Interaction of X- ray with matter

1. INTERACTION OF
X-RAY
WITH MATTER
Submitted by
Abhiram A B
Final year Part A

2. Contents
• Introduction
• Coherent scattering
-mechanism
• Photoelectric absorption
-mechanism
• Compton scattering
-mechanism
• reference

3. INTERACTION OF X-
RAYS WITH MATTER
• In dental and maxillofacial imaging , the X ray
beam enters the face of a patient , interacts with
hard and soft tissues , and strikes a digital
sensor or film.
• As the beam goes through the patient, it is
reduced in intensity. This attenuation results
from absorption of individual photons in the
beam by atoms in the tissues or by photons
being scattered out of the beam.
• The interactions is either absorption or
scattering.
• In a dental X-ray beam, there are three means of
beam attenuation;
a) Coherent scattering -7%
b) Photoelectric absorption-27%
c) Compton scattering 57%

4. Coherent
scattering/Classical,
Elastic/Thompson scattering
• Significance-It leads to minimal contribution to scatter
• This interaction accounts for only about 7% of the total
number of interactions (per exposure) in a dental
examination
• It causes very little film fog because of small quantity of
scattered photons and has low energy level to the film.

5. Mechanism
The incident photon interacts with
outer shell electron.
Causing it to become momentarily
excited.
The excited electron then returns to the
ground state and generates another X-
ray photon with the same frequency and
energy as in the incident beam, which
divert at different direction.

6. Photoelectric
Absorption
• It is important in diagnostic imaging.
• About 27% of photons incident from a
dental X-ray beams are reduced by
photoelectric absorption.
• Significance-It forms the basic
radiographic image formation.

7. Mechanism
Occurs when an X-ray beam displaces an
electron from inner shell causing vacancy.
An outer shell electron drops in to fill the void
in the inner shell, emitting a photon with
energy equivalent to the difference in the
orbital binding energies.

8. Compton
scattering
• Significance leads to maximum
scattering of the radiation.
Scattered radiation can degrade
image, expose personnel and
patient.
• About 57% of the photons that
are absorbed from a dental X-ray
beam are absorbed by this
process.

9. Mechanism
Compton scattering occurs when
the incident photon collides with
an outer electron.
This interaction causes production
of incident photon ion into different
directions and ejection of recoil
electron from target atom.
Intensity of scattered
photon=intensity of incident
photon-(Kinetic energy gained by
outer electron +Its binding energy)

10. Reference
• Peeyush shivhare
Text book of oral medicine
and oral radiology 2nd Edition

11. Thank you