Solution

Gamma rays are classically produced by the decay of atomic nuclei as they transition from a high energy state to a lower state known as gamma decay, but may also be produced by other processes. Paul Villard, a French chemist and physicist, discovered gamma radiation in $$1900$$, while studying radiation emitted from radium. Villard's radiation was named "gamma rays" by Ernest Rutherford in $$1903$$.
Hence, the rays or waves produced by the changes in the nucleus of an atom is Gamma rays.