Three types of nuclear change are fission, fusion, and radioactive decay. Nuclear change happens in nuclear reactions that change the number of protons in the reaction products.
Nuclear change is not the same as chemical change because nuclear change transforms the nucleus of atoms. In nuclear fission reactions, an atom heavier than iron splits into two or more smaller atoms. One example is uranium-235 splitting into barium-137, krypton-97 and some extra neutrons. Fission is an exothermic reaction, meaning it produces thermal energy. This process often produces free neutrons and photons in the form of gamma rays, and releases a very large amount of energy even by the energetic standards of radioactive decay.
Nuclear fusion is the opposite of fission. A fusion reaction consists of two or more atoms smaller than iron that combine to make larger atoms. Fusion is what happens in the sun when two atoms of hydrogen fuse together into helium. It is also an exothermic reaction.
There are three types of nuclear decay: alpha, beta and gamma. In alpha decay, the atomic number of the radioactive element is reduced by two and an alpha particle is emitted. In beta decay, the atomic number of the radioactive element increases by one and releases an electron and an antineutrino. Gamma decay does not change the identity but the shape of the nucleus.