How does the energy of a scattered photon compare to the incoming primary beam photon?

When a photon interacts with matter, such as during the process of scattering, it can transfer some of its energy to the electrons in the material. As a result, the scattered photon will typically have less energy than the incoming primary beam photon. This phenomenon occurs because some of the photon's energy is absorbed during the interaction.

In Compton scattering, for instance, the incoming photon collides with a loosely bound outer shell electron, which results in the electron being ejected from the atom and the photon being scattered at a different angle. The conservation of energy dictates that the total energy before the interaction (the energy of the incoming photon) equals the total energy after (the energy of the scattered photon plus the kinetic energy of the ejected electron). Since the scattered photon has lost some energy to the electron, its energy will be less than that of the primary beam photon.

Understanding this concept is crucial for interpreting the results of X-ray imaging, as variations in photon energy can affect the quality of the image and the information gathered from the scan.