Advanced co-dispersed multi-phase nanocomposites for nuclear engineering: Mixed gamma attenuation, computational fast neutron moderation, and Monte Carlo simulation validation.

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 (HVLn) 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.