## 3 Results and Discussion  
The MCNP-5 simulated MAC values for the studied alloys and calculated MAC values using the XCOM software are presented in Table 2 and Figure 2. The maximum MAC values for all the investigated alloys were achieved at a low photon energy of 0.015 MeV. The maximum MAC values varied between 72.938 and 59.259 cm\({}^{2}\cdot\)g\({}^{-1}\) for alloys encoded as MAR-302 and Nimocast-75, respectively. The MAC values sharply decrease with the increase in gamma energy because of the photoelectric interaction (PE). Around a gamma photon energy of 0.02 MeV, a slight increment in the MAC values was observed for the Inconel-625 and Inconel 718 alloys. This small increase was due to the K-absorption edges of niobium (Nb) and tantalum (Ta), which appeared at 0.019 and 0.02 MeV, respectively. The small increase in the MAC values reflects the small concentration of Nd and Ta in the Inconel-625 and Inconel 718 alloys. Another increase in the MAC values was observed around 0.07 MeV for alloys encoded as MAR-302, MAR-247, and WI-52. This peak was due to the K-absorption edge of tungsten (W), which appears at 0.069 MeV. Above 0.2 MeV, the MAC values reduced more slowly with the increase in the incident photon energy because of the dominance of Compton scattering (CS) at this energy, which is proportional to Z.E\({}^{-1}\)[14,32]. Above several MeV, the MAC values demonstrated a reverse trend and had a slightly upward trend when increasing the incident photon energy. This slight upward trend was due to the pair production (PP) process, which is proportional to Z\({}^{2}\cdot\)Log (E) [33]. The lowest MAC was achieved at high gamma photon energy (15 MeV) and varied in the range of 0.0323-0.0348 cm\({}^{2}\cdot\)g\({}^{-1}\) for alloys encoded as MAR-302 and Inconel-625. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Energy** **(MeV)**} & \multicolumn{1}{c}{\multirow{2}{*}{**MAR-274**}} & \multicolumn{1}{c}{**MAR-302**} & \multicolumn{1}{c}{**Inconcell 825**} & \multicolumn{1}{c}{**Inconcell 278**} & \multicolumn{1}{c}{**Nimocust**} & \multicolumn{1}{c}{**W1-52**} & \multicolumn{1}{c}{**Nimocust**} &The MCNP-5 simulated MAC values were compared with the values obtained by the XCOM software (Table 2 and Figure 2). The comparison revealed that the simulated and calculated results were close to one another for all the investigated alloys. The comparison also showed that the highest MAC was obtained for alloys encoded as MAR-302 (range 0.035-72.94 cm\({}^{2}\cdot\)g\({}^{-1}\)) and MAR-274 (range 0.035-71.98 cm\({}^{2}\cdot\)g\({}^{-1}\)). The small variation between the MAC of the MAR-302 and MAR-247 alloys was due to the difference in the main constituent elements of alloys: cobalt and nickel. The lowest MAC was obtained for the alloy encoded as Inconel-625 and varied in the range of 0.0323-59.308 cm\({}^{2}\cdot\)g\({}^{-1}\) for photon energies between 0.015 and 15 MeV. The half-value layer (HVL) of the studied alloys was theoretically calculated using the simulated MAC for \(\gamma\)-ray energies between 0.015 and 15 MeV and the results are illustrated in Figure 3. It can be observed that the HVL values were close to one another at low energies such as at 0.015 MeV. After that, the HVL values progressively increased with the increase in photon energy due to the PE interaction. Above 0.2 MeV, the HVL values steadily increased with an increase in gamma energy, based on the CS process. At energies greater than several MeV, the HVL values were observed to decrease with an increase in photon energy due to the pair production process, which is the main interaction for high energy gamma-rays. The MAR-247 alloy possessed the thinnest HVL, which varied in the range of 0.001-2.159 cm, while the Inconel-625 alloy had the thickest HVL, which varied between 0.001 and 2.604 cm. Figure 2: The mass attenuation coefficient (MAC) of the studied alloys using the MCNP-5 code and XCOM software.