137 Cs), and the specification of these sources, as well as its figur were tabulated in Table 2. The mass attenuation coefficient (MAC) of the present glass samples was measured through a narrow beam technique. The NaI(Tl) scintillation detector was used [21][22][23][24]. The illustration of this detector is shown in Figure 3. The Genie 2000 software was used to analyze the output spectrum, which is a comprehensive set of capabilities for acquiring and analyzing spectra. First, the detector was calibrated using two point sources ( 137 Cs and 60 Co). Before any measurement, the calibration process of the detector (energy and efficiency calibration) is carried out, and then a substance with a known attenuation coefficient, such as lead, was measured, which was followed by validating the experimental results. Four point sources were used for the measurements to cover the required energy ( 241 Am, 133 Ba, 152 Eu, and 137 Cs), and the specification of these sources, as well as its figures, were tabulated in Table 2.
The MAC was evaluated using the next equation [25]: where I and I 0 are the intensity or the net count rates in the presence and absence of the studied glass sample, respectively, d (g/cm 2 ) is the mass thickness (d = ρx) with ρ (g/cm 3 ) being the density of the sample, and x (cm) is the thickness of the sample. Figure 4 shows the incident and transmitted spectra for three different BCrBi-20 glass samples with different thicknesses at the same energy (0.662 MeV).   The MAC was evaluated using the next equation [25]: where and I0 are the intensity or the net count rates in the presence and absence of the studied glass sample, respectively, d (g/cm 2 ) is the mass thickness (d = x) with ρ (g/cm 3 ) being the density of the sample, and x (cm) is the thickness of the sample. Figure 4 shows the incident and transmitted spectra for three different BCrBi-20 glass samples with different thicknesses at the same energy (0.662 MeV).   The relative deviation between the experimental and XCOM results was calculated from the following equation [26]: The relative deviation between the experimental and XCOM results was calculated from the following equation [26]: where (MAC) XCOM and (MAC) Expt are the theoretical and experimental mass attenuation coefficients, respectively. The uncertainty of the experimental results of MAC was calculated according to the following equation: where σ N and σ d are the uncertainty in the count rate and mass thickness of the measured sample, respectively. The linear attenuation coefficient (LAC) is a very important parameter to evaluate HVL, where the experimental LAC can be estimated from (LAC = MAC × ρ).
The HVL was determined from the next equation [27]: It is also important to calculate the efficiency of this manufactured system in attenuation or shielding at different energies. The radiation protection efficiency (RPE) was calculated from the following relationship [28]: Finally, the effective atomic number (Z eff ) has a positive relationship to understanding and interpreting the results of the attenuation coefficient. Z eff is given by the following equation [29]: where f i , A i , and Z i refer to the mole fraction, atomic weight, and atomic number of the i th constituent element in the selected glass sample, respectively. A final term to be discussed is the "effective neutron removal" (R), which refers to the process of removing neutrons from matter in time. At a defined and specific cross-section, the total amount of nuclear energy generated in a fission event from the first (or fast) neutron is equal to the average expected amount of nuclear energy generated in a fission event. Therefore, the fast neutron removal cross section (∑ R) values for a substance can be calculated using the following equation: where ∑ R/ρ (cm 2 ·g −1 ) is the mass removal cross section and w i is the partial density of the ith element (g/cm 3 ).

