Assessment of the usability conditions of Sb₂O₃–PbO–B₂O₃ glasses for shielding purposes in some medical radioisotope and a wide gamma-ray energy spectrum

1 Introduction

Radiation shielding is not a matter of choice but rather a strictly regulated legal procedure. Selecting the most appropriate shielding barriers is also a very significant necessity, even though the functioning of this process is achievable with the enlightened knowledge of the employees and the society [1,2]. This is because ionizing radiation is being used more often in scientific and technological endeavors as well as in the treatment of disease in humans. The benefits of this radiation type are being employed in energy production, radiotherapy, medical diagnostics, nuclear power, and other industrial processes. Time, distance, and shielding are the three primary concepts in radiation protection. Increasing a shielding material’s capacity to soak up various forms of ionizing radiation [3] might improve its effectiveness. The most effective shielding materials have often been made of lead (Pb). Novel targeted radioisotopes have led to the widespread use of radioisotope therapy in nuclear medicine clinics, especially for the treatment of cancer. It is important for nuclear medicine facilities to have certain timing, distance, and shielding characteristics in place to reduce radiation exposure to both staff and patients [3,4]. These goals include increasing exposure to radioactive sources among workers, patients, and the public; keeping all radioisotope and radiopharmaceutical activity under tight supervision; and preventing the spread of contamination [5,6,7]. Because of these drawbacks, researchers have been working hard to manufacture next-generation shielding materials that could be an improvement over the current crop [8]. Glass is a valuable radiation barrier due to its ability to absorb gamma rays and neutrons, as well as its transparency and simplicity of compositional modification. Borate glasses are essential optical materials owing to their low melting temperatures, excellent transmittance, and good thermal stability [9]. Typically, they are used in the production of insulating and dielectric materials. Adding transition metal ions to their structure, however, results in semi-conductivity. Due to their existence in two or more valence states, which influences structural and optical properties [10,11,12,13,14,15,16,17], transition metals are widely employed in glasses at present. In addition to optical and structural properties of borate glasses, studies reported that their radiation shielding properties are quite satisfactory as proportional to their ratios when they are doped with transition metals [18,19,20]. Moreover, boron has neutron capture property and in addition to doping concrete with boron [21] and glasses also benefited from this property. Studies related to the binary glass that B₂O₃ forms when merged with PbO are mostly on the investigation of structural properties [22]. However, the unique property of PbO in respect to shielding gamma and X-rays, and furthermore, boron’s success in capturing neutrons revealed that the glass structure that these two elements form together might have an important place in radiation shielding. However, since the density of the final composition would be relatively lower compared to PbO, there are studies in the literature on the enrichment of glass by doping with different elements and especially improvement of the density is encountered [23,24]. Glasses containing heavy metal oxides such as Sb₂O₃ are frequently being investigated due to their unique transmittance properties in the infrared region in the field of optics [25]. Studies on the impact of glasses containing heavy metal oxides on radiation shielding are increasing with each passing day [26,27]. Studies on the impact of the presence of both PbO and Sb₂O₃ oxide compounds within the same glass structure on radiation shielding properties set forth interesting results [28,29]. In this work, we provide the results of a complete examination of the optically defined xSb₂O₃·(40 − x)PbO·60B₂O₃·0.5CuO (where, 0 ≤ x ≤ 40 mol%) glass systems. This study’s results provide insight into how the addition of Sb₂O₃ to the glass compositions under study led to a proportionate increase in absorption, which might be valuable in assessing the materials created in the cited article on a larger scale.

