What type of scatter occurs at energy levels throughout the diagnostic X-ray range of 40 to 125 kVp?

Compton scatter is the correct answer because it is the dominant type of scatter radiation that occurs in the energy range of 40 to 125 kVp, which is commonly used in diagnostic radiology. In this scenario, as X-ray photons collide with matter, particularly electrons in the atoms of body tissues, they lose energy and change direction. This interaction is significant because it leads to both image degradation and potential radiation dose to the patient.

The photoelectric effect, while also an important interaction in the diagnostic range, primarily involves complete absorption of the X-ray photon by an atom, rather than scattering. It typically occurs at lower energy levels compared to Compton scattering and is more significant in areas with high atomic number tissues.

Airborne contamination and fomites are unrelated to the interaction of X-ray photons with matter; instead, they refer to biological contamination and surfaces that can harbor pathogens, respectively. These options do not pertain to the topic of X-ray scatter physics. Thus, Compton scatter is recognized as the primary mechanism of scatter radiation in the specified energy range used in diagnostic imaging.