## 4 Discussion  
Radiation-shielding equipment in medical institutions relies mainly on lead, whose toxicity has created urgency for an alternative [33, 34, 35, 36]. This study investigated the potential of powdered oyster shell as a new eco-friendly shielding material. The seafood industry generates a vast amount of waste in the form of discarded shells such as oyster shells, much of which goes to landfills. As such, the recycling of oyster shells is an important issue because of the environmental pollution caused by odors and leachate from their waste, and the damage they cause to the natural landscape [37, 38, 39]. Therefore, the radiation-shielding efficiency was evaluated to broaden the scope of shellfish recycling. Table 4 summarizes the composition of several types of shellfish [40]; furthermore, calcium carbonate accounts for the vast majority in each case. Oyster shells are the most abundant of the shells discarded by aquaculture and are easily accessible [41]. Moreover, the radiation shielding efficiency of limestone has been studied [42], and limestone has been observed to comprise calcium carbonate as its main component. As the low density of calcium carbonate has a significant impact on its shielding effect, plastic working was investigated as a means of increasing its density and enhancing its radiation-attenuation capacity. This approach was reasonably successful, with plastic working reducing the inter-particle distance by decreasing the distance from the center of \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Type of Shellfish**} & \multicolumn{8}{c}{**Elemental Composition (\%)**} \\ \cline{2-9}  & **CaO** & **Na2O** & **CI/MnO** & **SiO2** & **SO3** & **Al2O3** & **Fe2O3** \\ \hline \hline Clams & 94.97 & 1.01 & - & 1.83 & 0.52 & 0.45 & 0.58 \\ \hline Cockles & 95.95 & - & - & 1.68 & 0.65 & 0.58 & 0.59 \\ \hline Manila clams & 92.79 & 1.13 & 0/0.13 & 3.09 & 0.59 & 0.98 & 0.63 \\ \hline Oysters & 84.59 & 5.92 & 5.15/0 & 1.63 & 1.19 & 0.45 & 0.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Chemical compositions of different shellfish [19]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{\
\begin{tabular}{c} **X-ray Tube** \\ **Voltage (kVp)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Effective X-ray** \\ **Energy (keV)** \\ \end{tabular} } & \multicolumn{8}{c}{**Mean Exposure (\(\mu\)R)**} & \multicolumn{8}{c}{**Shielding Rate (\%)**} \\ \cline{3-10}  & & **Nothing** & **0**\({}^{\circ}\)C & **600**\({}^{\circ}\)C & **1200**\({}^{\circ}\)C & **0**\({}^{\circ}\)C & **600**\({}^{\circ}\)C & **1200**\({}^{\circ}\)C \\ \hline
40 & 24.6 & 106.90 & 87.72 & 84.47 & 67.01 & 17.94 & 20.98 & 37.32 \\ \hline
60 & 28.7 & 381.63 & 334.07 & 320.83 & 278.97 & 12.46 & 15.93 & 26.90 \\ \hline
80 & 32.5 & 799.70 & 738.57 & 702.13 & 630.80 & 7.64 & 12.20 & 21.12 \\ \hline
100 & 48.5 & 1318.33 & 1199.00 & 1180.67 & 1079.67 & 9.05 & 10.44 & 18.10 \\ \hline
120 & 54.9 & 1648.33 & 1510.33 & 1484.67 & 1372.67 & 8.37 & 9.93 & 16.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between the shielding efficiencies of oyster shell-based shielding sheets fabricated with and without plastic working.