Final answer:
Option 3: The Compton effect refers to the scattering of a photon by an electron, which results in the photon having reduced energy and momentum.
Step-by-step explanation:
The phenomenon referred to in the question is known as the Compton effect. It is observed when X-rays scatter off materials, leading to a change in their wavelength due to energy transfer from the X-ray photons to the electrons they interact with. As a result of this scattering, the scattered photon has reduced energy and momentum. While the Compton effect is significant in X-ray imaging, it is not the correct term for the reduction in resolution due to higher tube currents.
The Compton effect becomes increasingly significant as the X-ray energy increases and is crucial for understanding the attenuation of X-rays during imaging procedures. This effect also confirms that photons have momentum, as proven by studying the reduction in both energy and momentum of scattered photons. The reduction in resolution often seen with the use of higher tube currents in a single focus tube is actually not correctly described as the Compton effect; none of the options provided in the question (scatter radiation, quantum mottle, Compton effect, or thermal noise) accurately describes the phenomenon of resolution reduction due to higher tube currents.