This document provides information on atomic structure and radiation physics. It discusses how atoms are made up of protons, neutrons, and electrons. The number of protons determines the atomic number and different elements have different numbers of protons. Radiation is emitted when high-speed electrons collide with atoms in an x-ray tube. This produces two types of x-rays: Bremsstrahlung and characteristic radiation. X-ray machines use high voltages and currents to accelerate electrons and produce x-rays, while transformers, filters and cooling systems manage the heat produced.

1. Radiation physics
Dr kamal alhadama

2. Atomic structure
• The number of electrons equals the number of proton in
an atom so the atom has no net charge ( electrically
neutral).
• Different materials( gold, lead, copper…etc) will have
different numbers of protons/electrons in their atoms.
However, all the atoms in a given material will have the
same number of electrons and protons.

3. Atomic structure
Atomic number(Z);
• Number of protons in the nucleus of an atom
Neutron number(N);
• Number of neutrons in the nucleus of an atom
Atomic mass number( A);
• Sum of the number of protons and neutrons in an atom
Isotopes
• Atoms with the same atomic number but different
atomic mass
Nucleons
• Proton and neutron together

4. Electrostatic force: Is the attraction between positive
protons and negative electrons. This attraction causes the
electrons to be pulled toward the protons in the nucleus.
In order to keep the electrons from drooping into the
nucleus, the Centrifugal force, pulls the electrons away
from nucleus.
Electrostatic and centrifugal force

5. Balance between electrostatic force
and centrifugal force keeps electrons
in orbit around nucleus
EF
CF

6. The amount of energy required to overcome the
electrostatic force to remove an electron from its
orbit. Depends on atomic number (# of protons).
Te higher the atomic number, the higher the
electrostatic force will be for all electrons in that
atom.
Binding Energy

7. Ionization : Ejection of electron from the orbit
(atom gained a positive charge) by energy that is
greater than binding energy of electron.

8. • Excitation; Electrons transferred from high
binding energy level to low binding energy
level ( neutral excited atom) by energy that
is not great enough to make ionization.

9. Radiation
• Is the emission and propagation of energy in the
space and substance in the form of waves or
particles
• Particulate Radiation :Tiny particles of matter
that possess mass and travel in straight lines at
high speeds.

10. The movement of energy through space as a
combination of electric and magnetic fields
oscillating perpendicular to each other and to the
path of traveling .
Examples : x-ray, Radio-wave, Tv-waves, visible
light and gamma ray.
Travel at the speed of light (3 x 108
meters/second) (186,000 miles/second)
Electromagnetic Radiation

11. Electromagnetic radiation
Particle concept:
Radiation travel as a discrete bundles of energy
called photons or quanta with no mass or charge
traveling in the space at the speed of light in
straight lines
Wave concept:
Radiation travel a waves and focuses on the
properties of waves ( velocity, wavelength and
frequency).

12. Wavelength x Frequency = Speed of light
F
W
W

14. X-ray Energy
• The energy of a waves of electromagnetic
radiation represents the ability to penetrate an
object.
• The higher the energy, the more easily the wave
will pass through the object.
• The shorter the wavelength and the higher the
frequency the greater the energy will be.

15. X-ray Characteristics
1) High energy waves (short wavelength and high
frequency)
2) No mass
3) No charge (neutral)
4) Travel at speed of light
5) Invisible
6) Travel in straight line
7) Cannot be focused to a point
8) Differentially absorbed by different materials
9) Cause fluorescence to some material
10) Harmful to living tissue
11) Diverges when travel to and through the object.

