## 2 Materials and Methods
We used high-density polyethylene (HDPE) as the polymer material for stirring with the shielding material during the manufacturing process; HDPE has excellent strength and is \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Microparticle** & **Nanoparticle** \\ \hline Particle size distribution (\(\upmu\)m) & 100–400 & 0.4–0.9 \\ Specific surface area (m\({}^{2}\)/g) & 24.45–31.2 & 8.5–10.5 \\ Tap density (g/cc) & 5.2–7.2 & 2.5–3.7 \\ Purity (\%) & 99–99.8 & 99–99.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Shielding-material particle-processing conditions. used primarily as a disposable plastic product [31]. The HDPE used in this study had a molecular weight of 4 million or more and a density of 0.91 g/cm\({}^{3}\). The material composed of tungsten particles was dried at 70 \({}^{\circ}\)C for 12 h prior to use. As a solid polymer was used, a casting solution was prepared using N-dimethylformamide (DMF, 99.5%) as a solvent. DMF was dissolved in a stirrer with polyethylene at a ratio of approximately 10 wt % to produce the casting solution. In addition, tungsten powder was added to the finished casting solution and stirred at 5000 rpm to disperse the tungsten particles. The plasticizer used to remove the porosity inside the shielding sheet was diisononyl phthalate, and it was used in the range of 0.85-0.95 wt %. To maintain the uniform shielding performance of the final casting solution, we used a filter to remove foreign substances, and then performed a bubble removal operation. The final shielding sheet was finished with a calendar process of compression molding, and the size of the final shield sheet was 100 \(\times\) 100 \(\times\) 0.3 mm, which is the same as that shown in Figure 2.  
In this experiment, changes in shielding efficiency according to particle size and arrangement were observed. In particular, the total amount of tungsten was adjusted to the same thickness of a single structure to estimate the appropriate particle size when manufacturing lightweight shielding clothing used in medical institutions. Three types of shielding sheets were manufactured, namely, a shielding sheet containing microsized particles, a sheet containing nanosized particles, and a sheet developed by mixing equal amounts of nanoparticles and microparticles. The three types of sheets had the same size and thickness, but the weights differed slightly depending on the mixing amount of the shielding material. The particle size and dispersibility of the shielding material were observed using a field-emission scanning electron microscope (FESEM; Hitachi, S-4800) through thin-film intercepts of the shielding sheet. Shielding efficiency was tested 10 times using an X-ray generator (Toshiba E7239, 150 kV-500 mA, 1999, Tokyo, Japan), and the average value was used. X-ray energy shielding test conditions were as follows: tube voltage, 60-120 kVp; tube current, 200 mA; and irradiation time, 0.1 s. The dose detector was DosiMax plus 1 (2019.iba Dosimetry Corp., Schwarzenbruck, Germany), and it was used after inspection and calibration. The radiation-shielding test was evaluated by applying the lead-equivalent test method (KS A 4025: confirmed in 1990, 1995) of X-ray protection products of the Korean industrial standard. In addition, the photon-scattering effect was measured at a distance of 50 cm, as shown in Figure 3, to prevent backscattering on the detector. Figure 2: Appearance of final shielding sheet. (**A**) microparticle sheet; (**B**) nanoparticle sheet; (**C**) mixed nanoparticles and microparticles sheet). To evaluate shielding performance, the experiment consisted of a radiation experiment [32; 33], as shown in Figure 3, and the shielding-efficiency measurement of the fabricated shielding sheet was calculated as shown in Equation (6). \[\text{S}=\left(1-\frac{e}{e_{0}}\right)\times 100, \tag{6}\]  
where S is shielding efficiency, \(e\) is the incident dose (mR), and \(e_{0}\) is the transmitted dose (mR).