Advanced co-dispersed multi-phase nanocomposites for nuclear engineering: Mixed gamma attenuation, computational fast...

This study presents the fabrication and evaluation of a sustainable, lead-free hybrid nanocomposite designed for advanced mixed-field (n/γ) radiation shielding barriers. The composite utilizes post-consumer recycled high-density polyethylene (r-HDPE) as a matrix reinforced with bismuth oxide (α-Bi₂O₃) nanoparticles hosted on two-dimensional Ti₃C₂Tx MXene nanosheet templates. This co-dispersed multi-phase network achieves a synergistic "interlocking" atomic architecture that suppresses heavy metal macro-agglomeration, ensuring excellent microstructural homogeneity. Experimental testing with a High-Purity Germanium (HPGe) spectrometer confirms that the optimized 30 wt% hybrid composite yields an absolute 12% synergistic gain in Radiation Protection Efficiency (RPE = 71.2%) at 0.662 MeV over conventional single-filler blends. Concurrently, the material maintains superior fast neutron moderation capabilities under a²⁵²Cf fission spectrum due to the preserved hydrogen density of the recycled polyolefin matrix, yielding an experimentally validated macroscopic removal cross-section (∑_R) of 0.645 ± 0.009 cm^-1 and a narrow neutron half-value layer (HVL_n) of 1.074 ± 0.015 cm. Thermo-mechanical analysis shows that the interlocking filler framework significantly improves matrix durability, shifting the polymer crystallinity from 55% to 62%, raising the thermal degradation onset threshold from 410^°C to 435^°C, and increasing the tensile strength by 31% to 32.1 ± 1.2 MPa (Young's Modulus of 1.78 GPa). High-fidelity radiation transport modeling using Geant4 and MCNP6 codes reveals a near-perfect alignment (R² > 0.998) with laboratory spectral datasets, validating this digital twin framework as a highly predictive design tool for next-generation, lead-free nuclear safety barriers.