Results and Discussion
The mass attenuation coefficients (MACs) of the BCrBi glass samples were experimentally measured using various radioisotopes at 11 energies ranging from 0.0595 MeV to 1.408 MeV. The experimental data were compared with the theoretical results obtained from the XCOM, and both results are listed in Table 3 and plotted in Figure 5. The relative difference between the experimental and theoretical MAC values are also tabulated in Table 3. For all the samples at all tested energies, the relative deviation between the samples is less than 3%, which confirms the experimental setup used in this work, and signifies that the experimental data can adequately be used to evaluate the shielding ability of the glasses.  Figure 6 demonstrates the ratio between the intensity of the photons that pass through the glass and the total photons that are emitted, I/I 0 , known as "the transmission factor (TF)". TF provides insight into the glass's performance as a radiation shield, because if the ratio is in close unity, this means that most of the incoming radiation can pass through the glass. In other words, the glass is not effective in attenuating radiation. On the other hand, if the transmission factor is small, then the intensity I must be much smaller than I 0 , which means that most of the photons are stopped by the glass. Thus, the goal is to find a glass with a small TF. From Figure 6, it can be seen that the transmission factor is small at low energies and increases as the energy increases. It can also be said that the attenuation ability of the glasses is high at low energies, and reduces with increasing the energy. TF is very small at low energies for all samples except BCrBi-0, since this glass does not contain any Bi 2 O 3 , causing it to have relatively high TF values. Since Bi has a high atomic number, the addition of Bi 2 O 3 leads to reduction in the TF values, which improves the shielding performance of the glass system. Naturally, BCrBi-25 has the lowest transmission factor due to the high amount of Bi 2 O 3 in its composition. At energy of 0.0810 MeV, BCrBi-25 has TF of 0.130, while at 1.1120 MeV, TF is equal to 0.833. Altogether, the figure reveals that the glasses are more effective at low photon energies, and the BCrBi25 glass sample has the best shielding performance because of its high Bi 2 O 3 content.
where / (cm ·g ) is the mass removal cross section and wi is the partial density of the i th element (g/cm 3 ).

Results and Discussion
The mass attenuation coefficients (MACs) of the BCrBi glass samples were experimentally measured using various radioisotopes at 11 energies ranging from 0.0595 MeV to 1.408 MeV. The experimental data were compared with the theoretical results obtained from the XCOM, and both results are listed in Table 3 and plotted in Figure 5. The relative difference between the experimental and theoretical MAC values are also tabulated in Table 3. For all the samples at all tested energies, the relative deviation between the samples is less than 3%, which confirms the experimental setup used in this work, and signifies that the experimental data can adequately be used to evaluate the shielding ability of the glasses. In Figures 7 and 8, we plotted RPE versus the glass thickness at photon energies of 0.0596 and 0.6617 MeV, respectively. In both figures, RPE increases with the increase in the thickness. This can be explained according to the fact that the probability of photon-glass interaction increases with the increase in the thickness of the glass, where more photons are attenuated by the thick glass sample. This suggests that one effective way to enhance the shielding ability of the samples is to increase the glass thickness. Additionally, we can observe that the RPE values at low energies depend highly on the composition of the glasses, since the difference between RPE and the BCrBi-X is very notable. At higher energies, the composition of the glasses has a weak role on the RPE values and thus on the attenuation performance of the glasses. In Figures 7 and 8, we plotted RPE versus the glass thickness at photon energies of 0.0596 and 0.6617 MeV, respectively. In both figures, RPE increases with the increase in the thickness. This can be explained according to the fact that the probability of photonglass interaction increases with the increase in the thickness of the glass, where more photons are attenuated by the thick glass sample. This suggests that one effective way to enhance the shielding ability of the samples is to increase the glass thickness. Additionally, we can observe that the RPE values at low energies depend highly on the composition of the glasses, since the difference between RPE and the BCrBi-X is very notable. At higher energies, the composition of the glasses has a weak role on the RPE values and thus on the attenuation performance of the glasses.  