1. BASIC INTERACTIONS BETWEEN X
RAYS AND MATTER

2. Atoms are bound into molecules by electrons
in the outermost shell.x ray photons interact
either with the orbital electrons or with the
nucleus
In the diagnostic range, the interactions are
with orbital electrons
Interaction between X-rays and matter
•Coherent Scattering
•Photoelectric effect
•Compton Scattering
•Pair Production
•Photodisintegration

6. Low energy photons,only scattering,no ionisation and only little
energy loss,

7. • Two types of coherent scattering
• Thomson scattering-a single electron is
involved in the interaction
• Rayleigh scattering-results from a
cooperative interaction with all electrons of
an atom

8. • Rayleigh Scattering (Coherent Scattering)
1 . Photons are scattered by bound electrons
2. Atoms are neither excited or ionized
3. Scattering from different parts of electron cloud - coherent scattering

10. The tighter an electron is bound,more likely it is involved in photoelectric reaxn

12. Photoelectric effect
X ray

14. • The charecteristic radiation– secondary
radiation
• Only iodine and barium in diagnostic
radiology emit charecteristic radiation
energetic enough to leave the patient and
fog film
• Application of photoelectric effect-produces
images of good quality becoz there is no
scatter and it enhances tissue contrast
• But patient gets more radiation

15. Compton scattering
• Almost all scatter in diagnostic radiology comes
from compton scatter
• Rel high energy incident photon strikes a free
outer shell electron and ejects it
• The photon is deflected.part of its energy goes to
the electron.rest is retained.the amount retained
dep on initial energy and angle of deflection off
the electron
• At narrow angles of deflection,the scattered
photon retains more of its org energy

17. Compton scatter

19. The most significant object producing scattered radiation in an x-ray procedure is the patient's
body. The portion of the patient's body that is within the primary x-ray beam becomes the actual
source of scattered radiation. This has two undesirable consequences. The scattered radiation
that continues in the forward . direction and reaches the image receptor decreases the quality
(contrast) of the image; the radiation that is scattered from the patient is the predominant source
of radiation exposure to the personnel conducting the examination.

21. Pair production and photo disintegration do not occur in
diagnostic energy range
A photon with Energy > 1.02Mev might completely disappear
under the production of an electron and a positron (electron with
positive charge)
Pair production