Three borate glass systems with chemical formula 65 B2O3 + 30 Na2O + 5 (x) wt%; x = Al2O3, MgO, and Li2O were fabricated by the common melting-annealing method and coded as BNAl, BNMg, and BNLi, respectively. XRD pattern revealed the non-crystalline form and the glassy states of the prepared samples. UV-optical absorption spectra showed UV cutoff peaks in the range 320–340 nm and optical energy gap (Eopt) by Tauc’s model (ETauc’s) and ASF method (EASF) revealed quite similar values ranged from 2.60 to 3 eV before irradiation and 2.23 to 2.60 eV after 20 kGy of gamma irradiation. Raman spectra show three detectable regions at; (i) 250–600 cm−1, (ii) 500–1000 cm−1 and (iii) 1000–2000 cm−1 correlated to different borate forms. Many radiation shielding parameters were theoretically calculated using Phy-X/PSD and simulated via Monte Carlo code (MCNP-5) in photon energy range (0.015–15 MeV). Mass attenuation coefficient (MAC), linear gamma attenuation coefficient (LAC), effective atomic number (Zeff), fast neutron macroscopic cross section (∑R), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) at various penetration depths PD, as well as half (HVL) and tenth value layers (TVL) and mean free path (MFP) were also estimated. The shielding parameters showed the order of (MAC, LAC)BNAl > (MAC,LAC)BNMg > (MAC, LAC)BNLi. The stability of the glasses optical, and structural properties against gamma irradiation indicate the capable use of the glasses for radiation shielding applications specially Al2O3 glass with the heaviest atomic weight and the highest capacity for radiation shielding protection.
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1 Introduction
Natural and artificial radiations are the main two types of ionizing radiation. The natural sources of radiation include radioactivity from radioactive isotopes, while the artificial sources include radiation technologies used for several applications, such as radioisotope nuclear reactors, particle accelerators and radiotherapy, nuclear medicine, food processing, environmental monitoring and protection (El-Sharkawy et al. 2020; Abou Hussein et al. 2021a, 2022; Abou Hussein and Barakat 2022).
Many dangers are caused by ionizing radiation with matter; biologically on human and living organisms and industrially in the failure of many electronic processes e.g., in aerospace and radiation medical devices (Abou Hussein and Abdel-Galil 2023). For obstructing the pathway of radiation to the safe border that does not unevenly affect matters (Abou Hussein and Abdel-Galil 2023; Marzouk and Abou Hussein 2019), radiation shielding materials are highly required in order to avoid dangers caused by ionizing radiation. Borate glasses can be used for this purpose, as they have many outstanding and distinguishing features make them suitable for many applications. In addition to, the ease of preparation, shaping, and low cost-productivity (Abou Hussein and Abdel-Galil 2023; Abou Hussein 2023), borate glasses are very appropriate host for different alkali, rare earth (RE) and transition metal (TM) ions. Therefore, they can be used in many other applications including memory and optical switching, biomedical applications, electrical threshold, scintillation detectors, optoelectronic devices, and recently in radiation shielding and dosimeter applications (Abou Hussein 2023; Gaafar et al. 2009; Batal et al. 2020; Kurtulus et al. 2021a, b, 2023; Kavas et al. 2021).
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Unlike silicate and phosphate glasses, which only form tetrahedral units with oxygen, borate glasses form a variability of structural networks with modifier ions (Abou Hussein and Barakat 2022; Halimah et al. 2019). Usually, the structure of borate glass network involves three and four coordinations, and it can change its coordination number with oxygens between three and four, resulting mainly in the trigonal BO3 and the tetrahedral BO4 structure (Abou Hussein and Barakat 2022; Abou Hussein and Abdel-Galil 2023; Marzouk and Abou Hussein 2019; Abou Hussein 2023). Consequently, other structural borate units can be obtained in the glassy network depending on the percentages of bridging (BO) and non-bridging oxygen (NBO) e.g., diborate, tetraborate, pentaborate and boroxol ring…etc. Accordingly, borate glasses containing alkali or transition metal ions have wide industrial, scientific, and medical applications (Abou Hussein et al. 2021a; Batal et al. 2020; Abou Hussein 2019a; Abdel Maksoud et al. 2021; Barakat et al. 2024; Abou Hussein and Marzouk 2023).
On the other side in silicate glass structure Si atom is the crucial atom surrounded by four non-bridging oxygen atoms to create tetrahedral structural units of ortho-silicates SiO4, and hosting metal oxides like alkali ions can cause disruptions in silicate network e.g., a depolymerization of Si–O–Si network and formation of meta, pyro or ortho-silicates (Abou Hussein 2019b; Abou Hussein et al. 2021b). Moreover, phosphate glasses obtain highly corrosive nature or limited chemical durability that would restrict their applications (Abou Hussein et al. 2021c).
