1 Introduction

Ionizing radiation is an important term to be considered along with its benefits and potential risks. Despite its benefits in medical diagnosis and treatment practices, the risk status on living biological structures should always be considered and minimized. Gamma radiation shielding is a very important application because γ-rays have risky effect on human health. The ALARA principle suggests the use of the most suitable shielding material to reduce the amount of ionized radiation exposed. Technological developments have brought with the use of new methods for radiation shielding studies. Moreover, the development and use of radiation shielding materials that are environmentally friendly, low cost and have high material durability is one of the most popular research topics in the literature in recent years. Glass materials which are new and promising material types in terms of structural development, transparency, high durability and environmental friendliness features used for radiation shielding have gained a very useful place in nuclear reactors, fusion reactors and modern accelerator technology. As it is clearly seen from the previous studies, lead (Pb) materials which have various disadvantages to protect against gamma rays have been replaced by various types of materials such as concrete and glass to protect them from gamma rays [1,2,3]. Glass materials [4,5,6,7,8] are a very reliable material used in radiation shielding instead of concrete [9,10,11]. Various phosphate glass systems (PG) with characteristics such as low dispersion power, low refractive index, high gain density, low melting point and high thermal stability are being developed day by day by combining glass-forming oxides (SiO2 and TeO2) and modifying oxides (Al2O3, CaO, K2O, PbO, Na2O, BaO, MgO, CaF2, Fe2O3, ZnO, TiO2, etc.). By adapting the chemical mixtures of phosphate-based glass structures, it can be quite suitable material types which can be manufactured for different functional applications.

The addition of Al2O3 to phosphate-based glass samples has the effect of increasing cross-links between PO4 units that form Al–O–P bonds. These Al–O–P bonds are more covalent than P–O–P bonds. On the other hand, P–O–P bonds have a straight impact on some characteristic features [chemical resistance, glass transition temperature (Tg), density and thermal expansion coefficient (α)] of glass samples. In addition, as alkali metal oxide (e.g., Na2O) is added to the glass materials, it causes the P–O–P bonds to break, the three-dimensional networks turn into linear phosphate chains and the formation of NBOs consisting of P–O–Na (K) bonds that are weaker than P–O–Al bonds. CoO, added to glass materials, has a positive effect due to its easy processing, stability at high temperatures and adjustable release kinetics [12,13,14,15,16,17,18,19,20,21,22,23,24]. In this paper, five different glasses based on (59.5–x) P2O5–30Na2O–10Al2O3–0.5CoO–xNd2O3 system were examined in terms of structural and gamma ray shielding properties. To examine the shielding properties of the materials, the most basic parameter used is the mass attenuation coefficient (µm). The attenuation principle of photons is interpreted in three different processes. The first of these interaction processes are photoelectric absorption, which is effective in low energies; the second is Compton scattering, which is effective in medium energies; and lastly pair production that is active in high energies. The total value of the mass attenuation coefficient is equal to the sum of these three processes and is related by the primary energy of the photon, average atomic number (Z) and chemical system of the substance [25, 26]. In this study, five different glasses encoded ND1, ND2, ND3, ND4 and ND5 based on (59.5–x) P2O5–30Na2O–10Al2O3–0.5CoO–xNd2O3, where x = 1, 2, 3, 4 and 5 (mol%) glass system, were fabricated. In addition, X-ray powder diffraction (XRD) was utilized for structural analyses. Next, an experimental gamma-ray transmission setup was established for calculation of mass attenuation coefficients of fabricated glasses. We used 0.356- and 0.662-MeV gamma photons energies emitted from point isotropic gamma sources, namely 133Ba and 137C. It is worth to mention that this study aimed to observe the total impact of P2O5 replacement by Nd2O3. Therefore, the hypothesis of recent investigation can be highlighted by Nd2O3 reinforce effect and multiple impact on structural and gamma-ray attenuation properties of fabricated glasses. To provide the infrastructure of this hypothesis, Al205, Na2O and CoO ratios were kept constant and the effect of Nd2O3 ratio, which increased with partial decrease of P2O5 ratio (Table 1), was investigated. On the other hand, the theoretical mass attenuation coefficient values were examined using the XCOM program at 356-keV and 662-keV photon energy values. X-ray diffraction (XRD) was characterized for fabricated glasses. The investigated properties of novel glasses can be listed as follows:

  • X-ray powder diffraction (XRD) of fabricated glasses.

