Existence of Dynamic Functional Connectivity Variations of Brain Networks in Psychogenic Non-Epileptic Seizures Through Resting-state Functional Magnetic Resonance Imaging.

BACKGROUND

Long-duration space missions expose astronauts to hazardous radiation, including Galactic Cosmic Rays (GCRs) and Solar Particle Events (SPEs), producing secondary neutrons that penetrate spacecraft. Traditional aluminum shielding is inefficient and generates secondary particles, necessitating lightweight, multifunctional composites for effective radiation protection.

OBJECTIVE

This study aims to optimize neutron shielding composites using Cadmium (Cd) and Lithium (Li) compounds within an Unsaturated Polyester Resin (UPS) matrix, targeting maximum attenuation of fast and thermal neutrons, validated through both experimental measurements and Geant4 simulations, while assessing mechanical properties for spacecraft use.

MATERIAL AND

METHODS

This study combined experimental and simulation methods. Seven composites, each with 90 weight percentage (wt%) UPS and 10 wt% Cd and Li compounds (LiOH or LiBr), were synthesized. Neutron attenuation was tested using a 239Pu-Be source, measuring thermal (<0.5 eV) and fast (>0.5 MeV) neutron fluxes. Mechanical properties were evaluated via nanoindentation, with Geant4 Monte Carlo simulations providing comparative data.

RESULTS

The Cd₅_LiOH₅ composite achieved 92.35% thermal neutron attenuation (99.65% simulated) at 25 mm, while Cd₂.₅_LiOH₇.₅ exhibited 36.2% fast neutron attenuation (38.7% simulated) at 25 mm. Simulations demonstrated strong agreement with experiments across most composites, with relative differences generally below 10%, except for thin samples or materials with heterogeneous filler distribution. The Cd₂.₅_LiBr₇.₅ composite showed superior hardness (0.10 GPa) and modulus (0.7 GPa).

CONCLUSION

UPS-based composites with Cd and Li offer effective neutron shielding and enhanced mechanical properties, validated by Geant4 simulations. These materials are promising for radiation protection in deep space missions.