Which is the only photon-tissue interaction that does not result in ionization?

Which is the only photon-tissue interaction that does not result in ionization?

• A. Photoelectric interaction
• B. Coherent scatter
• C. Compton interaction
• D. Pair production

Answer: (B)

The fundamental idea here is elastic versus inelastic interactions. Coherent scattering, also known as Rayleigh scattering, is an elastic process in which the photon interacts with the whole atom and is deflected with essentially the same energy. Because the atom remains in its ground state and no electrons are ejected, there is no ionization of the tissue. In contrast, the other interactions involve transferring energy to electrons. The photoelectric interaction absorbs the photon and ejects a bound electron, causing ionization. The Compton interaction scatters the photon and ejects a recoil electron, which ionizes the medium. Pair production converts the photon into an electron-positron pair in the field of a nucleus; these charged particles then ionize as they travel. So, coherent scattering is the only interaction among the options that does not ionize tissue.

The fundamental idea here is elastic versus inelastic interactions. Coherent scattering, also known as Rayleigh scattering, is an elastic process in which the photon interacts with the whole atom and is deflected with essentially the same energy. Because the atom remains in its ground state and no electrons are ejected, there is no ionization of the tissue.

In contrast, the other interactions involve transferring energy to electrons. The photoelectric interaction absorbs the photon and ejects a bound electron, causing ionization. The Compton interaction scatters the photon and ejects a recoil electron, which ionizes the medium. Pair production converts the photon into an electron-positron pair in the field of a nucleus; these charged particles then ionize as they travel.

So, coherent scattering is the only interaction among the options that does not ionize tissue.