2 Materials and methods

2.2 Shielding parameters and gamma transmission factors (TFs)

The ability of radiation-shielding materials to absorb a part of the initial radiation quantity that impacts an attenuator is a further essential characteristic. This criterion may be expressed in terms of a value determined by primary and secondary radiation quantities. The term TF [1,31,32] is a crucial parameter that enables researchers to measure the attenuation of incident gamma rays as a function of secondary gamma-ray intensity. This research analyzed the TF values of glass samples tested for a variety of radioisotopes used for nuclear-type disease therapy and diagnostics. The radioisotopes indicated ⁶⁷Ga (0.0086, 0.0093, 0.1840 MeV), ⁵⁷Co (0.0144, 0.1221, 0.1365 MeV), ¹¹¹In (0.0230, 0.1710, 0.2450 MeV), ¹³³Ba (0.0532, 0.0796, 0.0810, 0.2764, 0.3029, 0.3560, 0.3838 MeV), ²⁰¹Tl (0.0710, 0.1350, 0.1670 MeV), ^99mTc (0.1405 MeV), ⁵¹Cr (0.3201), ¹³¹I (0.2843, 0.3645, 0.6370, 0.7229 MeV), ⁵⁸Co (0.5110, 0.8108 MeV), ¹³⁷Cs (0.6617 MeV), and ⁶⁰Co (1.1732, 1.3325 MeV) specific energies [8]. This portion of the investigation simulates a large transmission assembly using the MCNPX method [33]. The MCNPX method’s resulting configuration is seen in three dimensions in Figure 1. The graphic illustrates that the quantity of gamma rays that are absorbed by the glass material between the two detection zones is the most important aspect that is considered when calculating the TF values. The modeling approach was predicated on the production of the MCNPX input file, and it was considered complete when the tally values were exported from the output file and the TF values were specified.

Figure 1

(a) 2-D view of designed MCNPX simulation setup. (b) 3-D illustration of designed MCNPX setup (2-D and 3-D views are obtained from MCNPX Visual Editor VisedX22S).

