Final answer:
Beam hardening refers to the increase in the average energy of the photons that reach the detectors, occurring when lower energy photons are absorbed more, leaving higher energy photons in the beam.
Step-by-step explanation:
Beam hardening refers to c. the increase in the average energy of the photons that reach the detectors. This phenomenon occurs when a polychromatic beam, such as an X-ray, passes through a material and experiences absorption. Lower energy photons are more likely to be absorbed, leaving the higher energy photons to pass through, which results in an increased average photon energy at the detector. This can affect the quality of an image, such as in a CT scan, by creating artifacts, as detectors register this harder beam. Understanding beam hardening is important in fields like medical imaging, where careful calibration and correction strategies are employed to minimize its impact.