Radiation Protection Course For Orthopedic Specialists: Lecture 1 of 4: Introduction To Radiation Physics And X-ray Production

1. Radiation Protection Course For
Orthopedic Specialists
Lecture 1 of 4
Introduction To Radiation Physics
And X-ray Production
Prof Amin E AAmin
Dean of the Higher Institute of Optics Technology
&
Prof of Medical Physics
Radiation Oncology Department
Faculty of Medicine, Ain Shams University

2. Introduction
• Over half of all important decisions for the welfare of patients
are based on radiological procedures.

3. The Need For Radiation
Protection
• The need for radiation protection exists
because exposure to ionizing radiation can
result in deleterious effects that manifest
themselves not only in the exposed individual
but in his descendants as well.

4. What is radiation?
• Radiation can be defined as the propagation of energy through
matter or space. It can be in the form of electromagnetic waves
or energetic particles.

5. WHAT DO WE MEAN BY
RADIATION?
❖Particles emitted from radioactive substances
❖Electromagnetic Wave
➢Visible
➢Invisible

7. Radiation
Ionizing
Non-
Ionizing

8. Non-ionizing radiation
• Non-ionizing radiation does not have enough energy to ionize
atoms in the material it interacts with.

9. Non-
Ionizing
Radiation
Ultra-
violet
(UV)
Infrare
d (IR)
lasers
Radio-
waves

10. Ionizing Radiation
Radiation that has enough energy to ionize
atoms
i.e. has the ability to knock an electron
from an atom

11. IONIZING RADIATION
❖ Ionising radiation includes X-rays, gamma rays, and
cosmic rays and also the particles that are emitted from
radioactive substances.
❖ It does not include UV, visible light, infrared, microwaves
or radiowaves.

12. Ionizing Radiation
• Examples of ionizing radiation include:
– alpha particles
–beta particles
–neutrons
–gamma rays
–x-rays

13. Ionizing
Radiation
Directly
Ionizing
Radiation
Indirectly
Ionizing
Radiation

14. Indirectly Ionizing Radiation
X-rays
Gamma
Rays
Neutrons

15. Directly Ionizing Radiation
Beta
particles
Electron
beams
Alpha
Particles
Positrons Pions Ions

16. Wilhelm Roentgen
• Discovered X-rays
on 8th November
1895.

17. Discovery of X-Rays
• On November 8, 1895, at the University of Würzburg, Wilhelm
Röntgen's attention was drawn to a glowing fluorescent screen
on a nearby table.
• Röntgen immediately determined that the fluorescence was
caused by invisible rays originating from the partially evacuated
glass Hittorf-Crookes tube he was using to study cathode rays
(i.e., electrons).
• Surprisingly, these mysterious rays penetrated the opaque black
paper wrapped around the tube.
• Röntgen had discovered X rays, a momentous event that
instantly revolutionized the field of physics and medicine.

18. Wilhelm
Conrad
Roentgen
Discovery of X rays (1895)

19. • Dr. Roentgen used a
Crookes-Hittorf tube
to make the first x-ray
image.
• Note that there is no
shielding around the
tube so x-rays were
emitted in all
directions.
History of X-Ray Discovery

20. History of X-Ray Discovery
• Hathor Temple has a relief
sometimes known as the
Dendera light because of a
controversial thesis about its
nature. The Dendera light
images comprise five stone
reliefs (two of which
contain a pair of what some
theorists refer to as lights)
in the Hathor temple at the
Dendera Temple complex
located in Egypt.

21. • The tube which is
imaged on the walls of
Hathor Temple in
Dendera is exactly
similar to Crookes-
Hittorf tube which has
been Roentgen in the
discovery of X-rays.
History of X-Ray Discovery

22. X-Ray Tube

23. X-Ray Tube
The X-ray tube is a device which
is designed to produce fast
moving electrons and to cause
them to decelerate rapidly.
X-rays are produced when
electrons (i. e. produced by the
cathode) lose a considerable
amount of energy.
+-
C
A
+
-
Basic X-ray Circuit

24. X-Ray Tube
• The x-ray tube is made of Pyrex glass that encloses a
vacuum containing two electrodes (this is a diode tube).

25. The Anode
• The positive electrode in a vacuum electron tube.
• In an X-ray tube, the electrons are accelerated towards the
anode and are stopped in the anode.
• When this occurs, X-rays and heat are produced.
• Of the electrical energy released over the X-ray tube at
exposure, more than 99% is converted to heat.
• The construction of the anode is therefore highly
dependent on different heat removal mechanisms.

26. The Cathode Assembly
• The cathode assembly Consists of
- A wire filament
- A circuit to provide filament current
- A negatively charged focusing cup 0

27. The Cathode Assembly
• The cathode assembly performs two functions:
–The controlled source of electrons for x-ray generation.
–Acts as the negative electrode.

28. Filament Circuit
• The electric circuit to produce the heating current, in the region
of 5 A at the voltage of 12 V, to the filament wire of an X ray
tube.
• The circuit is basically a step down transformer from the mains
e.g. 220 V supply to low voltage but high current.

29. Thermionic Emission
• Thermionic Emission may be defined as the emission of
electrons resulting from the absorption of thermal energy.

30. Glass Envelope
• The above components are sealed into a glass envelope.
• This allows for gases and other impurities to be pumped out of
the tube, creating the vacuum necessary for proper
performance.
• The x-ray creation process must occur in a vacuum so as not to
disrupt the electron beam, and also to allow for proper filament
performance and durability.

31. X-Ray Tube

32. The Bremsstrahlung Process
• A large potential difference is applied across the two electrodes in
an evacuated (usually glass) envelope.
• Negatively charged cathode is the source of electrons.
• Positively charged anode is the target of electrons.
• Electrons released from the cathode are accelerated towards the
anode by the electrical potential difference and attain kinetic
energy.

33. Bremsstrahlung
• Continuous spectrum of EM radiation
is produced by abrupt deceleration of
charged particles (“Bremsstrahlung” is
German for “braking radiation”).
• Deceleration is caused by deflection of
electrons in the Coulomb field of the
nuclei.
• Most of the energy is converted into
heat, ~0.5 % is x-ray.
K
K’
hn
Nucleus

34. Characteristic X-Ray
• Narrow lines of intense x-ray at
characteristic energies are
superimposed on the continuous
bremsstrahlung spectrum.
• Caused by removal of inner shell
electrons and subsequent filling of
hole with electrons from higher
shell under emission of x-ray at
shell-energy difference.
-
-
-
-
--
- -
--
-
hn
K
LM
-

35. Characteristic X-Ray
• Lines are named after the lower
shell involved in the process;
the upper shell involved is
denoted by Greek letters:
Dn = 1 → a-transitions, Dn = 2
→ b-transitions, ...

36. X-Ray Spectrum
• A bremsstrahlung spectrum
depicts the distribution of
x-ray photons as a function
of energy.
• The unfiltered a. spectrum
shows a ramp-shaped
relationship between the
number and the energy of x-
rays produced, with the
highest x-ray energy
determined by the peak
voltage (kVp) applied across
the x -ray tube.