I've already learnt alpha and beta emissions but I really don't understand gamma emission. How come an element come to the excited state and is it only the energy which is emitted by the element, which is called "gamma" radiation?!

• Gamma radiation is defined as a particular (very high frequency) portion of the electromagnetic spectrum. As far as an element becoming in an excited nuclear state, if it only emits gamma, its probably because the transition from the excited state is a higher order one (rather than a simple dipole transition), thus it can have a significant half life. Jul 14, 2017 at 2:57

Gamma ray (also called gamma radiation), denoted by the lower-case Greek letter gamma (γ or $$\gamma$$), is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays. Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays.