Understanding neutron absorption and scattering in a polymer composite material

摘要

The neutron transmission and scattering from a composite of 25% weight boron carbide and nylon (Addbor N25) has been measured as a function of wavelength. Samples with different thicknesses on a support were prepared by an additive manufacturing (or 3D-printing) process, fused filament fabrication. Data are provided that demonstrate that the material is effective to absorb thermal and cold neutrons, and this information will permit calculation of performance as a shielding material. The results show that the attenuation by absorption can be predicted adequately using a simple dependence of the absorption cross-section on the reciprocal of velocity. The scattering at small values of the momentum transfer, Q, is dominated by a Porod law variation, 1/Q~4 that is consistent with particles dispersed in a hydrogenous polymer matrix of low scattering length density. At large momentum transfer, Q＞0.06 A~(-1), incoherent inelastic scattering is predominant, and this is seen to increase significantly with the wavelength of the incident neutrons. The new results are described in the context of various possibilities to fabricate shielding or absorbers in complex shapes, to replace the toxic alternative of cadmium and to exploit an engineering plastic as the basis of a neutron absorbing composite.