An extensive assessment of the impacts of BaO on the mechanical and gamma-ray attenuation properties of lead borosilicate glass

The current work deals with the synthesis of a new glass series with a chemical formula of 5Al2O3–25PbO–10SiO2–(60-x) B2O3–xBaO; x was represented as 5, 10, 15, and 20 mol%. The FT-IR spectroscopy was used to present the structural modification by rising the BaO concentration within the synthesized glasses. Furthermore, the impacts of BaO substitution for B2O3 on the fabricated borosilicate glasses were investigated using the Makishima-Mackenzie model. Besides, the role of BaO in enhancing the gamma-ray shielding properties of the fabricated boro-silicate glasses was examined utilizing the Monte Carlo simulation. The mechanical properties evaluation depicts a reduction in the mechanical moduli (Young, bulk, shear, and longitudinal) by the rising of the Ba/B ratio in the fabricated glasses. Simultaneously, the micro-hardness boro-silicate glasses was reduced from 4.49 to 4.12 GPa by increasing the Ba2+/B3+ ratio from 0.58 to 3.18, respectively. In contrast, the increase in the Ba/B ratio increases the linear attenuation coefficient, where it is enhanced between 0.409 and 0.448 cm−1 by rising the Ba2+/B3+ ratio from 0.58 to 3.18, respectively. The enhancement in linear attenuation coefficient decreases the half-value thickness from 1.69 to 1.55 cm and the equivalent thickness of lead is also reduced from 3.04 to 2.78 cm, at a gamma-ray energy of 0.662 MeV. The study shows that the increase in the Ba2+/B3+ ratio enhances the radiation shielding capacity of the fabricated glasses however, it slightly degrades the mechanical properties of the fabricated glasses. Therefore, glasses with high ratios of Ba2+/B3+ have high gamma-ray shielding ability to be used in hospitals as a shielding material.


Glasses preparation
To prepare the investigated glasses, of general formula 5Al 2 O 3 -25PbO-10SiO 2 -(60-x) B 2 O 3 -xBaO, where x was varied between 15, 10, 15, and 20 mol%, the melt quenching method was employed.The following oxides: MgO (purity of 99.99%), BaO (purity of 99.99%), SiO 2 (purity of 99.99%), B 2 O 3 (purity of 99.99%), and PbO (purity of 99.99%) were supplied by Sigma Aldrich (USA) and used for fabrication of the glasses in the current work.The required amounts of each metal oxide were accurately weighed and mixed using agate mortar to ensure a homogeneous and uniform glass structure.The powders in high-purity alumina crucibles were put in an electric furnace at 1100 °C for two hours.The glass was carefully poured into a metal mold once it had totally liquefied.The glasses followed an annealing procedure in a different furnace, where they were heated to 400 °C for 4 h, in order to reduce their internal stress.Figure 1 represents a photo of the prepared glass samples.In the mentioned figure the Ba/B ratios are 0.58 (for S1 glass sample), 1.27 (for S2 glass sample), 2.12 (for S3 glass sample), and 3.18 (for S4 glass sample).
Using the method outlined by Archimedes in Eq. (1), the density of the synthesized S-S4 glasses was measured.The weights of the S1-S4 glasses in liquid and air are denoted by W a and W L .Additionally, the density of the submerged liquid used in the current study is ρ L ≈1 g/cm 3 for water 36 .
Furthermore, the characterization of the S1-S4 glasses was performed using a Shimadzu-IRSpirit Fourier transform infrared (FTIR).It is used to explore the functional groups and vibration bonds for glasses within the wavenumber range from 500 to 2000 cm −1 .
The V t, and G t are the respective packing density and dissociation energy per unit volume of the utilized metal oxides.

