X ray production & emission

1. X-Ray Production

2. Objectives:
X-ray tube interactions
Characteristic and Bremsstrahlung X-
rays
X-ray emission spectrum

3. X-ray Imaging System
PRINCIPAL PARTS
Operating Console
High-voltage generator
X-ray tube
PRIMARY FUNCTION
The system is designed to provide a large
number of e-at cathode with high kinetic
energy focused to a small target at anode.

4. Radiographic Equipment
X-ray Tube Construction
G
F
E
D
C
A
B

5. How “X-rays” are created
Power is sent to x-ray tube via
cables
mA (milliamperage) is sent to
filament on cathode side.
Filament heats up –electrons are
produced
Negative charge

6. How “X-rays” are created
Positive voltage (kVp) is applied to anode
Negative electrons are attracted across
the tube to the positive anode.
Electrons slow down and finally come to
rest
Electron beam is focused from the cathode
to the anode target by the focusing cup

7. The distance between filament and the x-
ray tube target is 1 cm.
Velocity of electron is raised from
zero............half the speed of light

8. E-traveling from cathode to anode
Projectile electroninteracts with the
orbital electronof the target atom.
This interaction results in the
conversion of electron kinetic energy
into thermal energy(heat) and
electromagnetic energyin the form
of infrared radiation (also heat) and
x-rays.

9. Tube Interactions
Heat(99%)
x-rays(1%)
X-rays = Characteristic
Bremsstrahlung

10. Heat
Most kinetic energy of projectile e-is
converted into heat –99%
Projectile e-interact with the outer-shell
e-of the target atoms but do not transfer
enough energy to the outer-shell e-to
ionize
Outer shell electrons are simply raised to
an excited/ higher energy level.

11. Heat production
Outer shell electrons immediately drop
back to their normal energy level with the
emission of infrared radiation.
The constant excitation and return of
outer shell electrons are responsible for
most of the heat generation

12. Heat is an excitation
rather than an ionization

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

14. Efficiency of x-ray production is
independent of the tube current
Efficiency of x-ray production increases
with increasing kVp.
At 60 kvp.........0.5%
At 100 kVp.......1%
At 20 MV..........70%

15. Characteristic Radiation
Projectile electron interact with inner shell
electron
Projectile e-with energy high enough to
totally remove an inner-shell electron of
the target atom e.g. tungsten
Characteristic x-rays are produced when
outer-shell e-fills an inner-shell

17. Only K-characteristic x-rays of tungsten
are useful for imaging

18. Bremsstrahlung Radiation
Bremsstrahlung is produced by projectile
e-interacting with the nucleusof a target
atom

19. Bremsstrahlung Radiation
A projectile e-that completely avoids the
orbital e-as it passes through a target
atom may come close enough to the
nucleus of the atom to come under the
influence of its electric field
projectile e-kinetic energy to EM energy
electrostatic force

20. Bremsstrahlung Radiations
As the projectile electro passes by the
nucleus, it is slowed down and changes its
course, leaving with reduced kinetic
energy in a different direction .
This loss of kinetic energy reappears as an
x-ray.

21. Bremsstrahlung
is a German
word meaning
“slowed-down
Radiation”

22. X-ray energy
Characteristic x-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

23. Discrete spectrum
Contains only specific values

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

25. Characteristic x-ray emission spectrum

26. Continuous Spectrum
Contains all possible values

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

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

29. Quality
The farther to the right the higher the
effective energy or quality

30. Quantity
The more values in the curve, the higher
the x-ray intensity or quantity

31. mAs
A change in mA results in the amplitude
change of the x-ray emission spectrum at
all energies
The shape of the curve will remain the
same

32. mA increase from 200 to 400

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

34. Filtration
Adding filtration is called hardening the x-
ray beam because of the increase in
average energy
Filtration more effectively absorb low-
energy x-rays than high energy x-rays
Characteristic spectrum is not affected &
the maximum energy of x-ray emission is
not affected

35. Filtration
Adding filtration to the useful beam
reduces the x-ray beam intensity while
increasing the average energy (higher
quality)
Lowering the amplitude and shifting to the
right

36. What A does this graph indicate?

37. 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

38. Target material

39. 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

40. Voltage generators

41. Factors affecting X-Ray beam quality
and quantity
Anincrease in Results in
Current(mAs) An increase in quantity;no change in
quality
Voltage (kVp) An increase in quantity and quality
Added filtration A decease in quantity and an increase in
quality
Target atomic number(Z) An increase in quantity and quality
Voltage ripple A decrease in quantity and quality