Since introducing of each metal oxide in the glassy network acquires the glass a specific property or at least modifies it, then the reason of selecting a new and simple glass compositions of alkali borate glasses with three different valence states of alkali ions can be elucidated. For example, to avoid the known low chemical resistance of borate glasses some modifiers or intermediate oxides can be introduced e.g. Na2O, Li2O, MgO and Al2O3. Na2O can give stable ionic glasses and Al2O3 solidifies the glassy network and enhances its reluctance to compression. Additionally Na2O that present mainly in the three investigated glasses works as a flux and reduces the melting temperature required for preparing glasses. The incorporation of any amount of Al2O3 in the glassy network inclines to decline the region of crystallization considerably on cooling (Abou Hussein and Barakat 2022; Batal et al. 2020). Li2O and MgO enhance also the optical and thermal properties of the glasses and help in retarding the glass devitrification and facilitating the solubility of the glassy matrix (Abou Hussein et al. 2021c). Many studies have revealed a link between host glass structure and doped ions features, thus enabling the design of glasses for radiation shielding applications from silicate, tellurite, or phosphate glasses and displayed different measuring techniques can provide this application (El-Agawany et al. 2020; Abouhaswa et al. 2020, 2019; Taha and Rammah 2016; Rammah et al. 2019; Tekin 2022). For instance optical UV–visible spectroscopy is a supportive technique used to recognize the optical properties and structural environment of the glasses, as well as calculating important optical parameters such as optical energy band gap (Eopt) and Urbach energy (EU), whenever, the structural environment and dynamics of glasses can be estimated by Raman spectroscopy and/or FTIR technique. Moreover, the theoretical Phy-X/PSD and simulated Monte Carlo programs are common methods used to evaluate the radiation protection efficiency of the glass to be used in radiation shielding applications.
The present work focuses on the preparation and characterization of three alkali borate glasses to make a comparison study regarding the effect of different valence metal oxides; Al2O3, MgO and Li2O on some of the glass optical, structural and radiation shielding properties. Optical UV–visible and Raman spectroscopy were used to study optical and structural characteristics of the glasses before and after 20 kGy of gamma radiation. Furthermore, many glass shielding parameters by Phy-X/PSD and Monte Carlo code MCNP-5 were investigated e.g., MAC, LAC, Zeq, EBF, EABF, ∑R, HVL, TVL and MFP, Therefore, the most stable and efficient glass can be detected for the required radiation shielding application.
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2 Experimental works
2.1 Preparation process
Borate glasses with three different alkali metal oxides were prepared by the traditional melting- annealing technique. Analytical pure reagents from H3BO3, Na2CO3, Al2O3, MgCO3 and Li2CO3 from Sigma Aldrich Company, were used in the preparation of three glassy systems with the composition of 65% B2O3 + 30%Na2O + 5% Al2O3 /MgO /Li2O (wt.%). The three glass batches were perfectly weighed using a sensitive balance (four digits, accuracy ± 0.0001), mixed carefully and grinded using a gate mortar. Formerly, they were melted in porcelain crucibles in a muffle furnace regulated at 950 °C for 90 min. During melting, the crucibles were revolved at time breaks for achieving homogeneity and removing air bubbles from the prepared glasses. The melted glasses were then cast on stainless steel molds with dimensions of 3 × 1 × 0.3 cm and relocated quickly to an annealing furnace at a temperature range 300–350 °C. After 1 h, the annealing muffle furnace was turned off, keeping the glass samples inside overnight till it reaches room temperature in a cooling rate ± 25 °C /h. The prepared glass samples were then cut and polished, or crumpled to fine powders according to the requisite measuring technique. The three glass samples are coded as BNAl, BNMg, and BNLi according to the present alkali metal ion; Al3+, Mg2+ and Li+, respectively.
XRD measurement was performed using a X-ray diffraction (XRD; Shimadzu XRD-6000, Japan) in the range of 2θ = 5° to 90°. Optical UV–visible absorption spectra were detected in the UV–visible range 200–900 nm using UV–visible spectroscopy (Type JASCO Corp.v-570, Rel-100 Japan) with recording double-beam spectrophotometer; the samples were dignified twice to check the correctness of absorption peaks. Raman spectroscopy was studied by Confocal Raman Microscope (Wltec, 300R-Germany). The used gamma ray source in this study was 60Co gamma cell (2000 Ci, dose rate of 0.717 kGy/h at 25 ± 5 °C). The glass samples were positioned in the gamma cell in a mode where all glass samples were exposed identically to the requisite dose.
2.2 Radiation shielding parameters
Monte Carlo simulation (MCNP-5) code (Computer Code Collection and MCNPX User’s Manual Version 2002) and Phy-X/PSD software (Şakar et al. 2020) are applied in the present work to determine the fundamental gamma-ray shielding parameters. The mass-attenuation coefficients (MAC) of the investigated glasses are estimated using Phy-X/PSD software according to the mixture rule (Şakar et al. 2020):
where Ai and fi are the atomic mass and molar fraction of ith constituent pure element in the glass.
