interaction of x ray

1. INTERACTION OF X RAY WITH
MATTER

5.  Incoming photon
has sufficient
energy to knock a
K-shell electron
from its orbital
 No new photon
arises
 The electron has
kinetic energy
and can ionize
other atoms

6.  The incoming
photon collides
with an outer
orbital electron.
 Ejected electron
has kinetic
energy and
precise angle
 Secondary
Photon has
precise energy
and angle

7.  Photon energy (h) > electron binding energy
EB
 The probability of interaction decreases as h
increases
 It is the main effect at low photon energies
 The probability of interaction increases with Z3
(Z: atomic number)
 High-Z materials are strong X Ray absorber
Photoelectric Effect

8.  Variation of Compton effect according to:
 energy (related to X Ray tube kV) and
material
 lower E  Compton scattering process 
1/E
 Increasing E  decreasing photon
deviation angle
 Mass attenuation coefficient  constant with
Z
 effect proportional to the electron density
Compton Effect

9.  Z < 10 predominating Compton effect
 higher Z increase photoelectric effect
• at low E: photoelectric effect predominates in
bone compared to soft tissue
• (total photon absorption)
 contrast products increased photoelectric
absorption
high Z (Barium 56, Iodine 53)
 use of photoelectric absorption in radiation
protection
e.g., lead (Z = 82) for photons (E > 0.5 MeV)
Dependence on Atomic Number Z