Gamma rays are high-energy photons with very short wavelengths. They are typically emitted during nuclear processes because such processes involve changes in the nucleus of an atom, which has a much higher energy scale compared to electron transitions within the electron cloud surrounding the nucleus.
In an atom, electrons occupy discrete energy levels or orbitals. When an electron transitions from a higher energy level to a lower one, it releases energy in the form of a photon. These emitted photons can have various wavelengths, ranging from radio waves to X-rays, depending on the energy difference between the initial and final electron states.
The energy differences associated with electron transitions are typically in the range of electron volts (eV) or a few kiloelectron volts (keV) at most. This corresponds to the energy of photons in the X-ray regime or below. Gamma rays, on the other hand, have much higher energies, typically in the range of kiloelectron volts to millions of electron volts (keV to MeV) or even higher.
To emit gamma rays, nuclear processes involving changes in the nucleus itself are required. These processes include nuclear reactions such as radioactive decay, nuclear fission, or nuclear fusion. In these processes, the nucleus undergoes changes such as the emission of particles (alpha particles, beta particles) or the rearrangement of nucleons (protons and neutrons). These nuclear changes involve much larger energy differences compared to electron transitions, resulting in the emission of gamma rays.
In summary, gamma rays are emitted in nuclear processes because those processes involve changes in the nucleus, which has significantly higher energy scales compared to electron transitions within the electron cloud.