16. X-ray Machine
Tubehead
Support arms
Control panel

17. PID, BID
(cone)
PID = position indicating device
BID = beam indicating device
X-ray Tubehead

18. tubehead
support arms
control panel

19. Control Panel

20. Metal housing :
•is filled with oil which surrounds
the transformers and x-ray tube.
•It ground the high voltage
component and protect the x-ray
tube.
Oil:
1.it insulate the electrical
components.
2.Help to cool the anode
3.Act as a filtration of x-ray.
Tube head seal:
• Prevent the oil from leaking
out of the tubehead but still
allow most x-rays to pass
through

21. X-ray tube components

22. X-ray tube components
1.focusing cup: focusing electrons on target ( made of
molybdenum)
2.Filament: release electron when heated.
3.Vacume :
 No air or gases inside x-ray tube that might
interact with electrons
 Prevent oxidation of tungsten filament
 Increase velocity of electrons
4.Target: x-ray produced when electron striking target
5. Copper stem: remove heat from target
6: leaded glass: keeps x-ray from exiting tube in wrong
direction
7: unleaded glass window: it allow x-ray to pass
through

23. (molybdenum)
(tungsten)
Cathode
Focusing
cup
Filament

24. Increase current, increase heat
Increase heat, increase # electrons
Thermionic Emission
Release of electrons
from hot filament

25. Anode
Copper stem
Target
(tungsten)
Dental x-ray machines have stationary anode

26. Tungsten
( filament and target)
• High atomic number ( 75)
• Transfer head readily
• High melting point
• Can be drown to fine wires
• Lowe vapor pressure.

27. X-ray Machine
Components
Control Panel
X-ray
Tubehead
110, 220 line Timer
Exposure switch
mA selector
kVp selector
Autotransformer
Step-down transformer
Step-up transformer
X-ray Tube
Wires
Oil

29. ELECTRICAL CIRCUTES
• The low- voltage circuit: control the heating of
the filament. There are no x-rays produced
during this time.
• The high-voltage circuit: control the flow of
electrons across the x-ray tube. When you
depress the exposure button, the high-voltage is
activated. X-rays are produced until the
exposure time ends.
• The length of time the high-voltage circuit is
operating represents the exposure time.

32. Exposure Button
• The timer determines the length of exposure,
not how the long you hold down the exposure
button.
• You can’t overexpose by holding the exposure
button down for extended period. However, you
can underexpose by releasing the exposure
button too soon (the exposure terminates as soon
as you release the button).

33. milliampere (mA) selector
• Determine the amount of current that
will follow through filament.
• The higher the mA setting, the higher
the temperature of filament, the
greater the electrons that will produced.

34. Step-Down Transformer
110 or 220 volt 3 – 5 volts
Filament Circuit

35. Step-Down Transformer
Primary
Secondary

36. kiloVolt peak (kVp) control
• kVp Control: regulates the voltage across the x-ray
tube.
• 1 kv ( kilovolts)= 1000 v (volts)
• 70 kvp setting means the peak ( maximum voltage) is
70,000 volts.
• The higher the voltage, the faster the electrons will
travel from the filament to the target.
• The kVpcontrol knob regulate the autotransformer.

37. Autotransformer
Controls voltage between anode
and cathode
Regulated by kVp knobe ( selector)
(Similar to a rheostat)

38. 110 V
65 V
current
flow
Autotransformer

39. 110 V
80 V
current
flow
Autotransformer

40. 65 - 90 V 65,000 - 90,000 V
(65 kVp - 90 kVp)
kVp = kiloVoltage peak
Step-Up Transformer

41. Step-Up Transformer
Primary
Secondary

42. The smaller the focal spot (target), the sharper
the image (teeth) will be.
The larger the focal spot( target), the higher the
work load capacity.
During x-ray production, a lot of heat is
generated. If the target is too small, it will
overheat and burn up.
In order to get a small focal spot, while
maintaining an adequately large target, the line
focus principle is used.
Line focus principle

43. Line focus principle
• The target is at an angle ( not perpendicular) to the
electron beam from 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
apparent focal spot provides the sharper image needed
for proper diagnosis.

44. Actual focal spot size: refers to size of the
area on anode target tat is exposed to bombarding
electrons from cathode
Effective focal spot size: refers to focal spot
size as measured directly under the anode target

45. X-ray production
• 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-ray.
• 99% of the interactions result in heat
production.
• There are two types of x-rays produced in the
target of x-ray tube. The majority are called
Bremmstrahlung radiation and others are called
characteristic radiation.