Monte Carlo simulation investigation
The radiation shielding parameters of the glasses under investigation were simulated and evaluated using the Monte Carlo N-particle transport code, 5th version (MCNP-5) 40 .During the simulation, the gamma-ray energy (E γ , MeV) was chosen to vary over a wide range, from 0.033 to 2.506 MeV, in order to encompass nearly all of the actual γ-ray energies.The ENDF/B-V.8 nuclear database, which has the interaction cross-sections needed to assess the radiation shielding capabilities of the examined glasses, was linked to the MCNP-5 code.An input file should be created with all the details required to describe the simulation components (cell, surface, material, importance, source, and cutoff cards) in order to carry out such a simulation.The mentioned input file indicates that the geometry is encircled by a 5 cm-thick lead shielding cylinder.The dry air inside the outer shielding cylinder had a density of 0.001225 g/cm 3 .Subsequently, a radioactive disk source was positioned at the center of the outer shielding cylinder (POS = 0 0 0), measuring 2 cm in diameter and 0.5 cm in thickness.A flux of γ-ray photons (PAR = 2) is released by the source along a long + Z axis (AXS = 0 0 1).The source card of the input file also included the distribution and emission probability of the radioactive source.The released photon flux was guided towards the sample using a lead collimator that measures 7 cm in height and 2 cm in diameter.The material card was modified to include the chemical compositions and densities of the materials constituting the created geometry so that the collimated photon flux could interact with the examined glasses.The fabricated glasses, shaped in cylinders, measure 3 cm in diameter and 1 cm in height.The scattered photons were then directed toward the detector through a second collimator, with a diameter of 5 cm and a height of 3 cm, after the photon flux had interacted with the electrons and atoms in the glasses.To estimate the average flux per unit glass cell and the average track length (ATL) of γ photons within the glasses under investigation, the current work uses the "F4 tally" function embedded in MCNP-5 code.By using the cutoff card, which is set up to be 10 8 , the photon-electron interaction is managed.Within the output file after the simulation runout, the simulated ATL of γ-photons was included.The mentioned output file indicates ± 1% for the relative error [41][42][43][44] .Using Eqs.(9 and 10), the linear attenuation coefficient (µ, cm −1 ) and mass attenuation coefficient (µ m , cm 2 /g) of the fabricated composites were calculated based on the obtained ATL of γ-photons.
(2) where I o and I t values refer to the photon flux before and after interaction with the fabricated glasses.The half-value thickness (Δ 0.5 , cm) describes the thickness of the material required to diminish the photon flux by 50%.It is inversely varied with the µ values according to Eq. (11).
Additionally, the transmission factor (TF, %) for the fabricated S1-S4 glasses was estimated according to Eq. 12, where the I o I t represents the ratio of transmitted photons.On the contrast, the RPE (%) describes the amount of photons absorbed within the fabricated glasses thickness.It is calculated based on Eq. 13.
In addition to being evaluated through Monte Carlo simulation, the µ m was theoretically calculated with XCOM software.The (µ m ) glass can be theoretically computed using Eq. ( 14) 45 .ρ, ω i , and ( µ m ) i describe the density of fabricated glasses, the weight fraction of i th element within the glass sample, and µ m for the i th constituent element, respectively.

