Comprehensive study of optical, thermal, and gamma-ray shielding properties of Bi 2 O 3 – ZnO – PbO – B 2 O 3 glasses

: The Bi 2 O 3 – ZnO – PbO – B 2 O 3 (BiZPB) glasses are prepared using the melt-quenching technique. As the concentration of lead oxide increases, the band gap energy ( E g ) decreases from 2.864 to 2.671 eV. The BiZPB glasses exhibit remarkable stability under thermal stress, as indicated by the thermogravimetric analysis graph, with only a marginal 0.5% loss in their initial mass. The decrease in the glass transition temperature ( T g ) of BiZPB glasses, with an increase in the PbO concentration, can be attributed to the speci ﬁ c in ﬂ uence of PbO on the glass structure and properties. The radiation shielding performance for the prepared glasses is evaluated using Phy-X software. The transmission factor (TF) for the 10B 2 O 3 – 10ZnO – 40PbO – 40B 2 O 3 glass sample is almost zero at 0.122 MeV, which means that this glass sample can attenuate almost all the photons with an energy of 0.122 MeV, whereas the TF values for this sample with thicknesses of 0.5 and 1 cm are 88 and 77%, respectively., it can be observed from the TF values that the prepared glasses have good attenuation performance against low energy (0.122, 0.245, and 0.344 MeV), while they have weak shielding performance against high energy radiation. The addition of PbO causes a reduction in TF, which means that the addition of an extra amount of PbO into the glasses results in an enhancement in the radiation shielding competence of the samples. The average half-value layer ( HVL̅ ) is also calculated. The results demonstrated that HVL̅ is at its lowest between 0.248 and 0.411 MeV, ranging between 0.396 and 0.513 cm.


Introduction
The probability of human exposure to gamma radiation has been increasing in last few years due to the increased utilization of gamma radiation in nuclear, medical, agricultural, archaeology, and research sectors [1][2][3].Accordingly, studies have focused on developing novel shielding materials to protect people from the potentially harmful impacts of gamma radiation over the past few years [4,5].For protection from X-ray and gamma radiation, traditionally, lead and concrete have been used.Despite its economical nature and structural flexibility, concrete has several limitations due to its composition and water content [6,7].When there is a high concentration of water in the constituents of concrete, the material's structural strength and density start to decrease and the water itself has the potential to vaporize in hot environments due to the radiation energy absorption that occurs.On the other hand, due to its low cost, high density, and good shielding performance, lead is the element that is most frequently used in the utilization of radiation protection.However, lead has limitations such as inflexibility, poor mechanical strength, and toxicity [8,9].
Hence, the radiation shielding industry has focused on and explored a range of shielding materials, including polymers, nanocomposites, ceramics, glasses and alloys [10][11][12][13][14].In light of these different materials, glass has recently gained popularity among researchers as a prospective radiation shielding material due to its interesting properties [15,16].Glasses have promising optical properties in addition to good mechanical and physical properties.Also, one can prepare glasses by different methods at low cost.Additionally, one can easily prepare glasses in different sizes and shapes.The density of glass can be enhanced by incorporating heavy elements.Also, it can be recycled and reused, making it also environmentally friendly.All these properties encourage the researchers to develop glasses as alternative radiation shielding materials [17][18][19][20].In the last few years, several glass kinds including silicate, borate, tellurite, phosphate, germinate and glasses doped with HMO have been studied theoretically and experimentally or, even via simulations [21,22].Theoretical investigations of the radiation shielding properties involve applying different equations and mathematical models.These theoretical studies help the investigators to examine the basic principles controlling the behaviour of the shielding materials and make predictions of the attenuation performance of the medium without the need for the experimental work.In addition to the theoretical research, experimental studies are performed straightforwardly to measure the radiation shielding factors.Experimental studies involve conducting measurements on the shielding materials by using different radioisotopes and detectors.In the experimental work, one can determine the attenuation factors and validate the theoretical techniques [23,24].On the other hand, Monte Carlo simulation offers a costeffective and adequate method to examine the interaction between the gamma radiations with the glasses [25][26][27].The combination of the three different approaches in determining the radiation shielding factors has contributed to an in-depth understanding of the radiation attenuation performance.The information obtained from these investigations can result in the improvement of the current radiation shielding materials and the development of new glasses with certain features for specific optical, electrical and construction applications.Generally, the recent research in the radiation shielding properties by using theoretical, experimental or simulation approaches has advanced the glass industry research and opened the door for recent ideas for real applications [28][29][30][31][32][33][34].The quest for scientific information, technical improvements, industry-specific needs, and the need to address new difficulties all contribute to a dynamic and ever-expanding radiation-shielding glass landscape.Radiation shielding glasses will become more important in guaranteeing safety and radiation protection across a wide range of industries and settings as scientists continue to investigate novel materials, production methods, and uses.The primary goal of this study is to investigate the optical, thermal, and gamma-ray shielding properties of Bi 2 O 3 -ZnO-PbO-B 2 O 3 (BiZPB) glasses.

