Translocation of tungsten ( VI ) oxide/gadolinium ( III ) ﬂ uoride in tellurite glasses towards improvement of gamma - ray attenuation features in high - density glass shields

: This study investigates the e ﬀ ect of substituting tungsten ( VI ) oxide/gadolinium ( III ) ﬂ uoride in tellurite glasses whose densities varies from 5.0879 to 5.3246 g/cm 3 on gamma - ray absorption properties. A range of fundamental absorption parameters, including attenuation coe ﬃ cients, half - value layer thicknesses, e ﬀ ective atom and electron numbers, e ﬀ ective conductivity, exposure, and energy absorption buildup factors, were studied for ﬁ ve di ﬀ erent glass samples with varying substitution ratios. The ratio of tungsten ( VI ) oxide to gadolinium ( III ) ﬂ uoride varied between 0 and 20 mol%, as well as the TeO 2 ratio in the composition was maintained between 90 and 80 mol%. The sample with the composition of 80 – 20 mol% TeO 2 /WO 3 , which attained the maximum density value with 20 mol% WO 3 addition, showed the highest gamma - absorption cap - abilities based on the obtained ﬁ ndings in the range of 0.015 – 15 MeV. In consideration of the mechanical and physical properties of WO 3 in tellurite glasses, it can be concluded that WO 3 incorporation is a crucial monotonic process that may be utilized to further improve the proper - ties of glass shields.


Introduction
Ionizing radiation is one of the natural phenomena that people encounter on a daily basis, coming from outer space, the air, and the earth; yet, in recent years it has also become a man-made phenomenon with medical, industrial, and commercial processes [1][2][3][4][5].Nuclear research, agriculture, and food technology have benefited from the radiation industry's innovative applications [6,7].However, there are risks to the environment and human health linked with the use of ionizing radiation in addition to its advantages.In addition to the benefits of employing alpha, gamma, and X-rays in medical applications, the detrimental radiation effects may result in severe chromosomal abnormalities and carcinogenic consequences [8][9][10].Ionizing radiation is considered to cause harmful damage to living tissues in direct and indirect ways by changing cell structure and damaging their genetic material (DNA).Radiation damage depends on the sensitivity of an organ as well as the amount of energy and type of radiation being absorbed, whether it was due to exposure to high levels of radiation, which would have an immediate effect, or stochastic effects, which are probabilistic and can occur at unexpected times during increasing radiation exposure.For this reason, scientific researchers have focused on the importance of radiation shielding and radiation protection [11][12][13][14].Different materials have been used to protect against radiation by blocking its initial intensity to a degree that is not harmful [15][16][17].In addition to other principles and guidelines for radiation protection, such as reducing exposure duration and increasing distance from the radiation source, shielding materials are considered to be the most beneficial method along with the rest [18][19][20].Conventional lead (Pb) and other materials such as tungsten, antimony, and barium are typically used for protection shielding materials such as clothes for medical personnel and patients going under radiation [21][22][23][24].In recent years glass materials [25][26][27] proved to show efficient radiation protection properties and applications.Due to its transparency, high thermal stability, and permeability, as well as the ease with which it can be fabricated and shaped.Many scientists and engineers have taken these advantages into consideration to utilize glass materials as optical and radiation shielding applications [28][29][30].After witnessing the drawbacks of conventional shielding materials such as Pb and concrete [31,32], glass materials have shown to be non-toxic and have a high level of endurance, making them an intriguing option for shielding investigation and development [33].Tellurite glass compared to other glass materials have showed interesting features such as gain high density, transmission of infrared, low melting temperature, and high dielectric constant [34].Our goal in this research is to investigate the physical and optical properties of TeO 2 with WO 3 and GdF 3 [35], since tellurite glass needs secondary ingredient to form glasses [36].In this study, WO 3 was chosen because of its anti-crystallization ability as well as to improve the glass transition temperature [37].The GdF 3 is used in this research as it is widely employed as a host for fluorescents thanks to its various outstanding material properties during the glass manufacturing process [38,39].In the TeO 2 -WO 3 -GdF 3 glass system [35] five different types of glasses have been prepared in variable proportions with WO 3 as a different glass former and GdF 3 as a modifier.The first and second samples were formed by adding 80 mol% of TeO 2 and varying the WO 3 and GdF 3 compositions (mol%) to achieve different densities, by adding in the first sample 10 mol% of WO 3 while keeping GdF 3 at a stable 0 mol%, and in the second sample, we have reversed the compositions process by keeping the WO 3 at a stable 0 mol% and adding 10 mol% of GdF 3 , as shown in Table 1.By altering the mol% composition of the five glass samples, various densities were determined to investigate the optimum composition of the TeO 2 --WO 3 -GdF 3 glass system, in addition to identifying the glass system with the best radiation protection qualities.This study's extensive findings may contribute to the comprehension of the absorption characteristics of WO 3 -doped tellurite glasses.In addition, the results of this study may provide a comprehensive analysis with comparable glass compositions published in the literature, therefore facilitating the employment of the most appropriate material structures into radiation protection process through glass shields.

