X RAY MACHINE-DR NIMISHA

2.  Wilhelm C. Rontgen with a Crooke’s tube studying
the property of gases under an electric field

3. Roentgen’s Lab
Crooke’s Tube

5. • X-rays – weightless package of pure energy
without electrical charge & that travel in waves
along a straight line with specific frequency and
speed
• Electromagnetic radiation – propagation of wave
like energy without mass through space or matter
• Electromagnetic spectrum – electromagnetic
radiation arranged according to their energy

6. PROPERTIES OF XRAY
PHYSICA
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PHYSIO-
CHEMICAL
CHEMICAL
BIOLOGICA
L

7. PHYSICA
L
1. They travel through space in a wave motion.
2. In free space they travel in a straight line.
3. They travel with the same speed as that of visible
light
4. As they travel through space, they can produce an
electrical field at right angles to their path of
propagation and a magnetic field at right angles to
the electric field.
5. Remain undetected by the human senses).
6. They cannot be focused by a lens.
7. They cannot be reflected, refracted or deflected by a
magnet or electric field as they do not possess any
charge.
8. They show the properties of interference, diffraction
and polarization, similar to that of visible light.
9. They do not require a medium for propagation.
10. X-rays are pure energy, no mass and they transfer
energy from place to place in the form of quanta
11. In free space they obey the inverse square law
12. X-rays are produced by the collision of electrons with
tungsten atoms
13. Heating effect

8. CHEMICA
L
• Induce color changes of several substances or their
solutions
• Cause destruction of the fermenting power of enzymes
BIOLOGICAL
• Property of excitation used in treatment of malignant
lesions
• Germicidal or bactericidal effect used for sterilization
and preservation of food.
PHYSIO-
CHEMICA
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• Photographic effect: photographic paper or film when
exposed to X-ray radiation and then developed will be found
blackened

9. Dr. Charles Edmund Kells DDS
(1856-1928)
• FATHER OF DENTAL RADIOLOGY
FIRST EVER DENTAL X-RAY
OF A LIVING PERSON

10. FIRST patient was his Assistant; X-Ray taken in
April,1896
Made own film holder using thin Aluminium
plate and Gutta Percha
Exposure time : 15 minutes

16.  Consists of
◦ Electron source
◦ Focusing cup
 Electron source
◦ Thermionic Emission (Hot cathode)
◦ Field Emission (Cold cathode)

17.  Thermionic Emission
◦ Tungsten wire – diameter 2 mm, length 1 cm
◦ Other materials: Cerium hexaboride, Lanthanum
hexaboride
 Ideal properties of a thermionic electron emitter
◦ High melting point
◦ Low work function
◦ Low vapour pressure
◦ High electron emissivity
◦ High mechanical strength

18.  Advantages of tungsten
◦ High melting point 3422 C
◦ Little tendency to vaporize – long life
◦ Can be drawn into a thin wire that is quite strong
 Disadvantages
◦ Must be heated to 2200 C to emit useful number of
electrons
◦ Not very efficient at emitting electrons
 1% thorium
◦ Increases release of electrons from tungsten
◦ Prolongs life of filament
◦ Thorium is radioactive and toxic

19.  Field Emission
◦ Type of cold cathode
◦ Does not require heat to release electrons
◦ Uses carbon nanotube technology, diameter of which
is in nanoscale
◦ Arrangement is like a bed of nails
◦ Passage of electric field causes electrons to be
pushed out
 Advantages
◦ Energy savings
◦ No metallic deposition that causes arcing
◦ Can be quickly switched on and off
◦ Current passed is directly translated to electrons
emitted

20.  Focusing cup
◦ Made of Molybdenum, Nickel
◦ Negatively charged concave reflector
◦ Electrons repel each other and flare out
◦ Electric field from focusing cup causes electrons to
converge over a small area – focal spot

21.  Factors determining the size of focusing cup
◦ Size and shape of filament
◦ Dimension of focusing cup
◦ Depth at which the coil is kept in the slot
◦ Electric field associated with focusing cup

22. Focal spot size determines
• Amount of x-rays falling on image
receptor
• Sharpness of image

23.  2 types of anodes
◦ Stationary anode
◦ Rotating anode

24. Stationary Anode
◦ Tungsten target (2 - 3 mm)
◦ Copper stem
 Alternate target material
◦ Molybdenum (Mammography)
 Target converts the kinetic energy of the colliding
electrons into x-ray photons
 Copper stem dissipates the heat from tungsten
preventing it from melting

