Xray Tubes in
X-Ray Tubes
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Target atom
Electron shells
Ejected K shell
M electron
Nucleus
Incident electrons
Close interaction
Moderate energy
Distant interaction
Maximum energy
Low energy
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Filament
Made of tungsten wire
Good thermionic emitter
Low vapor pressure
Can be made into a thin wire
Amount of thermionic emission is determined by its temperature
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Filament heated to approximately 2600°C
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HT Supply
High Tension = High Voltage
HT transformer converts 415v 3-phase alternating current mains supply to direct current with voltage from 50-150kV
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Tube envelope
May be made of glass (Pyrex) or metal
Re-entrant seals to allow for thermal expansion
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Increasing the kV on the HT circuit will make the electrons move faster.
As the electrons move faster this increases the energy of the x-rays generated.
Increasing the filament current makes the filament hotter, emitting more electrons.
This increases the intensity of the resultant x-ray beam.
Page 36:Tungsten
High atomic number (Z=74), therefore:
High melting point (3370°C)
Low rate of evaporation
More efficient bremsstrahlung production
Page 45:Tube Housing
Stainless steel outer casing with lead lining.
Serves as a very strong support for the rather delicate x-ray tube
HT Cable Ports
Page 57:Focussing cup
(molybdenum/nickel alloy)
Focal spot (1 - 2 mm^2)
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Anode angle: 15°
Copper anode
Tungsten target
Page 71:Dielectric
(Electrically Insulating) Oil
Aids cooling of the anode
Provides electrical insulation
Page 85:Rotor / Stator Induction Motor
Anode is attached to the copper rotor by a small diameter molybdenum stem to reduce transfer of heat to the bearings
Stator is a set of electric coils that produces a very strong magnetic field outside of the glass envelope that spins the rotor at between 3,200 – 10,000 RPM
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Collimator leaves
Mirror
Bulb
Collimation field
Light Beam Diaphragm