Materials and methods
Using five designed samples of varied compositions of the TeO 2 -WO 3 -GdF 3 glass system [35], we determined numerous essential gamma-ray shielding parameters in this study.The five different samples designated G1, G2, G3, G4, G4, and G5 for this investigation were previously synthesized using the conventional melt-quenching method.In this study, gamma-ray absorption properties were examined in the range of 0.015-15 MeV using Py-MLBUF [40] software to conclude gamma ray absorption parameters.Next, they were displayed using the ORIGIN2018 software.The linear attenuation coefficients, half-value thickness, and mean free path lengths were obtained and examined as a function of energy for each glass sample.In addition, exposure and energy absorption buildup factors were also calculated in the 0.015-15 MeV energy range over a broad variety of mean free path values, ranging from 0.5 to 40 mfp.From our previous studies [41] and other published works [42,43], one may acquire more comprehensive technical information and theoretical calculation approaches related to these determined critical parameters for the current glasses.

Results and discussion
In this study, five different composition samples of TeO 2 -WO 3 -GdF 3 glass system were taken under investigation

Glass code
Glass composition (mol%) for gamma-ray absorption parameters.Gamma-ray absorption properties were taken through critical calculation software separately.In many instances, the density of materials used to absorb ionizing gamma and X-rays correlates with their absorption characteristics.The tendency for the incoming radiation to be absorbed through internal interactions and interact with more electrons explains how high-density materials are more effective at absorbing this type of radiation.This investigation has revealed that the five analyzed samples had varying densities.Figure 1 depicts the density of the tested glass samples.As can be seen, the G5 sample, which contains 20 mol% of WO 3 and 80 mol% of TeO 2 , has the maximum glass density value at 5.3355 g/cm 3 .In this example, TeO 2 has the lowest concentration while WO 3 has the highest concentration among the studied glass samples.The quantitative changes in the calculated gamma-ray absorption characteristics will be determined as a function of the density change as a result of the WO 3 incorporation into glass system, which is the primary objective of this study.In the gamma-ray absorption parameters, first, linear attenuation coefficients were calculated in the energy range of 0.015-15 MeV.The μ values can be calculated through a typical transmission setup (Figure 2).The intensity of incident gamma-ray beam would change as a function of absorber thickness as well as linear attenuation coefficient (μ) value of the absorber at a certain energy.Figure 3 depicts the variation in linear attenuation coefficient (μ) of the five analyzed glass samples as a function of increasing energy.The reported changes in μ values reflect the behavior of the incident photon, whether it was partially absorbed, and the other half was dispersed, or whether it was completely absorbed by the electrons on the atomic orbits.It seems that photons in low energies were greatly affected from photoelectric effect, which explains the high attenuation values in the lower energies.As energy increased, the Compton scatter effect subsequently increased.The graph shows a sharp drop between 0.01 and 0.03 MeV, then an incline approximately after 0.04 MeV.Through the drop and rise in the low energies, a steady decrease appeared from 0.05 to 8 MeV.Our results showed that G5 sample with the maximum WO 3 and minimum TeO 2 contribution in its composition has the highest μ values at almost all energy levels.As seen in Figure 3, there were also some minor deviations around the k-absorption edge points of the samples.However, it is likely that an increase in WO 3 doping in telluride glasses may have a similar effect on the linear attenuation coefficients.Another gamma-ray shielding parameter, which is a density-independent parameter, is known as mass attenuation coefficient (μ m ).This  Linear Attenuation Coefficients (P, cm -1 ) Linear Attenuation Coefficients (P, cm -1 ) matter interactions and, therefore, photon energy regions.