Materials and methods
To ensure the utmost quality of BiZPB glasses, a specialized technique known as melt quenching was employed [35][36][37].The primary objective was to achieve an exceptional end product.The process commenced with precise measurements of AR-grade Bi 2 O 3 , ZnO, PbO oxides and H 3 BO 3 of exceptional purity, using an electronic scale with a remarkable accuracy of 0.001 g.These measured compounds were meticulously ground in an agate mortar, renowned for its ability to finely grind materials.This grinding process yielded a consistent and reliable mixture.Subsequently, the mixture was placed in a muffle furnace and heated to a precise temperature of 1,050°C, all while being continuously stirred.The stirring action ensured an even distribution of the components throughout the mixture and prevented any separation.Following this, a dedicated annealing furnace was employed to maintain a constant temperature of 300°C in a graphite mould.Great care was taken during the pouring of the molten substance into the mould, minimizing internal tensions and preventing any potential fractures.After a carefully controlled annealing period of 2 h, the samples were gradually cooled to ambient temperature.The photos of the samples are shown in Figure 1.The Archimedes principle was employed to determine the density of each sample accurately [38,39].By monitoring the buoyant forces experienced by the samples in a fluid with a known density, the densities of the samples were meticulously calculated.
For the collection of UV-Vis spectra spanning from 180 to 800 nm, the Perkin Elmer Lambda 19 UV-Vis-NIR spectrophotometer was chosen for its renowned flexibility.The computation of the energy band gap and the assessment of other optical properties relied on Tauc's approach, which was based on the UV-Vis absorption data, as previously detailed in our publications.
During the characterization of materials, the STA 6000, a sophisticated thermal analysis instrument developed by Perkin Elmer, was utilized.This advanced tool incorporated dual-furnace technology, enabling simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).The TGA feature of the STA 6000 tracked changes in the sample weight during heating or cooling, providing valuable insights into thermal stability and breakdown.
To evaluate the effectiveness of the manufactured glasses in terms of radiation shielding, Phy-X software was employed [40].This software offered a comprehensive method for analyzing attenuation factors and other shielding parameters, enabling a thorough assessment of the radiation shielding capabilities of the glasses.

