Final answer:
The phenomenon where the radiation intensity is greater on the cathode side of the x-ray field than on the anode side is known as the heel effect or anode heel effect. This happens due to the geometry of the angled anode surface in the x-ray tube, affecting radiation absorption.
Step-by-step explanation:
An unfortunate consequence of the line focus principle in x-ray imaging is that the radiation intensity on the cathode side of the x-ray field is greater than that on the anode side. This effect is known as the heel effect or anode heel effect. In x-ray tubes, electrons are emitted from the cathode and accelerated towards the anode. Due to the geometry of the angled anode surface, x-rays produced closer to the cathode side have a lower chance of being absorbed within the anode material than those produced near the anode edge. Thus, the intensity of radiation is greater on the cathode side of the field. The production of x-rays involves two distinct processes: the production of bremsstrahlung radiation when high-speed electrons are decelerated in the anode material, and the production of characteristic x-rays which result from atomic excitations unique to the anode material. The latter contributes to the discrete lines observed in the x-ray spectrum, which are indicative of the anode's atomic structure.