Rare-Earth Oxides as Alternative High-Energy Photon Protective Fillers in HDPE Composites: Theoretical Aspects

Abstract

This work theoretically determined the high-energy photon shielding properties of high-density polyethylene (HDPE) composites containing rare-earth oxides, namely samarium oxide (Sm₂O₃), europium oxide (Eu₂O₃), and gadolinium oxide (Gd₂O₃), for potential use as lead-free X-ray-shielding and gamma-shielding materials using the XCOM software package. The considered properties were the mass attenuation coefficient (µ_m), linear attenuation coefficient (µ), half value layer (HVL), and lead equivalence (Pb_eq) that were investigated at varying photon energies (0.001-5 MeV) and filler contents (0-60 wt.%). The results were in good agreement (less than 2% differences) with other available programs (Phy-X/PSD) and Monte Carlo particle transport simulation code, namely PHITS, which showed that the overall high-energy photon shielding abilities of the composites considerably increased with increasing rare-earth oxide contents but reduced with increasing photon energies. In particular, the Gd₂O₃/HDPE composites had the highest µ_m values at photon energies of 0.1, 0.5, and 5 MeV, due to having the highest atomic number (Z). Furthermore, the Pb_eq determination of the composites within the X-ray energy ranges indicated that the 10 mm thick samples with filler contents of 40 wt.% and 50 wt.% had Pb_eq values greater than the minimum requirements for shielding materials used in general diagnostic X-ray rooms and computerized tomography rooms, which required Pb_eq values of at least 1.0 and 1.5 mmPb, respectively. In addition, the comparisons of µ_m, µ, and HVL among the rare-earth oxide/HDPE composites investigated in this work and other lead-free X-ray shielding composites revealed that the materials developed in this work exhibited comparable X-ray shielding properties in comparison with that of the latter, implying great potential to be used as effective X-ray shielding materials in actual applications.

Keywords: Eu2O3; Gd2O3; HDPE; Sm2O3; X-ray; XCOM; gamma; photon; shielding.

Figure 1

µ_m values of (a,b) Sm₂O₃/HDPE, (c,d) Eu₂O₃/HDPE, and (e,f) Gd₂O₃/HDPE composites with filler contents of 0, 20, 40, and 60 wt.%, determined at photon energies of (a,c,e) 0.001–0.2 MeV and (b,d,f) 0.2–5 MeV using XCOM.

Figure 2

µ_m values of Sm₂O₃, Eu₂O₃, Gd₂O₃, and HDPE showing K-edge and L-edge behaviors of Sm, Eu, and Gd at photon energies of (a) 0.001–0.2 MeV and (b) 0.03–0.06 MeV.

Figure 3

µ_m values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites with filler contents varied from 0–60 wt.%, determined at photon energies of (a) 0.1 MeV, (b) 0.5 MeV, (c) 1 MeV, and (d) 5 MeV using XCOM.

Figure 4

µ values of (a,b) Sm₂O₃/HDPE, (c,d) Eu₂O₃/HDPE, and (e,f) Gd₂O₃/HDPE composites with filler contents of 0, 20, 40, and 60 wt.%, determined at photon energies of (a,c,e) 0.001–0.2 MeV and (b,d,f) 0.2–5 MeV using XCOM.

Figure 5

µ values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites using XCOM, with filler contents varied from (a,c,e,g) 0–60 wt.%, and (b,d,f,h) 40–60 wt.%, determined at photon energies of (a,b) 0.1 MeV, (c,d) 0.5 MeV, (e,f) 1 MeV, and (g,h) 5 MeV.

Figure 6

HVL values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites using XCOM, with filler contents varied from (a,c,e,g) 0–60 wt.%, and (b,d,f,h) 40–60 wt.%, determined at photon energies of (a,b) 0.1 MeV, (c,d) 0.5 MeV, (e,f) 1 MeV, and (g,h) 5 MeV.

Figure 7

Comparative µ_m values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites with other common Pb-free HDPE composites (Bi₂O₃/HDPE, WO₃/HDPE, and Fe₂O₃/HDPE) at filler contents of 20, 40, and 60 wt.% and photon energies of (a) 0.1 MeV, (b) 0.5 MeV, (c) 1 MeV, and (d) 5 MeV.

Figure 8

Comparative µ values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites with other common Pb-free HDPE composites (Bi₂O₃/HDPE, WO₃/HDPE, and Fe₂O₃/HDPE) at filler contents of 20, 40, and 60 wt.% and photon energies of (a) 0.1 MeV, (b) 0.5 MeV, (c) 1 MeV, and (d) 5 MeV.

Figure 9

Comparative HVL values of Sm₂O₃/HDPE, Eu₂O₃/HDPE, and Gd₂O₃/HDPE composites with other common Pb-free HDPE composites (Bi₂O₃/HDPE, WO₃/HDPE, and Fe₂O₃/HDPE) at filler contents of 20, 40, and 60 wt.% and photon energies of (a) 0.1 MeV, (b) 0.5 MeV, (c) 1 MeV, and (d) 5 MeV.