1. The problem statement, all variables and given/known data I have a 137Cs source which decays to 137Ba. When the Ba nucleus decays, it gives off a photon which can undergo Compton scattering. 2. Relevant equations 3. The attempt at a solution The spectrum shows something that looks like a saddle on the left (it has two high peaks on either end and dips down in the middle). Then on the right there is a very high, sharp peak. The high peak that shows the full energy of the photons is showing the photons that got absorbed directly by the device. Right? It says 91.1 % of photons have that energy. So the other ~10% must undergo compton scattering, which is the saddle thing. But what causes the high peaks on both sides of it? It has something to do with photons giving up energy to electrons. Can anyone explain, I would like to understand. Thanks!