# How is the energy spectrum of a gamma ray in a material?

I'm trying to solve the following problem for a course in radiation physics.

A thin ray of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity and the energy of the photons after having travelled a distance d?

I know that the intensity decreases as a negative exponential, but I was wondering how to calculate the change in the energy.

The only process relevant for this I think that must be incoherent scattering (because in both pair production and photoelectric effect the photon is absorbed) so I thought about calculating the energy transferred by the photons and subtracting it from the initial energy.

I also thought about calculating the energy transfer coefficient but I think that I lack information to do it this way.

How can I calculate the energy after having travelled a distance d?