What is gamma decay? Explain with a proper example.

(N/A) The process of $\gamma$-ray (photon) emission during the disintegration of a radioactive nucleus is called gamma decay.
$\gamma$-rays emitted in gamma decay have no mass and no charge,so the mass number and atomic number of the daughter nucleus do not change. Its general equation is as follows:
${ }_{Z}^{A} X^* \rightarrow{ }_{Z}^{A} X+{ }_{0} \gamma^{0}$
where ${ }_{Z}^{A} X^*$ represents the nucleus in an excited state and ${ }_{Z}^{A} X$ represents the nucleus in the ground state.
Atomic energy level spacings are of the order of $eV$,while the differences in nuclear energy levels are of the order of $MeV$.
When a nucleus in an excited state spontaneously decays to its ground state (or to a lower energy state),a photon is emitted with energy equal to the difference in the two energy levels of the nucleus. This is called gamma decay.
Example: Cobalt-$60$ $(^{60}_{27}Co)$ undergoes $\beta^-$ decay to form an excited state of Nickel-$60$ $(^{60}_{28}Ni^*)$. This excited nucleus then returns to the ground state by emitting two successive gamma photons with energies $1.17 \ MeV$ and $1.33 \ MeV$.