Results and discussion
The substitution of B 2 O 3 by the BaO compound increases the Ba 2+ ions while it decreases the B 3+ ions in the borosilicated glasses.This affects the color of the synthesized boro-silicate glasses.The transparent color is transferred to a light yellow and then to a dark yellow color by increasing the Ba 2+ /B 3+ ratio between 0.58 (S1 glass sample) and 3.18 (S-4 glass sample), as illustrated in Fig. 1.The ratio of Ba/B plays an important role in controlling the density, molar weight, and molar volume of the fabricated glasses, as illustrated in Table 1 and Fig. 2. The increase in BaO concentration increases the Ba 2+ ions, which in turn increases the Ba/B ratio due to the substitution of B 3+ by Ba 2+ ions.The increase in Ba 2+ /B 3+ ratio is associated with an increase in the molar weight of the fabricated glasses, where the molar weight increases from 112.86 to 125.42 mol/g, when rising the Ba 2+ /B 3+ ratio between 0.58 and 3.18, respectively.Moreover, the experimental measurements of the fabricated glass density show an increase from 4.48 to 4.97 g/cm 3 , when rising the Ba/B ratio between 0.58 and 3.18, respectively.The increase in the fabricated glasses density is attributed to the partial replacement of Ba (ρ = 3.34 g/cm 3 ) for the B (ρ = 2.46 g/ cm 3 ) ions.The increase in the density and molar weight of the developed glasses is found to be accompanied by a negligible increase in the molar volume of the fabricated glasses, which varies from 25.17 to 25.21 cm 3 /mol.The aforementioned negligible increase in the V m values is attributed to the close comparable V m values for both B 2 O 3 and BaO compounds, where the (V m ) B2O3 = 28.30cm 3 /mol and (V m ) BaO = 26.805cm 3 /mol.
Fourier transform infrared (FTIR) is an instrument used to analyze functional groups and provide information about chemical bonding and molecular structure for various materials.Table 2 and Fig. 3 illustrate the functional groups for the glass system.It can be noted in four bands.A small band is located at 550 and 560 cm −1 , which is related to the O-Si-O bending vibration mode 35 , while the band appearance at 690 and 703 cm −1 can be assigned to bending vibration B-O-B 46 .The large band centered at 906 to 971 cm −1 and 1039 to 1076 cm −1 can correspond to the B-O stretching of the tetrahedral BO 4 unit 48 The last band at high wavenumbers from 1388 to 1453 cm −1 and 1202 and 1247 cm −1 is associated with B-O stretching of trigonal BO 3 47 .On the other hand, it can be noted that the change in band position for the BO 3 band with adding a further amount of BaO is due www.nature.com/scientificreports/ to transforming BO 3 to BO 4 and forming nonbridging oxygen.Here, it can be concluded that the BaO plays a modifier in the glass system.Table 3 depicts the variation in the mechanical properties of the fabricated glasses with the increasing of Ba 2+ / B 3+ ratio.Rising the Ba 2+ /B 3+ ratio between 0.58 (for S1) and 3.18 (for S4) is found to reduce the total dissociation energy G t from 60.87 to 54.37 kcal/cm 3 and the packing density V t from 0.57 to 0.50 m 3 /mol.The reduction in the G t and V t values are attributed to the packing factor V i and dissociation energy (G i ) for both B 2 O 3 and BaO compounds, where the B 2 O 3 compound has G i = 82.8kcal/cm 3 and V i = 20.8m 3 /mol while for BaO compound G i = 39.5 kcal/cm 3 and V i = 9 m 3 /mol 48 .The replacement of B 2 O 3 (high G t and V i values) with BaO (low G i and V i  The radiation shielding properties of the fabricated glasses were investigated utilizing the Monte Carlo simulation (MCNP-5) code and the XCOM theoretical program, as illustrated in Fig. 4 (a and b).The gamma-ray shielding evaluations show a dependence of the shielding ability on some parameters related to the γ-ray source and the examined materials.Regarding the γ-ray source, the source energy (E γ , MeV) greatly affects the µ values of the fabricated glasses, where greeting the E γ is associated with a reduction in the µ values.The reduction in the µ values is a result of the reduction in the interaction cross-section of γ-photons, where the cross-section varied with E −3.5 γ and E −1 γ for photoelectric (PE) and Compton scattering (CS) interactions 49 .Figure 4-a shows that the high µ values are 51.51 cm −1 , 53.52 cm −1 , 55.52 cm −1 , and 57.52 cm −1 for samples S1, S2, S3, and S4, respectively, at 0.033 MeV.Then, the µ values obtained at 0.033 MeV were reduced by approximately 85.3% for all samples when the E γ values are increased to 0.122 MeV.This high reduction is attributed to the PE cross-section.After that, when increasing the E γ values above 0.122 MeV, the µ decreased by 88.8%, 89.6%, 88.8%, and 88.7%, respectively, S1, S2, S3, and S4.In particular, the reduction in the µ values, for E γ interval between 0.244 and 2.506 MeV, is due to the CS interaction 50 .
Based on the measured µ, the µ m values were calculated for the fabricated glasses, the results are grouped in Table 4.The µ m values reduced in the interval between 11.488-0.041cm 2 /g for sample S1, 11.516-0.040cm 2 /g for sample S2, 11.542-0.040cm 2 /g for sample S3, and 11.567-0.040cm 2 /g for sample S4, all when rising the E γ values from 0.033 to 2.506 MeV.Moreover, Table 4 shows an agreement between the simulated MCNP and XCOM calculated µ m values with a difference of less than ± 2% in average.www.nature.com/scientificreports/ The reduction in µ values due to the E γ increase is followed by an increase in the Δ 0.5 values, as illustrated in Fig. 5.The Δ 0.5 values increased under the effect of PE and CS interactions between 0.0-3.81cm for sample S1, 0.01-3.69cm for sample S2, 0.01-3.57cm for sample S3, and 0.01-3.46cm for sample S4, with rising E γ between 0.033-2.506MeV.As illustrated earlier, the increase in the E γ values reduces the PE and CS cross-sections, leading to a reduction in the photon-electron interactions 51 .Therefore, the transmitted photons I t increased while the absorbed photons I a increased, resulting in a reduction in the µ values and an increase in the Δ 0.5 values of the fabricated glasses, where µ = 0.693/Δ 0.5 .
The mode of variation in the µ values for the fabricated samples affects their Δ eq values, where the increase in E γ values decreases the Δ eq of the fabricated glasses, as presented in Fig. 6.The reduction in the Δ eq values is attributed to the comparable reduction in both µ values for Pb and fabricated glasses.While increasing the E γ values in the PE interval, the µ values of all tested samples were reduced by approximately 85.3%.Simultaneously, the increase in the E γ values in the same PE energy interval (0.033 MeV ≤ E ≤ 0.122 MeV) decreases the µ values for lead by 85.8%.The comparable reduction in the µ values for both fabricated glasses and Pb is the main reason behind the exponential reduction in the Δ eq values.Additionally, due to the K-absorption of Pb, the Δ eq values increased around 0.081 MeV because of the high µ values of lead at this energy.In the PE interval, the Δ eq values were reduced by 15.58%, 21.41%, 14.93%, and 13.78% for samples S1, S2, S3, and S4, respectively.Furthermore,  the increase in E γ values above 0.122 MeV (i.e., CS interval) leads to a moderate reduction in the Δ eq values.This reduction was achieved due to the moderate reduction in the µ values for both fabricated samples and Pb, obtained by rising the E γ between 0.244 and 2.506 MeV, where the µ value of lead was reduced by 93.1%, while the µ values were reduced by 88.8%, 89.6%, 88.8%, and 88.7% for samples S1, S2, S3, and S4, respectively.In the CS interaction interval, while rising the E γ values between 0.244 and 2.506 MeV, the Δ eq for S1, S2, S3, and S4 was reduced by 38.28%, 33.37%, 38.16%, and 38.72%, respectively.The increase in E γ values is accompanied by an increase in the I t photons and a reduction in the I a photons.Since the I t /I o ratio determines the TF value and the I a /I o determines the RPE values, the TF value increased while the RPE values decreased with rising the E γ value, as presented in Fig. 7. Due to the PE interaction behavior at low energy, the photon energy was transferred to one electron, and the photon disappeared in the medium, leading to a reduction in the I t photons and TF values 52 .The TF values in the interval between 0.033 and 0.122 MeV are less than 1% for a 1 cm thickness of the fabricated samples S1 and S4.In contrast, the I a photon number increases and reaches its maximum, leading to an increase in the RPE values, where the RPE values are close to 100% for all samples.Increasing the E γ values between 0.244 and 2.506 MeV is associated with a high increase in I t photons and a reduction in the I a values due to the CS behavior.Therefore, the TF was highly increased, while the RPE values were reduced with rising E γ values.For example, increasing the E γ values between 0.244 and 2.506 MeV increases the TF values of a 1 cm thickness of the fabricated glasses between 19.68-83.37%for sample S1 and 16.91-81.84%for sample S4.On the other hand, the RPE values were reduced by a factor ranging between 80.32-16.63%for sample S1 and 83.09-18.16%for sample S2, when rising the E γ between 0.244 and 2.506 MeV.
The glass thickness also greatly affects the values of I t and I a which then affect the TF and RPE values.Rising the fabricated glass thickness reduces the TF, while increasing the RPE of the fabricated glasses, as shown in Fig. 8.In fact, the increase in glass thickness increases the pass length of γ-photons, which leads to an increase in the Figure 6.Variation of the lead equivalent thickness (Δ eq , cm) against the γ-photon energy.www.nature.com/scientificreports/interaction probability between photons and surrounding electrons 53 .Therefore, the I a photons increased and the I t photons decreased, leading to an increase in the RPE and a reduction in the TF values.For example, increasing the glass thickness from 0.5 to 3 cm increases the RPE values at E γ of 1.275 MeV between 11.64-52.41%for sample S1 and 12.61-55.47%for sample S4.On the other hand, for the same thickness variation, the TF values decreased by 46.14% and 49.04% for samples S1 and S4, respectively.Increasing the substitution of B 2 O 3 by BaO compounds increases the Ba/B ratio within the fabricated glasses, which affects the glass density and its molar weight, as presented earlier.The impact of the Ba 2+ /B 3+ ratio on the µ values is illustrated in Fig. 9, where increasing the Ba/B ratio is found to slightly increase the µ values.Increasing the Ba 2+ /B 3+ ratio also increases the electron density and Z eff of the fabricated glasses.Since the interaction cross-section proportion to Z eff increased, the µ values increased as the Ba 2+ /B 3+ increased.Figure 9 shows that the increase in Ba/B ratio from 0.58 to 3.18 is associated with an increase in the µ values by 11.8%, 9.4%, and 8.94%, respectively, at E γ of 0.122, 0.662, and 1.275 MeV.The impacts of Ba 2+ /B 3+ on the Δ 0.5 and Δ eq values are opposite to those reported for the µ values.Figure 10 shows a reduction in the Δ 0.5 values from 1.69 to 1.55 cm (at E γ of 0.662 MeV) and from 3.81 to 3.46 cm (at E γ of 2.506 MeV), when rising the Ba/B ratio between 0.58 and 3.18, respectively.The reduction in the Δ 0.5 values is attributed to the reverse proportionality of µ and Δ 0.5 values.Also, the Δ eq values were reduced, while rising the Ba 2+ /B 3+ ratio, where the Δ eq values reduced from 3.04 to 2.78 cm at E γ of 0.662 MeV and from 2.70 to 2.45 cm at E γ of 2.506 MeV.The increase in the Ba 2+ /B 3+ ratio increases the Ba 2+ ions within the fabricated glasses, which increases the resistance of the material to the transposed photons.Therefore, the number of photon-electron interactions increased, I t decreased, and I a and µ values increased.The increase in µ values of the fabricated glasses compared to the µ values of lead is the main reason for the reduction of Δ eq .Furthermore, the increase in I a photons and the decrease in I t photons affect the values  concentrations of dense metal oxides TeO 2 and BaO, where their ratios reach 70 mol% and 20 mol%, respectively.The comparison shows high shielding capacity for the developed glasses compared to the commercial-based PbO compounds and those glasses reported recently for gamma ray shielding applications.Therefore, the fabricated glasses are suitable candidates for mid-energy gamma-ray shielding applications.

