Monte Carlo analysis of neutron shield design optimization with iron-polyethylene system

Theoretical analysis of experimental benchmarks on shield design optimization is carried out using Monte Carlo code, MCNP. This preliminary investigation not only aims at the evaluation of the shielding effectiveness of the materials for neutrons but also helps to validate our methodology in using MCNP code for such kind of studies. Validation of computational results against experimental measurements strengthens the confidence in usage of the code and cross-section data. Dose rate attenuation profile (dose rate as a function of thickness) of a 252Cf neutron source has been analyzed for different materials like polyethylene, water, graphite, paraffin, stainless steel (SUS 304) and iron separately and for the combination of iron-polyethylene system. Further, the impact of using new neutron flux to dose conversion factors, ICRP-74 on calculated neutron dose rates is also studied. As expected, materials polyethylene and paraffin with high hydrogen content are observed to have better dose rate attenuation profile for 252Cf neutron source compared to all other materials and that too paraffin to greater extent. The good agreement observed been MCNP results and the available experimental data validates our computational methodology. The study also demonstrates the effect of using a combination of shield materials in shield design optimization. (author)