Computational and experimental comparison of boron carbide, gadolinium oxide, samarium oxide, and graphene platelets as additives for a neutron shield

Neutron shielding materials are used in aerospace, space, medical, and nuclear applications and there is a growing need of neutron shielding materials with increased temperature resistance. This is difficult to achieve with the current approach of using borated or lithium enriched polyethylene or polyamide composites because their hydrogen content limits temperature resistance to 200 degrees C. To address this challenge, an elastomer-based neutron shielding material has been developed with a degradation temperature greater than 300 degrees C and a macroscopic neutron cross section better than that of 5% borated polyethylene. By compensating for the low number of hydrogen atoms in this material, compared to polyethylene or polyamides, iron and additives with a high neutron absorption cross section such as gadolinium and samarium are incorporated to achieve the necessary attenuation properties. Graphene platelets were also added to evaluate graphene's ability to mitigate secondary gamma from the neutron absorption by gadolinium and samarium. A computational study was first completed in Monte Carlo N-Particle (MCNP) to benchmark existing materials and compare the loading of the potential additives. The maximum experimental fast neutron cross-sections for each absorber additive were 0.021 cm(-1) in 9% B4C, 0.031 cm(-1) with 27% Gd2O3, and 0.030 cm(-1) with 3% Sm2O3 compared to only 0.023 cm(-1) for 5% borated polyethylene. The sample containing 10% Gd2O3 and 2% B4C attenuated neutrons better than the borated polyethylene with a fast neutron cross section of 0.026 cm(-1) and exhibited the lowest amount of secondary gamma photons of all the material combinations.