Final answer:
The random distribution of photons in the x-ray beam that causes variation in image density or noise is known as quantum mottle, a consequence of the discrete interaction of photons with the detector.
Step-by-step explanation:
The random distribution of photons in the x-ray beam is known as quantum mottle. This phenomenon occurs because photons are distributed randomly when they strike a detector, leading to a variation in the image density or noise. It is a result of the discrete nature of photon interactions with the detector material. In scenarios like Compton scattering, where a beam of monochromatic X-rays strikes a crystal, the X-rays are scattered in all directions by the atoms of the crystal.
As these scattered waves combine through interference, an interference pattern is formed based on the probability that a photon will strike a certain spot. This pattern is indicative of the wave nature of light, aligning with the principles demonstrated in double slit interference experiments.