Conclusion
The current study concludes with the efficiency of new BaO-doped lead borosilicate glasses adopted for gammaray shielding applications.The effects of partially replacing B 3+ with Ba 2+ ions on the developed glasses' mechanical, gamma-ray attenuation, and physical characteristics were assessed.The color of the fabricated glasses was turned to dark yellow with increasing the Ba 2+ /B 3+ substitution ratio.Additionally, the density of the fabricated glasses enhanced by 11% from 4.48 to 4.97 g/cm 3 , increasing the Ba 2+ /B 3+ substitution ratio from 0.58 to 3.18, respectively.The replacement of B 3+ ions by Ba 2+ ions reduces the mechanical moduli of the developed glasses, where they reduced by 21.84%, 31.61%,19.61%, and 26.36% for Young, bulk, shear, and longitudinal moduli when the Ba 2+ /B 3+ substitution ratio increased between 0.58 and 3.18.Also, the micro-hardness of the fabricated samples decreased by 8.12% (between 4.49 and 4.12 GPa).The reduction observed in the mechanical properties is attributed to the reduction in the packing density and dissociation energy due to the substitution of B by Ba ions.Additionally, the Monte Carlo simulation proves that the linear attenuation coefficient of the fabricated glasses was enhanced by 48.23%, 11.83%, 9.40%, and 10.13%, rising the Ba/B substitution ratio between 0.58 and 3.18, respectively.The enhancement in the linear attenuation coefficient reduces the half-value thickness and the equivalent thickness for lead.Compared to the shielding capacity of some commercial glasses and borate-based glasses, the developed glasses S1-S4 have suitable radiation shielding properties to be used in nuclear medicine applications at hospitals.

