Rutile single-crystal TiO2were irradiated by 2.5 MeV neutrons from D-D reaction on a neutron generator at Lanzhou University.Positron annihilation lifetime spectra and X-ray diffraction(XRD) patterns of the irradiated samples were compared with those of the virgin.Considering the fact that the threshold displacement energy of titanium atoms is almost two times of that of oxygen atoms

more oxygen vacancies(VO) would be produced than that of titanium vacancies(VTi) under the neutron irradiation.Lifetime results indicated that the irradiated samples had larger electron density of titanium vacancies than the virgin rutile

as a result of increased oxygen vacancies surrounding the Ti vacancy

because of the coulombic repulsion.From the XRD results

distance along the c-axis shrank slightly and the crystallinity became weaker after the neutron irradiation.