Optical properties
The experimental results reveal significant changes in the density (ρ) and molar volume (V m ) of the BiZPB glass samples as the lead oxide concentration increases.The density increased from 4.835 to 5.671 g/cm³, while the molar volume increased from 35.546 to 38.430 cm³.The observed changes in the density and molar volume of the BiZPB glass samples as the lead oxide concentration increases reflect alterations in the packing and arrangement of atoms within the glass structure.An increase in density suggests higher compactness of the glass network, potentially due to the incorporation of lead oxide atoms that occupy additional space and contribute to a denser structure.Similarly, the increase in molar volume indicates an expansion of the glass matrix, likely resulting from the larger size of lead oxide ions compared to the original glass constituents.
In our recent publication [37], derivation of the absorption spectrum fitting method has been used to study the optical band gap energy of the selected glasses.In continuation of the work, to study the optical properties in the present investigation, Tauc's plot (Figure 2) was employed to analyze the synthesized BiZPB glass samples.According to Davis and Mott, Tauc's plot has been used to obtain the optical band gap energy by extrapolating the(αhν) 1/2 vs hν plot to zero [41]: where hν is the energy of incident photons, α is the absorption coefficient, E g is the optical band gap energy and B is the tailing parameter.
As the lead oxide concentration increased, the E g of the glass samples decreased.The E g values ranged from 2.864 to 2.671 eV, indicating a decrease in the energy required for electronic transitions within the glass structure.It is due to the structural changes induced by an increase in the nonbridging oxygens (NBOs) [42][43][44].The incorporation of lead oxide promotes the formation of NBOs, which introduce additional energy levels within the band structure and effectively lower the band gap energy.
The band gap energy value obtained from Tauc's plot serves as a fundamental parameter for calculating other optical properties.Table 1 displays various optical parameters derived from the band gap energy value.As the lead content increases, the refractive index (n), dielectric constant (ε) and optical dielectric constant values also increase.The refractive index values range from 2.435 to 2.492, the dielectric constant values range from 5.928 to 6.209, and the optical dielectric constant values range from 4.928 to 5.209 (Figure 3a).This increasing behaviour (eV suggests the enhanced influence of NBOs in the glass network [36,38].The reflection loss (R L ) values increase from 0.174 to 0.183, whereas the transmission coefficient (T) decreases from 0.703 to 0.691 (Figure 3b), indicating a reduction in the amount of incident light transmitted through the glass.To determine the metallic or non-metallic nature of the glass samples, metallization (M) is considered.
According to Dimitrov and Komatsu [45], a metallization value below unity indicates non-metallic behaviour.In this study, the metallization values range from 0.365 to 0.378, confirming the non-metallic nature of the glass samples.Additionally, the energy band gap-based metallization (M (E g )) criterion and refractive index-based metallization (M (n)) criterion values range from 0.072 to 0.067 and 0.378 to 0.365, respectively, which are also less than unity [42][43][44].These results provide further evidence of the non-metallic characteristics exhibited by the glass samples.This finding aligns with the amorphous nature of the glass structure and the absence of metallic bonds.Furthermore, optical electronegativity (χ*), non-linear optical susceptibility (χ 3 ), and non-linear refractive index (n 2 optical ) values show a decreasing trend with increasing lead oxide concentration.The values range from 0.770 to 0.718 for χ*, from 1.612 × 10 −15 to 1.379 × 10 −15 esu for χ 3 , and from 2.495 × 10 −14 to 2.086 × 10 −14 esu for n 2 optical (Figure 3c).This indicates a reduction in the optical response, non-linear optical effects, and the ability of the glass to manipulate light in a non-linear manner [44].In contrast, the linear dielectric susceptibility (χ (1) ) demonstrates an increasing trend with the lead oxide concentration.The values range from 0.392 to 0.415, indicating an enhanced response to an electric field within the glass network (Figure 3d).This behaviour provides insights into the dielectric properties of the glass samples and their ability to store and release electrical energy [36,38].The molar refractivity (R m ) is a parameter dependent on the polarizability of the glass matrix.As the concentration of NBO increases, the glass network becomes more polarized, leading to an increase in the molar refractivity value.In this study, the molar refractivity values range from 22.095 to 24.386 cm³/mol, signifying an enhanced response of the glass to electric fields [42,47].This increase in polarizability influences the values of molar polarizability (α m ) and electronic polarizability (α e ), which range from 8.764 × 10 −24 to 9.672 × 10 −24 cm 3 and from 8.823 × 10 23 to 9.007 × 10 23 , respectively (Figure 3e).These findings highlight the glass's ability to polarize in the presence of an electric field, affecting its optical and electrical properties [42][43][44].

Thermal properties
TGA makes use of variations in weight as a function of temperature.Figure 4 shows the TGA plot of BiZPB glasses.The TGA graph showed that the BiZPB glasses were remarkably stable under thermal stress, losing just around 0.5% of their initial mass.The composite seems to have remarkable resistance to thermal deterioration, as shown by its ability to withstand elevated temperatures without suffering appreciable changes to its structure or characteristics.Water molecules and/or volatile components that may be present in the composite evaporate, accounting for the small weight loss seen [46].The DSC plot for the BiZPB samples is presented in Figure 5.The glass transition temperature (T g ) is marked on the plot and it is found to increase to 312, 325, 329 and 332°for the BiZPB1, BiZPB2, BiZPB3 and BiZPB4 respectively.The decrease in the T g of BiZPB glasses with an increase in the PbO concentration can be attributed to the specific influence of PbO on the glass structure and properties.T g determines the material's thermal stability and processing conditions.The addition of PbO can lead to changes in the overall chemical composition.This change in composition affects the packing and bonding of the glass network, leading to a reduction in T g [47,48].The increased concentration of PbO may lead to a disruption of the glass network, reducing the energy barrier for the glass transition  to occur.Incorporation of PbO may introduce structural defects or changes in the glass matrix, leading to a more disordered and less stable arrangement.This could result in a decrease in the energy required for the glass transition process.The incorporation of PbO could lead to increased free volume or larger interstitial spaces in the glass network, which could facilitate molecular movement and decrease T g .