3 Results and discussion
Figure 1 demonstrates a photographic picture of the prepared glasses and their XRD patterns that revealed broad hump peaks with no crystalline peaks, signifying the amorphous natures of the samples and their glassy states.
Fig. 1
A photographic picture and XRD patterns of the prepared alkali borate glasses
×
3.1 Optical characterizations
3.1.1 Absorption spectra and optical band gap (Egap)
UV–visible spectroscopy is a supportive technique used to recognize the structural and chemical environment of glasses and recognize changes occurred in the glassy network due to doping of specific elements and/or irradiation as well as calculate many important optical parameters in such amorphous systems e.g., optical energy band gap (Eopt). TM ions (even at very low concentrations) induce an electronic transfer mechanism that involves electron transition from coordinated oxygen atom orbitals to metal orbitals. This phenomenon produces obvious UV bands as a result of this electronic transfer mechanism (Abou Hussein and El-Alaily 2018).
Figure 2a and b depict the absorbance spectra of the fabricated glasses (BNAl, BNMg, and BNLi) before and after 20 kGy of gamma irradiation, respectively. As shown, there are only obvious cutoff UV peaks in the three investigated glasses appeared in the wavelength range 320–340 nm. As know, appearance of peaks in the UV region 200–350 nm associated with amorphous glass structure and Fe3+ ion absorbance convoyed to chemicals used in preparing glasses. Duffy (1997) has attributed the strong UV absorption in glasses to the presence of some transition metal ions (e.g. Fe3+ and Cr6+) because of the possible charge electron transfer mechanism, even the traces of impurities are in ppm level, they could impart a strong absorption. Many glass scientists (Moncke and Ehrt 2004; Moncke 2015) concluded also that presence of traces from iron ions as impurities lessens transmittance of the optical glasses and they suggested the necessity of highly pure chemicals for preparing superior optical glasses.
Fig. 2
Absorbance spectra of the studied glasses a before and b after 20 kGy of gamma irradiation
×
According to the glass compositions investigated in Table 1 as there are no transition metal ions included in the compositions, the obvious UV- peaks appeared before 400 nm in Fig. 2a, can be attributed to the absorption of Fe3+ ions traces as chemical impurities, since types of the modifier ions e.g., Na+, Al3+, Mg2+ or Li+ ions do not alter the coordination equilibrium of borate structure (Wen and Tanner 2015; Lakshminarayana and Buddhudu 2006).
Table 1
Chemical composition and Wt. fraction of elements in samples in the system 65 B2O3 + 30 Na2O + 5 (x) wt%; x = Al2O3, MgO, and Li2O
Sample code
Sample chemical composition
X
Wt. fraction of elements in each sample
Density
B
O
Na
Mg
Li
Al
g.cm−3
BNAl
65 B2O3 + 30 Na2O + 5 (x) wt%
Al2O3
0.201871
0.549109
0.222557
0.000000
0.000000
0.026463
2.3871
BNMg
65 B2O3 + 30 Na2O + 5 (x) wt%
MgO
0.201871
0.545420
0.222557
0.030152
0.000000
0.000000
2.3860
BNLi
65 B2O3 + 30 Na2O + 5 (x) wt%
Li2O
0.201871
0.552343
0.222557
0.000000
0.023228
0.000000
2.380
In the present work, the optical band gap (ETauc’s) was estimated via Tauc’s model (Tauc 1974) and the absorption spectrum fitting method (ASF, EASF) (Alarcon et al. 2007; Souri and Tahan 2015). The model well-known by Tauc's (Tauc 1974) can be written as:
where hυ is the energy of the incident photons and (ETauc’s) is the optical band gap value. The power n = 0.5 for indirect transition and n = 2 for the direct transition (Mott and Davies 1979), and G is a constant depends on the transition probability. Figure 3a and b shows the variation of (αhν)2 with (hν) of the investigated glasses before and after gamma irradiation. The optical band gaps were deduced by extrapolating the linear region of curves at (αhν)2 = zero. The obtained values of (ETauc’s) of the investigated glasses are shown in Fig. 3.
Fig. 3
Variation of (αhν)2 with (hν) of the studied glasses a before and b after 20 kGy of gamma irradiation
×
In ASF method, optical band gap can be evaluated from \(\lambda_{cut - off}\) via the next relationship (Alarcon et al. 2007; Souri and Tahan 2015):
\(\lambda_{cut - off}\) values can be evaluated for each glass sample by extrapolating (A/λ)2 linear region versus (λ−1) curve at (A/ λ)2 = zero. Figure 4a and b illustrate the variation of (A/λ)2 with (λ−1) for direct transitions before and after gamma irradiation, respectively. The evaluated values of EASF are shown in Fig. 4.
