Final answer:
The ratio of absorbed x-ray photons depends on factors such as material density, thickness, and x-ray energy.
Step-by-step explanation:
The ratio of x-ray photons absorbed by the phosphor crystals to the x-ray photons incident upon the phosphor layer depends on various factors, including the material's density, thickness, and the energy of the x-rays. As the x-ray energy increases, the Compton effect becomes more important in the attenuation of the x-rays. Low-energy x-rays provide better contrast but are more absorbed by thicker materials.