Ceramah bagi Kursus Asas Keselamatan Sinaran di JKN Terengganu (April 2012)

1. Basic Of X-Ray Production
By : M. Khalis , JKN Johor

2. Atoms
 All atoms share the same basic
structure.
 During past 200 years, scientist have
proposed different models.

3. Dalton’s Model

4. Thomson’s Model
 End of 1800’s
 Thompson discovered that atoms
were not simple, solid spheres.
 Atoms contained subatomic particles.
- very small, negatively charged
- ELECTRONS

5. Thomson’s Model
 Also knew that atoms were electrically
neutral
- Most contain enough positive charge
to balance negative charge of
electrons.
 Developed model where electrons
were stuck into a positively charge
sphere.
- Like chipsmore

6. Thomson’s Model

7. Rutherford’s Model
 By early 1900s, scientist knew that
positive charge of atom comes from
subatomic particles called protons.
 1911 – Rutherford begins to test
theory
 His experiment led him to believe that
protons are concentrated in a small
area at center of atom.
- called this area the nucleus

8. Rutherford’s Model
 Rutherford’s model describes an atom
as mostly empty space, with a center
nucleus that contains nearly all the
mass.
- seperti biji dalam buah rambutan.

9. TRIVIA
A hydrogen atom lost its electron and
went to the police station to file a
missing electron report. He was
questioned by the police: "Haven't you
just misplaced it somewhere? Are you
sure that your electron is really lost?“
"I'm positive." replied the atom.

10. Bohr’s Model
 Modified Rutherford’s model in 1913
 Proposed that each electron has a
certain amount of energy.
- Helped electron move around
nucleus.
 Electrons move around nucleus in
region called energy levels.
 Energy levels surround nucleus in
rings, like layers of onion

11. Bohr’s Model
 Has been called planetary model
- Energy levels occupied by electrons
are like orbits of planets at different
distances from the sun (nucleus)

12. Electron Cloud Model
 Model accepted today
 Electrons dart around in an energy
level
 Rapid, random motion creates a
“cloud” of negative charge around
nucleus
 Electron cloud gives atom its size and
shape

13. Electron Cloud Model

14. Objective
 Review x-ray production requirements
 X-ray tube interactions
 X-ray emission spectrum

15. Productions Of X-Ray
Requirements:
◦ a source of fast moving electrons
◦ must be a sudden stop of the
electrons’ motion
◦ in stopping the electron motion, kinetic
energy (KE) is converted to EMS
energies
 Infrared (heat), light & x-ray energies

17. Productions Of X-Ray
 Power is sent to x-ray tube via cables
 mA (milliamperage) is sent to filament
on cathode side.
 Filament heats up – electrons “boil off”
 Negative charge

18. Productions Of X-Ray
 Positive voltage (kVp) is applied to
ANODE
 Negative electrons = attracted across
the tube to the positive ANODE.
 Electrons “slam into” anode –
suddenly stopped.
 X-RAY PHOTONS ARE CREATED

19. Productions Of X-Ray
 Electronbeam is focused from the
cathode to the anode target by the
focusing cup
 Electronsinteract with the electrons
on the tungsten atoms of target
material
 PHOTONS sent through the window
PORT – towards the patient

20. QUIZ
C B

21. Principles Part Of X-Ray
Imaging System
 Operating Console
 High-voltage generator
 X-ray tube
 The system is designed to provide a
large number of e- with high kinetic
energy focused to a small target

22. QUIZ 2
 Projectilee- interacts with the
orbital e- of the target atom. This
interaction results in the
conversion of e- ___ energy into
________ energy and ________
energy.

23. Tube Interaction
3 possible tube interactions
 Tube
interactions are generated from
_____ slamming into ________?
 Heat (99%), EM energy as infrared
radiation (heat) & x-rays (1%)
 X-rays = Characteristic (20%) or
Bremsstrahlung (80%)

24. Heat
 Mostkinetic energy of projectile e- is
converted into heat – 99%
 Projectilee- interact with the outer-
shell e- of the target atoms but do not
transfer enough energy to the outer-
shell e- to ionize

25. Heat is an excitation
rather than an ionization

26. Heat Production
 Production of heat in the anode
increases directly with increasing x-
ray tube current & kVp
 Doubling the x-ray tube current
doubles the heat produced
 Increasing kVp will also increase heat
production

27. Bremsstrahlung Radiation
 Heat& Characteristic produces EM
energy by e- interacting with tungsten
atoms e- of the target material
 Bremsstrahlung is produced by e-
interacting with the nucleus of a
target tungsten atom

28. Bremsstrahlung Radiation
A projectile e- that completely avoids
the orbital e- as it passes through a
target atom may pass close enough to
the nucleus of the atom to convert
some of the projectile e- kinetic
energy to EM energy
 Because of the electrostatic force?

29. Bremsstrahlung Radiation

30. Characteristic Radiation – 2
Steps
 Projectilee- with high enough energy
to totally remove an inner-shell
electron of the tungsten target
 Characteristic
x-rays are produced
when outer-shell e- fills an inner-shell
void
 All
tube interactions result in a loss of
kinetic energy from the projectile e-

31.  It is called
characteristic
because it is
characteristic of
the target element
in the energy of
the photon
produced

32. X-ray energy
 Characteristicx-rays have very
specific energies. K-characteristic x-
rays require a tube potential of a least
70 kVp
 Bremsstrahlung x-rays that are
produced can have any energy level
up to the set kVp value. Brems can be
produced at any projectile e- value

33. Discrete spectrum
 Contains only specific values

34. Continuous Spectrum
 Contains all possible values

35. Characteristic X-ray Spectrum
 Characteristic
has discrete energies
based on the e- binding energies of
tungsten
 Characteristicx-ray photons can have
1 of 15 different energies and no
others

36. Characteristic X-Ray
Spectrum

37. Bremsstrahlung X-ray
Spectrum
 Brems x-rays have a range of
energies and form a continuous
emission spectrum

38. Factors Affecting
the x-ray emission spectrum
 Tube current, Tube voltage, Added
filtration, Target material, Voltage
waveform
 Thegeneral shape of an emission
spectrum is always the same, but the
position along the energy axis can
change

39. Quality And Quantity ??

40. mAs
 A change in mA or s or both results in
the amplitude change of the x-ray
emission spectrum at all energies
 The shape of the curve will remain the
same

41. mA increase from 200 to 400

42. kVp
 A change in voltage peak affects both
the amplitude and the position of the
x-ray emission spectrum

43. Target Material
 The atomic number of the target
affects both the quantity and quality of
x-rays
 Increasing the target atomic number
increases the efficiency of x-ray
production and the energy of
characteristic and bremsstrhlung x-
rays

44. Target material

45. Voltage Waveform
 5 voltage waveforms: half-wave
rectification, full-wave rectification, 3-
phase/6-pulse, 3-phase/12-pulse, and
high-frequency.
 Maintaining high voltage potential

46. Voltage Generators

47. X-Ray Interaction with Matter
1. Photoelectric absorption
2. Coherent scattering
3. Compton scattering
4. Pair production
5. Photodisintegration

48. Question ???