Optical Properties of Tin Oxide Thin Films Before and After Thermal and Fast Neutron Irradiation

This study investigates the effect of thermal and fast neutrons on the optical properties of a tin oxide (SnO₂) thin film, which was prepared by thermal evaporation in a vacuum. The thickness of the film ranged from 90 to 110 nm. The samples were irradiated using an americium–beryllium (Am–Be) neutron source, providing thermal neutrons (≈0.025 eV) and fast neutrons (≈5 MeV), with a flux of 3x10⁵ n/cm²s. The optical properties of the thin film were examined before and after the irradiation. Before irradiation, the energy gap (E₆) of the film was 3.307 eV. After one week of irradiation with thermal neutrons, the energy gap decreased to 3.259 eV, and after two weeks, it further decreased to 3.217 eV. For fast neutrons, however, the results indicated that the energy gap remained unchanged even after 14 weeks of irradiation. Regarding the transmittance, it was observed to increase with longer irradiation periods by thermal neutrons in the wavelength range from 190 to 686 nm. In comparison, no change was observed for wavelengths longer than 686 nm. For fast neutrons, no significant changes were observed in transmittance, likely because the cross-section of interaction between tin and fast neutrons is much smaller compared to the interaction between tin and thermal neutrons. Absorbance showed an inverse trend relative to transmittance and remained unaffected by fast-neutron irradiation. The behaviour of absorbance was similar to that of reflectivity before and after irradiation. As for the extinction coefficient (Kₒ), it was found to increase with thermal neutron irradiation, while fast neutrons did not affect it.