Final answer:
Characteristic x-rays are emitted when an inner-shell electron vacancy is filled, common in heavy elements like tungene. They provide sharp imaging contrasts, especially at lower kVp, and are used to identify elements and visualize internal body structures. Their energy is generally proportional to the square of the atomic number, and their absorption is dependent on the material's density and thickness.
Step-by-step explanation:
The phenomenon where absorbed radiation increases at lower kilovolt peak (kVp), particularly in the inner electron shell, is related to the production of characteristic x-rays. When the kVp is sufficient to knock out an inner-shell electron, such as in heavy elements with a high atomic number, the resulting vacancy is filled by an electron from a higher energy level.
This transition releases a photon of energy corresponding to the difference in energy levels, which is referred to as a characteristic x-ray and depends on the element's atomic number.
Characteristic x-rays are so named because they are characteristic of the element from which they are emitted. These emissions increase as the atomic number squared (Z²), and hence heavier elements with tightly bound inner-shell electrons emit more energetic x-rays.
The absorption of these x-rays is dependent on the density of the material and its thickness, leading to increased contrast in low-energy x-ray imaging, particularly when substances with large atomic numbers, like barium or iodine, are injected into the body.
Characteristic x-rays offer a method to identify elements and visualize structures within the body in medical imaging, providing sharp images and valuable diagnostic information.