Figure 1 .
Figure 1.A picture of the synthetic glasses demonstrated how the color changed as the Ba/B ratio increased.

Figure 2 .
Figure 2. Impact of Ba 2+ /B 3+ ratio on theoretical density, molar weight, and molar volume of the fabricated glasses.

Figure 7 .
Figure 7. Impact of the applied γ-photon energy on TF and RPE values, for the fabricated glasses S1 and S4.

Figure 8 .
Figure 8. Impact of the glass thickness on TF and RPE values for the fabricated glasses, at 1.275 MeV.

Figure 12 .
Figure 12.Comparison between the linear attenuation coefficient of the developed glasses and some commercial and recently reported borate-based glasses.

Table 1 .
Chemical composition of the prepared glass samples.

bond and functional groups (cm −1 )
FTIR results for Al 2 O 3 -PbO-B 2 O 3 -SiO 2 -BaO glasses.) is the main reason for the reduction in both G t and V t of the fabricated glasses.The reduction in the G t and V t for the fabricated glasses reflects on the mechanical moduli.The increase of substitution ratio Ba/B between 0.58 and 3.18 decreases the moduli from 69.35 to 54.21 GPa (for Y modulus), from 47.41 to 32.43 GPa (for K modulus), from 27.60 to 22.19 GPa (for S modulus), and from 84.22 to 62.02 GPa (for L modulus).Additionally, the Poisson ratio is slightly reduced from 0.26 to 0.22, associated with a similar reduction in the micro-hardness of the fabricated glasses from 4.49 to 4.12 GPa.After that, the increase in the fractal bond conductivity from 2.33 to 2.74 confirms a transformation of the glassy structure to a 3D network.

Table 3 .
The mechanical properties for the fabricated BaO doped lead borosilicate glasses.

Table 4 .
Comparison between the simulated MCNP-5 and XCOM theoretical calculated µ m values for the fabricated glasses.