The Importance Of Photoelectric Interactions

Photoelectric interaction is one of the main interactions in producing x-rays. This occurs when an inner shell electron is knocked out leaving a hole that needs to be filled. It will be filled by an outer shell electron which will be filled by an auger electron eventually. Photoelectric interaction doesn’t have as much scatter compared to the other interactions. This is due to the photons being almost completely absorbed by the patient as the photons pass through the body to hit the image receptor.

There are a lot of photon interactions throughout the radiologic field. The interactions between photons play a major role in how we create images. The photons are produced when matter and excited electrons interact with each other at the same

This interaction can only occur when the photons energy interacts with the inner shell electrons in order to displace it . The photons energy has to be equal to or greater than the electrons binding energy it will be hitting in order for displacement to happen. Electron displacement is also known as a photoelectron (Shepard 2003). If the x-ray photons energy is fifty KeV or lower, the interaction will occur better rather than if the KeV was greater than fifty. If the KeV is greater than fifty, the photons will have too much energy and will create scatter, which could lead to the energy going through another interaction or it could just continue colliding into another electron. To determine the probability of an x-ray photon this interaction is a function for the energy and the atomic number for the atom it interacts with. For this we use the equation of incident electron (Ei) equals binding electron (Eb) plus kinetic energy electron (Eke). (Bushong

This hole has to be filled in order for the atom to become stable again. This is where characteristic cascade begins. Characteristic cascade is when an electron is ejected from the outer shell and fills in that hole in the inner shell; this is when it becomes a photoelectron. It causes each layer to drop until the atom becomes stable again. The excess energy is being emitted as characteristic radiation or Auger electrons (Huda 2003). That energy will then be released as a characteristic photon (Shepard 2003). The space created in the outer shell is filled with a higher energy electron, producing another secondary energy exchange (Bushong 2008). This exchange continues to occur, leading to secondary x-ray or characteristic x-ray being produced. It occurs until a higher energy level doesn’t exist in providing another electron. The fluorescent radiation is when a characteristic photon is produced by incoming photons and is the number of photons being produced. It can be converted to light or x-rays, which depends on the binding energy level of material absorbed. Fluorescent yield refers to the number of characteristic photons that are being produced. Photons being absorbed have a direct relationship with interacting matter and doesn’t scatter as much as compton, leaving the photons interacting more with matter (Huda