TWO PEAKS. “The nonshifted peak shown in (Figure 1) is due to photon collisions with tightly bound inner electrons in the target material.”
https://opentextbc.ca/universityphysicsv3openstax/chapter/the-compton-effect/#:~:text=The%20Compton%20effect%20is%20the,wavelength%20of%20the%20incident%20radiation