Neutron irradiation effect on amorphous porous silica

Porous silica is widely used as antireflection films in inertial confinement fusion facilities and be irradiated by high fluence neutron. To date, the neutron irradiation effect of amorphous porous silica is still unclear. In this paper, we give a comprehensive insight into neutron irradiation effect on microstructure, mechanical, and optical properties of porous silica under 14 MeV neutron irradiation by using molecular dynamics and density-functional theory-based methods. We find that, for microstructure, neutron irradiation elongates Si-O bond distance, obviously reduces the max value of Si-O-Si bond angle, coordination number distribution, and increases Si3+ and non-bridging oxygen defects. The bulk modulus, shear modulus, and Young's modulus are all obviously reduced due to neutron irradiation, but Poisson's ratio changes relatively small. The light transmittance is reduced, and the optical absorption coefficient is increased after neutron irradiation, especially in the photon energy range of 3-4 eV, which is detrimental to the resistance of laser-induced damage. Moreover, we find that neutron irradiation has more influence on high-porosity porous silica than low-porosity porous silica, which is mainly due to the higher defect percentage in high porosity. Present work is expected to be valuable in the study of degradation mechanism of nuclear material under neutron radiation.