Fig. 4
Variation of (A/λ)2 with (1/λ) of the studied glasses a before and b after 20 kGy of irradiation
×
3.1.2 Effect of gamma irradiation on the optical spectra
As obviously shown, the optical spectra of the studied glasses after gamma irradiation reveals almost the same as those before irradiation, where the UV-cutoff peaks appear approximately at the same positions, and the absorbance intensity depicts very similar values before and after irradiation as shown in Fig. 2 a and b. The aforementioned optical data designate the absence of extra or major defects produced within the glassy networks by exposing glasses to 20 kGy of gamma radiation. Only insignificant variations in absorbance intensity or slight sharpness of the UV peaks can be observed, correlated to the present trace iron impurities in glasses Fe2+ and/or Fe3+ during irradiation process. Some of the lower valence state of Fe2+ ions can react with the generated positive holes, forming additional Fe3+ or (Fe2+)+ through a photochemical reaction (photo-oxidation process). This assumption can elucidate the sharpness increase of UV peaks in their characteristic sites (Bishay 1970).
It is clearly from Fig. 2a and b that the wavelength cut-off (λcut-off) and absorbance rate values rise after irradiation. Therefore, the optical band gap will be decreased after irradiation process as seen from Figs. 3 and 4, where the irradiation process has a positive effect for decreasing slightly the values of Eopt for the three investigated glasses.
The observed decrease in Eopt after irradiation can be correlated to the growth of the disorder degree in glassy networks because ionizing radiation reasons some deficiencies in the glass structure by creating some atomic dislocations or breaking bonds. Therefore, more localized states can be obtained, enhancing more electronic transitions from HOMO (highest occupied molecular orbitals) to LUMO (the lowest unoccupied molecular orbitals), Consequently, a decrease in Eopt values can be observed (Chimalawong et al. 2010; Baccaro et al. 2008; Abu et al. 2003). Mott and Davis (1979) supposed that the conversion of linked bridging oxygens BO in the glassy network to non-bridging oxygens NBO causes a drop in Eopt values due to the growth of localized states in the band structure.
3.2 Raman spectroscopic measurements
Raman spectroscopy is a useful procedure utilized to investigate the structure of the glass melt. It can determine the large structures that involve several atoms and follow changes in the network structure (Padmaja and Kistaiah 2009). Structure, environment and dynamics of glassy materials can be evaluated by Raman spectroscopy. Raman spectra of the investigated alkali borate glasses enclosing Al3+, Mg2+ or Li+ ions are shown in Fig. 5. As shown there are three detectable regions in Raman spectra: (i) 250–600 cm−1, (ii) 500–1000 cm−1 and (iii) 1000–2000 cm−1. The small kinks at 495 cm−1 and sharp bands at ~ 570–578 cm−1 are observed in the three investigated glasses related to the isolated diborate groups and the plane-bending mode of BO3 units (Edukondalu et al. 2014), or Na–O, Li–O, Mg-O or Al-O bond vibrations (Padmaja and Kistaiah 2009). A strong sharp band detected in the three alkali glasses at ~ 765 cm−1 is distinctive to a six-membered ring with one or two BO4 tetrahedral units. This band is assigned to the formation of six membered rings with one BO4 tetrahedron that might be in triborate, tetraborate or pentaborate forms. While, six-membered rings with two BO4 tetrahedra that may be diborate, di-triborate or di-pentaborate are shifted to this lower frequency. According to the results shown in Fig. 5, the band at 765 cm−1 refers to the six membered rings with one BO4 tetrahedron; triborate, tetraborate or pentaborate forms (Edukondalu et al. 2014).
Fig. 5
Room temperature Raman spectra of the studied alkali borate glasses before irradiation
×
The peak at 808 cm−1, which is allocated to the boroxol ring with the triangle BO3 structure, cannot be observed obviously in Raman spectra as shown in Fig. 5. This behavior indicates that about 35% of alkali content in the glassy network consisting of 30 Na2O and 5 Al2O3/MgO/ Li2O (wt%) is controlled by the four-coordinated boron. While, the small observed bands around 960 and 1140 cm−1 can be correlated to the different diborate groups in the glass structure. These peaks appear in a relative high frequency regions because of BO2O− triangles connected to BO4 units and BO2O− triangles connected to other triangular units (Ryichi and Norimasa 2001; Chryssikos et al. 1990).
Additionally, obvious peaks are observed at around 1300 cm−1, especially for BNLi glass that shows very strong high frequency peak around 1308 cm−1. Kamitsos et al. (1987) have attributed the high frequency Raman bands to the B–O− bonds linked to large borate groups’ i.e., metaborate triangles connected to the tetrahedral BO4− groups display their B–O− stretching activity at lower frequencies by means of π-electronic interactions. Therefore, the spectral outline of the B–O− stretches works as an indirect probe for the BO4− units in the glassy network. As familiar in most cases pentaborate glass network consisted borate arrangements containing the tetrahedral BO4− and the triangular metaborate units, where there is an isomerization between the three- and four-coordinated units.
