Design and optimization of lead-free composite shielding for 40-200 keV medical X-rays

Conventional X-ray shielding largely relies on lead (Pb) or lead-based materials; however, their high weight, limited flexibility, and toxicity raise concerns for modern medical and industrial applications. In addition, Pb-based shielding is not optimized for attenuation across the full diagnostic X-ray energy range, particularly below 100 keV. Consequently, recent research has focused on developing lead-free, non-toxic shielding materials with improved performance and reduced weight, including composites based on tungsten (W), bismuth (Bi), and lanthanum (La). This study investigates lead-free multi-element composites optimized for wide-spectrum (40-200 keV) medical X-ray shielding by integrating rare-earth elements such as samarium (Sm), erbium (Er), and europium (Eu), into non-toxic heavy-metal matrices. Monte Carlo simulations were employed to calculate linear and mass attenuation coefficients of candidate elements (W, Ta, Bi, La, Sm, Er, Eu) and their composites. Promising formulations were evaluated in terms of shielding effectiveness, equivalent dose reduction [H∗(10)], weight efficiency, and material cost. The results indicate that W and Ta exhibit superior attenuation at higher photon energies but reduced effectiveness below approximately 60 keV. The incorporation of rare-earth elements significantly enhances low-energy attenuation when blended with W-based matrices, while Bi contributes to improved mid-to-high energy performance. Among the evaluated formulations, W-rare-earth and W-Bi (70% W and 30% Bi) composites demonstrate balanced attenuation across the diagnostic energy range and reduce H∗(10) more effectively than Pb, while offering advantages in weight or cost depending on composition. These findings demonstrate that optimized tungsten-based, lead-free composites complemented by rare-earth elements can outperform conventional Pb shielding within targeted energy ranges, providing a theoretical framework for designing lightweight, non-toxic radiation shielding materials for medical and industrial applications.