46. X-ray Production
Bremmstrahlung
Characteristic

47. X-rays produced when high-speed
electrons from the filament are slowed
down as they :
1) pass close to the nuclei of the target
atoms
2) Strike the nuclei of the target atoms
Bremsstrahlung Radiation
(Braking radiation, general radiation)

48. continues to
next atom
Bremsstrahlung X-ray Production
high-speed
electron
decelerated
electron
+
x-ray

49. Bremsstrahlung X-ray Production
Maximum energy
high-speed
electron
maximum energy x-ray
+

50. The energy of the high-speed electron from
the filament must be higher than the binding
energy of the target electron with which it
interacts in order to eject the target electron
X-rays have energies characteristic of
the target material (energy = difference
between binding energies of target
electrons involved, e.g., K & L, K & M, etc.)
Characteristic Radiation

51. K-shell binding energy = 70 keV
L-shell binding energy = 11 keV
M-shell binding energy = 3 keV
Tungsten

52. Characteristic X-ray Production
L
K
High-speed electron
(at least 70 keV)
Ejected electron
Recoil electron
M

53. Characteristic X-ray Production
K
L
M
Characteristic x-ray (59 kev)
Outer-shell electron
drops into vacant spot

54. Heat dissipation
• The excess heat is controlled by :
1. High melting point of tungsten target
2. The conductive properties of the copper sleeve
3. Cooling by oil surrounding the x-ray tube.
• If the target gets too hot, electrons will( boil off) and
accelerate from the target to the filament during the
reverse half of alternating cycle when the target is
negative and the filament is positive.
• Undesired radiation will be produced and the filament
will be damaged by electron bombardment.

55. Heat capacity or tube rating
5 minutes are required after a
single continuous exposure of 17
seconds at 90kVp and 15mA for
adequate heat dissipation before
another exposure is made.

56. Exposure Factors
kVp
mA
Exposure time

57. Incorrect exposure factors
(increased exposure factors)
(too dark)
Correct exposure factors
Incorrect exposure factors
(decreased exposure factors)
(too light)

58. kVp (kiloVolt peak)
Increase kVp will increase the quantity and quality of
x-radiation.

59. mA (milliampere)
(kVp, exposure time constant)
Increase mA, will increase the quantity of x-
radiation only
10 mA
5 mA

60. Exposure time
(kVp, mA constant)
Increase exposure time, will increase the
quantity of x-radiation only
10 impulses
5 impulses

61. Filtration
Is the process of removing low-
energy x-rays from the x-ray beam

62. Filtration
Low energy x-ray do not contribute to formation of
an x-ray image; all they do is expose the body to
radiation. Therefore, we need to get rid of them.
Filtration increase the average energy ( quality) of
the x-ray beam
Inherent filtration, results from the materials
present in the x-ray machine that the x-rays have to
pass through. These include:
1. Unleaded glass window
2. Oil
3. Tubehead seal
This remove the very week x-ray.

63. Added filtration, removes the x-rays that had
enough energy to get through the inherent filtration
but are still not energetic enough to contribute to
image filtration.
Total filtration: is combined inherent and added
filtration for the x-ray machine.
As a general rule:
If x-ray machine is 70kVp or higher ,total
filtration is equivalent to 2,5 mm aluminum thickness
If x-ray machine is below 70kVp, total filtration is
equivalent to 1.5 mm aluminum thickness

64. Inherent
Glass window
of x-ray tube
Added
Aluminum filter (s)
Total 70 kVp
1.5 mm
2.5 mm
Total Filtration
Oil/Metal
barrier

65. Collimation
Regulates the size and/or
shape of the x-ray beam
area covered (less patient
exposure)
scatter radiation

66. 2.75 inches (7 cm)
(maximum diameter at end of PID)
Collimator

67. Collimator

68. The shape of opening in collimator determines
the shape of the x-ray beam.
 The size of the opening determine the size of
the beam at the end of PID.
Longer PID Have a smaller opening in collimator.
Rectangular collimation results in the patient
receiving 55% less radiation when compared to
what they would receive with a round PID.

69. Quality
Quantity
average energy
number of x-rays

70. (10) (20)
Quality(average energy) vs. Quantity(number of x-rays)
kVp
mA
Time
Filtration
No change
No change

71. Interaction of x-radiation
1. No interaction ( transmission)
2. Photoelectric absorption
3. Compton scatter
4. Coherent scatter