Which X-ray photons are most likely to be absorbed by the skin?

• A. High-energy photons
• B. Low-energy photons
• C. Photons of medium energy
• D. Photons with high frequency

Answer: (B)

The question tests how photon energy affects where X-ray energy is deposited in tissue. Low-energy photons are readily absorbed by superficial tissues like the skin, mainly through the photoelectric interaction, so they deposit most of their energy right at the surface. As energy increases, photons become more penetrating and are less likely to be absorbed in the skin, passing through or depositing energy deeper in the body. This is why dental beams are filtered to remove the low-energy portion: to reduce skin dose and keep the beam energy high enough to reach deeper tissues with less superficial absorption. High-energy photons (or high-frequency photons, which correspond to higher energy) are more penetrating and less absorbed by skin, while photons of medium energy fall somewhere in between.