# Can a $\gamma$-ray photon give some of his energy to an atom and accelerate it?

I know gamma-ray photon can only give its momentum energy to the electrons of an atom.

My question is: Can a photon give some of its momentum to the atom (including its nucleus) to give it heat or speed?

If yes, can you tell me how much energy can it give?

It is not very clear to me if you are asking about energy or momentum. You should also ask about a specific interaction process as there are many, this is required especially to answer your last, quantitative, question.

However, generally speaking, a $\gamma$ photon cannot give some of its energy to anything else: it is all or nothing. Even in the Compton scattering, in which you get a less energetic photon, the initial photon is destroyed. The momentum must be conserved as well, so yes: when a photon hits another particle this is accelerated, you can even generate some measurable pressure with a very intense radiation!

• can the photon accelerate every particle with mass on the atom? if yes its possible for the photon to accelerate the entire atom (for example hydrogen atom)? Sep 7 '14 at 10:14
• @Qu4terni0n Momentum conservation is a physical rule. It does not depend on the mass. When the photon interacts its momentum is transferred, this is not just a possibility, but how things work. Of course if you shoot a highly energetic gamma to a particle in a complex and delicate structure as an atom, most of the times that particle is ejected from the atom, without accelerating all of it. Sep 7 '14 at 10:48

Not merely can it transfer its momentum as well as its energy when it interacts, but it must.

If the target atom is in a fluid context (liquid, gas, plasma), then that energy and momentum must end up in the target or some other reaction products(s).

In a solid context the Mössbauer effect can be an issue, allowing the transfer of that momentum to a much more massive collection of mass resulting in lower recoil.

It is also worth noting that this requirement to transfer both energy and momentum is the reason a photon can not be absorbed on a isolated point target in free-space: $$\gamma + e \to e \tag{forbidden} \,,$$ though the same reaction is possible in the field of a massive partner $$\gamma + e + A \to e + A \tag{allowed}$$ or if the target is a compound object with excited states $$\gamma + A \to A^* \tag{allowed} \,.$$