INTERACTION OF X RAY WITH MATTER

SHANKAR PAVHANEADMIT

C.C.NO.455578

a Method of interactions a X ray intering in a patient can be absorbed,scaterd or transmited.

Absorption:- transfer of energy from the x ray photon to the absorbing material.Scatering :- x ray photon is redirected by scatering material.Transmited:- x ray pass through the patient without interaction

(most diagnostic x ray absorbed or scattered)

a ENERGY TRANFER a THERE ARE TWO BASIC TYPE OF ENERGY TRANFER.IONIZATION:-Incoming radiation causes the removal of an electron from an atom or molecule leaving the material with net positiove charge.EXCITATION:-X ray energy is transferred to the target material leaving it in excited state.

Photoelectric Effect Interaction

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

Compton Scattering The incoming

photon collides with an outer orbital electron.

Ejected electron has kinetic energy and precise angle

Secondary Photon has precise energy and angle

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

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 in the medium small variation with atomic number

(Z)

Compton Effect

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 absorptionhigh 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