Interactions of X rays with matter by Abubakar Mustapha Amanawa

1. APRESENTATION
ONTHETOPIC
INTERACTIONOFX-RADIATIONWITHMATTER
BY
ABUBAKARMUSTAPHAAMANAWA
INTEGRALUNIVERSITY,LUCKNOW.
SEPTEMBER2019.

2. INTRODUCTION
X-rays were discovered in Europe in the late nineteenth
century by German scientist Dr. Wilhelm Conrad
Roentgen. Although Roentgen discovered x-rays by
accident, he proceeded to study them so thoroughly that
within a very short time, he identified all the properties of
x-rays that are recognized today. Roentgen was more
interested in the characteristics of x-rays as a form of
energy than their practical application. X-rays are
classified as a specific type of energy termed
electromagnetic radiation, and like all other types of
electromagnetic energy, x-rays act like both waves and
particles.

3. Andthisxraysareproducedinavacuumtubeknownas
X–raytube,whencurrentispassedthroughthe
tungstenfilamentandheatsitup.Asitisheatedupthe
increasedenergyenableselectrons tobereleasedfrom
thefilamentthroughthermionicemission.Theelectrons
areattractedtowardsthepositivelychargedanodeand
hitthetungstentargetwithamaximumenergy
determinedbythetubepotential(voltage).

4. As the electrons bombard the target they interact via
Bremsstrahlung and characteristic interactions and
result in conversion of energy into heat (99%) and x –
ray photons (1%). The x-ray photons are released in a
beam with a range of energies (x-ray spectrum) out of
the window and form the basis for x-ray image
formation.
As a result of the release of this x – rays, interaction
occurs between the x – ray beam and matter.

5. INTERACTION OF X – RAY WITH MATTER
X – ray photons are created by the interaction of energetic
electrons with matter at the atomic level. Photons (x – rays)
end their lives by transferring their energy to electrons
contained in matter. X – ray interactions are important in
diagnostic examinations for many reasons. For example, the
selective interaction of x – ray photons with the structure of
the human body produces the image; the interaction of
photons with the receptor converts an x-ray or gamma image
into one that can be viewed or recorded.
This presentation considers the basic interactions between
x-ray and matter.

6. A beam of x – rays may be:
A. Transmitted: pass through unaffected
B. Absorbed: transfer all energy to matter and do not pass through the
patient to the film
C. Scattered: diverted with or without energy loss.
Attenuation refers to the reduction in the intensity (Amount) of x – rays
whenever it interacts with the medium.
Attenuated x – rays are those that are absorbed or scattered. It is
an exponential process and, therefore, the beam intensity never reaches
zero.
ATTENUATION

7. Attenuation of the beam can be represented numerically by:

8. 1. Half Value layer
2. Linear Attenuation Coefficient
3. Mass Attenuation Coefficient

9. FACTORS AFFECTING ATTENUATION
1. Decrease in atomic number increases attenuation
2. Increase in Atomic number decreases attenuation
3.Increase in thickness increase attenuation
4. Decrease in thickness decrease attenuation
5. When the x – ray quality decrease there will be decrease in attenuation
6. When the quality decrease there will be increase in attenuation
`

10. INTERACTIONTYPES
Recall that photons are individual units of energy. As an x – ray
beam or gamma radiation passes through an object, three possible
fates await each photon, as shown in this figure:
1. It can penetrate the section of matter without interacting.
2. It can interact with the matter and be completely absorbed by
depositing its energy.
3. It can interact and be scattered or deflected from its original
direction and deposit part of its energy.

11. As a result of the released x – rays with a range out of the window that
form the basis for x – ray image formation, the interaction occurs
between the x – ray beam and matter are of 5 types but 3 are mainly of
clinical importance which will be discussed. And these 5 types of
interactions are :
1. Coherent scattering
2. Photoelectric effect
3. Compton scattering
4. Pair production
5. Photo disintegration.
Of the above listed types of interaction that occur between the x – ray
and matter only the first three are of clinical importance which will be
discussed and the last two are not important in medical practice as
they do not occur in diagnostic energy range.

12. COHERENT SCATTERING
In coherent scattering the incident photon excites the entire atom
and it is an example of wave type of interaction of x – rays. It involves
only change in direction, cause no change in energy or unmodified
scattering. There is no ionization and no loss or gain of energy.
Coherent scattering occurs in with very low energy radiation videlicet
in mammography.
Types of coherent scattering
1.Thompson type : interaction with only single electron
2.Rayleigh type : interaction with all the electrons together.
Clinical importance
it constitutes 5% ( at 70KeV) and up to 12% ( in radiation of the range
of 30KeV) of all interactions in diagnostic energy range.

14. PHOTOELECTRIC EFFECT
This is the most important interaction of x – rays with matter
that occur in diagnostic radiology.
In photoelectric effect all the incident photon energy is
transferred to an electron, which is ejected from an atom. It is
an example of photon type or particle type interaction of x –
rays. The Kinetic energy of the ejected photoelectron is less
than the incident photon, as some energy is spent in
overcoming the binding energy of the orbital electron.
PRODUCTS
1. Characteristics Radiation
2. Photoelectron
3. Positive ion

16. Clinical Importance
1. No Secondary scatter, so image quality is good
2. Increases tissue contrast by amplifying the difference in
contrast (because it is proportional to Z^3).
However as the photon gives up all its energy it gets fully
absorbed to the target tissues, hence it leads to increased dose
to the patient. Increasing the kVp will increase the energy of the
photons in the x – ray beam leading to a reduction of PE effect.
It causes ionization and is, therefore, potentially dangerous for
the absorbed tissues.

17. COMPTON SCATTERING
A Compton interaction is one in which only a portion of the energy is absorbed and a
photon is produced with reduced energy. This photon leaves the site of the interaction
in a direction different from that of the original photon, Compton scattering is much
common type of interaction with soft tissue in the diagnostic energy range. It starts at
26 KeV and continues up to 30 MeV. It produces all the scattered radiation we come
across in diagnostic radiology. It is an interaction of high energy photon with loosely
bound outer shell (valence) electrons. Here the incident photon does not give up all its
energy and flies off as scatter radiation. The scattered electron can pass through the
medium without interaction or effect interaction depending on the photon energy it
contains. The scattered electron usually loses its energy near the scattering site.
PRODUCTS
1. Recoil electron ( only goes in forward direction)
2. Positive ion
3. Scatter Radiation or Scattered incident photon ( can only goes one direction)

19. Clinical Importance
As mentioned all the scatter radiation encountered in
diagnostic imaging comes from Compton scattering. In
diagnostic energy range ( 10 – 150kVp) for the tissues in the
human body which have fairly low atomic numbers, all the
electrons virtually behave as free electrons. Hence Compton
scattering plays an important role in radiology. Compton
scattering causes images degradation by causing the tissue
contrast, particularly at lower kV as all the energy is
transferred to the photon.

20. CONCLUSION
X – rays are produced in a vacuum tube known as the x – ray tube and as a
result of released of this x – rays that are produced through a medium,
interactions occurs between the x – ray and matter which are of five types
namely:
1. Photoelectric effect,
2. Compton effect,
3. Coherent scattering,
4. Pair production and
5. Photon disintegration.
But 3 of these are clinically important since they are the once that
occur at the diagnostic range (up to 150kVp) which have been discussed in
the presentation and the rest 2 did not occur at diagnostic range.