Finally, Fig. 5 shows a Raman band around 1490 cm−1 specially for BNLi glass that may be attributed to BO2O− triangles connected to other borate triangular units or the extending of B-O− bonds involved to a large number of borate groups (Kamitsos et al. 1987).
Figure 6 shows the influence of gamma irradiation on Raman spectra of Al3+, Mg2+ and Li+ alkali borate glasses. The spectra show different behaviors of the three alkali glasses because of irradiation with 20 kGy of gamma rays. The performance of these glasses can be correlated with the "mixed alkali effect" (MAE) observed in many glass systems including borosilicates, phosphates, and borates. Despite the fact that MAE in glass depends on many structural and electrodynamic theories, there does not appear to be a single model that provides an adequate explanation.
Fig. 6
Room temperature Raman spectra of the studied alkali borate glasses after gamma irradiation with 20 kGy
×
BNAl glass shows some disappearance of Raman peaks after gamma irradiation where, Al2O3 cannot affect the peaks resulted from the isolated diborate groups and metaborate group ring type polymerized to BO3 and BO4 units.
Irradiated BNMg glass is described by the presence of precise strong sharp peak around 808 cm−1 related to the coexistence of boroxol rings and over-modified borate units with a noticeable appearance of pyroborate dimers, B2ØO44. Coexisting of boroxol rings and pyroborate units in the irradiated glass structures below the metaborate stoichiometry can be investigated according to the disproportionation reaction shown in Fig. 7. The activity of this reaction related to the highly field strength of Mg2+ ions that need high anionic charge density positions for their coordinations; the charged oxygen atoms of pyroborate type unit, i.e. Ø–B–O22− can work as suitable ligands for coordinating Mg2+ (Kamitsos 2003).
Fig. 7
Coexisting of boroxol rings and pyroborate units
×
BNLi glass shows the division of the strong peak around 1308 cm−1 into two obvious peaks after irradiation because of ionizing radiation impact on the glassy structure by creating more non-bridging oxygens (NBO) and the transformation of metaborate triangles into BO4− tetrahedral units. Raman spectra of Li-B2O3 glass contain one part at 1308 cm−1 related to the stretching of B-O bonds of BO4 in the diborate polycrystals and by irradiation the strength of BO3 tetrahedron decreases and finally destroys.
The noticeable variations in intensities and positions of some Raman bands with the type of the introduced alkali ion in the studied borate glasses can refer directly to the nonlinear variations due to the mixed alkali effect (MAE), where the isomerization between the three and four-coordinated boron structure depends essentially on the behavior of Al3+, Mg2+ or Li+ ions and their coordination bonds in the glass network. While BNAl and BNMg glasses appear with more stable structure than BNLi after irradiation with 20 kGy of gamma rays.
3.3 Interpretation of shielding parameters
The shielding capability of the three studied glasses BNAl, BNMg, and BNLi was investigated depending on their chemical composition and the fraction weight of elements in the sample with the composition presented in Table 1. Mass attenuation coefficient (MAC) was investigated through Phy-X/PSD and MCNP-5 Monte Carlo code. The gained results of the two methods are gathered in Table 2 and the relative deviation ∆ (%) among the two methods was considered and found very close to each other (not exceeds 0.5%), assuring the good agreement between the two methods. The data are calculated in a wide-ranging photon energy from 0.015 up to 15 MeV. Figure 8 reveals a slight change in MAC values due to the difference in the chemical composition of the considered glasses, owing to the different induced alkali ions. As obvious, the three glasses have the same ratios of B2O3 and Na2O with a change only in X (Wt. %), where X = Al2O3 for BNAl, MgO for BNMg, and Li2O for BNLi. This change in X causes a variation in the molecular weight of glasses, resulting the obvious change in MAC values. As found BNAl has the highest values of MAC because of having 0.026463 Al ratios, however BNLi has the least values because of having 0.023228 Li ratio. This performance depends on the atomic weight of the introduced alkali oxide where Al3+ ions have the highest atomic weight among the other two alkali oxides glasses but Li ions have the lowest. In addition, MAC values dramatically decreased with a growth in photon energy up to 0.1 MeV, where the photoelectric PE interaction probabilities increase in this region and vary with Z4/E3.5 giving the highest values of MAC at the lowest photon energy region. In the intermediate region of photon energy, Compton scattering (CS) is dominant and a slight change in MAC was found. After that Pair Production represents the effectual interface at the high energy zone causing the noticeable trend of MAC. Regarding to Tables 1 and 2, the increase in atomic weight or the elemental composition of the consistent elements leads to a positive effect on MAC of the fabricated glasses and consequently (MAC)BNAl > (MAC)BNMg > (MAC)BNLi.