3 Results and discussion

By computing the radiation absorption characteristics of glass materials in accordance with specified parameters, the direct contribution of structural changes to their absorption qualities may be analyzed [34–41]. The radiation attenuation properties of five different glass samples doped with varied amounts of Sb₂O₃ were investigated. The Sb₂O₃ additive ratio was raised to its highest level in the S5 sample after being raised gradually in numerous glass compositions from S1 to S5. The density of the glass samples that were examined varies as shown in Figure 2 depending on the proportion of Sb₂O₃ that is present in the overall glass composition. There was a 0.75 g/cm³ difference in glass density between the lowest and highest Sb₂O₃ reinforcements due to the increased weight caused by the increased composition of the components. A feature of materials that shields against gamma rays is the linear attenuation coefficient (µ), which increases with increasing material density [42,43]. For any gamma-ray energy, the linear attenuation coefficient of a material may be determined, making it a crucial metric for determining many others. Figure 3 displays the variation in linear attenuation coefficients as a function of gamma rays, as measured for five different glass samples. The highest linear attenuation coefficient values may be seen in the low-energy part of the presented diagram. The fact that the k-absorption edge reached its peak and then gradually started to fade following this significant decrease in the low-energy region is evidence that Compton scattering was the predominate interaction in the mid-energy region and that the fall was followed by a lower increase. The values of the linear attenuation coefficients have been strongly impacted by the elemental compositions of the five different glass samples that were evaluated. The linear attenuation coefficients for all investigated energies were found to be highest in S5 samples with the highest Sb₂O₃ addition rate. This demonstrates that the linear attenuation coefficient of multi-glass samples improves when density rises due to Sb₂O₃ addition rate. Figure 4 depicts the variation pattern of the mass attenuation coefficient (µ _m). Overall, it was found that the linear and mass attenuation coefficients have a similar pattern. Since µ _m is a density-independent characteristic, it can be said that as the quantity of Sb₂O₃ steadily rose from S1 to S5, a clear pattern of rising m values was also seen. The linear attenuation coefficient may be used to calculate the half-value layer (HVL), a critically important feature of gamma-ray shielding [44,45]. Figure 5 shows that the HVL is a tangible depiction of the thickness at which the energy of a photon impinging on a material is decreased by half. This indicates that the gamma-ray attenuation capabilities of materials with a small half-value thickness are preferable. In other words, a material’s ability to shield against a certain photon energy is improved by decreasing its HVL value. HVL values between 0.015 and 15 MeV are shown in Figure 5 for each of the seven glass samples that were analyzed. The graph shows that, although HVL values are rather small for low photon energies, they have begun to grow proportionally when photon energy is raised. Consequently, the HVL values for the S5 sample were the lowest of all the samples. For all glasses studied, the tenth value layer’s (TVL) variability as a function of photon energy in MeV is shown in Figure 6. In all cases, the TVL parameter follows the same pattern as the HVL. Changes in the mean free path as a function of the incoming photon energy for glasses S1 through S5 are shown in Figure 7. This graph demonstrates that the concentration of Sb₂O₃ has a negative influence on the evolution of mean free path, which is an obvious indication of enhanced gamma-ray shielding characteristics. This is because of the decrease in the value of the mean free path implies that the distance between two successive gamma-ray contacts in the material reduces, indicating that the absorption process will be more efficient at shorter distances. Therefore, for a photon energy of 15 MeV, the values are lowest for the S5 glass sample and maximum for the S1 glass sample. Figures 8 and 9 demonstrate the gamma-ray energy (MeV)-dependent changes in the exposure build-up factor (EBF) and the energy absorption build-up factor (EABF) throughout a range of mean free path values, respectively. Both the EBF and EABF values are small in the low gamma-ray energy band because photoelectric absorption is responsible for the vast majority of entering gamma rays. Our results show that both EBF and EABF values decreased when Sb₂O₃ dosage was increased (i.e., from 0.5 to 40 mfp). The rate at which incident gamma rays collide with glass samples increases dramatically as the amount of Sb₂O₃ increases from S1 to S5. The gamma-ray TF values, which is a critical metric for shielding materials, was computed for S1, S2, S3, S4, and S5 glass samples for some well-known isotopes and their characteristic energies as ⁶⁷Ga (0.0086, 0.0093, 0.1840 MeV), ⁵⁷Co (0.0144, 0.1221, 0.1365 MeV), ¹¹¹In (0.0230, 0.1710, 0.2450 MeV), ¹³³Ba (0.0532, 0.0796, 0.0810, 0.2764, 0.3029, 0.3560, 0.3838 MeV), ²⁰¹Tl (0.0710, 0.1350, 0.1670 MeV), ^99mTc (0.1405 MeV), ⁵¹Cr (0.3201), ¹³¹I (0.2843, 0.3645, 0.6370, 0.7229 MeV), ⁵⁸Co (0.5110, 0.8108 MeV), ¹³⁷Cs (0.6617 MeV), ⁶⁰Co (1.1732, 1.3325 MeV). The TF values of the glasses were calculated using two different methods. Initially, glass thicknesses were used to analyze the TF factors of samples S1 through S5. In addition, Figure 10 displays the radiation shielding parameters ACS and ECS. Figure 10 shows how the ECS varies as a function of the photon energy entering the system, whereas Figure 11 shows how the ACS varies. Figures 10 and 11 show that the ACS and ECS values decrease with increasing photon energy. In every glass tested, the ACS values are larger than the ECS values. This is because the likelihood of total atomic interaction in any material is greater than the probability of complete electrical contact with incoming photons. Figure 12 displays the transmission functions of the studied glasses as a function of radioisotope energy and glass thickness (MeV). As the radioisotope’s energy rises, the TF shifts from 0.0086 to 1.3325 MeV. For all measured thicknesses, glass samples showed the lowest TF values when tested at low energies. Thicker samples may have an easier time attenuating low-energy gamma rays due to their high attenuation capacity. As a result, there is a significant difference of about 0.1 MeV. Glass samples become more reactive at gamma-ray energies greater than 0.1 MeV. Maximum attenuation was calculated for all glass samples at a thickness of 3 cm (i.e., minimum transmission). Increases in shield thickness have a negative effect on gamma-ray attenuation because shield thickness affects the effectiveness of any shielding material. The TF values of the glasses were then carefully assessed by considering the attenuation capabilities of various glass thicknesses (0.5, 1.5, 2.5, and 3 cm). Figure 13 displays the relationship between the transmitted energy (in MeV) and the glass thickness used for the experiment. The graph demonstrates the decline in TF values when gamma-ray energies are increased. The TF values of the glass samples examined were lowest for the thickness of 3 cm.

