Final answer:
The hardening of an x-ray beam is affected by a variation in kilovoltage peak (kVp), as this changes the energy of the x-ray photons, influencing their ability to penetrate through materials and the overall image contrast.
Step-by-step explanation:
A variation in kilovoltage peak (kVp) will affect the hardening of an x-ray beam. Increases in kVp raise the energy of the x-ray photons, which decreases the probability of photoelectric absorption and enhances the likelihood of the Compton effect. This effectively increases the beam's penetration, thus 'hardening' it as it's less likely to be absorbed by soft tissues and more capable of passing through denser materials. The density and thickness of tissues are also critical in influencing x-ray photon attenuation. Denser and thicker materials absorb more x-ray photons, creating a darker shadow on the x-ray image. While variations in these factors do not 'harden' the x-ray beam itself, they do affect the overall image quality and contrast due to differential attenuation of the beam as it passes through different types of tissue or materials.