The irradiation effects and the increase of neutron yield from the deuterium‐deuterium reaction in tantalum has been studied at a bombarding energy of 350 kev and a target current 100 &mgr;a. Saturation (the neutron yield becomes a steady maximum) is reached in a new target, maintained at temperatures below 45°C, after about 2 hours of steady bombardment or on the order of 1 coulomb of deuterons per square centimeter. The irradiated targets were annealed at temperatures from 45°C to 770°C. A thermal analysis shows that a prominent exothermic maximum in the annealing spectrum occurs at approximately 612°C. This maximum is associated with an increase in pressure, indicating an abrupt increase in diffusion of deuterium from the target at this temperature. From a study of diffusion of deuterium from the specimen at three temperatures, an activation energy of 0.24 ev is calculated for diffusion of deuterium in tantalum.X‐ray traces were taken of the specimen before and after bombardment and after annealing. These showed an expansion of the lattice together with changes in line intensities indicating a distortion in the lattice structure.