Meanwhile, the HVL of the BCrBi-20 sample is equal to 0.171, 0.986, 1.611, 3.047, and 4.334 cm, at the same respective energies. This direct trend occurs because higher energy photons tend to penetrate through the glasses with greater ease than lower energy photons, requiring a greater thickness to attenuate the same quantity of radiation. Additionally, we can investigate the influence of the amount of Bi 2 O 3 on the HVL values. Apparently, the HVL values decrease as the Bi 2 O 3 content in the glasses increases. This can be explained according to the relation between HVL of the medium and its density. As the density of the glass is increased with the addition of Bi 2 O 3 , then more photons will interact with the dense sample, so we need a relatively thin glass to attenuate half of the incoming photons. Therefore, the HVL is decreased with the addition of Bi 2 O 3 (or with increase in the density). In other words, BCrBi-0 has the greatest HVL at all tested energies (and the lowest Bi 2 O 3 content), while the BCrCi-25 glass has the smallest HVL (and the greatest Bi 2 O 3 content). For example, at 0.0810 MeV, the HVL values are 1.720, 1.018, 0.706, 0.531, 0.418, and 0.340 cm for BCrBi-0, BCrBi-5, BCrBi-10, BCrBi-15, and BCrBi-20, respectively, while at 0.9641 MeV, they are equal to 4.426, 4.231, 4.038, 3.849, 3.663, and 3.479 cm for the same respective glasses. Thus, since the BCrBi-25 has the greatest Bi 2 O 3 content, this sample can be said to be the most space-efficient out of the investigated glass samples. and 4.334 cm, at the same respective energies. This direct tr energy photons tend to penetrate through the glasses with gre photons, requiring a greater thickness to attenuate the same q tionally, we can investigate the influence of the amount of Bi2 parently, the HVL values decrease as the Bi2O3 content in the be explained according to the relation between HVL of the m the density of the glass is increased with the addition of Bi2O interact with the dense sample, so we need a relatively thin g incoming photons. Therefore, the HVL is decreased with the increase in the density). In other words, BCrBi-0 has the greates (and the lowest Bi2O3 content), while the BCrCi-25 glass has greatest Bi2O3 content). For example, at 0.0810 MeV, the HVL v 0.531, 0.418, and 0.340 cm for BCrBi-0, BCrBi-5, BCrBi-10, BCrB tively, while at 0.9641 MeV, they are equal to 4.426, 4.231, 4.038 for the same respective glasses. Thus, since the BCrBi-25 has this sample can be said to be the most space-efficient out of the  Figure 10 demonstrates the effective atomic number (Z eff ) of the glasses against energy. The BCrBi-0 glass can be seen to have much smaller Z eff than the other samples due to the lack of Bi-which has a relatively large atomic number-in its composition. In BCrBi-0, we can see that Z eff is almost constant for this glass, which can be explained according to the chemical composition of this glass, since it contains only B 2 O 3 and Cr 2 O 3 , and the atomic numbers of these elements are close to each other. The same trend for Z eff with energy was reported for other materials that contain different elements with close atomic numbers. For example, El-Kateb et al. reported the same trend in Z eff for some alloys, such as steel, bronze, and brass [30]. Additionally, Kaçal et al. [31] reported Z eff values for some polymers in the same energies used in this work and they found that the polymers which consist of H, C, O, and N have constant Z eff . and the atomic numbers of these elements are close to each other. The with energy was reported for other materials that contain different e atomic numbers. For example, El-Kateb et al. reported the same trend loys, such as steel, bronze, and brass [30]. Additionally, Kaçal et al. [3 ues for some polymers in the same energies used in this work and t polymers which consist of H, C, O, and N have constant Zeff. Additionally, the increase in Bi2O3 increases the Zeff of the glass why the BCrBi-25 sample has the highest Zeff out of the investigated gla increases, Zeff can be observed to sharply decrease at first, and then slo scent. The only exception is around 0.1 MeV, where a sharp spike in v the k-absorption edge of Bi (which is why the BCrBi-0 sample does n The sharp decrease in the Zeff values is due to the dominance of the ph low energies, while the slowed descent can be attributed to the Compt action that dominates in the moderate energy range. This figure once conclusion that the BCrBi-25 sample has the greatest potential for radi plications. The MAC of the last present sample (BCrBi-25) was compared borate glasses, as shown in Figure 11, like S5 (50B2O3 + 10BaO + 10 Bi2O [32], ZBP1 (10ZnO + 40 B2O3 + 50PbO) [33], and S6 (40B2O3 + 25Li2O results were 0.0838, 0.0926, 0.1002, and 0.0968 cm 2 /g for BCrBi-25, S5, ZB MeV, respectively. However, at 1.332 MeV, MAC is in the same orde 0.0554, 0.0552 cm 2 /g. The results indicated that the present prepared borate glasses) have a high attenuation, very close to commercial lead the other hand, the samples are environmentally friendly and the cost glass. Additionally, this glass is perfect for neutron shielding, whereas t Additionally, the increase in Bi 2 O 3 increases the Z eff of the glasses, which explains why the BCrBi-25 sample has the highest Z eff out of the investigated glasses. As the energy increases, Z eff can be observed to sharply decrease at first, and then slows down in its descent. The only exception is around 0.1 MeV, where a sharp spike in values occurs due to the k-absorption edge of Bi (which is why the BCrBi-0 sample does not have this spike). The sharp decrease in the Z eff values is due to the dominance of the photoelectric effect at low energies, while the slowed descent can be attributed to the Compton scattering interaction that dominates in the moderate energy range. This figure once again reaffirms the conclusion that the BCrBi-25 sample has the greatest potential for radiation shielding applications.