  • Half-value layer (HVL), mean free path (MFP).

  • Effective atomic numbers (Zeff).

  • Exposure buildup factors (EBF) and energy absorption buildup factors (EABF) at different penetration depths have been calculated at different Nd2O3 mol% levels and the energies (0.015–15 MeV).

  • A comprehensive mass attenuation coefficient investigation.

Table 1 Samples codes, elemental compositions and density (ρ) of glass samples
Full size table

The data achieved from this study can be useful for further research on the use of glass materials, a new generation material, in efficient and environmentally friendly shielding applications. The hypothesis of this research is to evaluate the multiple effects of increasing Nd2O3 additive amount on structural and ionizing radiation attenuation features of fabricated glass samples. Therefore, outcomes from recent investigation will be discussed in terms of increased Nd2O3 additive amount in manufactured glass samples. The obtained results from this experimental investigation can be useful for new approaches on novel, efficient and eco-friendly glass shields and their utilization for different types of ionizing radiation facilities such as medical radiation facilities, industrial radiation areas and research laboratories.

2 Materials and methods

Glass samples with chemical formula (59.5–x) P2O5–30Na2O–10Al2O3–0.5CoO–xNd2O3, where x = 1, 2, 3, 4, mol%). were prepared by the conventional melt quenching method and are given in Table 1. The materials that initiate the reaction are reagent grade (NH4)2HPO4, Na2CO3, Al2O3, CoO and Nd2O3. Powdered oxides were melted at 1050–1150 °C in a porcelain vessel in an air-conditioned electric oven for 35–45 min. To ensure homogeneity, melt shaking was performed during the preparation phase. Samples prepared by pouring the melt into preheated molds at 350 °C were left to anneal for a few hours at 450 °C. The oven was then left to cool to room temperature. The prepared samples were then ground and polished for XRD. XRD is often used to verify the glassy structure of the samples. When no peak is observed in the patterns obtained as a result of verification, the amorphous structure of the samples examined is verified. Gamma-ray shielding parameters of glass samples were measured using 0.356-MeV and 0.662-MeV gamma photons, which were emitted from point sources of 133Ba and 137Cs. The mass attenuation coefficients (µm) of the samples were evaluated using the NaI (T1) scintillation detector with the setup scheme depicted in Fig. 1. Some of the features of this detector are: Gammas of 0.662 MeV, emitted from 137Cs point source, have a 7.5% resolution and the thickness of the Al window is 0.5 mm. The measurement time for each sample was approximately 4 h and the measurement were repeated three times. Finally, densities of glasses have been determined with well-known Archimedes method. We remark that the measurement was repeated three times on each sample.

Fig. 1
figure 1

Narrow beam geometrical setup

Full size image

3 Theory

If the absorbent material is a chemical mixture or compound, the mass attenuation coefficient (µm) is estimated by the mixture rule and is expressed as given in the equation below [27, 28]:

$${\mu }_{\mathrm{m}}=\sum_{i}{w}_{i}{({\mu }_{\mathrm{m}})}_{i}.$$
(1)

Here, wi is partial mass component of the ith element in the investigated glass sample. In our work, the \({}_{\mathrm{m}}\) results of glass samples were obtained using the theoretical XCOM program. By the help of \({}_{\mathrm{m}}\) values, other shielding terms such as transmission factors (e.g., HVL, MFP) were then calculated by employing the equations as follows:

$$\mathrm{H}\mathrm{V}\mathrm{L}=\frac{\mathrm{L}\mathrm{n}(2)}{\mu },$$
(2)
$$\mathrm{M}\mathrm{F}\mathrm{P}=\frac{1}{\mu }.$$
(3)

