My knowledge in this area is very limited. Let's suppose we are cranking out more and more energetic gamma rays, as in we try to go far beyond one million electronvolts.

What happens when it interacts with an atom? I assume it's going to interact with the electron, but what about the protons and neutrons? I've seen the ionizing effects, but can high enough energies do something to the protons and neutrons themselves? With enough electronvolts, could it have effects on the atomic core, such as ripping it apart? Does it break a nucleon into quarks?

I thought that a gamma ray would strip electrons away, and not raise the temperature of the component(s) it hits.

This topic comes about because a friend of mine was telling me how a powerful enough gamma ray would turn a rock in space into glowing plasma. I said I don't know if this would happen, and a (friendly) argument ensued. He started talking about gamma ray bursts from stars doing things, but the discussion went over my head because I am not a trained physicist.

After the discussion, I went online looking for the answer and two things arose: First, Google's results were very poor (there was some stuff talked about the Compton Effect, Photoelectric effect, and electron-positron pair production but it never helped me answer my question), and second, I want to understand the physics behind what would happen here. It made me wonder "what does happen if higher and higher energies are used?"


2 Answers 2


A 9-MeV gamma photon can knock a neutron out of a tungsten nucleus. This neutron is called a photoneutron and I have had to design shielding to handle them when designing high-energy X-ray machines for scanning cargo containers. The process is known as photodisintegration more generally.


Lower energy gamma rays interact mostly with the electrons that surround the nucleus and with the electric field of the nucleus itself. The main form of interaction involves the gamma ray striking and bouncing off one of the electrons outside the nucleus. The more densely you pack together the electrons, the more likely a gamma ray will scatter off one. For this reason, atoms with the largest nuclei (lead, uranium, etc.) are most effective at shielding against gamma rays.

Higher energy gamma rays can make it through the electron cloud and strike the nucleus itself. Note that the protons and neutrons in a nucleus occupy discrete energy levels, and if the energy of the incoming gamma ray is a match to one of those energy levels, a nucleon in that energy level can be either kicked up into a higher energy level (from which it then decays) or knocked right out of the nucleus. For the right nucleus and gamma ray, it is also possible for the gamma ray to fission the nucleus.


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