What photon-tissue interaction results in a recoil electron and a scattered photon?

The interaction that results in a recoil electron and a scattered photon is Compton scattering. This phenomenon occurs when a photon collides with a loosely bound or free electron, causing the electron to be ejected from its atom. As a result of this collision, the incoming photon loses energy and is deflected at a different angle, which describes the scattering process.

Compton scattering is particularly significant in medical imaging and radiation therapy because it contributes to the attenuation of X-ray and gamma-ray beams as they penetrate tissue. The energy of the emitted recoil electron and the energy of the scattered photon depend on the angle at which the photon is scattered; this relationship is crucial in understanding how different tissues absorb ionizing radiation.

The other processes listed, while related to photon-tissue interactions, do not yield the same effect of an outgoing recoil electron alongside a scattered photon. For instance, the photoelectric effect involves the complete absorption of a photon by an electron, resulting in an ejected electron but no scattered photon. Rayleigh scattering involves the elastic scattering of photons without energy loss, where the photon is redirected but not deflected with an electron. Fluorescence refers to the absorption of photons with subsequent emission of lower-energy photons; it doesn't involve recoil electrons in the same