Gamma-ray shielding properties
In order to examine the radiation shielding performance of the prepared BiZPB glasses, the transmission factors (TFs) are evaluated.This parameter characterizes the intensity of the radiation that can penetrate via the shielding material, so when TF is high (close to 100%), then all the photons can penetrate the medium and this medium has a weak radiation shielding ability.However, if TF is small (close to zero), then this medium is able to stop most of the incoming radiation and it has practically perfect shielding performance.As shown in Figure 6, the TF for BiZPB1 as a function of the energy is plotted at two thicknesses (0.5 and 1 cm).The TF for BiZPB1 is plotted only as an example, but the other three glasses show the same trend.From this figure, the influence of the energy on the TF is examined.Evidently, the TF increases as the energy increases, approaching 88% for a thickness of 0.5 cm and 77% for a thickness of 1 cm at the maximum selected energy (i.e.1.46 MeV).At the lowest energy, i.e. 0.122 MeV, it is found that the TF is almost zero, which means that this glass sample can attenuate almost all the photons with an energy of 0.122 MeV.As the energy increases to 0.245 MeV, it is found that the TF increases to 30 and 9% for a thickness of 0.5 and 1 cm, respectively.The glass still has good attenuation performance at this energy, since it stops a high proportion of the photons with an energy of 0.245 MeV.At 0.344 MeV, it is found that the TF for a thickness of 0.5 cm is 54%, which means that almost half of the intensity of the incoming radiation that can penetrate is attenuated, while about 46% of the photons can penetrate this glass.From this observation, it is concluded that BiZPB1 glass (and this is also correct for BiZPB2-BiZPB4) is good at attenuating low-energy photons, while it has weak shielding performance against high-energy radiation.The TF of the glass is also affected by the thickness of the glass.Therefore, the TF for BiZPB1 with thicknesses of 0.5 and 1 cm at 0.411, 0.678 and 0.867 is plotted MeV in Figure 7.It is found that an increase in the thickness of BiZPB1 leads to a decrease in TF.For instance, at 0.678 MeV, the TF values at 0.5 and 1 cm are 78 and 62%, respectively.This means that a layer of BiZPB1 with a thickness of 0.5 cm can attenuate 22% of 0.678 MeV photons, while when the thickness of this layer is doubled, its shielding performance is enhanced, and 38% of the photons are attenuated by this layer.At an energy of 0.867 MeV, the TF for BiZPB1 is 83 and 69% for thicknesses of 0.5 and 1 cm, respectively.This investigation supports the idea that the increasing glass thickness improves radiation protection.
Figure 8 represents the relationship between the TF and the concentrations of PbO at an energy of 0.444 MeV and a thickness of 0.5 cm.The results at only one single energy level are presented to study the effect of the PbO content and the TF. Figure 8 shows that TF decreases as the content of PbO increases from 40 to 70 mol%, where the TFs follow the order of BiZPB4 < BiZPB3 < BiZPB2 < BiZPB1.Hence, the addition of an extra amount of PbO into the glasses results in an enhancement in the radiation shielding competence.From Figure 8, the TFs of BiZPB1 and BiZPB4 are around 67 and 59%, which means that when more PbO is added, the TF decreases and the protection efficiency of the glass is improved.According to this figure, adding PbO to these glasses may improve their shielding.
The impact of PbO on energy by calculating the relative reduction in TF (RD-TF) due to an increase of PbO from 40 to 70 mol% is studied and the RD-TF is plotted in Figure 9.It is clear that the maximum values of RD-TF occurred in the low-energy range.This is due to the domination of the photoelectric effect.The RD-TF is 32% at 0.245 MeV, 22% at 0.296 MeV, 17% at 0.344 MeV and 12% at 0.411 MeV.While the RD-TF is very small at higher energies (around 3% for E > 1.09 MeV).At higher energies, the Compton scattering is the main interaction process and the probability of occurrence of this process is weakly dependent on the atomic number of the absorber.
In order to deeply examine the impact of PbO on the thickness of the sample, the average half-value layer (HVL ̅ ) of the present glasses is calculated at four energy intervals.These four intervals are 0.248 to 0.411 MeV, 0.444 to 0.779 MeV, in these four intervals are plotted in Figure 10.It is clear that the HVL ̅ is at its lowest in interval 1, ranging between 0.396 and 0.513 cm for BiZPB4 and BiZPB1, respectively, increasing to 1.113-1.364cm in interval 2, and attaining its maximum at interval 4 (varied between 2.156 and 2.544 cm).This analysis demonstrated that a thin layer with a thickness of around 0.4-0.5 cm can be used to shield the radiation with energies of 0.245-0.411MeV.However, if the energy increases, a layer of thickness of 2.1-2.5 cm is needed to shield the radiation with high-energy values (i.e. between 1.11 and 1.46 MeV).Moreover, the enhancement in the LAC is evaluated with the addition of PbO by calculating the ratio of LAC between the glass with 70 and 40 mol% of PbO (i.e.BiZPB4 and BiZPB1).The results of this parameter are plotted in Figure 11.Clearly, the values of this parameter are greater than 1 at any energy, which means that the LAC for BiZPB4 is higher than the LAC for BiZPB1.Therefore, the addition of PbO at the expense of B 2 O 3 causes an increase in the LAC values.The influence of PbO on the LAC is more clear at low energy, where the enhancement in the LAC attains its maximum in the low energy interval.As the energy increases, the enhancement in the LAC decreases, and this means that the LAC for BiZPB4 is still higher than the LAC of BiZPB1, but the influence of PbO on the LAC is small.The small dependence of LAC on the PbO content in the high-energy range can be explained according to the Compton scattering process.The probability of interaction in this process is weakly affected by the atomic number of the shielding material.For this reason, it is found that at higher energies the enhancement in the LAC is around 1.17, which suggests that all the glasses have close LAC.This indicates that glasses with different concentrations of PbO have similar attenuation performance against high-energy radiation.
The radiation shielding properties of BiZPB4 glass are compared to other shielding materials (Al, Fe, RS-360 glass, RS-520 glass and lead).The LAC for BiZPB4 glass is divided by the LAC for the aforementioned shielding materials at 0.344 MeV and the results are plotted in Figure 12.For a certain material, if the ratio is higher than 1, then the LAC for BiZPB4 is higher than the LAC for this material.As can be seen from this figure, the ratio between BiZPB4 and lead is 0.45, which means that the lead has higher LAC values  than BiZPB4 which is an expected result, since the lead has very high attenuation ability and is one of the most common materials for radiation protection.However, the results in Figure 12 show that the BiZPB4 glass has higher LAC than Al, Fe, RS-360 glass and RS-520 glass, which means that BiZPB4 glass has better attenuation performance than Al, Fe, RS-360 glass and RS-520 glass.