Zeff values of fabricated glass samples were determined by the help of Eq. 4 [29,30,31]:

$${Z}_{\mathrm{e}\mathrm{f}\mathrm{f}}=\frac{{\sum }_{i}{f}_{i}{A}_{i}{\left(\frac{\mu }{\rho }\right)}_{i}}{{\sum }_{j}{f}_{j}\frac{{A}_{j}}{{Z}_{j}}{\left(\frac{\mu }{\rho }\right)}_{j}}.$$
(4)

In the formula, fi, μ, Zi and Ai indicate the fraction of each element, linear attenuation coefficient, atomic number and atomic weight, respectively. The equivalent atomic number (Zeq) values for the prepared glass samples were estimated using the equation given below [32,33,34].

$${Z}_{\mathrm{e}\mathrm{q}}=\frac{{Z}_{1}\left(\mathrm{l}\mathrm{o}\mathrm{g}{R}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}R\right)+{Z}_{2}(\mathrm{l}\mathrm{o}\mathrm{g}R-\mathrm{l}\mathrm{o}\mathrm{g}{R}_{1})}{\mathrm{l}\mathrm{o}\mathrm{g}{R}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}{R}_{1}}.$$
(5)

The terms of EBF and EABF give successful information about the number of photons, intensity, energy flux, and dose. Recently, EBF and EABF of ND1, ND2, ND3, ND4 and ND5 based on (59.5–x) P2O5–30Na2O–10Al2O3–0.5CoO–xNd2O3, where x = 1, 2, 3, 4 and 5 (mol%), were determined for gamma energies up to 15 MeV and for penetration depth up to 40 MFP using G-P fitting method. To estimate the buildup factors of fabricated glass samples, the equivalent atomic numbers (Zeq) are first determined. The Zeq can be determined based on the following interpolation equation [35,36,37]:

$${Z}_{\mathrm{e}\mathrm{q}}=\frac{{Z}_{1}\left(\mathrm{l}\mathrm{o}\mathrm{g}{R}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}R\right)+{Z}_{2}\left(\mathrm{l}\mathrm{o}\mathrm{g}R-\mathrm{l}\mathrm{o}\mathrm{g}{R}_{1}\right)}{\mathrm{l}\mathrm{o}\mathrm{g}{R}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}{R}_{1}},$$
(6)
$$C=\frac{{C}_{1}\left(\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{eq}\right)+{C}_{2}(\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{\mathrm{e}\mathrm{q}}-\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{1})}{\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{2}-\mathrm{l}\mathrm{o}\mathrm{g}{Z}_{1}},$$
(7)
$$B\left(E,X\right)=1+\left(\frac{b -1}{K -1}\right)\left({K}^{x}-1\right), \mathrm{f}\mathrm{o}\mathrm{r}K\ne 1$$
(8)
$$B\left(E, X\right)=1+\left(b-1 \right) x , \mathrm{f}\mathrm{o}\mathrm{r}K =1$$
(9)

where

$$K \left(E, x\right)=c{x}^{a}+d \frac{\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{h}\left(\frac{x}{{X}_{K}}-2\right)-\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{h}(-2)}{1-\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{h}(-2)} \quad \mathrm{f}\mathrm{o}\mathrm{r} \, x\le 40 \mathrm{m}\mathrm{f}\mathrm{p}.$$
(10)

Here, R is the ratio between Compton-attenuation and total attenuation ((µ/ρ)Comp/(µ/ρ)total). The next step is to obtain G-P fitting parameters using Zeq values utilizing the Eq. 8. Finally, the buildup factors of fabricated glasses were studied. These equations contain x as the distance between the source and the detector. At 1 mfp, the EBF is coded by b. K(E, X) factor has a meaning of dose multiplication [38, 39].

4 Results and discussion

4.1 XRD analysis

To initiate XRD measurement and verify the glassy structure of the samples, three of the powder samples were selected and shown in Fig. 2. As can be clearly seen from Fig. 2, a bump structure was observed at 15°–35° in all three examples; while, diffraction peaks confirming the non-crystalline glass structure of the prepared samples were not observed.