Figure 2

Variation of glass densities.

Figure 3

Variations of linear attenuation coefficient (1/cm) with photon energy (MeV) for all S1–S5 glasses.

Figure 4

Variations of mass attenuation coefficients (cm²/g) with photon energy (MeV) for all S1–S5 glasses.

Figure 5

Variations of HVL (cm) with photon energy (MeV) for all S1–S5 glasses.

Figure 6

Variations of TVL (cm) with photon energy (MeV) for all S1–S5 glasses.

Figure 7

Variations of mean free path (cm) with photon energy (MeV) for all S1–S5 glasses.

Figure 8

Variation of EBF of investigated glasses at different mean free path values.

Figure 9

Variation of EABF of investigated glasses at different mean free path values.

Figure 10

Variations of atomic cross-section with photon energy (MeV) for all S1–S5 glasses.

Figure 11

Variations of electronic cross-section with photon energy (MeV) for all S1–S5 glasses.

Figure 12

TFs of investigated glasses as a function of used radioisotope energy (MeV) at different glass thicknesses.

Figure 13

Comparison of the TFs as a function of used radioisotope energy (MeV) for different glass thicknesses.

4 Conclusion

B₂O₃, which has the tendency to form glasses as combined with various compounds, is effectively being used in the making of new structures. Glass structures that B₂O₃ forms by uniting with heavy metal oxides make ground with their extraordinary properties in linear and nonlinear optics. In addition, combination of B₂O₃ with heavy metal PbO yields promising materials in radiation shielding. When Sb₂O₃ is used in industrial glasses at low ratios, it has the property to remove bubbles within the glass and decolorize special glasses. When they are found in the structure at high ratios, they have the property to rearrange the glass network; thus, it changes the physical, optical, and structural properties of the glass to a high extent. The impact of gradual substitution of PbO with another heavy metal Sb₂O₃ in the glass network having Sb₂O₃–PbO–B₂O₃–CuO composition is found in the literature studies in which the examination of structural properties is prioritized. The effect of PbO/Sb₂O₃ change in the specified structure on radiation shielding properties was examined in this study in detail. Examining all radiation shielding parameters, we conclude that

1. The linear (µ) and mass attenuation (µ _m) coefficients trends as: S5 _µ,µm > S4 _µ,µm > S3 _µ,µm > S2 _µ,µm > S1 _µ,µm.

2. HVL, TVL, and MFP trends as: S1_HVL,TVLMFP > S2_HVL,TVL,MFP > S3_HVL,TVL,MFP > S4_HVL,TVL,MFP > S5_HVL,TVL,MFP.

3. Increasing the amount of Sb₂O₃ supplementation decreased the EBF and EABF levels in general (i.e., from 0.5 to 40 mfp). When the amount of Sb₂O₃ rises from S1 to S5, the collision rate of coming gamma rays in glass samples considerably increases.

4. The ACS and ECS values decrease when photon energy rises.

5. The ACS parameter values for all glasses are greater than the ECS parameter values. This is because the chance of full electronic contact with incoming photons is lower than the probability of complete atomic interaction in any substance.

6. According to the TF statistics, S5 exhibited the least transmission characteristic of all the investigated glass thicknesses.

Lastly, as a part of the scientific community’s ongoing work on the current promising glass system, we would like to provide some ideas for future study that may be performed. After taking several factors into account, we were able to present detailed results in our investigation. A few significant material properties relate to glass materials; thus, although the proposed glassy system shows potential, it will require ongoing optimization and development. Based on the data obtained, a broad overview of the Sb₂O₃-containing glass samples was presented. However, due to the important material qualities connected with glass components, continued work is required in terms of overall optimization and development of the suggested glass system.