Structural modifications of boron carbide irradiated by swift heavy ions

ABSTRACT As a result of its high capacity to absorb neutrons, boron carbide (B4C) is a ceramic widely used in control rods of nuclear reactors. Its behavior under irradiation is of importance especially in order to predict the lifetime of this material in future (Generation IV) reactors. In that context, we used ion irradiation to create damage in B4C at the laboratory scale. This paper is focused on the effects of high electronic stopping powers (Se) on the boron carbide structure modifications. Sintered B4C samples were prepared by spark plasma sintering. They were irradiated at room temperature, at the TANDEM accelerator facility at Orsay, with swift heavy ions (between 0.5 and 3 MeV•u−1) corresponding to Se values in the 4.1 to 15.4 keV•nm−1 range at the sample surface. The structural modifications were followed by Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. In order to investigate the structural changes as a function of depth, Raman mapping was performed on cross-section of the irradiated samples along the path of the incident ions. For the highest Se values, damage results in the creation of large hillocks at the surface of the samples along with the amorphization of the bulk. These results are explained, in the frame of the inelastic thermal spike model, by local melting in latent tracks that are created only when irradiations are performed above a Se threshold evaluated at around 9 keV nm−1.