## 3 Results and Discussion
Building factors are also key to clarifying the ability of a material to get rid of the emitted photons and to prevent their accumulation in the material bulk. The buildup factor is divided into two parts: the exposure buildup factor (EBF) and the energy absorption buildup factor (EABF). In order to calculate both the EBF and EABF, it is necessary to first determine the value of the equivalent atomic number (\(Z_{\text{eq}}\)), which describes a multielement material in terms of its equivalent element. However, unlike \(Z_{\text{eff}}\), \(Z_{\text{eq}}\) depends on the ratio of the Compton scattering mass, \(\mu_{\text{m}}\), to the total \(\mu_{\text{m}}\). Calculations of \(Z_{\text{eff}}\), \(Z_{\text{eq}}\), EBF, and EABF were performed using Phy-X/PSD software [25]. Figure 9 shows that the values of \(Z_{\text{eq}}\) were very small at low \(E_{\gamma}\) energies. This decrease in the \(Z_{\text{eq}}\) is related to the reduced values of (\(\mu_{\text{m}}\)) Compton scattering due to the predominance of the PE interaction. In the PE interaction region, \(Z_{\text{eq}}\) increases from 9.2 to 9.8 for Bi\({}_{2}\)O\({}_{3}\) 0%, from 12.4 to 26.4 for Bi\({}_{2}\)O\({}_{3}\) 5 %, and from 14.46 to 32.48 for Bi\({}_{2}\)O\({}_{3}\) 10 %. Above 100 keV, the \(Z_{\text{eq}}\) values were greatly increased due to the predominance of CS interactions, and the (\(\mu_{\text{m}}\)) Compton scattering was greatly increased compared to the total \(\mu_{\text{m}}\) values. EBF and EABF values were calculated and are presented in Figures 10 and 11 along with the \(\gamma\)-photon energy and Bi\({}_{2}\)O\({}_{3}\) doping concentration. The values of these factors were very low at low \(E_{\gamma}\) values, they then increase gradually with rising \(E_{\gamma}\) in the CS region. For the Bi 0% composite, without Bi\({}_{2}\)O\({}_{3}\), the EBF and EABF tend to reach maximum values at around 150 keV, where the EBF and EABF values were 117 and 164, respectively. Then, both EBF and EABF reduce gradually and drop to 29.2 and 32.6 under the effect of pair production (PP), which consumes the photon energy in the production of an electron and positron pair. Raising the Bi\({}_{2}\)O\({}_{3}\) concentration in the fabricated composites causes a high decrease in the EBF and EABF; the EBF values at 15 keV decreased from 1.09 to 1.06, whereas the EABF values decreased from 1.09 to 1.05. The results show that the addition of Bi\({}_{2}\)O\({}_{3}\) to the polyepoxide resin reduces the accumulation of photons in the fabricated composite. This observation can be attributed to the \(Z_{\text{eff}}\) of the composites, where increasing the Bi\({}_{2}\)O\({}_{3}\) composition causes an increase in the fabricated composite's \(Z_{\text{eff}}\). Hence, the PE interaction cross-section is directly proportional to \(Z^{+5}\). Consequently, the probability of this process increases with the increasing \(Z_{\text{eff}}\). Thus, the energy of the emitted photon is totally consumed in the interaction with the composite atoms and electrons. So, the  
Figure 8: Variation in the effective atomic number (\(Z_{\text{eff}}\)) of the synthesized polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites versus the emitted \(\gamma\)-photon energy. EBF and EABF values show a significant decrease with rising Bi\({}_{2}\)O\({}_{3}\) concentration in the fabricated composites. Figure 3.0 Variation in the EBF of the fabricated polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites versus the emitted \(\gamma\)-photon energy and Bi\({}_{2}\)O\({}_{3}\) concentration at 10 mfp. Figure 3.1 Variation in the equivalent atomic number (\(Z_{\rm eq}\)) of the fabricated polyepoxide-reinforced Bi\({}_{2}\)O\({}_{3}\) composites versus the emitted \(\gamma\)-photon energy. Moreover, raising the penetration depth in the unit of a mean free path (mfp) causes an increase in both EBF and EABF for the fabricated composites.