25.  Tungsten is an ideal target material
◦ High atomic number (74)
◦ High melting point (3422 C)
◦ High thermal conductivity (173 W/m/kg)
◦ Low vapour pressure

26. • Oil is present between the x-ray tube and
tube casing.
• Carries heat away from the copper stem
• Oil provides electric insulation in addition to
cooling
• Casing shields x-rays emitted in all directions

27. Rotating Anode
◦ Tungsten target - form of a beveled disc that rotates
when tube is in operation
◦ Electrons strike successive areas of the target
distributing heat over a wider area
◦ Has a focal track rather than a focal spot

28. Lubrication
◦ Rotation of bearings in the rotor requires lubrication
◦ Wet lubrication with oil can evaporate and
compromise the vacuum
◦ Dry lubrication with graphite can wear off as powder
and destroy the vacuum
◦ Metallic lubricants (silver) are used now

29. Heat dissipation
◦ Heat dissipated by radiating through the vacuum -
wall of the tube - into the surrounding oil
◦ Absorption of heat by anode assembly –
undesirable. Heat absorbed by bearings - expand
and bind
◦ Stem which connects target to remainder of anode
assembly - made of Molybdenum (high melting
point, poor heat conductor)

30.  Focal spot: Area of tungsten target bombarded by
electrons
 Most energy of electrons is converted to heat
 Less than 1% energy converted to x-rays
 Larger the focal spot, better the heat dissipated but
compromises radiographic detail (sharpness)

31.  Size and shape of focal spot - determined by size and
shape of electron beam
 Size and shape of electron beam determined by
◦ Dimensions of filament
◦ Construction of focusing cup
◦ Position of filament in focusing cup

32.  Anode is inclined at an angle with the plane
perpendicular to the incident beam
 Varies from 15° - 20° (Angle of truncation)
 Because of this angle, when slanted surface is viewed
from direction from which x-rays emerge, surface is
foreshortened and appears small

34.  So effective focal spot is smaller than actual focal
spot
 Actual focal spot 1mm x 3mm. Effective focal spot
1mm x 1mm
 As angle of anode is made smaller, effective focal
spot size also decreases

35. ◦ Prevents collision of electrons with gas molecules
◦ Prevents wide variation in energy levels of x-rays
produced
◦ Prevents oxidation/burnout of the filament

37.  Electrons accelerated towards target interact with
target atoms to produce
◦ 99% heat energy
◦ 1% x-ray photons
 X-ray photons are produced by formation of
◦ Bremsstrahlung radiation
◦ Characteristic radiation

38. Bremsstrahlung Radiation
◦ Means braking radiation
◦ Primary source of radiation from x-ray tube
◦ Produced by 2 mechanisms
 Direct hit interaction with tungsten nuclei -
rarely
 Near or wide miss interaction with
tungsten nuclei – frequently

39. e e
e
e
e
e
e
BREMSSTRAHLUNG RADIATION – DIRECT HIT
X-ray photon

41. e
BREMSSTRAHLUNG RADIATION – NEAR MISS
e
e
e
e
e
e
e
X-ray photon

43. ◦ Photons produced when electrons take a
direct hit have maximum energy – equal to
the voltage applied
◦ Electrons pass close by nucleus, get
deflected, slowed – loss of energy converted
to photon
◦ Photons with continuous spectrum of energy
produced

44. Characteristic radiation
e
e
e
e
e
e
e
e
e
Xray photon

45. • Contributes only small fraction of photons
• Happens when incident electron removes
electron from inner orbital of target
• Void is filled by electron from outer orbital
• Photon with energy equal to difference
between binding energy of two orbitals is
liberated
• Energy of photon is discrete and is
characteristic of the target atom

47. PRODUCTION OF XRAY
INSIDE X-RAY MACHINE

48. Production of dental X-ray
1. When filament circuit is activated, filament heats up & thermionic
emission occurs.
2. Exposure button is activated, electrons are accelerated from cathode to
anode.
3. Electrons strike tungsten target, and their kinetic energy is converted to
X-rays and heat

49. THANK YOU