Which interaction with matter involves an incident photon and an outer shell electron?

The interaction that involves an incident photon and an outer shell electron is the Compton effect. In this process, a photon collides with a loosely bound outer shell electron, resulting in the scattering of the photon and the ejection of the electron from its atomic orbit. This interaction is characterized by a change in the energy and direction of the incident photon, with the scattered photon having lower energy compared to its original state due to the transfer of some of its energy to the electron.

The Compton effect is significant in diagnostic radiology, particularly at the energy ranges of x-rays used in imaging procedures. Unlike the photoelectric effect, where the photon is completely absorbed by the inner-shell electron leading to its ejection and ionization of the atom, Compton scattering primarily involves interactions with outer shell electrons and does not result in complete absorption of the photon. This distinction is important because it affects how X-rays interact with matter, contributing to dose distribution and image contrast in radiographic techniques.

In summary, the Compton effect is the correct choice as it specifically describes the interaction of an incident photon with an outer shell electron, which leads to scattering and energy transfer, applicable to many practical situations in radiology.