Conclusions
The MAC of the (99-x)B2O3 + 1Cr2O3 + (x)Bi2O3 glass samples was meas a narrow beam technique using a NaI(Tl) scintillation detector. The expe were compared with the XCOM data to confirm the accuracy in the narro nique used in this work. The relative deviation between both techniques is which signifies that the experimental data can adequately be used to evalu ing ability of the glasses. The results showed that TF is small at low energies as the energy increases, and the addition of Bi2O3 leads to a reduction in BCrBi-25 has the lowest transmission factor due to the high amount of Bi2O sition. At energy of 0.0810 MeV, BCrBi-25 has TF of 0.130, while at 1.1120 Me concrete. In Figure 12, the values of ∑ are 0.1127, 0.1131, 0.1134, 0.1061, a for BCrBi-0, BCrBi-15, BCrBi-25, lead borate glass [35] and concrete [20], res

Conclusions
The MAC of the (99-x)B2O3 + 1Cr2O3 + (x)Bi2O3 glass samples was meas a narrow beam technique using a NaI(Tl) scintillation detector. The expe were compared with the XCOM data to confirm the accuracy in the narro nique used in this work. The relative deviation between both techniques is which signifies that the experimental data can adequately be used to evalu ing ability of the glasses. The results showed that TF is small at low energies as the energy increases, and the addition of Bi2O3 leads to a reduction in t BCrBi-25 has the lowest transmission factor due to the high amount of Bi2O3 sition. At energy of 0.0810 MeV, BCrBi-25 has TF of 0.130, while at 1.1120 Me to 0.833. The HVL data demonstrated that higher energy photons tend

Conclusions
The MAC of the (99-x)B 2 O 3 + 1Cr 2 O 3 + (x)Bi 2 O 3 glass samples was measured through a narrow beam technique using a NaI(Tl) scintillation detector. The experimental data were compared with the XCOM data to confirm the accuracy in the narrow beam technique used in this work. The relative deviation between both techniques is less than 3%, which signifies that the experimental data can adequately be used to evaluate the shielding ability of the glasses. The results showed that TF is small at low energies and increases as the energy increases, and the addition of Bi 2 O 3 leads to a reduction in the TF values. BCrBi-25 has the lowest transmission factor due to the high amount of Bi 2 O 3 in its composition. At energy of 0.0810 MeV, BCrBi-25 has TF of 0.130, while at 1.1120 MeV, TF is equal to 0.833. The HVL data demonstrated that higher energy photons tend to penetrate through the glasses with greater ease than lower energy photons. The BCrBi-0 glass was found to have a much smaller Z eff than the other samples due to the lack of Bi in its composition. Additionally, the Z eff results showed that increasing the Bi 2 O 3 causes an increase in the Z eff of the glasses, and thus the BCrBi-25 sample has the highest Z eff out of the investigated glasses. The different parameters presented in this study reaffirm the conclusion that the BCrBi-25 sample has the greatest potential for radiation shielding applications. A comparison of MAC for the prepared glasses with similar glasses (lead borate glasses) demonstrated that the present samples (bismuth borate glasses) have high attenuation that is very close to commercial lead borate glasses. The prepared glasses are less toxic than the lead borate glasses. Accordingly, we can conclude that the bismuth borate glasses presented in this work are promising radiation shielding materials due to their high attenuation performance, as well as their low cost and reduced toxicity.