Fig. 2
figure 2

X-ray diffraction (XRD) patterns for glass samples

Full size image

4.2 Radiation shielding parameters

High-density glass samples have larger atomic numbers and can be considered an effective material for the gamma-ray shielding. This is related to the chemical composition of the glasses as well as the commitment to photon energy. The experimental and theoretically (XCOM) calculated mass attenuation coefficients (µm) of glass samples prepared at 0.356- and 0.662-MeV gamma photons emitted from spot sources 133Ba and 137C can be seen from Table 2. According to Table 2, the µm values in the 0.356 MeV and 0.662 MeV energy increase with increasing Nd2O3 contribution (i.e., when switching from ND1 glass sample to ND5 glass sample) [40]. The µm values are highest for the ND5 sample, while the lowest for the ND1 sample (see Table 2). This is because the ND5 sample contains the highest amount of Nd2O3 additives than other samples. The experimental results and XCOM results are slightly different underlining the performance of the model in terms of both robustness and high correlation with experimental outcomes. As can be seen also from Fig. 3, the experimental and theoretical data of µm values are highly compatible and supportive. As seen in Fig. 3, a peak is observed at 0.4154 MeV, 0.5506 MeV, 0.6858 MeV, 0.821 MeV and 0.9562 MeV due to the K absorption edge of the Nd element for glass samples of ND1, ND2, ND3, ND4 and ND5, respectively. As it is known, photons interact with the material in three ways and the sharp decrease in µm values in Fig. 3 is caused by the photoelectric event from these interaction processes [41,42,43]. Because the microscopic cross-section value is directly proportional to Z4−5 and inversely proportional to E−3.5. While the change in µm values is quite low in medium energies where Compton scattering is effective, the µm values take almost constant value due to the dominant pair production in high energies [44, 45]. The effect of the Nd2O3 additive on the half-value layer (HVL) and the mean free path (MFP) measurement results in glass samples is shown in Figs. 4 and 5. As can be seen from the Figs. 4 and 5, these values decrease with increasing Nd2O3 contribution. On the other hand, when photon energy is high, HVL and MFP values are also high. The HVL, one of the well-known shielding parameters, is a shield or absorber that reduces the radiation level to half the original intensity. On the other hand, the MFP shows the average distance between two consecutive gamma photon interactions [45, 46]. These two concepts are quick and very practical in approximate shielding calculations. Therefore, HVL and MFP should be small to achieve a strong radiation shielding in glass samples means low HVL and MFP values indicate the best radiation shielding. That is, as the density values of the glass samples increase, the MFP and HVL values decrease [47]. Thus, the high density ND5 glass sample has the minimum value for these two measurements, i.e. ND5 glass sample is the best shielding material among the glass samples. In composite materials, the effective atomic number and density values affect the absorption and scattering of photon interactions. Composite materials are very successful at reducing gamma rays when they have a higher effective mass number, since they will have more electrons per atom. The effective atomic number (Zeff) values of the five glass samples were calculated using Eq. 4 in the energy region of 0.015–15 MeV and are shown in Fig. 6. As can be seen from the figure, Zeff value decreases for all glass samples with the increase of photon energy. In addition, instant changes in Zeff values are seen due to the K absorption edge. Also, the Zeff values increases as the Nd2O3 increases from 1 to 5 mol%. The two other important gamma shielding parameters are exposure buildup factor (EBF) and energy absorption buildup factor (EABF). While EBF expresses the energy absorption properties of air, EABF describes the energy absorbed or accumulated in the attenuator. The calculated values of equivalent atom number (Zeq), EBF and EABF are shown in Tables 3, 4, 5, 6 and 7, respectively, for glass samples ND1, ND2, ND3, ND4 and ND5. Figures 7 and 8 show EBF and EABF changes for five different glass samples in the energy region of 0.015–15-MeV photon energy and at different penetration depths (1 mfp, 5 mfp, 10 mfp, 20 mfp and 40 mfp). As can be seen from Figs. 7 and 8, the minimum EBF and EABF values of the glass samples were observed at low energies. The reason for this is perhaps the photoelectric effect process [7, 48, 49]. EBF–EABF values increase with increasing energy in the middle energy region and reach a maximum of approximately at 0.6-MeV energy and then decrease with increasing energy value. This response can be associated with multiple scattering caused by Compton effect. In addition, EBF and EABF values increase with increasing penetration depth values for glass samples. On the other hand, in Figs. 9 and 10, the EBF and EABF values of all glass samples at a certain penetration depth value of 15 mfp are examined depending on the energy. While the EBF and EABF values of ND1 glass sample with the lowest Nd2O3 additive (1%) are highest, the EBF and EABF values of ND5 glass sample with the highest Nd2O3 additive (5%) are minimum.