Table 2
Mass a ttenuation coefficient of the prepared alkaline glasses via MCNP-5 and
Energy (MeV)
Mass attenuation coefficient (cm2/g)
BNAl
BNMg
BNLi
MCNP-5
Phy-X
∆ (%)
MCNP-5
Phy-X
∆ (%)
MCNP-5
Phy-X
∆ (%)
0.015
2.3609
2.3610
-0.0042
2.3353
2.3350
0.0117
2.1612
2.1610
0.0114
0.03
0.4394
0.4392
0.0515
0.4362
0.4360
0.0525
0.4146
0.4144
0.0413
0.05
0.2230
0.2228
0.0821
0.2224
0.2222
0.0790
0.2174
0.2173
0.0354
0.08
0.1672
0.1672
-0.0123
0.1671
0.1671
0.0019
0.1655
0.1656
-0.0455
0.1
0.1530
0.1531
-0.0607
0.1530
0.1531
-0.0584
0.1520
0.1520
-0.0086
0.15
0.1330
0.1332
-0.1293
0.1331
0.1332
-0.0927
0.1325
0.1327
-0.1453
0.3
0.1042
0.1043
-0.0927
0.1043
0.1044
-0.1326
0.1039
0.1040
-0.0649
0.5
0.0850
0.0851
-0.1048
0.0850
0.0851
-0.1074
0.0848
0.0849
-0.0961
0.8
0.0690
0.0691
-0.0926
0.0690
0.0691
-0.0912
0.0688
0.0689
-0.0916
1
0.0619
0.0621
-0.2439
0.0620
0.0621
-0.2489
0.0618
0.0619
-0.2422
1.5
0.0504
0.0505
-0.2679
0.0504
0.0506
-0.2680
0.0503
0.0504
-0.2602
3
0.0350
0.0351
-0.3115
0.0350
0.0351
-0.3141
0.0349
0.0350
-0.2951
5
0.0271
0.0271
-0.2775
0.0271
0.0271
-0.2618
0.0269
0.0270
-0.2663
8
0.0221
0.0222
-0.2737
0.0221
0.0222
-0.2780
0.0219
0.0220
-0.2814
10
0.0204
0.0205
-0.2591
0.0204
0.0205
-0.2765
0.0202
0.0203
-0.2649
15
0.0183
0.0184
-0.3008
0.0183
0.0184
-0.2808
0.0181
0.0181
-0.3015
Fig. 8
MAC of the prepared alkali borate glasses via Phy-X/PSD and MCNP-5 program
×
Figure 9 shows that the values of Zeq affected primary by two parameters; the first is related to the gamma source energy, while the second is related to the glass chemical composition. The maximum values of Zeq is achieved at the mid-energy gamma photons around 1 MeV as shown in Fig. 9. In the mid-energy region, these high values are attributed to the CS as main gamma interaction. The maximum values of Zeq are 8.90, 8.84, and 8.61 for BNAl, BNMg, and BNLi glasses, respectively. While, the minimum Zeq values detected at high gamma energies (from 3 to 15 MeV) are 8.21, 8.20, and 7.97 due to the PP interaction effect. In the low gamma energy region from 0.015 to 0.1 MeV, the Zeq has small variation with the gamma photon energy. The glass composition also has a significant effect on the Zeq values, where BNAl glass with Al2O3 addition, has the highest values of the Zeq, while BNLi glass with Li2O has the least Zeq values over the other studied glasses.
Fig. 9
Zeq of the prepared alkali borate glasses in the 0.015–15 MeV photon energy
×
The Phy-x/PSD program was utilized to calculate the geometric progression (G-P) fitting parameters to evaluate the accumulated photons number in the fabricated materials. The calculation was performed for gamma photons energies ranged from 0.015 and 15 MeV. The photon accumulation in air is measured for the exposure buildup factor (EBF) while the accumulation of photons in the inner layers of the fabricated materials describes the energy absorption buildup factor (EABF). Both EBF and EABF values are calculated at different penetration depths (the PD varies between 0.5 and 40 mfp). Figures 10 and 11 show that the calculated values of EBF and EABF grows with PD values where the smallest amount of accumulation is achieved for the low PD values (i.e., 1 mfp), then they increased gradually with increasing the PD. For the low PD value, the incident photons penetrate the thickness with a small number of collisions with both air and fabricated material atoms. Thus, the number of photons accumulated in air and fabricated material decrease, leading to a decrease in the EBF and EABF values. In contrast, with the growth of PD values, the number of interactions occurred in air and material layers increase. This leads to an increase in the photon accumulation and values of EBF and EABF rise as a result.
