Radiation Protection Course For Radiologists Lecture 1 of 8 Introduction to Ionizing Radiation And X-ray Production

1. Radiation Protection Course For Radiologists
Lecture 1 of 8
Introduction to Ionizing Radiation
And X-ray Production
Prof Amin E A Amin
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

6. The Electromagnetic Spectrum

7. Classification of Radiation

8. Ionizing Radiation
Ionizing radiation has the ability (enough energy) to knock an
electron from an atom, i.e. to ionize an atom.

9. Ionizing Radiation
❖ Ionizing 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.

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

11. Ionizing Radiation

12. Directly Ionizing Radiation

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

15. Non-
Ionizing
Radiation
Ultra-
violet
(UV)
Infrared
(IR)
lasers
Radio-
waves

18. Wilhelm Roentgen
• Röntgen had discovered X
rays in 8th November 1895,
a momentous event that
instantly revolutionized the
field of physics and
medicine.

19. 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.

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

21. • 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

22. 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.

23. • 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

24. The First X-ray Image
• The first human radiograph was
taken for Mrs. Roentgen.
• It was a 15 minute exposure.
• For the first time, we were able to
see inside the body without
surgery.
• Early x-rays were taken on glass
photographic plates

25. • X-rays were discovered by Professor
Wilhelm Roentgen in the autumn of
1895, and he announced the discovery at
the end of that year.
• News of the discovery spread rapidly,
and in February of 1896, about six weeks
after the announcement by Roentgen,
Professor Almy at Grinnell College
successfully produced x-ray photographs.
History of X-Ray Discovery

26. Discovery of X-Rays
• This is an x-ray tube used to produce one of
the first photographs in 1896.

27. What are X-rays?
• X rays are a form of electromagnetic radiation with Wavelength
of 0.01 to 10 nanometers.
• X-rays arise as electrons are deflected from their original paths
or inner orbital electrons change their orbital levels around the
atomic nucleus.
• X rays, like gamma rays, are capable of traveling long distances
through air and most other materials.
• Like gamma rays, x rays require more shielding to reduce their
intensity than do beta or alpha particles.
• X and gamma rays differ primarily in their origin: X rays
originate in the electronic shell, gamma rays originate in the

28. X-Ray Tube
• Electrical device used for
the generation of x-rays.
• This is accomplished by
the acceleration of
electrons and then
suddenly decelerating
them.
• The energy of the x-rays is
dependent on the kinetic
energy of the electrons.

29. The X-Ray Tube
❖ The main components of an x-ray tube are the cathode and the anode,
sealed opposite to each other in a highly evacuated vacuum tube.
❖ The cathode is a tungsten filament which when heated emits electrons, a
phenomenon known as thermionic emission.
❖ The anode consists of a copper rod and a piece of tungsten target (for
producing the x-rays).
❖ When a high voltage is applied between the anode and the cathode, the
electrons emitted from the filament are accelerated toward the anode and
achieve high velocities before striking the target.
❖ The x-rays are produced by the sudden deflection or acceleration of the
electron caused by the attractive force of the tungsten nucleus.
❖ The x-ray beam emerges through a thin glass window in the tube envelope.

30. X-Ray Tube

31. Major Components Of X-ray
Tube And Their Functions
1.The cathode is to generate electrons.
2. The high voltage power supply provides energy to
pull the electrons generated by the cathode to
bombard the anode.
3. The anode serves as the bombarded target of the
electrons and then generates x-rays.
4. The enclosure glass seals the two electrodes (i.e.
the cathode and the anode) in a vacuum space.

32. X-Ray Tube

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

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

35. 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.

36. Thermionic Emission
➢ When tungsten coil is heated, its atoms absorb thermal
energy, and some of electrons in the tungsten acquire enough
energy to allow them to move a small distance from the
surface of the metal.
➢ This process of the electrons escaping is referred to as
thermionic emission.
➢ It requires at least 2200oC for tungsten to emit a useful
number of electrons (i.e. thermions.)

37. 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.

38. The Major Components Of The Anode
• Tungsten target with high melting point to withstand intense
heat produced by electronic bombardment
• Copper anode for removing the heat from target where it is
cooled by oil , water or air (rotating anodes to reduce the
temperature in diagnostic x-rays)
• Copper hood for preventing the electrons from striking the walls
• Focal Spot : target from where x-rays are emitted ( should be
smaller for diagnostic purpose and larger acceptable for
therapeutic purpose)

39. Glass Envelope
• The above components are sealed into a glass envelope.
• This allows for gases and other impuritites 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.

40. Protective Housing
Radiation:
– It is lead lined
– Absorbs isotropically emitted x-
rays
– Leakage limit: <100 mR/hour at 1
meter (FDA) when tube operated at
maximum continuous current for its
maximum rated kilovoltage
– Useful beam emitted through
“window”

41. Protective Housing
Electrical protection (Shields against
high voltage)
– electrically grounded
– Special high voltage cable receptables
– housing filled with oil which serves as an
electrical isulation

42. Protective Housing
• Heat:
• (depends on tube design); MAY HAVE:
– housing filled with oil (heat absorber
as well as electric insulator)
– Cooling fans
– Active Heat Exchanger using oil or
water
– bellows
• on end of tube
• allows oil to expand when hot

43. Basic X-ray Circuit
+-
C
A
+
-
• Well controlled electrical energy is supplied in the form
of electrical current to the x-ray tube.
• Inside the x-ray tube, electrical energy is converted to
x-rays.

44. X-Ray Production
• A large potential difference is applied across the two electrode an s
in an evacuated (usually glass) envelope.
• Negatively charged cathode is the source of electrons (e).
• 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.

45. The Bremsstrahlung Process
• About 99% of the KE is converted to heat via collision—like
interactions.
• About 0.5%-1% of the KE is converted into x 1% into x-rays via
strong Coulomb interactions (Bremsstrahlung).
• Occasionally (0.5% of the time), an e- comes within the proximity
of a positively charged nucleus in the target electrode.
• Coulombic forces attract and decelerate the e-, causing a
significant loss of kinetic energy and a change in the electron’s
trajectory.
• An x-ray photon with energy equal to the kinetic energy lost by
the electron is produced (conservation of energy).

46. The Bremsstrahlung Process
• This radiation is termed bremsstrahlung, a German word
meaning “braking radiation” .
• The impact parameter distance, the closest approach to the
nucleus by the e- determines the amount of KE loss.
• The Coulomb force of attraction varies strongly with distance
(a1/r2); as the distance decrease, deceleration and KE loss
increase.
• A direct impact of an electron with the target nucleus (the rarest
event) results in loss of all of the electron’s kinetic energy and
produces the highest energy x-ray.

47. 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.
K
K’
hn
Nucleus

48. The Bremsstrahlung Process

49. The Bremsstrahlung Process
• 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.

50. The Bremsstrahlung Process
• Filtration refers to the removal of x--rays as the beam passes
through a layer of material.
• A typical filtered b. spectrum shows that the lower energy x--
rays are preferentially absorbed, and the average x--ray
energy is typically about one third to one half of the highest
x--ray energy in the spectrum.
• X-ray production efficiency (intensity) is influenced by the
target atomic number and kinetic energy of the incident
electrons (which is determined by the accelerating potential
difference).

51. Spatial Distribution of X-Rays Around a
Thin Target

52. 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 differenc.
-
-
-
-
--
- -
--
-
hn
KLM
-

53. X-ray Energy Spectra
• X-ray photons produced
by the x-ray machine are
heterogenous in energy
• Spectrum shows a
continuous distribution of
energy (bremsstrahlung)
superimposed by discrete
energies (characteristic).