How does gamma decay change the energy of a nucleus without changing its chemical element?

In gamma decay, an unstable atomic nucleus dissipates excess energy to reach a more stable, lower energy level without changing its identity as a chemical element.1

This process occurs because the nucleus is in an "excited state," often as a result of previous alpha decay or beta decay. To reach its ground state, the nucleus releases this excess energy in the form of gamma rays—photons that possess no rest mass or electric charge. Because gamma rays carry away only energy and do not alter the number of protons or neutrons within the nucleus, the atomic number and mass number remain unchanged, meaning the element remains the same.1234

In addition to gamma emission, an excited nucleus may transition to a lower energy state through internal conversion, where energy is transferred to an orbital electron, or through internal pair production, where the energy is converted into an electron-positron pair.1