We have used positron annihilation spectroscopy to study the introduction and recovery of point defects in electron-irradiated n-type ZnO. The irradiation (E{sub el}=2 MeV, fluence 6x10{sup 17}cm{sup -2}) was performed at room temperature, and isochronal annealings were performed from 300 to 600 K. In addition, monochromatic illumination of the samples during low-temperature positron measurements was used in identification of the defects. We distinguish two kinds of vacancy defects: the Zn and O vacancies, which are either isolated or belong to defect complexes. In addition, we observe negative-ion-type defects, which are attributed to O interstitials or O antisites. The Zn vacancies and negative ions act as compensating centers and are introduced at a concentration [V{sub Zn}]{approx_equal}c{sub ion}{approx_equal}2x10{sup 16}cm{sup -3}. The O vacancies are introduced at a 10-times-larger concentration [V{sub O}]{approx_equal}3x10{sup 17}cm{sup -3} and are suggested to be isolated. The O vacancies are observed as neutral at low temperatures, and an ionization energy of 100 meV could be fitted with the help of temperature-dependent Hall data, thus indicating their deep donor character. The irradiation-induced defects fully recover after the annealing at 600 K, in good agreement with electrical measurements. The Zn vacancies recover in two separate stages, indicating that the Zn vacanciesmore » are parts of two different defect complexes. The O vacancies anneal simultaneously with the Zn vacancies at the later stage, with an activation energy of E{sub V,O}{sup m}=1.8{+-}0.1 eV. The negative ions anneal out between the two annealing stages of the vacancies.« less