Interactions of xrays with matter

Question 1

what is the photoelectric effect?

Answer 1

• PROCESS OF PURE X-RAY ABSORPTION
• the incoming x-ray photon interacts with a bound inner shell e- of the tissue atom
• the inner shell e- (photoelectron) is ejected with considerable energy into the tissues and will undergo further interactions until it runs out of energy
• THIS IS WHAT GIVES THE CONTRASTING EFFECT OF AN XRAY
• a vacancy now exists in the inner shell which is filled by e- dropping in from outer shells–> the excess energy is released as light/heat
• atomic stability is achieved by the capture of a free e-

Question 2

photoelectric equation

Answer 2

the probablity of a photoelectric event is proportional to:

-Z3 (atomic number3)
1/
-keV3 (energy of the x-ray beam3)

THE LOWER THE KILO VOLTAGE, THE HIGER THE PHOTO ELECTRIC EFFECT contrast is also beter

Question 3

what is the compton effect?

Answer 3

• X-RAY ABSORPTION AND SCATTERING PROCESS

- predominates with high energy photons (opposite to photoelectric effect)