Probing swift heavy ion irradiation damage in Nd-doped zirconolite

Abstract

Synroc minerals have been studied since decades for immobilization of high-level radioactive wastes released from nuclear weapons and nuclear reactors. Among them, the zirconolite, due to its high radiation and aqueous resistance and high waste loading, is considered as a potential candidate for containment purposes. Though irradiation damage effects of swift heavy ions in the material remain a major concern of study, a single phase Nd-doped zirconolite samples prepared through conventional solid-state reaction were irradiated with 120 MeV Au+ ions to study radiation damage effects. Irradiation-induced effects were investigated using ex-situ XRD and micro-Raman spectroscopic techniques. Zirconolite has been observed to undergo amorphization which is confirmed through disappearance of characteristic x-ray diffraction peaks and appearance of broad diffuse scattering bands. Amorphization trend with fluence appeared linear at lower fluences followed by saturation at higher fluences inferring therewith the formation of ion tracks. The ion fluence dependent Raman examination was also found to be in line with the XRD observations. However, the presence of Raman modes, characteristic of zirconolite in the 100–1000 cm−1 region, showed intact behavior of the local structure. To sum up, the 120 MeV heavy Au+ ions developed columnar defects, vacancies and induced micro-strains that lead to the bonds distortion and eventually amorphization of the zirconolite though retaining local ordering.