What happens to the x-ray beam as it travels away from the cathode?

As the x-ray beam travels away from the cathode, it experiences a decrease in intensity. This phenomenon occurs primarily due to the inverse square law, which states that the intensity of radiation (including x-rays) is inversely proportional to the square of the distance from the source. As the x-ray photons move further away from the cathode, they spread out over a larger area, resulting in a lower density of photons at any given point. Consequently, the intensity diminishes as the distance increases, which is essential to understand in both diagnostic imaging and radiation safety.

Other options do not accurately describe the behavior of an x-ray beam. The beam does not become uniform as it travels; instead, variations can occur based on factors such as scatter and absorption. Complete absorption does not happen, as x-rays can penetrate materials, and while the energy of individual x-ray photons remains constant as they spread out, the intensity (or the number of photons per unit area) decreases with distance. Thus, the intensity decrease is a fundamental characteristic of how x-ray beams propagate through space.