Maximum μ m values were recorded at low energies and vice versa.The G5 sample, with the maximum contribution of WO 3 , was reported with the highest μ m values.The atomic weight and density of the G5 sample allow it to have maximum linear and mass attenuation coefficient values within the range of 0.015-15 MeV.Half-value layer (HVL) is an essential parameter in investigating radiationshielding material, which represents the minimum thickness of the radiation shielding required to decrease its primary energy to its half value [13].If the thickness of the absorber remains in low levels, the efficiency of the material is proven to be more effective at attenuating the energetic photons.The graph seen in Figure 5 shows the relationship of the five glass samples with respect to HVL at a certain energy.As the energies start to increase, the HVL values increase as well, showing variation levels of values between the five samples, where G5 have the lowest HVL which give it advantages for determining radiation shielding materials.It is well-known that the linear attenuation coefficient has an inverse relationship with HVL.Eventually, it is a reasonable explanation for the low HVL sample to have high linear attenuation coefficient.For example, HVL values were reported as 3.5519, 3.4789, 3.3747, 3.3203, and 3.2688 cm for G1, G2, G3, G4, and G5 samples at 15 MeV, respectively.Accordingly, it can be said that G5, due to its greatest WO 3 contribution in the structure, would reduce the intensity of incoming photons to the lowest maximum thickness among the glass samples studied.On the other hand, mean free path values is another parameter that the result should be as low as possible, which represent the average path of a moving radiation between collisions, that would modify its direction or energy, in addition prove the ability of attenuation in a material.Lower mfp values for an attenuator material may be regarded as a good indicator of absorption if two consecutive interactions are conducted at short ranges.As illustrated in Figure 6, G5 was reported to have the lowest mfp value along with increasing energy.This can be considered as another positive effect of WO 3 on gamma-ray attenuation properties of glasses [44].Another important parameter to discuss is the effective atomic number (Z eff ) values of shielding materials [16].It is well-known that the number of electrons in the atomic orbit is related to Z number in the nucleus.Therefore, it is likely that atoms with higher Z values would also have a higher number of electrons, and incoming photons may be more likely to collide with electrons.The higher the collision, the greater the percentage of absorption due to the released energy of incoming photons in every collision with electrons [16,22], High density tellurite glass shields  7 Z number, which has a clear advantage over G1. Figure 8 represents the effective conductivity (C eff ) variation in all glass samples, where a clear and rapid decrease occurs while increasing the photon energy, mainly in the region where the photoelectric effect is dominant.G5 was the sample with the greatest C eff values at all energies among those examined.This may be attributed to the growing number of electrons in the G5 sample because of the addition of elements with a high Z number.Since the conductivity level is the result of electron mobility between atoms, one may anticipate that the highest C eff values of the G5 sample also reflect an increase in the number of electrons in the structure of G5. Figure 9 clearly depicts the changes in the number of electrons, which are the primary reason for the C eff parameter findings.Figure 8 depicts the variation in the effective electron density (N eff ) values of the examined glass samples as a function of energy.The change in electron value owing to the Z increase indicated in the previous section was seen as an upward trend in the N eff value from G1 to G5, with the highest values found for 0,01 0,1 G5.Electrons play a well-known role in the interaction of gamma rays with matter.The quantity of interaction in the G5 glass is likely to be the largest of the five investigated glasses, since more electrons would produce more interaction probabilities; this is a significant result pertaining to the G5's superior absorption features.The buildup factor also serves as a good approximation, and its low values suggest that the absorption process of the material in the calculated mean free path values is outstanding [45].This suggests that the rate of photon interactions in the glass doped with 20 mol% WO 3 is high.As is well-known, a large number of contacts between the incident photon and attenuator material is a vital signal that the absorption process would progress at a quicker pace, quantitatively [46][47][48][49][50][51][52].Overall calculated absorption properties for energetic photons were found to be consistent, and 20 mol% WO 3 -doped glass (i.e., G5) was shown to be the optimum composition for absorbing energetic gamma rays among the investigated glass samples.

