Re: Can PROTON or NEUTRON absorbs or emits photon ?

Dear Raja, thanks for posing that question.

Yes, protons and electrons can emit and also absorb photons. In fact, all particles with an electric charge can absorb and emit photons. Neutrons don't have charge, therefore they can't. But in fact neutrons consist of three quarks (as do protons). Quarks are charged, so they can emit and absorb photons.

If an atom either emits or absorbs a photon, it means that either one of the protons in the nucleus (or to be more exact, one of the quarks in the nucleus) or one of its electrons in the atomic shell has emitted or absorbed that photon.

Let us consider the electron first: An electron in an atom moves in certain orbits with defined energies. If the electron jumps to an orbit with lower energy, the energy difference is emitted as a photon of that specific energy. On the other hand, if the electron absorbs a photon, the energy of the photon must be equal to the energy difference between the orbit of the electron and some higher energetic orbit (otherwise the photon cannot be absorbed) and the electron jumps into that orbit with higher energy. If the energy of the photon is larger than the energy difference to any orbit, the electron will be hit out of the atom. The atom will be ionized.

Let us consider the nucleus of an atom: As the electrons, the protons and neutrons in the nucleus have certain energy levels (orbits, you may call them). The proton may now absorb photons whose energy equals the energy difference between two levels of the proton. The proton absorbs that photon and jumps into the higher energy level. If the energy of the photon is very high (e.g. x-rays or gamma radiation), the particle that absorbs the photon may be pushed out of the nucleus, resp. the atom; or the atom may split into various parts. It might also emit alpha radiation as a consequence.
If the proton jumps into a lower energy level, it emits a photon whose energy corresponds to the energy difference of the levels.

I hope this helps. Best regards,
Michael