Fig. 10
EBF of the prepared alkali borate glasses in the 0.015–15 MeV photon energy
Fig. 11
EABF of the prepared alkali borate glasses in the 0.015–15 MeV photon energy
×
×
Also, the photon energy has a weighty effect on photons buildup. According to the presented data in Figs. 10 and 11, the accumulation of photons passes through three different regions alongside the studied energy range from 0.015 to 15 MeV. The first area starts at 0.015 and extends to 0.08 MeV. In the mentioned zone, the photon accumulation is the lowest, by reason of the PE interaction where the energy photon is disposed of to produce a free electron, and photons are annihilated in the medium at the small energy area. Thus, both EBF and EABF are decreased in this energy zone. The second energy zone starts from 0.08 MeV to around 1 MeV. This zone has the most important variations in EBF and EABF with the incident gamma photon energies. The calculated values of EBF and EABF begin to grow with growing the CS interaction in the mid-energy region. In this region the incoming photons interact with air and material atoms with scattering interaction, where the photon loses a part of its energy to produce a free electron from the atom, while the photon with the rest energy scatters and changes its path length inside the fabricated material, thus the materials can’t get rid of photons. Accordingly, accumulation of photons in both air and material increases and the calculated values of EBF and EABF increase, giving their maximum values around 0.15 MeV. The maximum EBF values are 10,113, 10,352, and 11,510, while the maximum EABF values are 11,275, 11,493, and 12,568 for BNAl, BNMg, and BNLi glasses, respectively. After that, both EBF and EABF values decrease with decreasing the CS interaction. Above 1 MeV, the values of EBF and EABF are very small due to the PP interaction, where the air and material get rid of the photon energy in creating an electron–positron pairs. Thus, photons annihilated inside the medium and the values of EBF and EABF decrease (Zy et al. 2022; Rammah et al. 2022; Abou Hussein et al. 2021d).
The third factor is the type of glass modifier, where Figs. 10 and 11 show that the EBF and EABF values are minimum for BNAl glass with Al2O3 content. In contrast, the highest values of EBF and EABF are attained for BNLi glass with Li2O modifier content.
The fast neutron mass removal cross-section ∑R (cm2/g) was calculated theoretically for BNAl, BNMg, and BNLi glass samples. Figure 12a shows that the ∑R (cm2/g) takes values of 0.04221, 0.04229, and 0.04352 cm2/g, for BNAl, BNMg, and BNLi glasses, respectively. The values of ∑R (cm2/g) are related essentially to the type of induced modifiers, where the fast neutron macroscopic cross section of Al, Mg, and Li are 0.02934, 0.03070, and 0.08399 cm2/g, respectively.
Fig. 12
a ∑Rb Relation between ∑R values versus density for the prepared alkali glasses
×
Figure 12b displays the relation between the ∑R (cm−1) values versus the density of the prepared glasses. It is clear that the ∑R (cm−1) of the fabricated glass samples decrease gradually with increasing the density. The ∑R (cm−1) varies between 0.10357, 0.1009, and 0.10076 cm−1 with growing the glass density between 2.387, 2.386, and 2.38 g/cm3.
Figure 13a displays the variation of linear attenuation coefficient (LAC) of the prepared alkali glasses at various photo energies up to 10 MeV. As is obvious from Fig. 13a, the values of LAC have a decreasing trend with increasing photon energy. The observed trend of LAC has the same behavior of MAC shown in Fig. 8. The trend of LAC is dramatically decreased with increasing of photon energy up to 0.1 MeV, and this is attributed to the photoelectric (PE) interaction as shown previously (Abou Hussein et al. 2021d).
Fig. 13
a LAC of the prepared alkali borate glasses at different photo energies up to 10 MeV. b: LAC of the prepared alkali borate glasses at photo energy 0.015 MeV
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Figure 13b, shows the values of LAC of the prepared alkali glasses at photo energy 0.015 MeV. As shown in Fig. 13b, LAC of the BNAl glass sample is the greatest one, followed by BNMg, and BNLi. This result is correlated directly to the highest atomic weight of Al ions compared to the other ions (Mg and Li).
In the current study, the half value layer (HVL) of the examined alkali glasses is evaluated in Fig. 14 that depicts the variation of (HVL) of the glasses as a function of photon energy. Results confirm that the BNAL glass sample has the least HVL among the other two studied samples. This is because the BNAL sample has the highest density (2.3871 g/cm3).
Fig. 14
HVL of the prepared alkali borate glasses
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Figure 15 displays the mean free path (MFP) of the studied glasses which is another important radiation shielding parameter. The values of the MFP are evaluated at selected photo energies 0.015 MeV, 1 MeV, and 15 MeV, where BNAl glass sample has the least MFP among all studied samples.
