## 3 Results and Discussion  
The \(\upmu\) for the fabricated polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites was evaluated via determination of the MTL of the emitted \(\gamma\)-photons using MCNP-5 code in the \(\gamma\)-photon energy (E\({}_{\gamma}\), keV) interval between 15 and 661 keV, as illustrated in Figure 2. The studied E\({}_{\gamma}\) interval contains two different \(\gamma\)-photon interaction modes. The first is the photoelectric interaction (PE) which extends along the interval from 15 to 122 keV, where the \(\upmu\) values suffer from a high reduction with increasing E\({}_{\gamma}\) values. This high reduction in the \(\upmu\) value can be attributed to the PE cross-section, which varied inversely with E\({}^{3.5}\). The \(\upmu\) values decreased in the mentioned interval by factors of 95.0, 96.3, and 96.6% for the fabricated composites Bi\({}_{2}\)O\({}_{3}\) 0%, Bi\({}_{2}\)O\({}_{3}\) 5%, and Bi\({}_{2}\)O\({}_{3}\) 10%, respectively, when the E\({}_{\gamma}\) increased from 15 to 122 keV. The second mode of \(\gamma\)-photon interaction in the current work is Compton scattering (CS), which extended from 200 keV to 661 keV. In the second mentioned interval, the \(\upmu\) values decreased moderately under the effect of CS cross-section when the E\({}_{\gamma}\) value increased, where the CS cross-section was inversely correlated with E. For example, the \(\upmu\) values decreased by factors of 27.7, 34.2, and 39.6%, for composites Bi\({}_{2}\)O\({}_{3}\) 0%, Bi\({}_{2}\)O\({}_{3}\) 5%, and Bi\({}_{2}\)O\({}_{3}\) 10%, respectively, when E\({}_{\gamma}\) increased from 200 to 661 keV. The impact of the Bi\({}_{2}\)O\({}_{3}\) doping content on the \(\upmu\) of the fabricated composites is illustrated in Figure 3. The results presented in the figure show that the \(\upmu\) increased significantly with rising Bi\({}_{2}\)O\({}_{3}\) ratios. In the PE interaction mode, the \(\upmu\) values recorded a large increase with rising Bi\({}_{2}\)O\({}_{3}\) concentration. This large increase is attributed to the PE cross-section, which varies directly with \(Z_{\text{eff}}\)[4; 5], where \(Z_{\text{eff}}\) refers to the effective atomic number. In the aforementioned E\({}_{\gamma}\) interval, the \(\upmu\) values increased by factors of 362, 236, and 218% at E\({}_{\gamma}\) values of 15 keV, 59 keV, and 122 keV, respectively, when the Bi\({}_{2}\)O\({}_{3}\) doping concentration increased from 0 to 10 wt.%. The obtained results show that, in the CS interaction region, the \(\upmu\) values increased slightly with rising Bi\({}_{2}\)O\({}_{3}\) concentration. For instance, at an E\({}_{\gamma}\) of 661 keV, the \(\upmu\) values increased by 12% by raising the Bi\({}_{2}\)O\({}_{3}\) doping concentration from 0 to 10 wt.%. Figure 2: The linear attenuation coefficient of the polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites. The mass attenuation coefficient (\(\mu_{\rm m}\)) for the polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites was calculated, first based on the simulated results, then using the free program Phy-X/PSD [25]. Moreover, the \(\mu_{\rm m}\) for the selected composites was determined experimentally via the narrow beam transmission method using the \(\gamma\)-photons emitted from radioactive sources Am-241, Na-22, and Cs-137 with energies of 59, 511, and 661 keV, respectively. The measurements for the unattenuated photons (I\({}_{\rm o}\)) and the attenuated photons (I) were detected using a 3\({}^{\prime\prime}\)\(\times\) 3\({}^{\prime\prime}\) NaI (II) detector. Table 2 shows a comparison between the simulated, theoretically calculated (Phy-X/PSD), and the experimental measurements. The comparison depicts a difference (\(\delta\), %) in the range of \(\pm\)1% between MCNP and Phy-X data, whereas the difference between the experimental measurement and the MCNP simulation was found to be approximately \(\pm\)6%.