Understanding Impinging Particles in Physics

In physics, "impinging" refers to a situation where one object or particle collides with another, often resulting in a transfer of momentum or energy between the two objects.

In the context of your question, the impinging particle is the neutron that collides with the atomic nucleus, transferring some of its momentum and energy to the nucleus. This collision can cause the nucleus to become excited or ionized, leading to the emission of gamma rays.

The impinging particle can also be a photon, which is a type of particles that carries electromagnetic radiation such as light. When a photon collides with an atom or molecule, it can transfer its energy to the atom or molecule, causing it to become excited or ionized. This process is known as photoionization.