Monte Carlo Evaluation of the Radiation Shielding Performance of an Epoxy/Vermiculite/LaB₆ Hybrid Composite

In this study, a theoretical hybrid composite containing 30 wt.% epoxy, 25 wt.% vermiculite, and 45 wt.% lanthanum hexaboride (LaB₆) was designed for radiation shielding applications, and its shielding performance was evaluated using the EGSnrc Monte Carlo code system. The density of the proposed composite was calculated as 2.25 g/cm³, and its mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), and lead-equivalent thickness (Pb-Eq) were determined over the photon energy range of 1.0 keV to 3.0 MeV. Furthermore, three-dimensional dose distributions were calculated using the DOSXYZnrc user code to evaluate the dosimetric shielding performance of the composite. The results demonstrated that, despite its low density, the proposed hybrid composite exhibited superior photon attenuation performance compared with vermiculite and ordinary concrete over a broad energy range. Lead-equivalent analyses indicated that the composite thicknesses required to provide shielding equivalent to 0.25 and 0.50 mm Pb varied with photon energy, ranging from approximately 1.3 to 8.0 mm and 2.6 to 16.0 mm, respectively. Dosimetric analyses showed good agreement with the lead-equivalent calculations at photon energies of 120 and 140 keV, whereas at 364 keV the lead-equivalent approach did not accurately represent the actual dose distribution within the phantom, demonstrating that shielding performance at higher photon energies cannot be adequately assessed using conventional attenuation parameters alone. These findings indicate that the proposed Epoxy/Vermiculite/LaB₆ hybrid composite is a promising candidate for the development of lead-free shielding materials, particularly for nuclear medicine applications and for photon energies relevant to diagnostic radiology.