Long-wavelength X-rays will increase which of the following?

• A. Scattered radiation
• B. All of the above
• C. Absorption
• D. Compton

Answer: (C)

When X-ray energy is lowered (longer wavelength), absorption by the photoelectric effect becomes the dominant interaction. The probability of photoelectric absorption increases dramatically as energy decreases, and it is strongly dependent on the atomic number of the material—higher-Z materials absorb more photon energy this way. So more photons are absorbed rather than scattered, leading to an increase in absorption.

Compton scattering, on the other hand, is more significant at higher energies and its likelihood decreases as energy falls, so scattered radiation does not rise with longer wavelength. Scattering mechanisms overall don’t increase with lower energy in the same way absorption does. Therefore, the best answer is absorption.