Evaluating the impact of layer arrangement in shielding against solar particle events during deep space missions: a Monte Carlo study

This study explores the effectiveness of multi-purpose shelters using materials such as water (W), compacted waste, and polyester composites (C) containing lithium-boron compounds for shielding against solar particle events (SPEs). Using Geant4 Monte Carlo simulations, the research evaluated different layer arrangements (C-W, W-C, W-C-W) to mitigate radiation doses from the two distinct February 1956 and October 1989 SPEs. Results showed that placing the composite layer on the exterior (C-W configuration) minimized secondary neutron production, achieving equivalent dose reductions of 82.9%-83.1% for protons and 72 3%-73.1% for neutrons in the October 1989 SPE, and 55 9%-56.5% and 33 2%-35.7% in the February 1956 SPE, respectively. Water outperformed other materials in the reduction of total equivalent dose in the phantom and remains the most practical choice due to the shelter's mass constraints and the ready availability. Using LiCO3-loaded composite instead of B4C-loaded composite slightly enhances the shielding performance up to 1.71%. By evaluating secondary particle fluences, particularly neutrons, in the proposed shelter under different layer arrangements and SPE conditions, the configuration-dependent equivalent dose differences were demonstrated. This study reveals how shielding performance can be optimized based on both material type and the energy spectrum of SPEs. Additionally, this study accounts for real-world volume constraints, offering practical guidance for spacecraft-compatible shield design.