Transmission, buildup factors, and photon shielding capacity of vanadium reinforced tellurite glasses

The ionizing radiation shielding parameters of (90-y)TeO 2 -yV 2 O 3 -5CaO-5Na 2 O (TVCN): y= 5-20 mol% semiconductor glasses were investigated. The avarage track lengths of photons with different energies (0.015- 15 MeV) in the TVCN-glasses were simulated via MCNP-5 code, then the corresponding LAC were computed. Based on LAC values, the MACs were calculated and compared with values which obtained via XCOM software. The highest LAC achieved for low energy (0.015 MeV) and reduced from 199.549 to 169.891 cm -1, while the lowest values achieved for gamma photon with higher energies and reduced from 0.188 to 0.161 cm -1 with replacment of TeO 2 compound by V 2 O 5. The highest (I/I o ) achieved for TVCN20 glasses and decreased from 0.703 to 0.172., while the lowest (I/I o ) performed for TVCN5 glasses and decreased from 0.680 maximum values for glasses TVCN5 while the lowest EBF and EABF achieved for glasses TVCN20. Therefore, the glasses TVCN5 have a higher ability to attenuate the incident gamma photons. Thus, the TVCN-glasses can be applied in various radiation shielding applications in medical area.


Introduction
Recently, due to modern technology especially in nuclear medical field, artificial and natural sources of ionizing radiation (i.e., X-and gamma-photons) and their radioisotopes have been used in different applications. Sealed sources of 60 Co, 123 I, and 201 Tl are considered as isotopes applied in medicine for the treatment of health trauma, nuclear medicine, and sterilizing medical equipment. Furthermore, ionizing radiation can be applied preservation industries, food processing, and for material characterization, among others.
The use of shielding as a radiation protection procedure is an essential aim for continuous adoption of radiation in existing and modern applications. Therefore, in nuclear science and technology, research into radiation shielding materials becomes very active. The selection of radiation shielding materials depends on factors such as radiation energy and quality, cost, available space, required physical, thermal, mechanical, and optical features of the shield. The most important factor is that the shielding material must have high absorption cross-section for the radiation energy of interest. Photons (gamma-and Xradiation) and neutrons are of major concern due to their high penetration power. Therefore, shielding parameters for these radiations are essential when evaluating any material for ionizing radiation shielding effectiveness.
Formerly, concrete, lead (Pb), and depleted uranium are traditional shielding material have major disadvantages and have continuously limit application. Pure lead (Pb) and Pbbased composite have toxicity and cost related issues [1,2]; concrete suffers from unstable and cracking features due to thermal changes which leads to changes in its chemical (hydrogen) content [3]; uranium on its own is radioactive. Thus, research into novel materials such as glasses very attractive to research community to be applied as radiation shields [4][5][6][7][8][9][10][11][12][13][14].
Tellurium oxide (TeO 2 ) based glasses are one of the most significant considerable attention among other oxide glasses such as phosphate, borate and silicates because of their several unique and attractive physical and chemical properties such as high thermal expansion coefficient in the range of 120 x 10 -7 o C -1 to 170 x 10 -7 o C -1 , high index of refraction (1.8-2.3), low glass transition temperature (less than 300°C), dielectric constant in the range of 13-35, low melting temperature (less than 1000°C), and higher optical transmission in the infrared (IR) region from 0.4 to 6 μm) [15][16][17][18][19]. Therefore, TeO 2 -based glasses have been widely applied amplifiers and laser tools [18][19][20].
This article presents the ionizing radiation shielding capacity of TeO 2 -V 2 O 3 -CaO-Na 2 O (TVCN) semiconductor glasses. The mass and linear attenuation coefficients (MAC and LAC), half value layer and mean free path (HVL and MFP), effective and equivalent atomic numbers (Z eff and Z eq ), and photon energy absorption and exposure buildup factors (EABF and EBF) were evaluated.

