Which interaction predominates in the diagnostic x-ray range?

• A. Photoelectric effect
• B. Compton scatter
• C. Pair production
• D. Electron capture

Answer: (B)

In the diagnostic x-ray range, Compton scatter is the interaction that predominates. This is primarily due to the energy levels of x-rays used in diagnostic imaging, which typically fall within the range of 20 to 150 keV. In this energy range, the Compton effect becomes the most significant interaction between x-rays and matter, particularly human tissue.

Compton scatter occurs when an incoming x-ray photon interacts with a loosely bound outer-shell electron, resulting in the ejection of the electron and a decrease in energy of the photon, which scatters in a different direction. This scattering can produce contrast on radiographic images, which is essential for diagnostic purposes, as it contributes to image formation by providing information about the distribution of tissues.

While the photoelectric effect does occur and is important for producing contrast in certain situations (especially in denser materials like bone), it is not the predominant interaction in the diagnostic range overall. The other interactions listed, such as pair production and electron capture, are not relevant at the energies typically used in diagnostic radiography, as they require much higher energies than those found in standard x-ray procedures. Thus, Compton scattering is overwhelmingly responsible for interactions with tissues in the diagnostic x-ray range, making it the correct choice