1. The problem statement, all variables and given/known data Gamma rays of energy 1.02 MeV are scattered from electrons that are initially at rest. If the scattering is symmetric, that is, if θ = ϕ in Fig. 1, find i. the scattering angle θ ii. the energy of the scattered photons. 2. Relevant equations λ' - λ = (h/mc)[1 - cos(θ)] 3. The attempt at a solution I'm not entirely sure where to go on this one. The first thing I did was take the energy of the gamma ray and find its wavelength via the relationship: E = hf E = hc/λ λ = hc/E λ = 1.217E-22 m I've been scouring every resource I can but I cannot find a relationship for scattering angle dealing only with energy. I am certain that the fact that the scattering is symmetric has something to do with it, but I do not know how to apply that fact. Does anyone know how I can approach this problem?