Results and discussion
The Monte Carlo N-particle transport code (MCNP-5) was used to investigate the avarage track length of photons with different energies varied in range between 0.015-15 MeV in the studied TVCN-glasses. Based on the simulated avarage track length, the linear attenuation coefficent (LAC) was and ploted in Figure 1. The calculated values of the LAC presented in Figure 1 showed that the highest LAC values achieved for photons with lower energy (0.015 MeV). After that, a speedily diminish was observed in the calculated values of the HVL. This speedily diminish is due to the photo-electric interaction (PE) which is the main interaction for gamma photon with low energies. An Unpredicted increase in the calcuated values of the HVL was detected arround 31.8 keV. This unpredicted increase is due to the x-ray K-absorption edges of the tellerium element (Te). The Compton scattering is the major interaction for photons with intermegiate energy values between 0.15-3 MeV.
Thus, a softly decrease in the LAC values was observed. This softly decrease is due to the variation of the Comprton scattering cross section with the E -1 . The LAC values for photons with higher energies (E>3MeV) were observed to be nearly constant. This equiling values for the LAC is due to the Pair production interaction (PP) where the pair production cross section vary with log (E) [30,31]. The mass attenuation coefficent (MAC) was also calculated based on the simulated LAC according to Equation (1) [32,33]: .
The refers to the studied glasses density. The mass attenuation coefficent was estimated theoretically using XCOM program in the same energy range between 0.015 and 15 MeV.
The calculated values of the MAC using MCNP and XCOM were listed in Table 2 were agrement was observed for the MAC values calculated using XCOM and MCNP. The difference (%) between the XCOM and MCNP results was calculated and listed in Table   2. It is clear that the diff. (%) was found to be around 1% for all the studied TVCN glasses.
The transmission rate of gamma photons energy 662 keV was calculated for the studied TVCN-glasses at different thicknesses varied between 1 and 5 cm according to Equation The and refer to the (LAC) and the glass thickness, respectively. The result presented in Figure 2 showed that the highest transmission rate is obtained for 1cm thickness of the studied glasses and varied between 0.680 and 0.703 while the lowest transmission rate achieved at sample thickness 5 cm and varied between 0.145 and 0.172 for glasses TVCN5 and TVCN20. As the thickness of the glass increases, the number of gamma ray interactions with the glass atom increase. Thus, the thicker slides are more effective in absorb of the incident gamma photons. Figure 2  .
The calculated HVL for the studied TVCN glasses was presented in Table 3and  Compton cross section varies with . After that for high gamma photons energy, the PP interaction is main so values of the HVL were observed to decrease slowly with increase the incident gamma energy. The PP cross-section proportional to Z 2 log( ).
The thinner HVL was achieved for TVCN5 glasses with content 5 mol% V 2 O 5 and increases from 0.003 to 3.684 cm while the thicker HVL was achieved for TVCN20 with content 20 mol% V 2 O 5 and increases from 0.004 to 4.293 cm for gamma-photons with energy between 0.015 and 15 MeV. According the previous discussion we can concluded that the replacement of TeO 2 by V 2 O 5 contents reduce the ability of the studied glass to attenuate the incident gamma-rays.
The mean free path (MFP) is the shielding parameter which calculate the average distance between to following collisions inside the studied glasses. The MFP for the studied glasses calculated using Equation (4) [34,35] The computed values for the MFP was plotted in Figure 4  The dose rate received by an exposure at a definite distance from the radioactive source without a shielding material can be described by Equation (5).
Where Г, A and d represent the specific gamma ray constant, activity of the radioactive source and the measured distance between the radioactive source and the exposure, respectively. When a shielding material was used to shield the radioactivity outcome from the radioactive source, Equation (5) can be modified and written as the following.
Where refer to the LAC of the thickness of the studied TVCN-glass, respectively.
The dose rate received by an exposure at a distance 100 cm from radioactive gamma ray source 137 Cs with activity 1Ci was computed theoretically according to Equation (6) and the recorded results were plotted in Figure 5.
Where f i , A i , Z j and ( ) refer to the fractional abundance, mass number, atomic number, and the mass attenuation coefficient of the i th constituent element respectively.
Additionally, the effective electron density (N eff ) can be calculated based on the values of the Z eff as shown in Equation (8): Where N A and M refer to the Avogardo's number and the atomic mass in unit (g).
The Z eff of the studied TVCN-glasses were estimated using Phy-X/PSD program [36] and the obtained results plotted in Figure 6. The maximum values of the Z eff were observed at the lower energy while the lowest values of the Z eff obtained at higher energies due to the PP interaction. Around 31.8 keV, a raise in the calculated values of the Z eff was detected. This increase is due to the X-ray and K-absorption edges of the tellurium (Te) element. After that, a rapidly decrease in the Z eff values was detected due to the PE interaction. Due to the Compton scattering interaction is the main for gamma-photons with energy higher than 300 keV, a moderately reduction in the Z eff values was detected. For high gamma ray energy, the values of the Z eff began to increase again with increase the incident photon energy. This increase is due to the pair production cross section which varied with log (E). The highest values of the Z eff was recorded for glasses TVCN5 and

Conclusion
In this study, the ionizing radiation shielding parameters of In general, the results showed that replacment of TeO 2 compound by V 2 O 5 compounds has a negative effect in the density and LAC and MAC values of the TVCN-glasses, reduces the ability of the studied glass to attenuate the incident gamma photons, and increases the dose rate received by the exposure. Thus, the probability of photon interaction in TVCN5 glasses is higher than the other studied glasses. This means that the studied glasses TVCN5 have a higher ability to attenuate the incident gamma photons. Therefore, the TVCNglasses can be applied in various radiation shielding applications in medical area.