Chapter 10 - Neutron radiation shielding composites for deep space exploration: An introduction

Abstract

Any space exploration outside the protective shield of the Earth's magnetic field is a deep space mission. Thus, for example, a manned mission to the Moon or Mars as well as the permanence in a base on Moon or Mars is a deep space mission. The key problem in deep space missions is the crew's exposure to solar wind, solar particle events (SPE), and galactic cosmic rays. Thus, crew protection should be ensured not only from primary particles but also from secondary particles derived by the interaction of primary particles with the surface of the spacecraft or the “roofs” of the bases built on the Moon or on Mars. A particularly dangerous component of the space radiation is represented by the heavier nuclei component of cosmic rays accelerated to relativistic energies (HZE particles). The HZE particles create a series of secondary particles when they interact with target materials, ranging from nuclear fragments to protons and neutrons. Thus, the radiation shields for deep space mission should be designed by a hydrogen-rich polymeric matrix (which was shown to be the best material to slowdown the secondary particles), filled with neutron-adsorbing filler like, for example, boron or boron compounds to cut down the neutron component of the secondary radiation. Moreover, a polymer matrix based on a castable polyurethane (PUR) with soft segment made by polytetrahydrofuran polyol (or polytetramethylene ether glycol=PTMEG) derived from renewable sources was used for the preparation of the neutron shields. The PUR polymer matrix was filled with 20% amorphous boron, 20% hexagonal boron nitride (h-BN), or 20% boron carbide (B4C). The PUR composites were cast in foils of 2mm thickness and tested as thermal neutron shields against reference unfilled PUR foils or PUR filled with 20% milled graphite. The method of sandwiched copper wire activation till saturation was used for the determination of the neutron shielding effectiveness. Both the linear and massic attenuation coefficients of the PUR composites were determined. Unfilled PUR and PUR composites were studied with FT-IR spectroscopy and DSC before and after neutron processing with a total dose of 1.5×1013cm−2. No significant changes were detected in the FT-IR spectra or in the DSC thermal behavior confirming the excellent radiation resistance of PUR and its suitability as polymer matrix for neutrons and more in general radiation shielding.