Radiology physics introduction of x ray emission and x ray unit component

2. Radiation
Physics
By. Prof. Ebtesam Abdelkhalek Elzefzaf
Department. Oral Med,Periodontol,
diagnosis & Oral Radiol.
Faculty. Dentistry
University. Tanta

3. Radiation is the transmission mode from a hot body to
a cold body or surroundings with the help of electromagnetic
waves and
all bodies continuously radiate energy in the form of
electromagnetic waves. Radiation does not require a material
medium.
The speed of radiation is equal to the speed of light in that
medium
In physics, radiation is the emission or transmission of
energy in the form of waves or particles through space
or a material medium.

4. Objectives:
1- Present the fundamental concepts of molecular
and atomic structure
2- Define and characterize x radiation
3- Introduce x ray machine and to describe in detail
how x ray is produced
4- Types of x ray
5- To describe the reaction of x ray with the matter.
Intended Learning outcomes (ILO’s)

5. What is the Atoms:
----------------------------------
The units of elements,
may be broken down into smaller (subatomic)
particles by special high-energy techniques.
Subatom are :
(electrons, protons, and neutrons)
The generation, emission, and absorption of
radiation occur at the subatomic level.

6. An atom is composed of:
------------------------------------
electrons (with a negative charge)
protons (with a positive charge)
neutrons (no charge).
The protons and neutrons are found in the nucleus of the atom
and the electrons rotate (orbit) around the nucleus.
T he number of electrons equals the number of protons in an atom so
that the atom has no net charge (electrically neutral).

7. ATOMIC STRUCTURE
protons
neutrons
electrons

8. Forces that maintain the electrons in their
orbits around the nucleus;
Two opposing forces.
-------------------------------------
1- Elctrostatic force: is the attraction between
electrons and protons.
2- Centrifugal force: pulls the electrons away.
The balance between these two forces keeps
the electrons in orbit.

9. Electrons in the orbit closest to the nucleus (the K-shell)
have a greater electrostatic force than electrons in orbits
further from the nucleus.
Binding energy: is the amount of energy required to
overcome the electrostatic force to remove an electron
from its orbit.
The higher the atomic number of an atom (more protons),
the higher the electrostatic force will be for all electrons
in that atom.

10. Basic terminology
Radiation:
Is the process of emission, propagation and transmission
of energy in the form of waves.
Radiology:
science that deal with diagnosis ,therapeutic and
research application of high energy radiation.
Roentgenology:
science that deal with application of x ray on any field.
Dental radiography: The making of radiographs of the
teeth and adjacent structures by the exposure of film to
x-rays.

11. States of the atom:
----------------------------------
Ground state of an atom: any atom in the normal or
ground state is electrically neutral with equal numbers
of protons and electrons.
Excitation state: it is the process by which sufficient
energy ejects an electron from its normal level to a
higher energy level.
Ionization state: it is the process by which an atom
loses electrical neutrality and become an ion.
either by
if the electron is removed from the atom , the atom
becomes +ve ion .
While the removed electron is called – ve ion.
X rays are capable of causing this ionization of
atoms(fig 2) .

12. Ionization (fig. 2)

13. Types of ionizing radiation:
A- Particulate
Alpha particles, electrons
B-Electromagnetic
X-rays, gamma rays
Ionizing Radiation

14. 
given off from radium, radioisotopes and
during splitting of the atom.
Properties of Particulate Radiation
------------------------------------------------

They are minute particles.

have a mass.

have a very high velocity.
travel in straight lines.

have charge except neutrons.

not used in dentistry but used in therapeutic
means
Particulate Radiation

15. formed of units of pure energy
propagated in form of waves as a
combination of electric and magnetic
fields.
ELECTROMAGNETIC RADIATION
-----------------------------------------------------

16. D
W
W
F = 3
F = 2
The waves of electromagnetic radiation have two basic properties:
wavelength (λ), and frequency (ν)
The wavelength (W): is the distance from the crest of one wave to the
crest of the next wave.
The frequency (F): is the number of waves in a given distance.
(D)
If the distance between waves decreases (W becomes shorter), the
frequency will increase.