Conclusion
High-density glasses prepared using the conventional melt-quenching method have become the focus of many researchers in terms of their radiation shielding capacity.Based on the work in which amorphous glass structures were synthesized before, the ability to control glass densities relatively by changing the additive ratio is very valuable in terms of minimizing the destructive effects of radiation.The gamma ray attenuation parameters were investigated in this study for the TeO 2 -WO 3 -GdF 3 glass system.Glass materials have shown to be nontoxic and have a high level of endurance, making them an intriguing option for shielding investigation and development where many scientists and engineers have taken these advantages into considerations to utilize glass materials as optical and radiation shielding applications.Tellurite glass has attracted strong interest as a possible component for lasers, fibers, and nonlinear optical systems for its potential properties and high density.An investigation of the radiation shielding properties for the five glass samples were obtained with a broad spectrum of input photon energies in order to compare the nuclear attenuation shielding capabilities.Between the five sample G5 showed to have the highest density of 5.3355 (g/cm 3 ) while the rest of the glass samples varies from 5.0879 to 5.3246 (g/cm 3 ).MAC values at an energy of 0.8 MeV for G1, G2, G3, G4, and G5 samples were 0.066942, 0.067696, 0.067404, 0.068158, and 0.068911, making G5 the prominent sample.Moreover, throughout the investigation of HVL values, G5 was the prominent of having the least HVL value through the whole spectrum of photon energies.Furthermore, both the (Z eff ) and (C eff ) values in G5 sample were the highest of all samples.Making it more efficient at absorbing the incident photon energy as well as a potential option for gamma radiation shielding materials.In this study, it is an important result that WO 3 in the glass composition increases the effective atomic number of the glasses and significantly reduces the mean free path.Considering that the radiation shielding capabilities of the element changes, it was clearly seen from the results of this study that the WO 3 -doped glass structures exhibit superior properties On the other hand, thanks to new features such as optical band gap and glass densities added to glasses, it may be possible to gain new materials in various application areas.It is also an important factor that the glasses used as alternative radiation shielding materials are non-toxic compared to pure Pb or PbO-doped materials.

Figure 2 :
Figure 2: A typical setup for gamma-ray transmission measurements.

Table 1 :
[35]ity values and glass compositions of samples[35] Variation of EBF of G1 and G5 glasses at different mean free path values.
10 and 11 display the variation of computed exposure build-up factor (EBF) and energy absorption build-up factor (EABF) values for G1 and G5 glasses containing 0 and 20 mol% WO 3 at different mfp values from 0.5 to 40, respectively.The EBF and EABF values of the sample without the WO 3 additive are much greater compared to the sample with 20% WO 3 , as shown in Figures10 and 11.This is a consequence of the 20 mol% TeO 2 /WO 3 translocation and demonstrates improved absorption properties.
G5Figure11: Variation of EABF of G1 and G5 glasses at different mean free path values.High density tellurite glass shields  9