Radiation shielding performance of natural rubber composites: A Monte Carlo and XCOM-based study

Ionizing radiation, such as X-rays and gamma rays, is widely used in medical, industrial, and nuclear energy applications. However, prolonged exposure can pose serious health risks, depending on the absorbed dose. Effective shielding is therefore essential to ensure safety in radiation-prone environments. Lead is commonly used for its excellent attenuation properties; however, other factors, such as its toxicity, weight, and environmental impact, limit its long-term viability. As a safer alternative, polymer composites incorporating high atomic number fillers offer advantages such as good shielding, reduced toxicity, lightweight structure, mechanical flexibility, and cost-effectiveness. In this study, the radiation shielding performance of a natural rubber matrix filled with different weight proportions (10%, 20%, and 30%) of lead and bismuth oxide fillers is investigated using the PHITS simulation code. The simulation was performed for 150 keV gamma/X-ray photons, a standard gamma energy of 662 keV (¹³⁷Cs), and an actual ⁶⁰Co gamma source, and the calculated linear attenuation coefficient, mass attenuation coefficient, half-value layer, and tenth-value layer are reported. In this study, NR composites containing 30 wt% Pb exhibited the highest radiation attenuation capability. The mass attenuation coefficients for the same composite were calculated as 0.6942, 0.0904, and 0.0603 cm²/g at photon energies corresponding to 150 keV X-rays/gamma rays, ¹³⁷Cs, and ⁶⁰Co, respectively. Similarly, NR composites with 30 wt% Bi₂O₃ showed comparable attenuation performance, with μ_ρ values of 0.6551, 0.0902, and 0.0605 cm²/g at the same energy levels. These results indicate excellent shielding efficiency at lower photon energies, with attenuation effectiveness decreasing with increasing energy. To verify the simulation approach, the simulated mass attenuation coefficients were compared with standard reference values calculated from the National Institute of Standards and Technology XCOM database. The simulated results showed good agreement, with a relative error of less than 3%, thereby confirming the reliability of the PHITS code for evaluating radiation shielding materials. Overall, the findings support the potential of NR-Pb and NR-Bi₂O₃ composites as effective and safer alternatives to conventional lead shielding materials.