Fig. 15
Values of the MFP of the prepared alkali borate glasses at selected photon energies 0.015 MeV, 1 MeV, and 15 MeV
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Figure 16 shows the variation of the tenth value layer (TVL) parameter of the prepared alkali glasses as a function of photo energy ranged from 0.015 to 15 MeV. The trend of the TVL is similar as for HVL and MFP. Therefore, the sample coded as BNALl is the best sample for radiation protection applications.
Fig. 16
TVL of the prepared alkali borate glasses as a function of photon-energy in the range of 0.015 MeV-15 MeV
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4 Conclusion
A comparative study between three prepared borate glasses with different alkali metal oxides Al2O3, MgO or Li2O, shows quite differences depending on the valence state and atomic weight of each metal oxide. The UV–visible optical properties obtain obvious cutoff UV peaks in the wavelength range 320–340 nm, correlated to the trace of Fe3+ ions existing as chemical impurities in the used materials because modifier ions e.g., Na+ ions do not affect the coordination equilibrium ions in alkali borate structure. The optical energy gap Eopt calculated by Tauc’s model (ETauc’s) and ASF method (EASF) revealed values ranged from 2.60 to 3 eV before irradiation to 2.23 to 2.60 eV after gamma irradiation. The slight sharpness of the UV peaks after 20 kGy of gamma irradiation can be attributed to the possible photochemical reactions i.e., photo-oxidation process of the present trace iron impurities in glasses Fe2+ into Fe3+ or (Fe2+)+ by the reaction with the generated positive holes formed by irradiation procedure. Irradiation process has also a positive effect to decrease Eopt values slightly due to the possible conversion of BO to NBO and the possible electronic transitions. Raman spectra of the glasses display three active regions at 250–600 cm−1, (ii) 500–1000 cm−1 and (iii) 1000–2000 cm−1 that can be briefed as follows; (a) Small band at 495 cm−1 and sharp bands at ~ 570–578 cm−1 correlated to the separated diborate groups and the plane-bending mode of BO3 units or M–O bond vibrations, where M = Na+, Li+, Mg2+ or Al3+. (b) A strong band at ~ 765 cm−1 attributed to six-membered ring with one or two BO4 tetrahedral units; triborate, tetraborate or pentaborate forms. (c) Small bands around 960 and 1140 cm−1 correlated to the different diborate groups in the glass structure. Some differences are observed between the three alkali glasses on Raman spectra correlated to the mixed alkali effect” (MAE) that controlled by structural and electrodynamic theories, i.e., Al2O3 glass shows a disappearance of Raman peaks after gamma irradiation where, Al2O3 cannot affect the peaks resulted from the isolated diborate groups and the ring type metaborate groups polymerized by BO3 and BO4 units. MgO glass shows the appearance of strong peak at 808 cm−1 related to the coexistence of boroxol rings and pyroborate dimers B2ØO44. Li2O glass shows the division of strong peak at 1308 cm−1 into two peaks because of creating more non-bridging oxygens (NBO) and alteration of some metaborate triangles into BO4− tetrahedral units. The slight sharpness of UV peaks after irradiation and the small variations in Eopt values as well as the quiet stability of Raman structural bands correlated to MAE, indicate all the overall optical and structural stability of the glasses against gamma irradiation. The obtained results approve also that Al2O3 and MgO glasses have more stable behavior than Li2O glass. The same behavior is approved by the studied shielding parameters using Phy-X/PSD and MCNP-5 Monte Carlo code, as the increase in atomic weight of the introduced alkali metal ion causes a positive enhancement of the radiation shielding properties. The atomic weight order is Al2O3 > MgO > Li2O, therefore radiation shielding parameters for BNAl, BNMg, and BNLi glass samples would have the trend of (MAC, LAC)BNAl > (MAC,LAC)BNMg > (MAC,LAC)BNLi. However, HVL, MFP, and TVL parameters have the same trend as: (HVL, MFP, TVL)BNAl < (HVL, MFP, TVL)BNMg < (HVL, MFP, TVL)BNLi. Zeq reveals also the same order where Al2O3 has the highest Zeq values. EBF and EABF calculated at several penetration depths (the PD varies between 0.5 and 40 mfp) increase with increasing the PD values and increase gradually with increasing the PD. Also, ∑R values are related basically to the type of induced modifiers giving the lowest values for Al2O3 glass as it decreases gradually with increasing the density of the glass. Furthermore, Al2O3 glass obtains the lowest thicknesses of HVL and TVL and the lowest values of MFP.
Accordingly, the study recommended the suitable uses of the fabricated glasses with acceptable optical and structural properties and outstanding shielding features specially BNAl sample which is the best one for radiation shielding application.
Acknowledgements
We are gratefully acknowledging financial support from National Center for Radiation Research and Technology (NCRRT), Egyptian Atomic Energy Authority (EAEA) and Faculty of Science, Menoufia University for their fruitful assistance in completing this work.
Declarations
Ethical approval
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Conflict of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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