interactions with matter

• what is absorption


  x ray photons are completely absorbed by the patient and do not interact with the image receptor
• what is transmission 


  x ray photons pass straight through patients and interact with image receptor
• what is scatter


  x ray photons collide with atoms within patient and travel in different directions
• what is attenuation


  the reduction of the intensity of an x ray beam as it traverses matter
• name three factors that affect the amount of attenuation that takes place within a patient 


  • energy of the photons
  • density of the medium
  • atomic number of the medium
• what is compton scattering


  • occurs when an x ray photon collides with a ‘free‘ outer shell electron
  • the outer shell electron gains some kinetic energy and leave its shell
  • the x ray photon changes course and scatters
  • energy of the incoming x ray photon must be greater than the binding energy of the electron with which it interacts
• what is photoelectric effect 


  • occurs when an x ray photon collides with an inner shell electron
  • collision removes electron from its shell as a photoelectron
  • vacancy is filled by the transmission of an electron from outer shell
  • process continues until atom remits energy originally acquired from the photon