17. radio
waves
T.V
waves
visible
light
x-rays gamma
rays
cosmic
rays
Which of the above examples of electromagnetic radiation
has the shortest wavelength? Cosmotic ray
Which of the above has the lowest frequency?
Radio waves
Examples of electromagnetic radiation

18. A
B
C
Which of the above x-rays has the highest energy?
A: has the shortest wavelength, highest frequency

19. Travel in straight lines in wave motion .
Travel with the speed of light .
They are 0.1-1 A in (λ).
Invisible, can not be felt, smelled ,or heard.
have no weight or mass.
have no charge.
can not be focused or collected by lens.
can not be reflected by mirror.
can not refracted by fluid .
can not deviated by a magnet.
• can be deflected on heavy metals by being
deviated into a new linear direction.
 affect photographic film emulsion.
can cause certain substances to fluoresce
• cause ionization of atoms.
• have biological damaging effects
General properties of x rays

20. X-ray Machine Components
Control Panel
X-ray
Tube head
Exposure switch
Timer
mA selector
kVp selector
(Autotransformer)
Step-down transformer
Step-up transformer
X-ray Tube
Wires
Oil
Extension arm

21. Tube head
Extension arms
control panel

22. mA control kVp control
exposure time
kVp readout
Control Panel
(50-100)
(10-15)
(3 impulses-5 minutes)

23. Exposure Switch
Allows current to flow to complete high
and low voltage circuits.

24. PID
(cone)
X-ray
Tubehead
degrees
The x-ray tube head is attached to the support
arms so
can rotate up and down (vertically ;measured in
degrees) and
sideways (horizontally) to facilitate proper
alignment of the x-ray beam.
The PID (Position Indicating Device) is attached
to the x-ray tube head where the x-ray beam
exits and it identifies the location of the x-ray
beam.
Some people refer to the PID as a “cone”.

25. oil
barrier
material
Step-up
Trans
Step-down
Trans
The tube head is
filled with oil which surrounds
the transformers, x-ray tube and
electrical wires.
The primary function of the oil is:
-------------------------------------------------
Insulate the electrical
components.
It helps to cool the anode
 it helps in filtration of the x-ray
beam.
The barrier material prevents the
oil from leaking out of the tube
head but still allows most x-rays
to pass through.

26. Target
Beryllium Window
Focusing cup
X-ray Tube

27. X-ray Tube Metal Housing
Insulating oil
Unleaded glass window
Tube head seal
Leaded glass
housing
Vacuum

28. (tungsten)
Cathode
Focusing
cup
Filament
side view
(cross-section)
front view
(facing target)
The cathode is composed of a tungsten filament which is centered in a
focusing cup.
Electrons are produced by the filament and are focused on the target
of the anode where the x-rays are produced.
The focusing cup has a negative charge, like the electrons,
and this helps direct the electrons to the target (“focuses” them;
electrons can be focused, x-rays cannot).
Molybdenum
cup

29. Anode
Copper stem
Target
side view front view
Target
The anode in the x-ray tube is composed
of a tungsten target embedded in a
copper stem.
When electrons from the filament enter
the target and generate x-rays, a lot of
heat is produced.
The copper helps to take some of the
heat away from the target so that it
doesn’t get too hot.

30. •high atomic number (Z=74)
• Transfers heat readily
• High melting point (3370º C)
• Can be drawn into fine wire
• Low vapor pressure
(Filament and Target)
WhyTungsten

31. 1. Focusing cup: focuses electrons on target
2. Filament: releases electrons when heated
3. Electron stream: electrons cross from filament to
target during length of exposure
4. Vacuum: no air or gases inside x-ray tube that might
interact with electrons crossing tube
5. Target: x-rays produced when electrons strike target
6. Copper stem: helps remove heat from target
7. Leaded glass: Keeps x-rays from exiting tube in
wrong direction
8. X-rays produced in target are emitted in all directions
9. Beryllium window: this non-leaded glass allows
x-rays to pass through. The PID would be
located directly in line with this window.
Function of X-ray Tube Components

32. Line Focus Principle
The sharpness (detail) of images seen on a radiograph is
influenced by the size of the focal spot (area in the target
where x-rays are produced).
The smaller the focal spot (target), the sharper the image of
the teeth will be.
During X-ray production, a lot of heat is generated.
If the target is too small, it will overheat and burn up.
To get a small focal spot, while maintaining an adequately
large target, the line focus principle is used.

33. Line Focus Principle
Apparent (effective)
focal spot size
Actual focal
spot size
Target
(Anode)
Cathode
PID
The target is at an angle (not perpendicular) to the electron beam from the
filament .
Because of this angle, the x-rays that exit through the PID “appear” to come
from a smaller focal spot .
Even though the actual focal spot (target) size is larger (to withstand heat
buildup, the smaller size of the apparent focal spot provides the sharper
image needed for a proper diagnosis.