Conclusion
The concentration of PbO played a crucial role in influencing the properties of the BiZPB glasses.As the concentration of lead oxide increased, the E g of the glass samples decreased from 2.864 to 2.671 eV.Additionally, the BiZPB glasses demonstrated exceptional thermal stability, with only a slight 0.5% loss in their initial mass, as evidenced by the TGA graph.The observed reduction in the T g of BiZPB glasses, with an increase in the PbO concentration, can be attributed to the specific influence of PbO on the glass structure and properties.The radiation attenuation factors were reported in terms of TF, RD-TF, HVL ̅ and other related parameters.The TF increases as the energy increases, approaching 86-88% for a thickness of 0.5 cm and 74-77% for a thickness of 1 cm at 1.46 MeV.While, at very low energy (0.122 MeV, for example), the TF is almost zero, indicating that these samples can attenuate almost all the photons with energy of 0.122 MeV.An inverse relation between the TF and the thickness of the glasses is reported, and the TF for BiZPB1at 0.678 MeV decreases from 78 to 62% when the thickness increases from 0.5 to 1 cm, and the TF for the same sample at 0.867 MeV decreases from 83 to 69% due to the change in the thickness from 0.5 to 1 cm.The TF decreases when the amount of PbO increases from 40 to 70 mol%.The role of PbO on the radiation shielding performance is evaluated by determining the enhancement in the LAC.It is found that the enhancement in the LAC is also greater than 1, implying that the LAC for BiZPB4 is higher than the LAC for BiZPB1.Thus, the addition of PbO at the expense of B 2 O 3 causes an increase in the LAC values.Overall, BiZPB glasses produced by the melt quenching technique have tunable band gap energy, excellent thermal stability, variable glass transition temperature and excellent gamma ray shielding properties.These properties make the BiZPB glasses promising candidates for a wide range of applications, including optoelectronics, sensors, and other high-temperature environments.

Figure 1 :
Figure 1: Photographs of the samples.

Figure 3 :
Figure 3: Variation of (a) Refractive index, dielectric constant and optical dielectric constant, (b) Reflection loss and transmission coefficient, (c) Nonlinear optical susceptibility and-linear refractive index, (d) Linear dielectric susceptibility and optical electronegativity and (e) Molar refractivity, Molar polarizability and electronic Polarizability with % composition of PbO.

Figure 10 :Figure 11 :
Figure 10: The HVL ̅ of the present glasses at four energy intervals.

Figure 12 :
Figure 12:  The comparison between the radiation shielding properties of BiZPB4 glass with other shielding materials (Al, Fe, RS-360 glass, RS-520 glass and lead).

Table 1 :
Composition and optical parameters