## 4 Discussion  
In earlier research, the discovery of environmentally-friendly shielding materials with excellent processability was the primary objective, and the concepts of mass and density were important. Now, they are very important factors for the processability of an RSF. The durability and organization between a shield material and the process technology have been studied [17; 18]. For RSFs in the industrial field, an important condition for the safe transfer of contaminated substances after the Fukushima incident in Japan was that the minimum strength should support the weight. The RSF in the medical field is an important factor necessary for medical personnel wear. Radiation shielding has a larger shielding effect for a larger mass of material. However, it is not necessarily proportional to the shielding performance. As shielding performance is related to material density--and density is the relationship between the volume and the mass--processes such as blending the shielding materials are very important. The basic processing of the RSF was carried out by powdering, mixing, forming, aging, and extruding the material. The manufacturing process that increased the interval density--achieved by lowering the porosity for the removal of primary bubbles in the mixing process and secondary bubbles in the aging process--was very important in this experiment. In earlier studies, a mechanical method was selected to increase the degree of dispersion and packing of the shielding material [19]. However, we applied the porosity that is suggested in this study because the problem of tensile strength of the RSF after fabrication occurred. Consequently, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Shielding Film**} & **BaSO\({}_{4}\)** & **Bi\({}_{2}\)O\({}_{3}\)** & **WO\({}_{3}\)** \\ \cline{2-4}  & & **+Silicon Resin** & \\ \hline Penetration dose (mR) & 3.89 & 2.83 & 1.02 \\ \hline Lead equivalent (mm Pb) & 0.547 & 0.398 & 0.121 \\ \hline \hline \end{tabular} BaSO\({}_{4}\): barium sulfate, Bi\({}_{2}\)O\({}_{3}\): bismuth trioxide, WO\({}_{3}\): tungsten oxide powder. Penetration dose measurements are based on the prepared 0.6 mm sheet (200 mA, 0.1 s, 100 kVp).  
\end{table} 
Table 6: Shielding film of penetration dose (unit: mR). Figure 5: Correlation between porosity, tensile strength, and radiation shielding ratio (barium sulfate (BaSO\({}_{4}\)) 6 mm). (**a**) Comparison of tensile strength and porosity; (**b**) comparison of shielding performance and porosity; (**c**) comparison of shielding performance and tensile strength. the shielding performance could be predicted with the porosity when calculating the bulk density of the RSF. Therefore, in the RSF manufacturing process, to maintain a light weight, a shielding material such as WO\({}_{3}\), Bi\({}_{2}\)O\({}_{3}\), tin, or antimony trioxide is pulverized into micro units in a polymer silicone resin rather than excess added powder, to obtain uniform compounding. Bubble removal in the mixing process is also very important. To lower the porosity, the multi-gate method by stepwise dosing according to the particle size was proposed [20; 21; 22]. However, bubble removal has a considerable influence on the performance of the RSF. The porosity during the RSF manufacturing process varies depending on the shielding material and base material. However, generally, it is most stable between 12% and 20%, and the actual value, considering the tensile strength, is estimated to be approximately 15%. For such conditions, the shielding ratio can show an excellent performance of 90% or more. The thickness of the RSF also has a direct correlation with the shielding performance. If the shielding material is thick, the reason the shielding ratio does not decrease rapidly, owing to an increase in voids, may be a tendency of the radiation to be partially reduced through scattering and absorption in the internal structure of the particles [19; 23].