The fission of a heavy nucleus gives, in general, two smaller nuclei, two or three neutrons, some β-particles and some γ-radiation. It is always true that the nuclei produced

The nuclear fission differs  from  other  nuclear reactions in three respects.(i) the nucleus is deeply divided into two large fission fragments or nuclei of roughly equal mass. The nuclei or fission fragments fly apart at great speed thus posses large kinetic energies that carry off the greater part of the energy released.(ii) The mass decrease is appreciable and hence large energy is released.(iii) Other neutron, called fission neutrons, are emitted in the process. Small amount of energy is released in the form of radiation.