Hey all, im just studying for an upcoming medical imaging exam however im having some trouble understanding a concept: With regards to X-ray beam production, the effective photon energy of a beam is roughly 60-70% of the maximum photon energy (Emax) at a particular Tube voltage in the range of 40-150KV. For example a 100KV tube voltage produces an effective photon energy of approx. 60keV. My questions are: 1) Why does this occur, what is the physics behind the value being roughly 60% of Emax? 2) How is the effective photon energy different to the Average photon energy (the most frequent beam) or is this the same thing? Any help is greatly appreciated!