The annealing of γ-irradiation damage in crystalline barium nitrate at different temperatures in the range 370-430°C is a combination of a first-order process affecting a small portion of the fragments and a second-order process, with a higher energy of activation, governing the behaviour of the remainder ∼73%. The annealing data have been analysed on the models for simple interstitial vacancy recombination and also as a combination of a first-order and second-order process with an energy of activation of 10.9 and 24.0 kcal mole−1respectively. It is considered that the first-order process is the combination of close-correlated pairs of O and NO2fragments and the second order process involves the single reaction of random recombination of the fragments throughout the crystal.