Nuclei in a radium-226 radioactive source emit photons whose energy is 186 keV. These photons are scattered

Question:

Nuclei in a radium-226 radioactive source emit photons whose energy is 186 keV. These photons are scattered by the electrons in a metal target; a detector measures the energy of the scattered photons as a function of the angle θ through which they are scattered. Find the energy of the γ -rays scattered through θ = 90.0 ° and 180.0°.