Effects of MCNP Model Resolution on Predicting Water Equivalent Thickness of Nanocomposite Materials in High-Energy Proton Fields

Manned missions beyond low-Earth orbit present tremendous, multifaceted radiological challenges. The deep space radiation environment contains high-energy protons and heavy ions, which are not sufficiently shielded by the aluminum alloys that have historically been used in spacecraft. To address these shielding concerns, polymer-based nanocomposites have been proposed. Radiation transport simulations of these nanocomposite materials could reduce the lead time for materials development, however, the level of detail necessary in a model to accurately predict the water equivalent thickness (WET) of a nanoscale material is unknown. In this work, MCNP6.2 is used to simulate the transport of high-energy protons through several models, varying three parameters (experimental setup geometry, particle tracking physics, and nanocomposite geometry), and the results are compared to available experimental measurements. The MCNP results indicate that the inclusion of δ-ray production in the particle tracking physics alters both the magnitude of the Bragg peak and the simulated proton range. Altering the other two parameters showed less than a 1% change in proton range, which is within the statistical error. The simulated WET of the nanocomposite, modeled as a bulk homogeneous material, was comparable to the published experimental results, with a WET of 44.70 mm in a 105 MeV proton beam and 22.61 mm in a 63MeV proton beam, and computed/experimental ratios of 0.9572 and 1.025, respectively