Table 2 Experimental and theoretical mass attenuation with their relative difference (Δ) of glass samples
Full size table
Fig. 3
figure 3

Mass attenuation coefficient (μm) values as a function of photon energy glass samples

Full size image
Fig. 4
figure 4

Half-value layer (HVL) results as a function of glass samples

Full size image
Fig. 5
figure 5

Mean free path (MFP) values as a function of glass samples

Full size image
Fig. 6
figure 6

Effective atomic number (Zeff) values as a function of photon energy glass samples

Full size image
Table 3 (EBF and EABF) G-P fitting coefficients (b, c, a, Xk and d) of ND1 glass sample
Full size table
Table 4 (EBF and EABF) G-P fitting coefficients (b, c, a, Xk and d) of ND2 glass sample
Full size table
Table 5 (EBF and EABF) G-P fitting coefficients (b, c, a, Xk and d) of ND3 glass sample
Full size table
Table 6 (EBF and EABF) G-P fitting coefficients (b, c, a, Xk and d) of ND4 glass sample
Full size table
Table 7 (EBF and EABF) G-P fitting coefficients (b, c, a, Xk and d) of ND5 glass sample
Full size table
Fig. 7
figure 7

Exposure buildup factor (EBF) against photon energy of glass samples at 1, 5, 10, 20 and 40 mfp

Full size image
Fig. 8
figure 8

Energy absorption buildup factor (EABF) against photon energy of glass samples at 1, 5, 10, 20 and 40 mfp

Full size image
Fig. 9
figure 9

Exposure buildup factor (EBF) against photon energy of glass samples at 15 mfp

Full size image
Fig. 10
figure 10

Energy absorption buildup factor (EABF) against photon energy of glass samples at 15 mfp

Full size image

5 Conclusion

The glass system of (59.5–x) P2O5–30Na2O10Al2O3–0.5CoO–xNd2O3, where x = 1, 2, 3, 4 and 5 (mol%), has been successfully fabricated with the help of the melt quenching technique to indicate gamma shielding properties. Al205, Na2O and CoO ratios were kept constant and the effect of Nd2O3 ratio, which increased with partial decrease of P2O5 ratio, on the shielding properties of glass samples was investigated. The theoretical values of the mass attenuation coefficient were calculated using the XCOM program at 356-keV and 662-keV photon energy values with XCOM program. X-ray diffraction (XRD) was characterized for fabricated glasses. The µm values of the samples were measured using the NaI (T1) scintillation detector. Zeff, HVL, MFP, EBF and EABF gamma shielding parameters were calculated to examine the gamma radiation shielding features of ND1, ND2, ND3, ND4 and ND5 glass samples. The results highlighted that both the µm and Zeff values increased as the Nd2O3 concentration increased. On the other hand, HVL, MFP, EBF and EABF values decreased as the Nd2O3 concentration increased. ND5 glass has the lowest HVL, MFP, EBF and EABF values. Finally, the mass attenuation coefficient comparison has been done between experimental results and XCOM program. Theoretical and experimental data of µm values are highly compatible and supportive indicating the distinctive protection ability to attenuate photon radiation of ND5 glass sample. Thus, glass samples prepared have been shown to reduce the harmful effects of radiation. The data achieved from this study can be useful for further research on the use of glass materials, a new generation material, in efficient and environmentally friendly shielding applications. The different comprehensive measurements can be performed between traditional lead shields and studied glasses considering the significant parameters such as production cost, environmental effects, toxicity, durability. Hereby, it should be noted that continuous efforts on further improvements are necessary.