34. Transformers
Transformers work only with AC
•
Step-Down Transformer
•
Step-Up Transformer
•
Auto Transformer

35. The step-down transformer :
reduces the incoming voltage to the filament
to about 10 volts
which results in a current of 4-5 amps flowing
through the filament.
Step-Down Transformer

36. Step-Down Transformer
Primary
Secondary
7 coils
2 coils
↓ KV
↑ mA
110 or 220volt
3 – 5 volts
Filament Circuit

37. Step-Up Transformer
Primary
Secondary
65 - 90 V
65,000 - 90,000V
(65 KVp - 90 KVp)

38. Autotransformer
Similar to a rheostat)
•Controls voltage between anode and cathode
•Regulated by KVp selector

39. There are two electrical circuits operating
during an x-ray exposure.
The low-voltage circuit:
that controls the heating of the filament.
When the exposure button is depressed, this low voltage
circuit operates for ½ second or less to heat up the filament.
There are no x-rays produced during this time.
As you continue to depress the exposure button,
The high-voltage circuit is activated.
This circuit controls the flow of electrons across the x-
ray tube.
the negative electrons are pulled across the x-ray tube
to the positive target.
X-rays are produced until the exposure time ends.

40. oil
filter
timer
exposure
switch
collimator
PID
Step-up
Trans.
Step-down
Trans.
kVp
Auto
mA
The low-voltage circuit (green in diagram above) controls the heating of the
filament in the x-ray tube.
The mA control regulates the amount of voltage that passes through the
step-down transformer, which in turn reduces the voltage to about 5 volts;
this is enough to heat the filament and produce electrons.
X-ray Machine Components

41. The high-voltage circuit (red in diagram) controls the voltage across the x-ray
tube. It is regulated by the kVp selector (a rheostat) and the step-up
transformer, resulting in a very high voltage which pulls the electrons from
the filament to the target. The higher the kVp, the greater the energy
of the electrons
oil
filter
timer
exposure
switch
collimator
PID
Step-up
Trans.
Step-down
Trans.
kVp
Auto
mA
X-ray Machine Components

42. Filtration
Low-energy x-rays:
do not contribute to the formation of an x-ray image
It expose the body to radiation.
Therefore, we need to get rid of them.
Filtration: The process of removing low-energy x-rays from
the x-ray beam.
Filtration increases the average energy (quality) of the x-ray
beam.
There are two components to x-ray filtration.
Inherent filtration: results from the materials present in the
x-ray machine that the x-rays have to pass through:
1- beryllium window of the x-ray tube,
2- the oil in the tube head
3- the barrier material that keeps the oil from leaking out of the
tube head.

43. Filtration (continued)
Added filtration:
aluminum disks placed in the path of the x-ray beam .
These disks remove the x-rays that had enough energy
to get through the inherent filtration,
Total filtration :
Federal regulations require that an x-ray machine
capable of operating at 70 kVp or higher must have total
filtration of 2.5 mm aluminum equivalent. (The inherent
filtration is “equivalent” to a certain thickness of
aluminum).
X-ray machines operating below 70 kVp need to have a
total filtration of 1.5 mm aluminum equivalent.

44. Filtration
Inherent
beryllium window of x-
ray tube
Added
Aluminum filter (s)
Total
Oil/Metal barrier
filter
PID
collimator
barrier
material
beryllium
window

45. filter
PID
The filter is usually
located in the end of
the PID which
attaches to the tube
head.

46. Collimation
Restricts the size and
shape of the x-ray beam
patient exposure
scatter radiation

47. Collimation
The collimator is a lead disk with a hole in the middle
(basically a lead washer).
You are looking up through the PID at
the collimator (white arrows), which is
a circular lead washer with a circular
cutout in the middle. This will
produce a round x-ray beam. The light
gray area in the center is the
aluminum filter

48. 2.75 inches (7 cm)
(maximum diameter at end of PID)
Collimator

49. film
(4.5 cm long)
6 cm
7 cm
If you switch
from a 7 cm
round PID to a
6 cm round
PID, the
patient
receives 25%
less radiation.

50. The shape of the opening in the
collimator determines the
shape of the x-ray beam.
The size of the opening
determines the size of the
beam at the end of the PID.
PID’s come in varying lengths;
longer PID’s have a smaller
opening in the collimator.
round
rectangular
Collimation

51. primary x-ray
scattered x-ray
Collimation
(7 cm) is the maximum diameter of a circular beam or the
maximum length of the long side of a rectangular beam at the
end of the PID.

52. collimated
beam
collimator
target
(x-ray source)
Collimation

53. 3rd lecture
Types of X-ray Produced
• Braking (Bremmstrahlung) radiation
• Characteristic radiation

54. Braking means the sudden stopping of high-speed
electrons from the filament is slowed down as they pass
close to, or strike, the nuclei of the target atoms.
The closer the electrons are to the nucleus, the more
they will be slowed down.70 % of the ray produced is
general radiation.
The higher the speed of the electrons crossing the
target, the higher the average energy of the X-rays
produced.
The electrons may interact with several target atoms
before losing all of their energy.
Bremsstrahlung Radiation
(Also known as braking radiation or general
radiation)

55. Bremsstrahlung X-ray Production
Maximum energy
High-speed electron
from filament enters
tungsten atom and
strikes target, losing all
its energy and
disappearing
The x-ray produced has energy
equal to the energy of the high-
speed electron; this is the
maximum energy possible
+

56. Bremsstrahlung X-ray Production
+
High-speed
electron from
filament enters
tungsten atom
Electron slowed
down by positive
charge of nucelus;
energy released in
form of x-ray
Electron continues on in different
direction to interact with other
atoms until all of its energy is lost

57. Characteristic Radiation
Characteristic x-rays:
are produced when a high-speed electron from
the filament collides with( ‫يصطدم‬
) an electron in
one of the orbits of a target atom;
the electron is knocked out of its orbit, creating a
void (open space).
This space is immediately filled by an electron
from an outer orbit.

58. When the electron drops into the open space, energy is
released in the form of a characteristic x-ray.
The energy of the high-speed electron must be higher
than the binding energy of the target electron with which
it interacts in order to eject the target electron.
Both electrons leave the atom.
Characteristic x-rays:
have energies “characteristic” of the target material.
The energy will equal the difference between the binding
energies of the target electrons involved.

59. For example, if a K-shell electron is ejected and
an L-shell electron drops into the space, the
energy of the x-ray will be equal to the
difference in binding energies between the K-
and L-shells. The binding energies are different
for each type of material; it is dependent on the
number of protons in the nucleus (the atomic
number).
Characteristic Radiation (continued)
K-shell
M-shell
L-shell

60. Characteristic Radiation
Tungsten
K-shell binding energy = 70 keV
L-shell binding energy = 12 keV
M-shell binding energy = 3 keV
(58 & 67 keV)

61. K
L
M
What is the energy of the characteristic x-ray
produced? (M-shell binding energy = 3 keV)

62. X-ray production is a very inefficient process.
Only 1% of the interactions between the high-speed
electrons and the target atoms result in x-rays.
99 % of the interactions result in heat production.
So,The excess heat is controlled by:
-----------------------------------------------
1- the high melting point of the tungsten target,
2- the conductive properties of the copper sleeve
3- the cooling from
the oil surrounding
the x-ray tube.
heat

63. INTERACTIONS OF X-RADIATION
-----------------------------------------------------------
X-rays photons can pass through the patient :
1-without any interaction.
2- can be completely absorbed by the patient
(Photoelectric absorption).
3- photons can be scattered

64. 1-No Interaction
X-ray Matter

65. Inner-shell electron ejected
( the ejected electronis callled
photoelectron)
(T his the processs of Ionization
2-Photoelectric effect:

66. photoelectron
primary x-ray
Photoelectric Absorption

67. Photoelectric Effect
X-ray
+ ve ion
Photoelectron

68. 3- Scattering
--------------------
A- Compton Scattering:
------------------------------------------------------------
Outer shell electron ejected
(Ionization)
Scatter radiation result

69. -
-
-
X-ray
+ ve ion
Compton é
(Recoil é)
Compton Scatter
Scattered Photon

70. -
-
-
X-ray
+ ve ion
Compton é
(Recoil é)
Compton Scatter
Scattered Photon

71. Recoil electron
primary x-ray
scattered x-ray
a-Compton Scattering

72. b-Coherent Scattering
---------------------------------------
Low-energy x-ray interacts with outer-shell
electron and causes it to vibrate .
Scattered x-ray of same energy as primary
x-ray is then emitted, going in a different
direction than primary x-ray.
Electron not ejected from atom. (No
ionization).

73. Coherent Scatter
X-ray
Scattered Photon
Intended Learning outcomes (ILO’s)

74. References
1.Oralradiology:Principalsandinterpretation
BoockbyStuartC,White,MichaelJ.Pharoah.Edition7
2.WhiteandPharoah’sOralRadiology:Principalsandinterpetation
ByStuuartC,White,MichaelJ,PharoahEdition8